Diagnostic of immune graft tolerance

The present invention concerns a method for the in vitro diagnosis of a graft tolerant phenotype, comprising : determining from a grafted subject biological sample an expression profile comprising at least one gene identified in the present invention as differentially expressed between graft tolerant and graft non-tolerant subjects, optionally measuring other parameters, and determining the presence or absence of a graft tolerant phenotype from said expression profile and optional other parameters. The invention further concerns kits and oligonucleotide microarrays suitable to implement said method.

Currently, the long-term survival of an allograft is depending on the continuous administration of immunosuppressive drugs. Indeed, an interruption of the immunosuppressive treatment generally leads to an acute or chronic rejection, particularly in case of an early or abrupt diminution (Dantal J. et al . 1998. Lancet. 351:623-8) . However, long-term immunosuppressive treatments lead to severe side effects such as chronic nephrotoxicity, an increased susceptibility to opportunistic infections, and a dose-dependant increased propensity to develop cancers (Iman A. et al . 2001. Natl. Med. J. India. 14 (2) : 75-80) . Despite the difficulties encountered by many attempts to induce a persistent tolerance to allografts in human, it has been observed that some patients can

maintain the tolerance to their graft without any immunosuppressive treatment (Brouard S. et al . 2005. Am. J. Transplant. 5(2): 330-340), demonstrating that a tolerant state may naturally occur, even in humans. In the case of kidney graft, the real proportion of tolerant grafted subjects may be underestimated. Indeed, although the possibility to progressively stop the immunosuppressive treatment has never been investigated, a significant proportion of kidney grafted subject tolerate their graft with a minimal dose of immunosuppressive drug (cortisone monotherapy, <10mg a day) (Brouard S. et al . 2005. Am. J. Transplant. 5(2): 330-340). In addition, among patients developing posttransplantation lymphoproliferative disorders, leading to the interruption of their immunosuppressive treatment, a significant proportion do not reject their graft.

Thus, a significant proportion of kidney grafted subjects might display an unsuspected, total or partial, immune tolerance state to their graft. It would therefore be very useful to have a method to diagnose, without any previous modification of the immunosuppressive treatment, the level of immune tolerance of grafted subjects to their graft. Indeed, this would allow for an ethically acceptable, progressive, total or partial withdrawal of immunosuppressive drugs in subject with a high enough level of graft tolerance. Although well known biological parameters are used by clinicians for the evaluation of renal function (creatinine and urea serum concentrations and clearance) , these parameters are not sufficient for a precise diagnosis of tolerance or rejection. Currently, only a biopsy of the grafted kidney allows, through the analysis of the presence or absence of several

histological lesions types (Nankivell et al . 2003. N Engl J Med. 349 (24) :2326-33) , for the precise evaluation of said grafted kidney functionality. A biopsy is an invasive examination, which is not without danger for the grafted organ, and is thus usually not performed on grafted subjects that have stable biological parameters values. A non-invasive method of precise diagnosis of a graft tolerant phenotype is thus needed.

In addition, in the case of many grafted organ, when the values of standard biological parameters allow for the diagnostic of chronic rejection, the rejection process is already in progress and, although it may in certain cases be stopped, the lesions that have been induced generally cannot be reversed. Moreover, to confirm the diagnostic, a biopsy of the grafted organ is usually performed, which is, as stated before, not without danger. It would thus also be very valuable to have a non-invasive method allowing to diagnose chronic rejection at the earlier steps of the rejection process, which would permit to adapt the immunosuppressive treatment and might in some cases prevent the chronic rejection process.

Finally, a non-invasive method for an early and reliable diagnosis of a graft tolerant or non-tolerant phenotype would be very useful in clinical research, since it would allow for relatively short (6 months to 1 year), and thus less expensive, clinical trial studies.

At the present time, few genome-wide studies have been carried out in humans on the modifications of gene expression patterns after kidney transplant. In addition, these studies focused on the identification of genes implicated in graft acute or chronic rejection, and not

in graft tolerance. From the comparison of the expression level of about 40 000 genes in tolerant patients versus patients in chronic rejection, the inventors identified a few hundred genes that are significantly differentially expressed between the two groups of patients.

