The present invention relates to a polynucleotide comprising (i) a sequence encoding an anti- CRISPR (Acr) polypeptide and (ii) an miRNA target sequence and to vectors and host cells related thereto. The present invention further relates to a kit comprising (I) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence; and a Cas nuclease or a second polynucleotide comprising an expressible gene encoding a Cas nuclease; (II) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA- interference (RNAi) target sequence, said first polynucleotide further comprising an expressible gene encoding a first fragment of a Cas nuclease, and a second polynucleotide comprising an expressible gene encoding a second fragment of a Cas nuclease, wherein said first and second fragment of said Cas nuclease together reconstitute an active Cas nuclease; or (III) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide, (ii) an RNA-interference (RNAi) target sequence, and (iii) a sequence encoding a Cas nuclease; and a second polynucleotide comprising an expressible gene encoding an inhibitory RNA, preferably a siRNA or a miRNA hybridizing to said RNAi target sequence, more preferably a siRNA hybridizing to said RNAi target sequence. Further, the present invention relates to methods and uses related to the aforesaid means.

CRISPR (Clustered, Regularly Interspaced Short Palindromic Repeats) systems in bacteria and archaea mediate specific degradation of foreign, invading nucleic acids (Barrangou et al, 2007; Bhaya et al, 2011; Terns and Terns, 2011; Wiedenheft et al, 2012). They comprise a CRISPR-associated (Cas) nuclease which can be programmed by short guideRNAs (gRNAs) to induce double-strand breaks at specific, sequence-complementary DNA loci (Jinek et al, 2012). Diverse CRISPR-Cas systems have been adopted for genome engineering in mammalian cells and animals, most prominently the CRISPR-Cas9 system from Streptococcus pyogenes (SpyCas9) (Cong et al, 2013; Jinek et al, 2013; Mali et al, 2013). CRISPR-Cas9 systems have also been successfully applied for genome editing in embryonic stem cells (Wang et al, 2013) as well as in animals. For instance, transgenic mice were reported that stably express SpyCas9 and thus enable in vivo gene knockout screens (Piatt et al, 2014). Alternatively, transient and efficient in vivo delivery of the Cas protein and gRNA components via e.g. hydrodynamic plasmid DNA injection (Yin et al, 2014) or Adeno- associated viral (AAV) vectors (Senis et al, 2014; Ran et al, 2015) has also been achieved. Not surprisingly, the potential of CRISPR-Cas-based human gene therapy is considered to be enormous and motivates an ever increasing number of preclinical studies for treatment of genetic diseases (Schmidt and Grimm, 2015; Dai et al, 2016; Xue et al, 2016).

However, a number of challenges still hamper the straightforward application of CRISPR-Cas systems for basic or applied research especially in multi-cellular systems. One is the insufficient specificity of the Cas nuclease and hence the risk of unintended editing of non- target loci (Fu et al, 2013; Hsu et al, 2013; Cho et al, 2014; Wang et al, 2015; Zhang et al, 2015). This issue was attempted to be resolved by employing engineered Cas variants with an improved on-target specificity (Kleinstiver et al, 2016; Slaymaker et al, 2016) or by timely activating/de-activating the Cas nuclease. The latter can be achieved either by using Cas variants permitting control with exogenous triggers such as chemicals (Zetsche et al, 2015b; Maji et al, 2017) or light (Hemphill et al, 2015; Nihongaki et al, 2015a; Nihongaki et al, 2015b; Polstein and Gersbach, 2015), or by using synthetic gene circuits controlling CRISPR- Cas activation (Kiani et al., 2014; Petris et al., 2017) A second, major hurdle is the need for highly specific delivery of CRISPR-Cas into and/or its activation (solely) within the desired target tissue or cell, ideally even after systemic administration of the CRISPR-Cas components. Target tissues of (therapeutic) interest could be e.g. the skeletal muscles in case of Duchenne muscular dystrophy treatment, T-helper cells in the case of HIV therapy, the brain in case of Huntington's or Alzheimer's disease, the liver, the pancreas, a tumor or any other possible organ/tissue within the human body. An important consideration for tissue-specific CRISPR-Cas activation is the mode of delivery. AAV vectors are often considered as the prime choice for delivery of CRISPR-Cas into cells, animals or patients (Senis et al, 2014; Schmidt and Grimm, 2015). These are small, single- stranded and non-pathogenic DNA viruses belonging to the family of Parvoviridae. Besides their potency and safety for ex or in vivo gene delivery, AAVs are beneficial over other (viral) delivery systems due to the possibility to modulate tissue targeting as well as transduction efficacy after systemic vector administration in animals or humans. This can be achieved by "pseudotyping" AAV vectors, i.e. packaging the transgene-carrying genome into different natural or engineered AAV capsids (reviewed in Kay, 2011). Still, targeting specificity remains a major concern for most CRISPR applications, as none of the existing delivery systems, including pseudotyped/engineered AAV vectors, are absolutely stringent. Also, specific delivery into one out of several (histologically) closely related tissues (e.g. a specific type of neurons; a tumor, but not the surrounding healthy tissue; certain muscle types, e.g. skeletal muscles but not heart) is particularly challenging and close to impossible using existing delivery strategies. Hence, the risk of undesired CRISPR-Cas activation in off-target tissues and, consequently, of undesired side-effects during an in vivo CRISPR-Cas application including gene therapy in humans remains a major concern. Additional layers for controlling CRISPR-Cas activity in a tissue specific manner are, therefore, highly desired and urgently needed.

Endogenous microRNA (miRNA) signatures can be used to efficiently discriminate between different cell types and tissues. MicroRNAs are small, non-coding RNAs that play key roles in the regulation of mammalian gene expression. More than 1000 miRNAs have been described in humans (cf. e.g. www.mirbase.org), some of which (co-)occur mainly or exclusively in selected cell types or tissues, or which are dysregulated under specific conditions including diseases such as cancer. Several tissue-specific transgene expression strategies based on endogenous miRNA signatures exist (Xie et al, 2011; Geisler and Fechner, 2016). They commonly employ miRNA binding sites integrated typically into the 3' UTR (untranslated region) of a transgene. RNA interference (RNAi) mediated knockdown of transgene expression then occurs specifically within the tissue/cell type expressing the corresponding miRNA or miRNA set. This results in the negative regulation of transgene expression by endogenous miRNAs and thus transgene "exclusion" from unintended (off- target) tissues. A positive regulation of transgene expression by endogenous miRNAs ("miR- ON") has also been achieved (Amendola et al, 2013). In this case, a transcriptional repressor inhibiting the promoter driving a transgene is put under miRNA regulation, again by embedding miRNA binding sites into its 3' UTR. MicroRNA- induced knockdown of the repressor then releases transgene expression specifically within the tissue expressing the said miRNA (WO 2007/000668 A2). Moreover, two recent studies showed successful reduction of CRISPR-SpyCas9 activity in off-target cells by integrating miRNA target sites into the 3 ' UTR of the delivered Cas9 gene (Senis et al, 2014; Hirosawa et al, 2017). The latter study also created a tissue specific Cas-ON switch. To this end, the translational repressor L7Ae was put under miRNA control and Cas9 was expressed from an mRNA harboring an L7Ae binding motif (K-turn). However, the Cas-ON switch in the reported configuration is highly leaky and therefore unlikely to be of major benefit for ex vivo or in vivo studies as well as therapeutic applications.

There is, thus, a need in the art for improved means and methods for providing Cas nuclease activity in a cell- and/or tissue-specific manner. This problem is solved by the means and methods disclosed herein.

Accordingly, the present invention relates to a polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence.

As used in the following, the terms "have", "comprise" or "include" or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions "A has B", "A comprises B" and "A includes B" may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements. It will be understood that any component defined herein as being included may preferably be explicitly excluded from the claimed invention by way of proviso or negative limitation.

Further, as used in the following, the terms "preferably", "more preferably", "most preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting further possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding further embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other optional or non- optional features of the invention. Moreover, if not otherwise indicated, the term "about" relates to the indicated value with the commonly accepted technical precision in the relevant field, preferably relates to the indicated value ± 20%, more preferably ± 10%, most preferably ± 5%. Further, the term "essentially" indicates that deviations having influence on the indicated result or use are absent, i.e. potential deviations do not cause the indicated result to deviate by more than± 20%, more preferably ± 10%>, most preferably ± 5%. Thus, "consisting essentially of means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention. For example, a composition defined using the phrase "consisting essentially of encompasses any known acceptable additive, excipient, diluent, carrier, and the like. Preferably, a composition consisting essentially of a set of components will comprise less than 5% by weight, more preferably less than 3% by weight, even more preferably less than 1%, most preferably less than 0.1% by weight of non-specified component(s). In the context of nucleic acid sequences, the term "essentially identical" indicates a %identity value of at least 80%, preferably at least 90%, more preferably at least 98%, most preferably at least 99%). As will be understood, the term essentially identical includes 100% identity. The aforesaid applies to the term "essentially complementary" mutatis mutandis. The term "polynucleotide", as used herein, refers to a linear or circular nucleic acid molecule. The term encompasses single as well as partially or completely double-stranded polynucleotides. Preferably, the polynucleotide is RNA or DNA, including cDNA. Moreover, comprised are also chemically modified polynucleotides including naturally occurring modified polynucleotides such as glycosylated or methylated polynucleotides or artificially modified derivatives such as biotinylated polynucleotides. The polynucleotide of the present invention shall be provided, preferably, either as an isolated polynucleotide (i.e. isolated from its natural context) or in genetically modified form.

The polynucleotide of the invention, preferably, comprises at least one heterologous sequence, i.e. comprises sequences from at least two different species. Preferably, said sequences from two different species are the sequence encoding an Acr polypeptide and the R Ai target sequence. Also preferably, the polynucleotide comprises at least one heterologous sequence relative to a mammalian, preferably human, cell, i.e. comprises at least one nucleic acid sequence not known to occur or not occurring in a mammalian, preferably human, cell. Preferably, said heterologous sequence relative to a mammalian cell is at least the sequence encoding an Acr polypeptide. Also preferably, the polynucleotide comprises at least one sequence homologous to a sequence comprised in a mammalian cell; said homologous sequence, preferably, is the RNAi target sequence, which is, more preferably, an miRNA target sequence as specified elsewhere herein.