Thanks to identification of these genes that are significantly differentially expressed between tolerant patients and patients in chronic rejection, it is now possible to use a non-invasive method of in vitro diagnosis of a graft tolerant or, on the contrary, a graft non-tolerant phenotype . Such a method allows for the identification of grafted subject for whom a progressive, total or partial withdrawal of immunosuppressive drugs is possible. It also permits an early diagnosis of a chronic rejection process in patients whose biological parameters levels are still normal. Moreover, the diagnosis may be performed from a blood sample, which is completely harmless for the tested grafted subject.

The invention thus concerns a method for the in vitro diagnosis of a graft tolerant phenotype, comprising :

(a) determining from a grafted subject biological sample an expression profile comprising at least one gene from Table 1, and

(b) determining the presence or absence of a graft tolerant phenotype from said expression profile.

According to the present invention, a "graft tolerant phenotype" is defined as a state of tolerance of a subject to his graft. A "state of tolerance" means that

this subject does not reject his graft in the absence of an immunosuppressive treatment. As used herein, a "graft tolerant" subject is thus a subject displaying a graft tolerant phenotype, while a subject that do not display a graft tolerant phenotype will be referred to as a "graft non-tolerant" subject.

Immunosuppressive drugs that may be employed in transplantation procedures include azathioprine, methotrexate, cyclophosphamide, FK-506, rapamycin, corticosteroids, and cyclosporins. These drugs may be used in monotherapy or in combination therapies.

In the case of kidney graft, the following immunosuppressive protocols are usually used.

Subjects with primary kidney graft generally receive an induction treatment consisting of 2 injections of basiliximab (Simulect®, a chimeric murine/human monoclonal anti IL2-R0C antibody commercialized by Novartis), in association with tacrolimus (Prograf™, Fujisawa Pharmaceutical, 0.1 mg/kg/day) , mycophenolate mofetil (Cellcept™, Syntex Laboratories, Inc, 2 g/day) and corticoids (1 mg/kg/day) , the corticoid treatment being progressively decreased of 10 mg every 5 days until end of treatment, 3 months post transplantation.

Subjects with secondary or tertiary kidney graft, or subjects considered as exposed (percentage of anti-T PRA previously peaking above 25% or cold ischemia for more than 36 hours) , generally receive a short anti-thymocyte globulin (ATG) cure (7 days) , in association from day 0 with mycophenolate mofetil (Cellcept™, Syntex Laboratories, Inc, 2 g/day) ) , and corticoids (1 mg/kg/day) , the corticoid treatment being progressively decreased of 10 mg every 5 days until end of treatment, 3

months post transplantation, tacrolimus (Prograf™, Fujisawa Pharmaceutical) being introduced in a delayed manner at a dose of 0.1 mg/kg/day.

A "biological sample" may be any sample that may be taken from a grafted subject, such as a serum sample, a plasma sample, a urine sample, a blood sample, a lymph sample, or a biopsy. For the determination of an expression profile, such a sample must allow for the determination of an expression profile comprising at least one gene from Table 1. Preferred biological samples for the determination of an expression profile include samples comprising lymphocytes, such as a blood sample, a lymph sample, or a biopsy. Preferably, the biological sample is a blood sample, more preferably a peripheral blood sample comprising peripheral blood lymphocytes

(PBLs) . Indeed, such a blood sample may be obtained by a completely harmless blood collection from the grafted patient and thus allows for a non-invasive diagnosis of a graft tolerant or non-tolerant phenotype . By "expression profile" is meant a group of at least one value corresponding to the expression level of at least one gene. Preferably, the expression profile comprises at least 1, at least 2, at least 3, at least 4, at least 5, at least 8, at least 10, at least 15, at least 20, at least 30, at least 40, at least 50, at least 75, at least 100, at least 200, at least 300, or all genes from Table 1.

272 genes that were determined by the inventors to display significantly different expression levels between kidney graft tolerant subjects as defined above (ToI) and kidney transplanted subjects in chronic rejection (CR) are listed in the following Table 1.

Table 1. 272 genes differentially expressed between kidney transplanted subjects that are tolerant (ToI) or in chronic rejection (CR) .

In certain embodiments, the expression profile may further comprise at least one gene from Table 2. Preferably, the expression profile may comprise at least 1, at least 2, at least 3, at least 4, at least 5, at least 8, at least 10, at least 15, at least 20, at least 25, at least 30, or all genes from Table 2.

The following Table 2 comprises 38 additional genes that were determined by the inventors to display significantly different expression levels between kidney graft tolerant subjects as defined above (ToI) and kidney transplanted subjects in chronic rejection (CR) .

Table 2. 38 additional genes differentially expressed between kidney transplanted subjects that are tolerant (ToI) or in chronic rejection (CR) .

In a particular embodiment, the determination of the presence or absence of a graft tolerant phenotype is carried out by comparison of the obtained expression profile with at least one reference expression profile.

A "reference expression profile" is a predetermined expression profile, obtained from a pooled biological sample constituted of sample (s) from at least one subject with a known particular graft tolerance state. In particular embodiments, the reference expression profile may have been obtained from pooled biological samples respectively constituted of sample (s) from at least one graft tolerant subject ("tolerant reference expression profile"), or sample (s) from at least one graft non- tolerant subject ("non-tolerant reference expression profile"), in particular subjects in chronic rejection.

Preferably, at least one reference expression profile is a tolerant reference expression profile. Alternatively, at least one reference expression profile may be a non-tolerant reference expression profile. More preferably, the determination of the presence or absence of a graft tolerant phenotype is carried out by comparison with both tolerant and non-tolerant reference expression profiles. The comparison of a tested subject expression profile with a reference expression profile may be

performed using PAM (predictive analysis of microarrays) statistical method. A non supervised PAM 2 classes statistical analysis is performed. For comparison with a tolerant reference expression profile, a cross validation (CV) probability is calculated (CV _to i) , which represents the probability that the tested subject is tolerant. For comparison with a chronic rejection (non-tolerant) reference expression profile, a CV probability is calculated (CV _CR ) , which represents the probability that the tested subject is undergoing chronic rejection. The diagnosis is then performed based on the CV _to i and/or the CVcR probabilities. Preferably, a tolerant subject has a CVtoi probability of at least 0.80, at least 0.85, more preferably at least 0.90, at least 0.95, at least 0.97, at least 0.98, at least 0.99, or even 1.00, and has a CVcR probability of at most 0.20, at most 0.15, at most 0.10, at most 0.05, at most 0.03, at most 0.02, at most 0.01, or even 0.00.

The expression profile may be determined by any technology known by a man skilled in the art . In particular, each gene expression level may be measured at the nucleic and/or proteic level. In a preferred embodiment, the expression profile is determined by measuring the amount of nucleic acid transcripts of each gene. In another embodiment, the expression profile is determined by measuring the amount of each gene corresponding protein.

The amount of nucleic acid transcripts can be measured by any technology known by a man skilled in the art. In particular, the measure may be carried out directly on an extracted messenger RNA (mRNA) sample, or

on retrotranscribed complementary DNA (cDNA) prepared from extracted mRNA by technologies well-know in the art. From the mRNA or cDNA sample, the amount of nucleic acid transcripts may be measured using any technology known by a man skilled in the art, including nucleic microarrays, quantitative PCR, and hybridization with a labelled probe .

In a preferred embodiment, the expression profile is determined using quantitative PCR. In another preferred embodiment, the expression profile is determined by the use of a nucleic microarray.

According to the invention, a "nucleic microarray" consists of different nucleic acid probes that are chemically attached to a substrate, which can be a microchip, a glass slide or a microsphere-sized bead. A microchip may be constituted of polymers, plastics, resins, polysaccharides, silica or silica-based materials, carbon, metals, inorganic glasses, or nitrocellulose. Probes comprise nucleic acids such as cDNAs ("cDNA microarray") or oligonucleotides

("oligonucleotide microarray") , and the oligonucleotides may be about 25 to about 60 base pairs or less in length.

To determine the expression profile of a target nucleic sample, said sample is labelled, contacted with the microarray in hybridization conditions, leading to the formation of complexes between target nucleic acids that are complementary to probe sequences attached to the microarray surface. The presence of labelled hybridized complexes is then detected. Many variants of the microarray hybridization technology are available to the man skilled in the art, such as those described in patents or patent applications US 5,143,854; US

5,288,644; US 5,324,633; US 5,432,049; US 5,470,710; US 5,492,806; US 5,503,980; US 5,510,270; US 5,525,464; US 5,547,839; US 5,580,732; US 5,661,028; US 5,800,992; WO 95/21265; WO 96/31622; WO 97/10365; WO 97/27317; EP 373 203; and EP 785 280; the disclosures of which are herein incorporated by reference.