The polynucleotide of the present invention has the activities of (i) encoding an Acr polypeptide and (ii) comprising an RNA-interference (RNAi) target sequence, both as specified elsewhere herein; thus, as referred to herein, the polynucleotide has the activities of (i) causing production of a functional Acr polypeptide in a permissive host cell and (ii) of being degraded and/or translationally inhibited (in case the polynucleotide is an RNA) or of causing degradation and/or translational inhibition of an RNA expressed from said polynucleotide (in case the polynucleotide is e.g. a DNA) in the presence of the factors required for RNAi as specified herein below. Preferably, the RNAi target sequence is not comprised in the sequence encoding an Acr polypeptide; thus, preferably, the polynucleotide comprises said elements in the order 5'- RNAi target sequence(s) - sequence encoding an Acr polypeptide -3', or, 5'- RNAi target sequence(s) - sequence encoding an Acr polypeptide - RNAi target sequence(s) -3', or 5'- sequence encoding an Acr polypeptide - RNAi target sequence(s) -3'; more preferably the order is 5'- sequence encoding an Acr polypeptide - RNAi target sequence(s) -3'. Preferably, the polynucleotide comprises the nucleic acid sequence of SEQ ID NO:21, preferably encoding a polypeptide comprising the amino acid sequence of SEQ ID NO:20, and comprises an RNAi target sequence, preferably a miRNA target sequence, preferably selected from the list consisting of SEQ ID NOs: 40 to 43. As used herein, the term polynucleotide, preferably, includes variants of the specifically indicated polynucleotides. More preferably, the term polynucleotide relates to the specific polynucleotides indicated. The term "polynucleotide variant", as used herein, relates to a variant of a polynucleotide related to herein comprising a nucleic acid sequence characterized in that the sequence can be derived from the aforementioned specific nucleic acid sequence by at least one nucleotide substitution, addition and/or deletion, wherein the polynucleotide variant shall have the activities as specified for the specific polynucleotide. Thus, it is to be understood that a polynucleotide variant as referred to in accordance with the present invention shall have a nucleic acid sequence which differs due to at least one nucleotide substitution, deletion and/or addition. Preferably, said polynucleotide variant comprises an ortholog, a paralog or another homolog of the specific polynucleotide or of a functional subsequence thereof, e.g. of the sequence encoding an Acr polypeptide. Also preferably, said polynucleotide variant comprises a naturally occurring allele of the specific polynucleotide or of a functional subsequence thereof, in particular of the sequence encoding an Acr polypeptide. In the context of polynucleotide variants, the term "functional subsequence", as used herein, relates to a part sequence of the polynucleotide of the present invention mediating at least one activity thereof; thus, preferably, the term functional subsequence relates to (i) a part sequence causing production of a functional Acr polypeptide in a permissible host cell, or (ii) a part sequence being degraded and/or translationally inhibited (in case the part sequence is comprised in an RNA) or of causing degradation and/or translational inhibition of an RNA expressed from said polynucleotide (in case the polynucleotide is e.g. a DNA) in the presence of the factors required for RNA-mediated degradation. Polynucleotide variants also encompass polynucleotides comprising a nucleic acid sequence which is capable of hybridizing to the aforementioned specific polynucleotides or functional subsequences thereof, preferably, under stringent hybridization conditions. These stringent conditions are known to the skilled worker and can be found in Current Protocols in Molecular Biology, John Wiley & Sons, N. Y. (1989), 6.3.1-6.3.6. A preferred example for stringent hybridization conditions are hybridization conditions in 6x sodium chloride/sodium citrate (= SSC) at approximately 45°C, followed by one or more wash steps in 0.2x SSC, 0.1% SDS at 50 to 65°C. The skilled worker knows that these hybridization conditions differ depending on the type of nucleic acid and, for example when organic solvents are present, with regard to the temperature and concentration of the buffer. For example, under "standard hybridization conditions" the temperature differs depending on the type of nucleic acid between 42°C and 58°C in aqueous buffer with a concentration of O. lx to 5x SSC (pH 7.2). If organic solvent is present in the abovementioned buffer, for example 50% formamide, the temperature under standard conditions is approximately 42°C. The hybridization conditions for DNA:DNA hybrids are preferably for example O. lx SSC and 20°C to 45°C, preferably between 30°C and 45°C. The hybridization conditions for DNA:RNA hybrids are preferably, for example, O. lx SSC and 30°C to 55°C, preferably between 45°C and 55°C. The abovementioned hybridization temperatures are determined for example for a nucleic acid with approximately 100 bp (= base pairs) in length and a G + C content of 50% in the absence of formamide. The skilled worker knows how to determine the hybridization conditions required by referring to textbooks such as the textbook mentioned above, or the following textbooks: Sambrook et al, "Molecular Cloning", Cold Spring Harbor Laboratory, 1989; Hames and Higgins (Ed.) 1985, "Nucleic Acids Hybridization: A Practical Approach", IRL Press at Oxford University Press, Oxford; Brown (Ed.) 1991, "Essential Molecular Biology: A Practical Approach", IRL Press at Oxford University Press, Oxford. Alternatively, polynucleotide variants are obtainable by PCR-based techniques such as mixed oligonucleotide primer- based amplification of DNA, i.e. using degenerated primers against conserved domains of a polypeptide of the present invention. Conserved domains of a polypeptide may be identified by a sequence comparison of the nucleic acid sequence of the polynucleotide or the amino acid sequence of the polypeptide of the present invention with sequences of other organisms. As a template, DNA or cDNA from bacteria, fungi, plants or, preferably, from animals may be used. Further, variants include polynucleotides comprising nucleic acid sequences which are at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 98% or at least 99% identical to the specifically indicated nucleic acid sequences or functional subsequence thereof. Moreover, also encompassed are polynucleotides which comprise nucleic acid sequences encoding amino acid sequences which are at least 70%>, at least 75%, at least 80%>, at least 85%, at least 90%, at least 95%, at least 98% or at least 99% identical to the amino acid sequences specifically indicated. The percent identity values are, preferably, calculated over the entire amino acid or nucleic acid sequence region. A series of programs based on a variety of algorithms is available to the skilled worker for comparing different sequences. In this context, the algorithms of Needleman and Wunsch or Smith and Waterman give particularly reliable results. To carry out the sequence alignments, the program PileUp (J. Mol. Evolution., 25, 351-360, 1987, Higgins et al, CABIOS, 5 1989: 151-153) or the programs Gap and BestFit [Needleman and Wunsch (J. Mol. Biol. 48; 443-453 (1970)) and Smith and Waterman (Adv. Appl. Math. 2; 482-489 (1981))], which are part of the GCG software packet (Genetics Computer Group, 575 Science Drive, Madison, Wisconsin, USA 53711 (1991)), are to be used. The sequence identity values recited above in percent (%) are to be determined, preferably, using the program GAP over the entire sequence region with the following settings: Gap Weight: 50, Length Weight: 3, Average Match: 10.000 and Average Mismatch: 0.000, which, unless otherwise specified, shall always be used as standard settings for sequence alignments.

A polynucleotide comprising a fragment of any of the specifically indicated nucleic acid sequences, said polynucleotide retaining the indicated activity or activities, is also encompassed as a variant polynucleotide of the present invention. A fragment as meant herein, preferably, comprises at least 100, preferably at least 200, more preferably at least 250 consecutive nucleotides of any one of the specific nucleic acid sequences or encodes an amino acid sequence comprising at least 50, preferably at least 60, more preferably at least 75 consecutive amino acids of any one of the specific amino acid sequences. The polynucleotides of the present invention either consist, essentially consist of, or comprise the aforementioned nucleic acid sequences. Thus, they may contain further nucleic acid sequences as well. Specifically, the polynucleotides of the present invention may encode fusion proteins wherein one partner of the fusion protein is an Acr polypeptide being encoded by a nucleic acid sequence recited herein. Such fusion proteins may comprise as additional part polypeptides for monitoring expression (e.g., green, yellow, blue or red fluorescent proteins, alkaline phosphatase and the like) or so called "tags" which may serve as a detectable marker or as an auxiliary measure for purification purposes. Tags for the different purposes are well known in the art and are described elsewhere herein. Preferably, the polynucleotide encodes an Acr polypeptide fused to a nuclear localization sequence (NLS). Preferably, the polynucleotide does not comprise a nucleic acid sequence encoding a Cas nuclease; more preferably, the polynucleotide further comprises a nucleic acid sequence encoding at least a fragment of a Cas nuclease, preferably as specified elsewhere herein.

Preferably, the polynucleotide is an R A. More preferably, the polynucleotide is a DNA comprising a nucleic acid sequence expressible as a continuous RNA comprising said sequence encoding an Acr polypeptide and said RNAi target sequence. Preferably, in case the polynucleotide is DNA, the polynucleotide is operatively linked to expression control sequences allowing expression in prokaryotic or eukaryotic, preferably in eukaryotic host cells or isolated fractions thereof. Expression of said polynucleotide comprises transcription of the polynucleotide, preferably into a translatable mRNA. Regulatory elements ensuring expression in eukaryotic cells, preferably mammalian cells, are well known in the art. They, preferably, comprise regulatory sequences ensuring initiation of transcription and, optionally, poly-A signals ensuring termination of transcription and stabilization of the transcript. Additional regulatory elements may include transcriptional as well as translational enhancers. Examples for regulatory elements permitting expression in eukaryotic host cells are the AOX1 or GALl promoter in yeast or the SMVP-, U6-, HI-, 7SK-, CMV- EFS-, SV40-, or RSV-promoter (Rous sarcoma virus), CMV-enhancer, SV40-enhancer or a globin intron in mammalian and other animal cells. Moreover, inducible or cell type-specific expression control sequences may be comprised in a polynucleotide of the present invention. Inducible expression control sequences may comprise tet or lac operator sequences or sequences inducible by heat shock or other environmental factors. Suitable expression control sequences are well known in the art. Besides elements which are responsible for the initiation of transcription, such regulatory elements may also comprise transcription termination signals, such as the SV40-poly-A site or the tk-poly-A site, downstream of the polynucleotide.

The "clustered regularly interspaced short palindromic repeats" or "CRISPR" systems are known to the skilled person, as described herein above. As used herein, the term "gRNA" includes a crRNA/tracrRNA hybrid and a crRNA-tracrRNA fusion RNA of a Cas CRISPR system, as well as a guide RNA of a CPFl CRISPR system. More preferably, the term gRNA relates to a crRNA-tracrRNA fusion RNA of a Cas CRISPR system, as well as a guide RNA of a CPFl CRISPR system. Most preferably, term gRNA relates to a crRNA-tracrRNA fusion RNA of a Cas CRISPR system. Preferably, the gRNA comprises at least 15, preferably at least 18, more preferably at least 20 nucleotides complementary to the target sequence. As used herein, the term "complementary", if not otherwise noted, relates to at least 90%, more preferably at least 95%, still more preferably 99% complementarity. Most preferably complementarity relates to 100% complementarity over the aforementioned number of nucleotides. Moreover, preferably, the gRNA of the present invention further comprises a nucleotide sequence mediating binding of a Cpfl endonuclease or comprises tracrRNA sequence, preferably of a Cas CRISPR system, more preferably of a Cas9 CRISPR system. Preferably, the gRNA comprises a structure 5 '-targeting sequence-activation sequence-3', more preferably, the gRNA comprises a structure 5'-targeting sequence-linker loop-activation sequence-3', wherein said linker loop comprises a stem-loop comprising of from 10 to 30, more preferably of from 15 to 25 base pairs.