In a preferred embodiment, the nucleic microarray is an oligonucleotide microarray comprising at least one oligonucleotide specific for a gene from Table 1. Preferably, the oligonucleotides are about 50 bases in length.

The oligonucleotide microarray may further comprise at least one oligonucleotide specific for a gene from Table 2. Preferably, the oligonucleotides are about 50 bases in length.

Suitable microarray oligonucleotides specific for any gene from Table 1 or Table 2 may be designed, based on the genomic sequence of each gene (see Tables 1 and 2 Genbank accession numbers), using any method of microarray oligonucleotide design known in the art. In particular, any available software developed for the design of microarray oligonucleotides may be used, such as, for instance, the OligoArray software (available at nttp : / /berry . engin . umicn . edu/oligoarray/ ) , the GoArrays software (available at http : //www . isima . lr/bioinlo/goarrays/) , the Array Designer software (available at http : //www . premi erbi osoft . com/dnami croa rray/ ~ ndex . htπ ^" ) , the Primer3 software (available at nttp : / /frodo . wi .mit . edu/primer3/primer3_cooe . html) , or the Promide software (available at http : //oligos .molgcn ,mpg . do/) .

The invention is also directed to a method for the in vitro diagnosis of a graft tolerant phenotype from at least one biological sample of a grafted subject, comprising :

(a) measuring standard biological parameters specific for said subject grafted organ type,

(b) determining an expression profile comprising at least one gene from Table 1, (c) determining the presence or absence of a graft tolerant phenotype from the results of steps (a) and (b) .

According to the invention, "standard biological parameters specific for said subject grafted organ type" means biological parameters that are usually used by clinicians to monitor the stability of grafted subjects status and to detect graft rejection. These standard biological parameters specific for said subject grafted organ type usually comprise serum or plasma concentrations of particular proteins, which vary depending on the grafted organ type. However, these standard biological parameters specific for said subject grafted organ type are, for each organ type, well known of those skilled in the art . For instance, standard biological parameters specific for kidney include serum or plasma urea and creatinine concentrations. In a healthy subject, the serum creatinine concentration is usually comprised between 40 to 80 μmol/L for a woman and 60 to 100 μmol/L for a man, and the serum urea concentration between 4 to 7 mmol/L.

For instance, for liver transplantation, standard biological parameters include serum or plasma concentrations of gamma glutamyl transpeptidase (GGT) , aspartate aminotransferase (AST) , alanine aminotransferase (ALT) , lactate dehydrogenase (LDH) , and bilirubin (total or conjugated) .

These standard biological parameters have the advantage of being easily measurable from a blood sample, but are not sufficient to establish a precise graft tolerant or non-tolerant diagnosis, and are also not enough sensitive to allow an early chronic rejection diagnosis. However, when combined with the determination of an expression profile according to the present invention, the resulting method according to the invention makes it possible to detect graft tolerant subject whose immunosuppressive treatment could be progressively decreased, as well as apparently stable patients (relative to their biological parameters) who are actually on the verge of chronic rejection. Other parameters that cannot be used alone for a diagnosis but that have been described as displaying significantly different values between tolerant grafted subjects and subjects in chronic rejection may also be used to refine and/or confirm the diagnosis according to the above described method according to the invention combining the measure of standard biological parameters and the determination of an expression profile. These optional supplementary parameters include the percentage of CD4 ⁺ CD25 ⁺ T cells in peripheral blood lymphocytes (Brouard et al . 2005. Am J Transplant. 5 (2) : 330-40) , as well as parameters relative to the qualitative and quantitative analysis of the T cell repertoire (Brouard

et al. 2005. Am J Transplant. 5 (2) : 330-40) , such as the T cell repertoire oligoclonality and the level of TCR transcripts .

The percentage of CD4 ⁺ CD25 ⁺ T cells in peripheral blood lymphocytes may be determined by any technology known in the art, in particular by flow cytometry using labelled antibodies specific for the CD4 and CD25 molecules. Preferably, the percentage of CD4 ⁺ CD25 ⁺ T cells in peripheral blood lymphocytes of a tolerant subject is not statistically different from that of a healthy volunteer, whereas it is significantly lower (p < 0.05) in a non-tolerant grafted subject.