The terms "CRISPR-associated endonuclease" and "Cas nuclease", as used herein, both equally relate to an endonuclease, preferably an endo-DNase, recognizing a gRNA as specified herein, which is, in principle, known in the art. Preferably, the Cas nuclease is a type II CRISPR endonuclease. Preferably, the Cas nuclease is a CRISPR endonuclease from Prevotella and Francisella endonuclease, i.e. a Cpfl endonuclease . More preferably, the CRISPR endonuclease is a Cas9 endonuclease. Preferably, the Cas9 nuclease is a Cas9 endonuclease from Staphylococcus aureus or is a Cas9 endonuclease from Streptococcus pyogenes, more preferably is a Cas9 endonuclease from Streptococcus pyogenes. Preferably, the Cas nuclease has an amino acid sequence as shown in SEQ ID NO:36, preferably encoded by a nucleic acid sequence as shown in SEQ ID NO:37. The term "fragment of a Cas nuclease", as used herein, relates to a polypeptide fragment of a Cas nuclease which by itself is not catalytically active as a nuclease, however can be reconstituted to form a catalytically active nuclease by contacting said fragment with a second fragment which by itself is not catalytically active as well. Thus, a fragment of a Cas nuclease, as referred to herein, is a reconstitutable fragment. An example of a combination of fragments of a Cas nuclease corresponding to the above definition is shown herein in the examples. Preferably, reconstitution of Cas activity is accomplished by fusion of two non-identical fragments of a Cas polypeptide to auxiliary peptide sequences mediating binding between the two fragments. More preferably, as shown in the examples, reconstitution of Cas activity is accomplished by fusion of two non- identical fragments to auxiliary peptide sequences mediating trans-protein splicing between the two fragments, e.g. by fusing the two Cas fragments to split intein sequences, preferably amino acid sequences comprisisng the sequences of SEQ ID NOs:24 and 32, preferanly encoded by nucleic acid sequences comprising the sequences of SEQ ID NOs: 25 and 33, respectively). Accordingly, a fragment of a Cas nuclease, preferably has the amino acid sequence of SEQ ID NO:22, preferably encoded by a polynucleotide comprising SEQ ID NO:23 and/or or SEQ ID NO:30, preferably encoded by a polynucleotide comprising SEQ ID NO:31. The terms "anti-CRISPR polypeptide" and "Acr polypeptide" are known to the skilled person and relate equally to a polypeptide having the activity of inhibiting at least one Cas nuclease, preferably a Cas9 nuclease. Acr polypeptides are known in the art e.g. from Pawluk et al. (2016), Cell 167(7): 1829, and from Rauch et al. (2017), Cell 168(1-2): 150. The inhibitory activity of a polypeptide to inhibit a Cas nuclease can be determined by determining the activity of said Cas nuclease in the presence of the suspected Acr polypeptide, preferably as specified herein in the Example of Fig. 2. Preferably, a polypeptide is identified as an Acr polypeptide if the activity of at least one Cas nuclease is inhibited by at least 50% in an assay as specified above. More preferably, a polypeptide is identified as an Acr polypeptide if the activity of at least one Cas9 nuclease, more preferably of Cas9 endonuclease from Streptococcus pyogenes, is inhibited by at least 50%> in an assay as specified above. However, as will be understood by the skilled person, it is also within the capabilities of the skilled person to establish whether a polypeptide of interest is an Acr polypeptide for another Cas nuclease of interest. As will also be understood, preferably, the Acr polypeptide of the present invention is selected such that it inhibits the Cas nuclease intended to be used. Thus, e.g. in case the Cas9 endonuclease from Streptococcus pyogenes is intended to be used for genetic modification and shall be inhibited in at least a part of cells contacted therewith, an Acr polypeptide of a Listeria monocytogenes prophage may be used. Thus, preferably, the Acr polypeptide is an Acr polypeptide of a Listeria monocytogenes prophage, more preferably is an AcrIIA2 or AcrIIA4 polypeptide, most preferably an AcrIIA4 polypeptide. Preferably, the Acr polypeptide comprises, preferably consists of, an amino acid sequence as shown in SEQ ID NO:20, more preferably encoded by a nucleic sequence comprising, preferably consisting of, the sequence as shown in SEQ ID NO:21. The term "RNA- interference" (RNAi) is known to the skilled person to relate to an endogenous biological process of most higher cells, including in particular mammalian cells and higher plant cells, in which double-stranded RNA (dsRNA) molecules inhibit expression of genes comprising a sequence complementary to a double-stranded RNA, mediated by the RNA-induced silencing complex (RISC). Without wishing to be bound by theory, RNAi is generally used to silence expression of a gene of interest by targeting mRNA. Briefly, the process of RNAi in the cell is initiated by dsRNAs which are cleaved by a ribonuclease, thus producing interfering RNA. The interfering RNA binds to another intracellular enzyme complex which is thereby activated to target whatever mRNA molecules are sufficiently complementary to the interfering RNA sequence. The function of the complex is to target the homologous mRNA molecule through base pairing interactions between one of the interfering RNA strands and the target mRNA. The effect of this binding largely depends on the degree of similarity between the interfering RNA and the target: in case there is imperfect complementarity (at least one base mismatch), the effect mainly is translational inhibition, i.e. prevention of translation of the target mRNA; in case there is perfect complementarity (no mismatch) the effect mainly is degradation of the target mRNA: The mRNA is then cleaved approximately 12 nucleotides from the 3' terminus of the siRNA and degraded. In this manner, specific mRNAs can be targeted and translationally inhibited and/or degraded, thereby resulting in a loss of protein expression from the targeted mRNA. As is also known to the skilled person, RNAi can be caused by an exogenous (heterologous) dsRNA molecule, which is cleaved to provide a silencing RNA (siRNA), or may be initiated by an endogenous dsRNA molecule, cleaved to provide a micro-RNA (miRNA). Both pathways converge at the RISC, which, depending on the degree of homology between the dsRNA and its target, may induce translational repression and/or degradation of the targeted RNA. As is understood by the skilled person, the exogenous dsRNA causing RNAi may be provided to the cell as such, e.g. by transfection of a dsRNA, which may be a short hairpin RNA (shRNA), or may be provided by expressing an RNA forming such dsRNA. Thus, unless otherwise noted, the term siRNA includes shRNA. Accordingly, the term "RNAi target sequence", as used herein, relates to a nucleic acid sequence specifically hybridizing to a dsRNA inducing RNA interference (interfering RNA). Thus, the RNAi target sequence is a sequence essentially complementary to at least one RNAi inducing molecule (interfering RNA). Preferably, the RNAi target sequence is a miRNA target sequence or a siRNA target sequence, preferably is a miRNA target sequence. Thus, preferably, the present invention relates to a polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) a miRNA target sequence.

Preferably, the polynucleotide of the present invention comprises at least two RNAi target sequences. As will be understood, the two RNAi target sequences may be essentially identical, or may be different. Thus, in the first case, the at least two RNAi target sequences are essentially complementary to the same interfering RNA, preferably are essentially complementary to the same nucleic acid sequence of an interfering RNA. More preferably, in such case, the at least two RNAi target sequences are 100% complementary to the same miRNA, preferably are 100% complementary to the same nucleic acid sequence of an interfering RNA. In the second case, the at least two RNAi target sequences are not essentially identical, more preferably are less than 80%, even more preferably less than 70%, most preferably less than 60% identical to each other. Thus, preferably, in case the at least two RNAi target sequences are different, they are essentially, preferably 100%, complementary to two different interfering RNAs. As will be understood by the skilled person, the polynucleotide of the present invention may also comprise more than two RNAi target sequences, e.g. three essentially identical RNAi target sequences, or two essentially identical target sequences plus one RNAi target sequence non- identical to the other two, or an analogous constellation. As will be also understood by the skilled person, the polynucleotide of the invention may also comprise RNAi target sequences of different types, e.g. one siRNA target site and one miRNA target site; or three RNAi target sites of which two are miRNA target sites (which may be essentially identical, or not) and one siRNA target site. Preferably, the polynucleotide comprises at least one miRNA target site, more preferably at least two miRNA target sites, even more preferably at least two essentially identical miRNA target sites. According to the invention, inclusion of miRNA target sites is, preferably, used to ensure Cas nuclease activity in one or more specific tissue(s) and/or cell type(s) and inclusion of siRNA target sites is used to permit external induction of Cas nuclease activity.

The term "interfering RNA", as used herein, relates to an RNA molecule inducing RNA interference; as detailed elsewhere herein, the interfering RNA is an at least partially double- stranded RNA molecule; correspondingly, the term interfering single-stranded RNA (ss- iRNA) relates to a single-stranded RNA derived from an interfering RNA by the cellular silencing components and inducing RNA interference. The term interfering RNA preferably refers to RNA having a duplex structure comprising two complementary and anti-parallel nucleic acid strands. Not all nucleotides of a double-stranded portion of an interfering RNA necessarily exhibit complete Watson-Crick base pairs; the two RNA strands may be substantially complementary. The RNA strands forming the double-stranded portion of the interfering RNA may have the same or a different number of nucleotides, with the maximum number of base pairs being the number of nucleotides in the shorter strand of the RNA. Preferably, the double-stranded region of the interfering RNA is no more than 200, more preferably less than 100, even more preferably less than 50, most preferably between 19 and 23, nucleotides in length. The interfering RNA is subsequently degraded by a ribo nuclease enzyme into a short interfering RNA (siRNA) or a microRNA (miRNA). The complementary regions of the interfering RNA or ss-iRNA allow sufficient hybridization to the target RNA and thus mediate RNAi. In mammalian cells, ss-iRNAs are approximately 20-25 nucleotides in length. The ss-iRNA sequence needs to be of sufficient length to bring the ss-iRNA and target RNA together through complementary base-pairing interactions. The length of the ss- iRNA is preferably of sufficient length to stably interact with the target RNA; specifically 10- 30 nucleotides; more specifically is any integer between 10 and 30 nucleotides, most preferably 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30. By "stably interact" is meant interaction of the ss-iRNA with the target nucleic acid, preferably by forming hydrogen bonds with complementary nucleotides in the target under physiological conditions. Preferably, complementarity between the ss-iRNA and the RNA target is at least 80%, more preferably at least 90%, even more preferably at least 95%, still more preferably at least 98%. Most preferably, complementarity between the ss-iRNA and the RNA target is 100%. Preferably, said complementarity is calculated over the stretch of at least 20 nucleotides providing the highest complementarity value, more preferably is calculated over the whole length of the ss-iRNA. Methods relating to the use of RNAi to silence genes in organisms, including C. elegans, Drosophila, plants, and mammals, are known in the art (see, e.g., WO 0129058; WO 09932619; and Elbashir (2001), Nature 411 : 494-498). Preferably, the interfering RNA is a siRNA. In a narrow sense, the term siRNA relates to the short, single-stranded RNA molecule cleaved from a dsRNA precursor and incorporated into the protein complex mediating gene silencing; however, in a broader sense, the term is used both in the aforementioned sense and for the precursor dsRNA from which the single- stranded siRNA is cleaved; the latter, broader definition is the definition as used herein; for differentiation, the siRNA in the narrow sense is referred to as single-stranded siRNA. Thus, the term "siRNA", as used herein, refers to an exogenous dsRNA which is at least in part essentially complementary to an RNAi target sequence of the invention and which diminishes or abolishes gene expression by RNA interference (RNAi). The term "exogenous RNA", as used herein, relates to an RNA originating from the exterior of a cell; for the avoidance of doubt, the term includes RNA introduced into a cell as such, but also includes RNA for which a different polynucleotide, in particular a DNA, was introduced to a cell to cause expression of said RNA. Structures of appropriate siRNAs and methods for providing them are well- known in the art. Preferably, the siRNA is an RNA comprising inverted repeats, preferably intervened by a "loop" sequence, wherein said inverted repeat sequences comprise a sequence essentially complementary to an RNAi target sequence, preferably having a length and complementarity as specified herein above.