The T cell repertoire oligoclonality may be determined by any technology enabling to quantify the alteration of a subject T cell repertoire diversity compared to a control healthy subject. Usually, said alteration of a subject T cell repertoire diversity compared to a control healthy subject is determined by quantifying the alteration of T cell receptors (TCR) complementary determining region 3 (CDR3) size distributions. Indeed, in a control healthy subject, such a TCR CDR3 size distribution displays a Gaussian form, which may be altered in the presence of clonal expansions due to immune response, or when the T cell repertoire diversity is limited and reaches oligoclonality.

The level of TCR transcripts is preferably determined independently for each Vβ family by any technology known in the art. For instance, the level of TCR transcripts of a particular Vβ family may be determined by calculating the ratio between these vβ transcripts and the transcripts of a control housekeeping

gene, such as the HPRT gene. Preferably, in a graft tolerant subject, a significant percentage of vβ families display an increase in their transcript numbers compared to a normal healthy subject. Methods to analyze T cell repertoire oligoclonality and/or the level of TCR transcripts, as well as scientific background relative to T cell repertoire, are clearly and extensively described in WO 02/084567, which is herein incorporated by reference. Preferably, a graft tolerant subject, as well as a subject in chronic rejection, displays a T cell repertoire with a significantly higher oligoclonality than a normal healthy subject .

The cytokine expression profile of T cells may be determined using any technology known in the art, including quantitative PCR and intracellular flow cytometry analysis. Preferably, the oligoclonal Vβ families of a non-tolerant grafted subject express increased levels compared to a healthy volunteer of THl or TH2 effector molecules, including interleukin 2 (IL- 2), interleukin 8 (IL-8) , interleukin 10 (IL-10), interleukin 13 (IL-13) , transforming growth factor beta (TGF-β) , interferon gamma (IFN-γ) and perforin, whereas oligoclonal vβ families of a tolerant grafted subject do not express increased levels of those effector molecules compared to a healthy volunteer.

In a particular embodiment of the above described method according to the invention combining the measure of standard biological parameters and the determination of an expression profile, said method may thus further

comprise a (b2) step between steps (b) and (c) , which consists in studying at least one other parameter chosen in the group comprising:

- the percentage of CD4 ⁺ CD25 ⁺ T cells in peripheral blood lymphocytes,

- parameters relative to the T cell repertoire, such as the T cell repertoire oligoclonality and the level of TCR transcripts, and

- the cytokine expression profile of T cells oligoclonal Vβ families, and wherein step (c) further takes into account the results of step (b2) .

In a particular embodiment, step (c) is carried out by following a decision algorithm that takes into account the results of steps (a) and (b) , and optionally of step (b2) .

By a "decision algorithm" is meant a set of instructions allowing, for any particular steps (a) , (b) , and optionally (b2) results, the automated diagnosis of a graft tolerant or non-tolerant phenotype . Such an algorithm may be a list of dependant and/or independent instructions leading to a graft tolerant or non-tolerant phenotype diagnosis, or a software which, after entry of the different results, returns either a graft tolerant or non-tolerant phenotype diagnosis.

In a preferred embodiment of any above described in vitro diagnosis method according to the invention, said method is performed on a biological sample from a kidney transplanted subject. According to the invention, a "kidney transplanted subject" is a subject that was grafted with a non syngeneic, including allogenic or even

xenogenic, kidney. Said kidney transplanted subject may further have been grafted with another organ of the same donor providing the kidney. In particular, said kidney transplanted subject may further have been grafted with the pancreas, and optionally a piece of duodenum, of the kidney donor.

For such a kidney transplanted subject, step (c) of a method of in vitro diagnosis taking into account both standard biological parameters specific for said subject grafted organ type and an expression profile comprising at least one gene of Table 1, and optionally at least one gene of Table 2, is preferably performed using the following decision algorithm: (a) if the serum concentration of urea is superior to 7 mmol/L or the serum concentration of creatinine is superior to 80 μmol/L for a female subject or 100 μmol/L for a male subject, then the tested subject is diagnosed as not tolerant to his graft (b) if the serum concentration of urea is inferior to 7 mmol/L and the serum concentration of creatinine is inferior to 80 μmol/L for a female subject or 100 μmol/L for a male subject, then the diagnosis is performed by determining an expression profile according to the invention.

The invention further concerns a kit for the in vitro diagnosis of a graft tolerant phenotype, comprising : (a) at least one reagent for the determination of an expression profile comprising at least one gene from Table 1, and

(b) instructions for the determination of the presence or absence of a graft tolerant phenotype .

Such a kit for the in vitro diagnosis of a graft tolerant phenotype may further comprise at least one reagent for the determination of an expression profile also comprising at least one gene from Table 2.

In another embodiment, a kit for the in vitro diagnosis of a graft tolerant phenotype according to the invention may further comprise at least one reagent for the measure of standard biological parameters specific for at least one grafted organ type. Such as kit may still further comprise at least one reagent chosen in the group comprising reagents for the measure of the percentage of CD4 ⁺ CD25 ⁺ T cells in peripheral blood lymphocytes, reagents for the analysis of T cell repertoire, and reagents for the measure of the cytokine expression profile of T cells oligoclonal Vβ families.

In any kit for the in vitro diagnosis of a graft tolerant phenotype according to the invention, the reagent (s) for the determination of an expression profile comprising at least one gene from Table 1, and optionally at least one gene from Table 2, preferably include specific amplification primers and/or a nucleic microarray . In addition, the instructions for the determination of the presence or absence of a graft tolerant phenotype preferably include at least one reference expression profile. In a preferred embodiment, at least one reference expression profile is a graft tolerant expression profile. Alternatively, at least one reference expression profile may be a graft non-tolerant expression profile. More preferably, the determination of the level

of graft tolerance is carried out by comparison with both graft tolerant and graft non-tolerant expression profiles .

In a particular embodiment, the instructions for the determination of the presence or absence of a graft tolerant phenotype may further include a decision algorithm, as defined above. In the case of a kidney grafted subject, the instructions for the determination of the presence or absence of a graft tolerant phenotype may be constituted of the decision algorithm described above .

The invention is also directed to an oligonucleotide microarray comprising a plurality of oligonucleotides specific for a gene associated with a graft tolerant phenotype, wherein said oligonucleotides comprise at least one oligonucleotide specific for a gene from Table 1. Preferably, said oligonucleotide microarray allows for the detection of at least 1, at least 2, at least 3, at least 4, at least 5, at least 8, at least 10, at least 15, at least 20, at least 30, at least 40, at least 50, at least 75, at least 100, at least 200, at least 300, or all genes from Table 1.

In a particular embodiment, said oligonucleotide microarray may further comprise at least one oligonucleotide specific for a gene from Table 2. Preferably, said oligonucleotide microarray comprises oligonucleotides specific for at least 1, at least 2, at least 3, at least 4, at least 5, at least 8, at least 10, at least 15, at least 20, at least 25, at least 30, or all genes from Table 2.

The invention is also drawn to a method of treatment of a grafted subject, comprising:

(a) determining from a subject biological sample the presence or absence of a graft tolerant phenotype using a method according to the invention, and

(b) adapting the immunosuppressive treatment in function of the result of step (a) .

Having generally described this invention, a further understanding of characteristics and advantages of the invention can be obtained by reference to certain specific examples and figures which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

DESCRIPTION OF THE DRAWINGS

Figure 1. Validation of the diagnosis predictive value of dedicated microarrays comprising oligonucleotides specific for Tables 1 and 2 genes (A) or

Table 1 only genes (B) . The samples of individual tested patients are plotted in abscissa, the chronic rejection group (samples n°l to 8) on the left, the tolerant group (samples n°9 to 14) on the right (see separation bar) . In ordinates are plotted both the chronic rejection (black rhomb) and tolerant (gray square) CV probabilities for each patient sample. Probabilities to identify a tolerant patient (Ptoi) or a chronic rejection patient (P _CR ) , as well as the probability to correctly identify the phenotype of an individual subject (P) , are also stated.

EXAMPLE 1

Identification of differentially expressed genes between tolerant and non-tolerant patients (chronic rejection)

1.1 Patients selection

All patients were more than 18 years old and had been kidney transplanted for more than 5 years. Tolerant patients ("ToI group"; 52.29 ± 17.19 years old; n=7) had stable renal function and had taken no immunosuppressive drug treatment for at least 3 years.

Non-tolerant patients in chronic rejection ("CR group"; 50.45 ± 14.45 years old; n=ll) are defined thanks to histological chronic rejection lesions, with or without allograft glomerular disease and renal function degradation .