More preferably, the interfering RNA is a microRNA (miRNA). In analogy to the above, the term miRNA relates to the short, single-stranded RNA molecule cleaved from a miRNA precursor and incorporated into the protein complex mediating gene silencing; however, in a broader sense, the term is used both in the aforementioned sense and for the precursor miRNA from which the single-stranded miRNA is cleaved; the latter, broader definition is the definition as used herein; for differentiation, the miRNA in the narrow sense is referred to as single- stranded miRNA. Thus, the term "miRNA", as used herein, refers to an endogenous RNA which is at least in part essentially complementary to an RNAi target sequence of the invention and which diminishes or abolishes gene expression by RNA interference (RNAi). The term "endogenous RNA", as used herein, relates to an RNA originating from the cell itself; preferably, the miRNA is a nucleic acid transcribed from the genome of the cell. Preferably, the miRNA is a miRNA expressed in at most five tissues and/or cell types, more preferably at most four tissues and/or cell types, even more preferably at most three tissues and/or cell types, still more preferably at most two tissues and/or cell types; most preferably, expression of the miRNA is tissue- and/or cell type-specific. Specificity of expression in tissue and cell type are known for most miRNAs and can be derived from public databases. Moreover, methods for determining tissue and/or cell type specificity of a miRNA are known in the art, e.g. from Landgraf et al. ((2007), Cell 129(7): 1401, Guo et al. (2014), Scientific Reports 4, doi: 10.1038/srep05150; Babak et al. (2004), RNA 10: 1813; Liu et al. (2011), J Biomed Sci Eng 4(19): 666; Ludwig et al. (2016), NAR 44(8):3865; and Baker et al. (2017) JASN, doi: 10.1681/ASN.2016121280). Preferably, the miRNA is a mammalian, more preferably a human miRNA; e.g., the database miRBase (www.mirbase.org), release 21, lists 296 high-confidence human miRNAs. More preferably, the miRNA is selected from human miRNAs miR-1 (SEQ ID NO:44), miR-206 (SEQ ID NO:45), miR-208a (SEQ ID NO:46), miR-122 (SEQ ID NO:47), and miR-142 (SEQ ID NO:48). Advantageously, it was found in the work underlying the present invention that the activity of a Cas nuclease can be inhibited in a cell by expressing an Acr gene, but this inhibition can be relieved in a cell type-specific manner if a miRNA-dependent degradation signal is incorporated in the mRNA encoding the Acr. As will be understood, by appropriately selecting the miRNA target sequence, e.g. a miRNA expressed in more than one cell type, or by including target sequences for more than one miRNA, release of inhibition in more than one cell type and/or tissue is possible. Moreover, by providing a polynucleotide comprising only a siRNA target site by means of a cell type-specific delivery means, and by further providing a siRNA by a second delivery means, double specificity of Cas nuclease activity can be achieved; i.e. in case the first delivery means is specific for a first receptor on the surface of a cell, and the second delivery means is specific for a second receptor, activation of Cas nuclease will only occur in cells having both receptors. Of advantage is further that inhibition of the Cas nuclease takes place post-translationally. Hence, Cas activity can be efficiently suppressed at any point in time as transcription and translation of the small Acr (87 amino acids in case of AcrIIA4) is faster and more efficient as compared to the long Cas (>1,000 amino acids). Further, in contrast to existing miR-ON/Cas-ON strategies, the system of the invention is independent of specific regulatory elements required within the Cas transgene itself such as repressor-dependent promoter variants or repressor-targetable, regulatory elements within UTRs (untranslated regions) of the transgene. The definitions made above apply mutatis mutandis to the following. Additional definitions and explanations made further below also apply for all embodiments described in this specification mutatis mutandis. The present invention further relates to a vector comprising the polynucleotide according to the present invention.

As used herein, the term "vector" relates to a polynucleotide comprising structural determinants required for delivering into and/or stably maintaining and/or propagating the polynucleotide in a cell, said structural determinants optionally including the elements of an outer shell of a self-propagating entity, e.g. a virus. The term, preferably, encompasses phage, plasmid, and viral vectors as well as artificial chromosomes, such as bacterial or yeast artificial chromosomes. Thus, the vector may be or comprise R A or DNA. Moreover, the term also relates to targeting constructs which allow for random or site-directed integration of the targeting construct into genomic DNA. Such target constructs, preferably, comprise DNA of sufficient length for either homologous or heterologous recombination as described in detail below. The vector encompassing the polynucleotide of the present invention, preferably, further comprises selectable markers for propagation and/or selection in a host. The vector may be delivered into a host cell by various techniques well known in the art. For example, a plasmid vector can be introduced in a precipitate such as a calcium phosphate precipitate or rubidium chloride precipitate, or in a complex with a charged lipid or in carbon- based clusters, such as fullerenes. Alternatively, a plasmid vector may be introduced by heat shock or electroporation techniques. Should the vector be a virus, it may be packaged in vitro using an appropriate packaging cell line prior to application to host cells. Retroviral vectors may be replication-competent or replication-defective. In the latter case, viral propagation generally will occur only in complementing host/cells. Preferably, the vector is an adeno- associated virus, preferably a non-replication-competent adeno-associated virus. Targeted delivery, i.e. delivery of a polynucleotide or vector into one or more cell population(s) or tissue(s) with high specificity may be achieved by viral vectors, which may have a natural tropism for cell(s) and/or tissue(s) of interest or may be retargeted thereto; however, also non- viral targeting methods are known to the skilled person, e.g. from Harris et al. (2010), Biomaterials 31(5): 998. Preferably, in the vector of the invention the polynucleotide is operatively linked to expression control sequences as specified herein above. In this context, suitable expression vectors are known in the art such as Okayama-Berg cDNA expression vector pcDVl (Pharmacia), pBluescript (Stratagene), pCDM8, pRc/CMV, pcDNAl, pcDNA3 (ThermoFisher) or pSPORTl (Invitrogen). Analogous expression control vectors are also known for RNA vectors such as retroviruses. Preferably, the vector is an expression vector and a gene transfer or targeting vector. Expression vectors derived from viruses such as retroviruses, vaccinia virus, adeno-associated virus, herpes viruses, or bovine papilloma virus, may be used for delivery of the polynucleotides or vector of the invention into targeted cell population. Methods which are well known to those skilled in the art can be used to construct recombinant viral vectors; see, for example, the techniques described in Sambrook, Molecular Cloning A Laboratory Manual, Cold Spring Harbor Laboratory (1989) N.Y. and Ausubel, Current Protocols in Molecular Biology, Green Publishing Associates and Wiley Interscience, N.Y. (1994).

The present invention also relates to a host cell comprising the polynucleotide according to the present invention and/or the vector according to the present invention.

As used herein, the term "host cell" relates to any cell capable of receiving, and optionally maintaining and/or propagating, the polynucleotide and/or the vector of the present invention. Preferably, the cell is a bacterial cell, more preferably a cell of a common laboratory bacterial strain known in the art, most preferably an Escherichia strain, in particular an E. coli strain. Also preferably, the host cell is a eukaryotic cell, preferably a plant or yeast cell, e.g. a cell of a strain of baker's yeast, or is an animal cell. More preferably, the host cell is an insect cell or a mammalian cell, in particular a mouse or rat cell. Even more preferably, the host cell is a mammalian cell, most preferably is a human cell. The term "permissive host cell", as used herein, relates to a host cell as specified herein comprising all components required for RNA interference to occur being general for the pathway; i.e. in a permissive host cell RNA interference is expected to occur in case a target RNA and an interfering RNA are provided. Preferably, the permissive host cell is a plant or yeast cell, e.g. a cell of a strain of baker's yeast, or is an animal cell. More preferably, the permissive host cell is an insect cell or a mammalian cell, in particular a mouse or rat cell. Even more preferably, the permissive host cell is a mammalian cell, most preferably is a human cell. The present invention further relates to the polynucleotide according to the present invention and/or the vector according to the present invention and/or the host cell according to the present invention for use in medicine. The present invention further relates to the polynucleotide according to the present invention and/or the vector according to the present invention and/or the host cell according to the present invention for use in treatment and/or prevention of genetic disease, neurodegenerative disease, cancer, and/or infectious disease.

The means and methods of the present invention are, in principle, usable in treatment and/or prevention of each and every disease for which genetic modification of a cell, preferably a specific type of cell, is considered beneficial. Such is the case in particular in genetic disease, neurodegenerative disease, cancer, and infectious disease. As used herein, the term "genetic modification", preferably, includes modification of any kind of nucleic acid comprised in a host cell at a given time, including nuclear DNA, organelle DNA (mitochondrial DNA or plastid DNA), but also nucleic acid from an infectious agent, either as free nucleic acid or covalently connected to the DNA of the host cell. Preferably, genetic modification is modification of nucleic acid, preferably DNA, present in the nucleus of a host cell. The term "treatment" refers to an amelioration of the diseases or disorders referred to herein or the symptoms accompanied therewith to a significant extent. Said treating as used herein also includes an entire restoration of the health with respect to the diseases or disorders referred to herein. It is to be understood that treating as used in accordance with the present invention may not be effective in all subjects to be treated. However, the term shall require that, preferably, a statistically significant portion of subjects suffering from a disease or disorder referred to herein can be successfully treated. Whether a portion is statistically significant can be determined without further ado by the person skilled in the art using various well known statistic evaluation tools, e.g., determination of confidence intervals, p-value determination, Student ^' s t-test, Mann- Whitney test etc.. Preferred confidence intervals are at least 90%, at least 95%, at least 97%, at least 98% or at least 99 %. The p-values are, preferably, 0.1, 0.05, 0.01 , 0.005, or 0.0001. Preferably, the treatment shall be effective for at least 10%, at least 20%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of the subjects of a given cohort or population. The term "preventing" refers to retaining health with respect to the diseases or disorders referred to herein for a certain period of time in a subject. It will be understood that the said period of time is dependent on a variety of individual factors of the subject and the specific preventive treatment. It is to be understood that prevention may not be effective in all subjects treated with the compound according to the present invention. However, the term requires that, preferably, a statistically significant portion of subjects of a cohort or population are effectively prevented from suffering from a disease or disorder referred to herein or its accompanying symptoms. Preferably, a cohort or population of subjects is envisaged in this context which normally, i.e. without preventive measures according to the present invention, would develop a disease or disorder as referred to herein. Whether a portion is statistically significant can be determined without further ado by the person skilled in the art using various well known statistic evaluation tools discussed elsewhere in this specification.