1.2 Preparation, amplification, and staining of messenger RNA (mRNA)

A patient blood sample is diluted to ½ with PBS and deposited on Ficoll gradient. Extracted RNA quantity and quality are tested on Agilent 2100 Bioanalyser ^® .

The amplification and staining of mRNA is carried out using "Amino Allyl MessageAmp™ aRNA" kit (Ambion®; Austin, Texas) .

This method consist in the retrotranscription of mRNA with an oligo(dT) primer comprinsing a T7 promoter ("T7 oligo(dT) primer"), the in vitro transcription of resulting DNA with T7 RNA polymerase, generating anti- sens RNA copies of each mRNA. This kit allows for the incorporation of modified nucleotides, 5- (3-aminoallyl) -

UTP (aaUTP) in amplified RNA during in vitro transcription. aaUTP contains a primary amino group in uracile C5 position which is chemically linked to a fluorophore . Once purified, stained aRNA are used for hybridization on DNA microarrays . All words under quotation marks refer to reagents provided in the kit.

A mixture of 5 μg of total RNA, 1 μg of T7 oligo(dT) primer and RNase free water qsp to 12 μL is incubated for 10 minutes at 7O°C. 8 μL of a mixture consisting of 2 μL of "10X First Strand Buffer", 1 μL of "Ribonuclease inhibitor", 4 μL of "dNTP mix" and 1 μL of "Reverse Transcriptase", are added to each sample which is then incubated for 2 hours at 42°C.

63 μL of nuclease free water, 10 μL of "10X Second Strand Buffer", 4 μL od "dNTP Mix", 2 μL of DNA polymerase and 1 μL of RNase H are added to each sample, which is further incubated for 2 hours at 16°C. 250 μL of "cDNA binding Buffer" are added to each sample, which is then deposited on a purification column and centrifugated for 1 minute at 10000 g. The liquid is removed and 500 μL of "cDNA Wash Buffer" are added before further centrifugation for 1 minute at 10000 g. The column is then placed in a new receiving tube and 9 μL of RNase free water (pre-heated to 5O°C) are deposited in the centre of the column for 2 minutes, and then the column is centrifugated for 1.5 minute at 10000 g, thus eluting cDNA.

To 14 μL of cDNA are added 3 μL of "aaUTP Solution" (50 mM) , 12 μL of "ATP, CTP, GTP Mix" (25 mM) , 3 μL of "UTP Solution" (50 mM) , 4 μL of "T7 1OX Reaction Buffer" and 4 μL of "T7 Enzyme Mix". The reaction mixture is incubated for 6 to 14 hours at 37°C. Contaminating cDNA

is removed by the addition of 2 μL of DNase I for 30 minutes at 37°C. 58 μL of nuclease free water, 350 μL of "aRNA Binding Buffer" and 250 μL of ethanol are added to each sample, which is then deposited on a column and centrifugated for 1 minute at 10000 g. The column is then placed in a new tube and 650 μL of "aRNA Wash Buffer" are deposited onto the column, which is then twice centrifugated for 1 minute at 10000 g and transferred into a new tube. 50 μL of nuclease free water (pre-heated to 5O°C) is then deposited onto the column centre. After 2 minutes of incubation, the column is centrifugated for 1,5 minute at 10000 g.

Resulting aRNA is dosed thanks to Agilent 2100 Bioanalyser®, as previously. 5 to 20 μg of aRNA are concentrated to a final volume of 7 μL. 9 μL of "Coupling Buffer", 4 μL of "ester dye Cyanine 3" (Cy3) and 4 μL of "ester dye Cyanine 5" (Cy5) in DMSO (Amersham Biosciences; Orsay, France) are added to each sample. After 30 minutes incubation, 4.5 μL of "Hydroxylamine 4M" are added for 15 minutes. Then 500 μL of "Capture Buffer" are added to each sample, which is then deposited on a GFX column. After a 30 seconds centrifugation at 13000 rpm, columns are washed with 600 μL of "Wash Buffer" and centrifugated for 30 seconds at 13000 rpm. The washing step is repeated twice, then 60 μL of nuclease free water preheated to 7O°C are deposited onto the column centre. After 3 minutes incubation, columns are centrifugated for 1 minute at 13000 rpm.

The fluorophore incorporation is measured using spectrophotometry, and is expressed as the number of fluorophore molecules/1000 nucleotides, according to the following formula:

The coupling reaction is satisfactory if 20 to 50 fluorophore molecules/1000 nucleotides are incorporated.