The term "genetic disease", as used herein, relates to a disease causally linked to one or more modifications, preferably mutations in the genome of an individual. Thus, preferably, the genetic disease is causally linked to one or more epigenetic changes, more preferably is causally linked to one or more genetic mutations. As will be understood, symptoms of a genetic disease often are caused by expression of a mutated gene and/or lack of expression of a gene providing normal function of the gene product in one or more specific tissue(s) and/or cell type(s). Thus, it may be preferable to genetically modify by Cas activity only those cells in which the mutation contributes to disease. Preferably, the genetic disease is Duchenne muscular dystrophy, Huntington's disease, Hemophilia A/B, cystic fibrosis, myotubular myopathy, a glycogen storage disorder, or sickle cell anemia, the causes and symptoms of which are known to the skilled person from textbooks of medicine.

The term "neurodegenerative disease" relates to a disease caused by progressive loss of structure and/or function of neurons in the peripheral and/or central nervous system of an individual. Preferably, the neurodegenerative disease is a neurodegenerative disease of motoneurons and/or a neurodegenerative disease of the central nervous system. Preferably, the neurodegenerative disease is Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, or a spinocerebellar ataxia, preferably spinocerebellar ataxia type 1 (SCA1). As will be understood, many neurodegenerative diseases are genetic diseases. The term "cancer" is, in principle, understood by the skilled person and relates to a disease of an animal, including man, characterized by uncontrolled growth by a group of body cells ("cancer cells"). This uncontrolled growth may be accompanied by intrusion into and destruction of surrounding tissue and possibly spread of cancer cells to other locations in the body. Preferably, also included by the term cancer is a relapse. Thus, preferably, the cancer is a non-solid cancer, e.g. a leukemia, or is a tumor of a solid cancer, a metastasis, or a relapse thereof. As is known to the skilled person, cancer cells accumulate mutations in particular in oncogenes or in tumor-suppressor genes, which may be amenable to correction by genetic modification. Moreover, the means and methods of the present invention may be used to induce cell death, e.g. via apoptosis, specifically in cancer cells. Preferably, treating cancer is reducing tumor and/or cancer cell burden in a subject. As will be understood by the skilled person, effectiveness of treatment of e.g. cancer is dependent on a variety of factors including, e.g. cancer stage and cancer type. The term "infectious disease" is, in principle, understood by the skilled person. Preferably, the term as used herein relates to an infectious disease in which the replicative cycle of the infectious agent comprises at least one stage in which the genome of the infectious agent is present in a permissive host cell. Thus the infectious disease, preferably, is a viral infection, preferably is immunodeficiency virus infection, herpes virus infection, papillomavirus infection, or hepatitis B virus infection.

The present invention further relates to a kit comprising

(I) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence; and a Cas nuclease or a second polynucleotide comprising an expressible gene encoding a Cas nuclease;

(II) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence, said first polynucleotide further comprising an expressible gene encoding a first fragment of a Cas nuclease; and a second polynucleotide comprising an expressible gene encoding a second fragment of a Cas nuclease, wherein said first and second fragment of said Cas nuclease together reconstitute an active Cas nuclease; or

(III) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide, (ii) an RNA-interference (RNAi) target sequence, and (iii) a sequence encoding a Cas nuclease; and a second polynucleotide comprising an expressible gene encoding an inhibitory RNA, preferably a siR A or a miRNA hybridizing to said RNAi target sequence, more preferably a siRNA hybridizing to said RNAi target sequence.

The term "kit", as used herein, refers to a collection of the aforementioned compounds, means or reagents of the present invention which may or may not be packaged together. The components of the kit may be comprised by separate vials (i.e. as a kit of separate parts) or provided in a single vial. Moreover, it is to be understood that the kit of the present invention, preferably, is to be used for practicing the methods referred to herein above. It is, in an embodiment, envisaged that all components are provided in a ready-to-use manner for practicing the methods referred to above. Further, the kit, in an embodiment, contains instructions for carrying out said methods. The instructions can be provided by a user's manual in paper or electronic form. In addition, the manual may comprise instructions for interpreting the results obtained when carrying out the aforementioned methods using the kit of the present invention. Preferably, the first polynucleotide comprised in the kit is the polynucleotide of the present invention. Also preferably, expression of a nucleic acid sequence encoding a Cas nuclease or fragment thereof optionally comprised by a polynucleotide of the kit is driven by a cell type-specific promoter. Also preferably, the kit further comprises a polynucleotide encoding at least one guide RNA (gRNA). Preferably, the polynucleotide encoding at least one gRNA is the first or the second polynucleotide, more preferably is the second polynucleotide. As will be understood from the above, the description of the kit comprising polynucleotides, preferably, relates to a kit comprising corresponding vectors mutatis mutandis.

Preferably, the kit further comprises at least one delivery means for the polynucleotides it comprises, the term "delivery means" relating to any means suitable to cause a polynucleotide of the kit to enter the interior of a host cell, preferably a permissive host cell. Suitable delivery means are known in the art and include in particular transfection reagents, packaging means, and the like. Preferably, the polynucleotides of the present invention are pre-packaged in a delivery means, e.g. in viral particles. As specified herein above, the skilled person is aware of delivery means providing different specificities for cellular receptors. Accordingly, preferably, the first polynucleotide of the kit is packaged in a first delivery means targeting a first receptor of a permissive host cell; and said second polynucleotide is packaged in a second delivery means targeting a second receptor of said permissive host cell. Preferably, the first and second delivery means are non-identical and differ at least in the cellular receptor which they preferentially target. Also preferably, the first receptor and the second receptor are non-identical and are both present in an accessible manner, preferably on the surface of a target cell. In a first embodiment, the kit comprises a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence; and a second polynucleotide comprising an expressible gene encoding a Cas nuclease. Accordingly, by co-delivering the first and second polynucleotide into a host cell, Cas activity is inhibited, however, can be activated if the cell expresses a miRNA corresponding to the RNAi target sequence of the first polynucleotide or by additionally delivering a siRNA or shRNA corresponding to the RNAi target sequence of the first polynucleotide. Thus, preferably, in the first embodiment, the kit is for cell type- or tissue- specific Cas activation, or for inducible Cas activation.

In a second embodiment, the kit comprises a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence, said first polynucleotide further comprising an expressible gene encoding a first fragment of a Cas nuclease, and a second polynucleotide comprising an expressible gene encoding a second fragment of a Cas nuclease, wherein said first and second fragment of said Cas nuclease together reconstitute an active Cas nuclease. As will be understood, the fragments of a Cas nuclease expressed from the polynucleotides of the kit are non-active, however, together generate an active Cas nuclease, as specified herein above. Accordingly, by co-delivering the first and second polynucleotide into a host cell, Cas activity is reconstituted, however is inhibited by the Acr polypeptide; thus, Cas activity can be activated as detailed above for the first embodiment of the kit. As will be understood, in case the first and the second polypeptide are delivered by delivery means targeting two non-identical cellular receptors, specificity of delivery of Cas nuclease activity may be further increased.

In a third embodiment, the kit comprises a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide, (ii) an RNA-interference (RNAi) target sequence, and (iii) a sequence encoding a Cas nuclease; and a second polynucleotide comprising an expressible gene encoding an inhibitory RNA, preferably a siRNA or shRNA or a miRNA hybridizing to said RNAi target sequence, more preferably a siRNA hybridizing to said RNAi target sequence. As will be understood, in case the first and the second polypeptide are delivered by delivery means targeting two non-identical cellular receptors, Cas nuclease activation may be restricted to cells carrying both the first and the second receptor. The present invention further relates to a method for genetically modifying a host cell comprising

al) contacting said host cell with a polynucleotide according to the present invention; with the vector according to the present invention; and/or with the host cell according to the present invention; and further contacting said host cell with a Cas nuclease activity and a gR A; or a2) contacting said host cell with the components comprised in a kit according to the present invention and a gRNA;

and,

b) thereby, genetically modifying said host cell. The method for genetically modifying a host cell of the present invention, preferably, is an in vitro method. In an embodiment, the method may, however, also be applied in vivo. Moreover, the method may comprise steps in addition to those explicitly mentioned above. For example, further steps may relate, e.g., to providing host cells, preferably permissive host cells, for step al) and/or a2), or incubating said cells for an appropriate time in step b). Moreover, one or more of said steps may be performed by automated equipment.

The term "genetically modifying" is, in principle, understood by the skilled person and relates to introducing at least one modification into a nucleic acid of a host cell, wherein said modification causes altered expression of at least one gene. Thus, genetically modifying, preferably, includes introducing at least one mutation, as well as introducing at least one epigenetic modification, as disclosed e.g. in Jurkowski et al, (2015), Clin Epigenetics 7(1): 18. Preferably, genetically modifying is introducing at least one mutation into a nucleic acid, preferably DNA, more preferably the genome of the host cell. Preferably, said mutation is deletion of a part of the genome by a Cas nuclease activity and/or introducing a nucleic acid sequence comprising at least one mutation compared to the original sequence into the genome of said cell. Thus, more preferably, genetically modifying is exchanging a gene or a part thereof for a modified version thereof. Most preferably, genetically modifying is exchanging a non- functional copy of a gene for a functional copy thereof. The term "contacting", as used in the context of the methods of the present invention, is understood by the skilled person. Preferably, the term relates to bringing at least one polynucleotide, vector, and/or host cell of the present invention in physical contact with a host cell, preferably a permissive host cell e.g. allowing the sample and the compound(s) to interact. Preferably, contacting includes delivery of at least one polynucleotide of the present invention into the interior of a host cell, preferably via a delivery means.

The present invention also relates to a method for treating genetic disease, neurodegenerative disease, cancer, and/or infectious disease in a subject suffering therefrom, said method comprising

al) contacting said host cell with a polynucleotide according to the present invention; with the vector according to the present invention; and/or with the host cell according to the present invention; and further contacting said host cell with a Cas nuclease activity and a gR A; or a2) contacting said host cell with the components comprised in a kit according to the present invention and a gRNA; and,

b) thereby, treating genetic disease, neurodegenerative disease, cancer, and/or infectious disease in said subject.

The method for treating a subject of the present invention, preferably, is an in vivo method. In an embodiment, the method may, however, also be applied in vitro. Moreover, the method may comprise steps in addition to those explicitly mentioned above. For example, further steps may relate, e.g., to providing a sample of host cells, preferably permissive host cells, for step al) and/or a2), or incubating said cells for an appropriate time in step b). Moreover, one or more of said steps may be performed by automated equipment.

According to the present invention, the polynucleotide, the vector, the host cell, and/or the components of the kit are, preferably, administered to a sample of the subject comprising permissive host cells, e.g. a blood sample, and said sample or cells derived thereof are re- administered to said subject after they were genetically modified. More preferably, the polynucleotide, the vector, the host cell, and/or the components of the kit are administered to the subject directly, e.g. by intravenous injection or topical application.

Thus, preferably, the polynucleotide, the vector, the host cell, and/or the components of the kit of the present invention are provided as a pharmaceutical composition. The term "pharmaceutical composition", as used herein, comprises the compounds of the present invention and optionally one or more pharmaceutically acceptable carrier. The compounds of the present invention can be formulated as pharmaceutically acceptable salts. Acceptable salts comprise acetate, methylester, HC1, sulfate, chloride and the like. The pharmaceutical compositions are, preferably, administered topically or systemically. Suitable routes of administration conventionally used for drug administration are oral, intravenous, or parenteral administration as well as inhalation. However, depending on the nature and mode of action of a compound, the pharmaceutical compositions may be administered by other routes as well. For example, polynucleotide compounds may be administered in a gene therapy approach by using viral vectors or viruses or liposomes, as specified herein above. Moreover, the compounds can be administered in combination with other drugs either in a common pharmaceutical composition or as separated pharmaceutical compositions wherein said separated pharmaceutical compositions may be provided in form of a kit of parts. The compounds are, preferably, administered in conventional dosage forms prepared by combining the drugs with standard pharmaceutical carriers according to conventional procedures. These procedures may involve mixing, granulating and compressing or dissolving the ingredients as appropriate to the desired preparation. It will be appreciated that the form and character of the pharmaceutically acceptable carrier or diluent is dictated by the amount of active ingredient with which it is to be combined, the route of administration and other well-known variables.

The carrier(s) must be acceptable in the sense of being compatible with the other ingredients of the formulation and being not deleterious to the recipient thereof. The pharmaceutical carrier employed may be, for example, either a solid, a gel or a liquid. Exemplary of solid carriers are lactose, terra alba, sucrose, talc, gelatin, agar, pectin, acacia, magnesium stearate, stearic acid and the like. Exemplary of liquid carriers are phosphate-buffered saline solution, syrup, oil such as peanut oil and olive oil, water, emulsions, various types of wetting agents, sterile solutions and the like. Similarly, the carrier or diluent may include time delay material well known to the art, such as glyceryl mono-stearate or glyceryl distearate alone or with a wax. Said suitable carriers comprise those mentioned above and others well known in the art, see, e.g., Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, Pennsylvania. The diluent(s) is/are selected so as not to affect the biological activity of the combination. Examples of such diluents are distilled water, physiological saline, Ringer's solutions, dextrose solution, and Hank's solution. In addition, the pharmaceutical composition or formulation may also include other carriers, adjuvants, or nontoxic, nontherapeutic, nonimmunogenic stabilizers and the like.

A therapeutically effective dose refers to an amount of the compounds to be used in a pharmaceutical composition of the present invention which prevents, ameliorates or treats the symptoms accompanying a disease or condition referred to in this specification. Therapeutic efficacy and toxicity of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., ED50 (the dose therapeutically effective in 50% of the population) and LD50 (the dose lethal to 50% of the population). The dose ratio between therapeutic and toxic effects is the therapeutic index, and it can be expressed as the ratio, LD50/ED50.

The dosage regimen will be determined by the attending physician and other clinical factors; preferably in accordance with any one of the above described methods. As is well known in the medical arts, dosages for any one patient depends upon many factors, including the patient's size, body surface area, age, the particular compound to be administered, sex, time and route of administration, general health, and other drugs being administered concurrently. Progress can be monitored by periodic assessment. A typical dose can be, for example, in the range of 1 to 1000 μg; however, doses below or above this exemplary range are envisioned, especially considering the aforementioned factors. Generally, the regimen as a regular administration of the pharmaceutical composition should be in the range of 1 μg to 10 mg units per day. If the regimen is a continuous infusion, it should also be in the range of 1 μg to 10 mg units per kilogram of body weight per minute, respectively. Progress can be monitored by periodic assessment. However, depending on the subject and the mode of administration, the quantity of substance administration may vary over a wide range to provide from about 0.01 mg per kg body mass to about 10 mg per kg body mass. In case a viral vector, in particular adeno-associated viral vector is administered, preferred doses are from 5 x 10 ¹¹ , to 2 x 10 ¹³ viral particles or viral genomes / kg body weight; as will be understood, these exemplary doses may be modified depending, in addition to the factors described above, on additional factors like type of virus, target organ, and the like. The pharmaceutical compositions and formulations referred to herein are administered at least once in order to treat or ameliorate or prevent a disease or condition recited in this specification. However, the said pharmaceutical compositions may be administered more than one time, for example from one to four times daily up to a non-limited number of days.

Specific pharmaceutical compositions are prepared in a manner well known in the pharmaceutical art and comprise at least one active compound referred to herein above in admixture or otherwise associated with a pharmaceutically acceptable carrier or diluent. For making those specific pharmaceutical compositions, the active compound(s) will usually be mixed with a carrier or the diluent, or enclosed or encapsulated in a capsule, sachet, cachet, paper or other suitable containers or vehicles. The resulting formulations are to be adopted to the mode of administration, i.e. in the forms of tablets, capsules, suppositories, solutions, suspensions or the like. Dosage recommendations shall be indicated in the prescribers or users instructions in order to anticipate dose adjustments depending on the considered recipient.

Furthermore, the present invention relates to the use of the polynucleotide according to the present invention; the vector according to the present invention; the host cell according to the present invention; and/or the kit according to the present invention for genetically modifying a host cell.

Also, the present invention relates to the use of a polynucleotide according to the present invention; the vector according to the present invention; the host cell according to the present invention; and/or the kit according to the present invention; the manufacture of a medicament for treating genetic disease, neurodegenerative disease, cancer, and/or infectious disease.

In view of the above, the following embodiments are particularly envisaged:

1. A polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) a RNA-interference (RNAi) target sequence.

2. The polynucleotide of embodiment 1, wherein said Acr polypeptide is an AcrIIA4 polypeptide.

3. The polynucleotide of embodiment 1 or 2, wherein said sequence encoding an Acr polypeptide comprises

a) the nucleic acid sequence of SEQ ID NO:21; b) a nucleic acid sequence being at least 70% identical to the sequence of SEQ ID NO:21; c) a nucleic acid sequence encoding a polypeptide comprising the amino acid sequence of SEQ ID NO:20; or

d) a nucleic acid sequence encoding a polypeptide comprising an amino acid sequence being at least 70% identical to the sequence of SEQ ID NO:20.

4. The polynucleotide of any one of embodiments 1 to 3, wherein said R Ai target sequence is a miRNA target sequence or a siRNA target sequence, preferably is a miRNA target sequence.

5. The polynucleotide of any one of embodiments 1 to 4, wherein said polynucleotide comprises at least two RNAi target sequences, preferably at least two non- identical RNAi target sequences, more preferably at least two RNAi target sequences being less than 80%>, even more preferably less than 70%, most preferably less than 60% identical to each other.

6. The polynucleotide of any one of embodiments 1 to 5, wherein said polynucleotide comprises at least two RNAi target sequences, preferably at least two miRNA target sequences essentially complementary to the same miRNA, more preferably at least two target sequences being essentially complementary to the same nucleic acid sequence of a miRNA.

7. The polynucleotide of any one of embodiments 1 to 6, wherein said miRNA is a tissue-specific and/or cell type-specific miRNA.

8. The polynucleotide of any one of embodiments 1 to 7, wherein said miRNA is selected from human miRNAs miR-1, miR-206, miR-208a, miR-122, and miR-142.

9. The polynucleotide of any one of embodiments 1 to 8, wherein said polynucleotide further comprises at least one promoter causing transcription of said expressible nucleic acid sequence.

10. The polynucleotide of any one of embodiments 1 to 9, wherein said promoter is a constitutive promoter.

11. The polynucleotide of any one of embodiments 1 to 10, wherein said polynucleotide comprises the nucleic acid sequence of SEQ ID NO:21 and at least one of SEQ ID NOs: 40 to 43.

12. The polynucleotide of any one of embodiments 1 to 11, wherein said sequence encoding an Acr polypeptide is located upstream of said RNAi target sequence, preferably of all RNAi target sequences comprised in said expressible nucleic acid sequence.

13. The polynucleotide of any one of embodiments 1 to 12, wherein said polynucleotide is an RNA. 14. The polynucleotide of any one of embodiments 1 to 13, wherein said polynucleotide is a DNA comprising a nucleic acid sequence expressible as a continuous RNA comprising said sequence encoding an Acr polypeptide and said R Ai target sequence.

15. The polynucleotide of any one of embodiments 1 to 14, wherein said polynucleotide does not comprise a nucleic acid sequence encoding a CRISPR-associated (Cas) nuclease.

16. The polynucleotide of any one of embodiments 1 to 14, wherein said polynucleotide further comprises a nucleic acid sequence encoding at least a fragment of a CRISPR- associated (Cas) nuclease.

17. A vector comprising the polynucleotide according to any one of embodiments 1 to 16. 18. The vector of embodiment 17, wherein said vector is an adeno-associated virus vector.

19. A host cell comprising the polynucleotide according to any one of embodiments 1 to 16 and/or the vector according to embodiment 17 or 18.

20. A polynucleotide according to any one of embodiments 1 to 16 and/or the vector according to embodiment 17 or 18 and/or the host cell according to embodiment 19 for use in medicine.

21. A polynucleotide according to any one of embodiments 1 to 16 and/or the vector according to embodiment 17 or 18 and/or the host cell according to embodiment 19 for use in treatment of genetic disease, neurodegenerative disease, cancer, and/or infectious disease.

22. The polynucleotide, vector, and/or host cell for use of embodiment 21, wherein said genetic disease is Duchenne muscular dystrophy, Huntington's disease, Hemophilia A/B, cystic fibrosis, myotubular myopathy, a glycogen storage disorder, or sickle cell anemia; wherein said neurodegenerative disease is Alzheimer's disease, amyotrophic lateral sclerosis (ALS), Parkinson's disease, or spinocerebellar ataxia type 1 (SCAl); wherein said cancer is hepatocellular carcinoma, pancreatic cancer, osteosarcoma, leukemia or colorectal cancer; and/or wherein said infectious disease is human immunodeficiency virus infection, herpes virus infection, papillomavirus infection, or hepatitis B virus infection.

23. A kit comprising

(I) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence; and a Cas nuclease or a second polynucleotide comprising an expressible gene encoding a Cas nuclease;

(II) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide and (ii) an RNA-interference (RNAi) target sequence, said first polynucleotide further comprising an expressible gene encoding a first fragment of a Cas nuclease, and a second polynucleotide comprising an expressible gene encoding a second fragment of a Cas nuclease, wherein said first and second fragment of said Cas nuclease together reconstitute an active Cas nuclease; or

(III) a first polynucleotide comprising (i) a sequence encoding an anti-CRISPR (Acr) polypeptide, (ii) an RNA-interference (RNAi) target sequence, and (iii) a sequence encoding a Cas nuclease; and a second polynucleotide comprising an expressible gene encoding an inhibitory RNA, preferably a siRNA, shRNA or a miRNA hybridizing to said RNA-mediated degradation target sequence, more preferably a siRNA or shRNA hybridizing to said RNA- mediated degradation target sequence.

24. The kit of embodiment 23, wherein expression of said Cas nuclease or fragment thereof is driven by a cell type-specific or tissue-specific promoter.

25. The kit of embodiment 23 or 24, wherein the Acr polypeptide encoded by the first polypeptide is a Listeria monocytogenes AcrIIA4 and wherein said Cas nuclease or fragment thereof is a Streptococcus pyogenes Cas9 nuclease.

26. The kit of any one of embodiments 23 to 25, wherein said kit comprises a polynucleotide encoding at least one guide RNA (gRNA), preferably wherein said polynucleotide encoding at least one gRNA is the first or the second polynucleotide, more preferably is the second polynucleotide.

27. The kit of any one of embodiments 23 to 26, wherein said first polynucleotide is packaged in a first delivery means targeting a first receptor of a permissive host cell and wherein said second polynucleotide is packaged in a second delivery means targeting a second receptor of said permissive host cell.

28. The kit of embodiment 27, wherein said first and second receptor are non-identical.

29. The kit of embodiment 27 or 28, wherein said first and second delivery means are non- identical.

30. The kit of any one of embodiments 23 to 29, wherein said first polynucleotide is a polynucleotide according to any one of embodiments 1 to 16.

31. A method for genetically modifying a host cell comprising

al) contacting said host cell with a polynucleotide according to any one of embodiments 1 to 16; with the vector according to embodiment 17 or 18; and/or with the host cell according to embodiment 19; and further contacting said host cell with a Cas nuclease activity and a gRNA; or

a2) contacting said host cell with the components comprised in a kit according to any one of embodiments 23 to 30;

and, b) thereby, genetically modifying said host cell.

32. A method for treating genetic disease, neurodegenerative disease, cancer, and/or infectious disease in a subject suffering therefrom, said method comprising

al) contacting said host cell with a polynucleotide according to any one of embodiments 1 to 16; with the vector according to embodiment 17 or 18; and/or with the host cell according to embodiment 19; and further contacting said host cell with a Cas nuclease activity and a gRNA; or

a2) contacting said host cell with the components comprised in a kit according to any one of embodiments 23 to 30;

and,

b) thereby, treating genetic disease, neurodegenerative disease, cancer, and/or infectious disease in said subject.

33. Use of the polynucleotide according to any one of embodiments 1 to 16; the vector according to embodiment 17 or 18; host cell according to embodiment 19; and/or the kit according to any one of embodiments 23 to 30; for genetically modifying a host cell.

34. Use of the polynucleotide according to any one of embodiments 1 to 16; the vector according to embodiment 17 or 18; the host cell according to embodiment 19; and/or the kit according to any one of embodiments 23 to 30 for the manufacture of a medicament for treating genetic disease, neurodegenerative disease, cancer, and/or infectious disease.

All references cited in this specification are herewith incorporated by reference with respect to their entire disclosure content and the disclosure content specifically mentioned in this specification. Figure Legends

Fig. 1 : Cell- and tissue-specific activation of CRISPR-Cas9 using Anti-CRISPR proteins regulated by endogenous miRNAs. (A) Binding sites for miRNA(s) highly abundant in the target cell/tissue of interest, but not in relevant off-target cells/tissues are embedded into the 3' UTR of the acr transgene. Upon co-delivery of Acr and the CRISPR-Cas components (Cas and guideRNA; vector schemes, top part), knockdown of Acr and concurrent release of Cas activity occurs only within the intended target tissue (bottom part). (B) Any miRNA binding site can be easily introduced into our Acr expression vectors (cloning scaffold, SEQ ID NO:49) via BsmBI restriction sites. In all experiments, Acr constructs bearing the miR-122 target sites (lower part, SEQ ID NO: 50) were compared to vectors bearing the scaffold identical in length (upper part). miR-122 target site has SEQ ID NO:40.

Fig. 2: Hepatocyte-specific activation of Cas9-mediated reporter cleavage. (A) Schematics of used constructs. The AcrIIA4 vector either bears 2x miR-122 binding sites within its 3' UTR or not (as control). The luciferase reporter also carries a constitutive Renilla expression cassette for normalization purposes (not shown in schematic). (B) Huh-7 cells (high endogenous miR-122 levels) or HELA cells (control, no endogenous miR-122) were triple- transfected with the constructs in A. The ratio of transfected AcrIIA4 to Cas9 constructs is indicated. Forty-eight h post-transfection firefly and Renilla luciferase activity were measured by dual- luciferase assay. Firefly luciferase photon counts were normalized to Renilla photon counts. 1, reporter only (negative control); 2, reporter + Cas9 (positive control); 3, CMV promoter-driven AcrIIA4 with 2x miR-122 binding sites; 4, CMV promoter-driven AcrIIA4, no miR-122 binding sites ("scaffold"); 5, EFS promoter-driven AcrIIA4 with 2x miR-122 binding sites; 6, EFS promoter-driven AcrIIA4, no miR-122 binding sites ("scaffold"); 3-6 also all contain reporter + Cas9; n.s., not significant. Error bars indicate the standard error of the mean, 3 replicates.

Fig. 3: Cas9 inhibition and release is dependent on the supplied Acr dose. Experiment was performed in Huh-7 cells and as in Figure 2B, but the ratio of AcrIIA4 to Cas9 construct during transfection was varied as indicated. 1, reporter only (negative control); 2, reporter + Cas9 (positive control); 3, CMV promoter-driven AcrIIA4 with 2x miR-122 binding sites; 4, CMV promoter-driven AcrIIA4, no miR-122 binding sites ("scaffold"); 5, EFla promoter- driven AcrIIA4 with 2x miR-122 binding sites; 6, EFl promoter-driven AcrIIA4, no miR- 122 binding sites ("scaffold"); 3-6 also contain reporter + Cas9 (Figure 2A). Error bars indicate the standard error of the mean, 3 replicates.

Fig. 4: Coupling of Cas9 and AcrIIA4 delivery results in tight, miR-dependent Cas regulation. (A) Experimental overview and schematics of used constructs. SpyCas9 was split into two separate fragments (CasN and CasC), fused to a split-intein (N-intein and C-intein, respectively). Co-delivery of both Cas-intein parts results in re-assembly of an active, full- length Cas9. AcrIIA4 is located on the CasC vector and either bears 2x miR-122 binding sites within its 3' UTR or not (scaffold). The luciferase reporter-encoding vector also carries a constitutive Renilla expression cassette for normalization purposes (not shown in schematic). (B) Huh-7 cells (high endogenous miR-122 levels) or HELA cells (control, no endogenous miR-122) were triple-transfected with the constructs in A in equimolar amounts. Forty-eight h post-transfection firefly and Renilla luciferase activity were measured by dual-luciferase assay. Firefly luciferase photon counts were normalized to Renilla photon counts. 1, reporter only (negative control); 2, reporter + full-length Cas9 (positive control); 3, reporter + Cas9N + Cas9C (without Acr cassette; positive control); 4-6 Cas9N + Cas9C (specified below) + reporter; 4, CMV promoter-driven AcrIIA4 carrying 2x miR-122 binding sites; 5, CMV promoter-driven AcrIIA4, no miR-122 binding sites ("scaffold"); 6, EFS promoter-driven AcrIIA4 with 2x miR-122 binding sites; 7, EFS promoter-driven AcrIIA4, no miR-122 binding sites ("scaffold"), n.s., not significant. The dashed line indicates reporter activity in absence of Cas9. Error bars indicate the standard error of the mean, 3 replicates.

Fig. 5: Cas9 inhibition in off-target cells is independent of the CasN:CasC vector ratio. Huh-7 cells (high endogenous miR-122 levels) or HELA cells (control, no endogenous miR-122) were co-transfected with the CasN-N-intein and CasC-C-intein construct (bearing the CMV promoter-driven acr with 2x miR-122 target sites) as well as a corresponding luciferase cleavage reporter. Forty-eight h post-transfection firefly and Renilla luciferase activity were measured by dual-luciferase assay. Firefly luciferase photon counts were normalized to Renilla photon counts. 1, reporter only (negative control); 2, reporter + full-length Cas9 (positive control); 3, reporter + Cas9N + Cas9C (without Acr cassette; positive control); 4, Cas9N + Cas9C co-transfected at the indicated ratios. The dashed line indicates reporter activity in absence of Cas9. Error bars indicate the standard error of the mean, 3 replicates.

Fig. 6: MiR-122 dependent induction of gene expression by dCas9-VP64. (A) Experimental overview and schematics of used constructs. The AcrIIA4 vector either carries 2x miR-122 binding sites within its 3' UTR or not (as control). (B) Huh-7 cells (high endogenous miR-122 levels) were co-transfected with the constructs in A as well as a constitutive Renilla luciferase expression vector (not shown in the vector schematic in A). The ratio of transfected AcrIIA4 to Cas9 constructs is indicated. Forty-eight h post-transfection firefly and Renilla luciferase activity were measured by dual-luciferase assay. Firefly luciferase photon counts were normalized to Renilla photon counts. 1, reporter only (negative control); 2, reporter + dCas9- VP64 (positive control); 3, CMV promoter-driven AcrIIA4 with 2x miR-122 binding sites; 4, CMV promoter-driven AcrIIA4, no miR-122 binding sites ("scaffold"); 3-4 also contain reporter + dCas9-VP64; error bars indicate the standard error of the mean, 3 replicates. The following Examples shall merely illustrate the invention. They shall not be construed, whatsoever, to limit the scope of the invention.

Example 1 : Methods

1.1 Plasmids

pAAV-SMVP-Cas9N (Addgene #80930) and pAAV-SMVP-Cas9C (Addgene #80931) were gifts from George Church. Further vectors used herein have SEQ ID NOs: 3 to 19 (cf. Nihongaki et al. (2015), Chem Biol. 22(2): 169-74; Konerman et al. (2015), Nature 517(7536):583-8).

1.2 Cell Culture

Human cervix adenocarcinoma cells (HELA) and the human liver carcinoma cells (Huh-7) were maintained at 37 °C and 5 % C0 ₂ in a humidified tissue culture incubator. Cells were cultured in 75 cm ² flasks (STARLAB) (Table 1) and passaged every 2 to 3 days.

Table 1 : Media Compositions

1.3 Cell seeding and transient trans fection

For experiments, cells were seeded into transparent, tissue culture-treated 96-well plates (STARLAB) (6,000 cells per well and in 100 μΐ media). Transfection was performed 12 to 16 hours after seeding. Lipofectamine™ 3000 (Invitrogen) was used for all transfections according to the manufacturer's protocol.

For experiments involving the catalytically active Cas9, 20 ng Cas9 expression vector and 20 ng luciferase cleavage reporter were co-transfected (amounts are per well). AcrIIA4 expression vectors with or without miR-122 target sites were added in a ratio AcrIIA4:Cas9 = 1 : 1 to 1 :80 during transfection as indicated in the figure legends.

For experiments involving the Split Cas9 constructs, 20 ng of each, the luciferase cleavage reporter, the CasN-N-intein and the CasC-C-intein constructs were co-transfected, if not indicated otherwise in the figure legend. For experiments involving dCas9-VP64, 20 ng of each, the dCas9-VP64 vector, the TetO guideRNA vector as well as the TetO-dependent firefly luciferase reporter were co- transfected alongside 1 ng of pRL-TK (Promega; encodes Renilla luciferase). AcrIIA4 expression vectors with or without miR-122 target sites were added in a ratio AcrIIA4:dCas9- VP64 = 3 : 1 to 1 :20 during transfection as indicated in the figure legend.

The total amount of DNA transfected per well was 100 ng or, in case of dCas9-VP64 experiments, 101 ng. DNA was topped up with inert stuffer DNA if required. Six hours post- transfection the medium was exchanged. 1.4 Luciferase Assay

Forty-eight hours post-transfection firefly and Renilla luciferase activity was determined using the Dual Luciferase® Reporter Assay System (Promega) according to the manufacturer's recommendations. In brief, media was aspirated and cells were washed with 100 μΐ PBS. 30 μΐ of the supplied lysis buffer was added to each well and plates were shaken for 30 minutes at 450 rpm and at room temperature. 10 μΐ of lysate was then transferred to a white 96-well plate (greiner bio-one) and luminescence was measured using a GloMax® 96 Microplate Luminometer (Promega) equipped with automated injectors. First, the firefly luciferase signal was measured by adding 35 μΐ Luciferase Assay Reagent II. Second, the reaction was quenched, and the Renilla luciferase reaction was simultaneously initiated by adding 35 μΐ of the Stop & Glo® reagent. Signal integration time was 10 s preceded by a 2 s delay. For data analysis, firefly values were divided by Renilla values. Data are means plus/minus standard error of the mean, 3 experimental replicates.

Example 2: Results

We generated a set of modular AcrIIA4 expression constructs with variable AcrIIA4-driving promoters (cytomegalovirus promoter, CMV; elongation factor alpha promoter, EF-l ; EF-l shortened promoter, EFS) as well as a modular 3' UTR for simple insertion of any miRNA target site(s) (Figure 1A). We then introduced a concatemer of two target sites for miR-122 into our AcrIIA4 constructs, a miRNA specifically expressed in hepatocytes, but not in any other cell type (Figure IB).

When co-delivered into hepatocytes together with SpyCas9 and a corresponding gRNA, one would expect a potent knockdown of AcrIIA4 and hence a release in Cas9 activity (Figure 1A). In any other cell type, i.e. in the absence of miR-122, AcrIIA4 should remain highly expressed and therefore efficiently repress Cas9 activity. To test our hypothesis, we co- transfected Huh-7, a hepatocellular carcinoma cell line expressing high amounts of miR-122, as well as HELA cells (cervix carcinoma cell line not expressing miR-122, as control) with different AcrIIA4-encoding vectors, an SpyCas9 expression vector, and a luciferase-based cleavage reporter to monitor Cas9 catalytic activity (Figure 2A).

The AcrIIA4-encoding vectors differed in the promoter driving AcrIIA4 expression (CMV or EFS), as well as the presence or absence of two miR-122 binding sites within the AcrIIA4 gene 3' UTR. As expected, AcrIIA4 vectors not bearing miR-122 binding sites potently inhibited Cas9 activity in both, Huh-7 as well as HELA cells (Figure 2B). In contrast, for the AcrIIA4 constructs carrying the miR-122 target sites, we observed a strong release in Cas9 activity (i.e. potent luciferase knockdown) exclusively in Huh-7, but not in HELA cells, indicating successful, miR-122-dependent activation of Cas9 (Figure 2B).

Next, we repeated the experiment in Huh-7 cells, this time titrating the amount of AcrIIA4 and thereby altering the ratio of AcrIIA4:Cas9 constructs transfected between 1 : 1 and 1 :80. As AcrIIA4-driving promoters, we used either CMV or EFl (non-shortened). Cas9 inhibition by AcrIIA4 was dose-dependent (Figure 3). At intermediate Acr:Cas ratios, a potent release in Cas9 activity (up to 8-fold increase in reporter knockdown) was observed exclusively in Huh-7 and in presence of the miR-122 binding sites within the acr 3' UTR. In contrast, a very high AcrIIA4:Cas9 transfection ratio resulted in efficient Cas9 inhibition, even in the presence of the miR-122 binding sites in the acr gene, probably due to a saturation of endogenous RNAi components (e.g. Argonaute-2 (Ago-2), the catalytic subunit of the RNA-induced silencing complex (RISC)) or sequestration of the majority of endogenous miR-122. On the other hand, a low AcrIIA4:Cas9 ratio led to noticeable Cas9 activity even in the absence of the miR-122 binding sites on the AcrIIA4 vector. This is expected, as AcrIIA4 acts as a competitive inhibitor and therefore needs to be provided in excess as compared to its Cas9 target to efficiently function (Dong et al., 2017; Shin et al., 2017; Yang and Patel, 2017).

In the aforementioned experiments Acr and Cas9 expression cassettes were located on different vectors (Figure 2A). This may be suboptimal, as the Acr:Cas9 vector ratio upon delivery and hence the corresponding Acr:Cas9 expression ratios within the target cells will likely strongly vary. This may result in an undesired leakiness due to a very low Acr:Cas9 ratio occurring with a certain probability (refer to Figure 3). To address this issue, we devised a strategy directly coupling Cas9 activity to the amount of acr transgene present. Our strategy grounds on a SpyCas9-AAV vector design reported by the group of George Church at Harvard University (Chew et al, 2016). In their design, the SpyCas9 was split into two separate pieces (CasN and CasC), fused to Rhodothermus marinus derived split-intein sequences. The CasN-N-Intein and CasC-C-Intein constructs are completely inactive by themselves. However, upon co-delivery, intein-mediated protein trans-splicing results in re- constitution of an active, full-length Cas9. We adopted this design and inserted a U6-promoter driven guide-RNA expression cassette into the reported CasN-N-Intein AAV vector (Addgene #80930) and an AcrIIA4 expression cassette (with or without 2x miR-122 binding sites) into the corresponding CasC-C-Intein AAV vector (Addgene #80931) (Figure 4A). Efficient re-assembly of SpyCas9 should now only be possible, if a cell receives sufficient amounts of both the CasN as well as the Acr- encoding CasC vectors, thereby tightly linking Cas9 activity to AcrIIA4-mediated Cas regulation. To validate our strategy, we again co-transfected Huh-7 or HELA cells with these split-SpyCas9 vectors alongside our firefly luciferase cleavage reporter indicating Cas9 catalytic activity. As expected, we observed a potent, miR-122 dependent rescue in Cas9 catalytic activity (Figure 4B). Importantly, no considerable leakiness (Cas9 activity) was observed in absence of the miR-122 binding sites, suggesting tight regulation of Cas9 by Acr. Next, we repeated this experiment, this time titrating the CasN-N-Intein and CasC-C-Intein vector co-encoding the CMV promoter-driven acr with 2x miR-122 target site against each other in ratios of 1 :20 - 20: 1. We observed a potent luciferase reporter knockdown, i.e. strong miR-122 dependent rescue in Cas9 catalytic activity, for CasN:CasC ratios between 1 :4 and 4: 1 (Figure 5). Higher or lower CasN:Cas9 ratios resulted in noticeably reduced Cas9 activity, likely due to the low expression of one out of the two required split Cas9 fragments. Remarkably, in HELA cells, Cas9 remained inactive for all tested CasN:CasC ratios, once again indicating successful coupling of AcrIIA4 expression and Cas9 re-assembly in off- target cells (Figure 5).

It has been shown that AcrIIA4 efficiently inhibits a catalytically dead (d)SpyCas9 in bacterial cells (Rauch et al, 2017), suggesting that AcrIIA4 could be used for cell type- or tissue-specific control of virtually any dCas9-based tool, e.g. dCas9-based transcriptional regulators or epigenetic modifiers (Maeder et al, 2013; Hilton et al, 2015). Concurrently, by using endogenous miRNA signatures for controlling AcrIIA4 expression, one might be able to activate any dCas9-based tool in a cell type- or tissue-specific manner. To validate this idea, we again titrated the amount of AcrIIA4 vector (with 2x miR-122 binding sites or empty scaffold) co-transfected with a dCas9-VP64 transactivator, a tetracycline (tet) operator targeting gRNA expression construct, as well as a corresponding firefly luciferase reporter driven from a minimal promoter preceded by tet operator repeats (Figure 6A).

We observed pronounced luciferase reporter activation only when using dCas9-VP64 in combination with the miR-122 target site-bearing AcrIIA4 construct, but not when using the scaffold AcrIIA4 control vector, indicating an efficient miR-122-mediated rescue of dCas9- VP64 reporter transactivation (Figure 6B). Inhibition in the absence of miR-122 target sites and release of dCas9-VP64 activity in the presence of the miRNA target sites was again dose- dependent. At very low AcrIIA4:dCas9-VP64 transfection ratios the luciferase reporter was active independent of the presence or absence of miR-122 traget sites in the acr 3' UTR. At high AcrIIA4:dCas9-VP64 ratios, the reporter activation upon miR-122-mediated AcrIIA4 knockdown was still potent, but incomplete. This is in line with our experiments employing the catalytically active Cas9 (compare Figure 3 and 6B), and, once again, shows that the AcrIIA4:Cas9 expression ratio is a critical parameter to consider when employing our CasON approach.

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