1.3 Hybridization of aRNA on microrarrays Slides preparation: Pan-genomic microrarrays (MWG Biotech; Courtaboeuf, France) are incubated for 15 minutes at 5O°C in a solution comprising ethanolamine (50 mM; Sigma; St Quenyin Fallavier, France) , Tris-base 100 mM pH9, SDS 0.1% (BIO-RAD; Marne-la-Coquette, 5 times going up and down for each wash) , and then incubated for 15 minutes at 5O°C in SSC 4X (Invitrogen; Cergy Pontoise, France), 0.1% SDS. After 1 hour prehybridization at 42°C in 150 mL of SSC 3.5X, SDS 0.3%, BSA 1% (Sigma; St Quenyin Fallavier, France) , microarrays are washed in 5 water baths at room temperature, and further centrifugated for 3 minutes at 500 rpm at room temperature.

Hybridization: aRNA are denaturated for 2 minutes at 95°C and then incubated for 30 minutes at 37°C. RNA are placed on the spotted zone and a lamellae is put on the microarray in such a way to prevent bubbles formation. The ensemble is placed in an hybridization chamber, 20 μL of SSC 3X are put in the chamber tank, and 3 droplets of SSC 3X are deposited on the microarray, near from the lamellae. The hybridization chamber is hermetically closed and immersed overnight in obscurity in a closed water bath at 42°C. Microarrays are then immersed in a SSC 2X, SDS 0.1% buffer, and further transferred in a SSC IX buffer and stirred for 2 minutes. After a 2 minutes

wash in SSC 0.2X, they are centrifugated at room temperature for 3 minutes at 500 rpm. They are then treated with 350 μL of Dyesaver (Genisphere) and dried 3 minutes in open air. Hybridized microarrays must be protected from light and dust and stored at room temperature .

1.4 Data acquisition and analysis

Microarrays reading is performed using a ScanArray® scanner (GSI Lumonics) at two distincts wavelengths: 633 nm for Cyanine 5 excitation and 532 nm for Cyanine 3 excitation. Resulting images are analyzed using GenePix Pro 5.1® (Axon Instruments, Inc) software. This software allows, via customizable grids, to ascribe each spot identity and to determine if each spot is or not valid in function of its homogeneity and intensity. A manual proofreading permits to validate and/or correct the software analysis. Raw results are then further analyzed using a macro developed on IFR26 website: "MADSCAN" (MicroArray Data Suites of Computer Analysis) , accessible on http://www.madtools.org/. This macro is useful for data filtration (signal ratio values, background noise value, saturation value...) , data normalization by non linear regression, outliers detection, and data integration. The obtained results are then analyzed by a supervised technology (SAM, "Significance Analysis of Microarray") .

Genes expressed on at least 2 microarrays out of 4 for which a "one class" SAM analysis has been performed were selected. This analysis allows for the determination of genes that are significantly differentially expressed between the ToI and the CR group (q<5%) .

1.5 Results: differentially expressed genes between the ToI and CR groups

Using the above described protocol, the inventors identified 310 genes that are significantly differentially expressed between kidney graft tolerant subjects and kidney transplanted subjects in chronic rejection. These genes are listed in above inserted Table 1 and Table 2.

EXAMPLE 2

Validation of the predictive value of an expression profile comprising genes listed in Table 1, or Table 1 and Table 2

2.1 Principle and methods

The genes listed in Tables 1 and 2 were identified as differentially expressed between tolerant patients and patients in chronic rejection using pangenomic microarrays (around 40000 genes) and pooled tolerant and chronic rejection samples, respectively constituted of several tolerant patients samples and several samples from patients in chronic rejection.

To assess the predictive value of a diagnosis performed using an expression profile comprising genes from Table 1, or Table 1 and Table 2, a validation step was performed with dedicated oligonucleotide microarrays comprising oligonucleotides specific for genes of Table 1 and Table 2, on individual patients with a phenotype of tolerance (6) or chronic rejection (8) .

This validation step allows to determine the predictive value of such an expression profile in an

individual, which is crucial for diagnosis since each patient will be tested autonomously.

The validation process uses PAM (predictive analysis of microarrays) statistical method. Only genes for which data is available for at least 50% of tolerant and under chronic rejection patients are taken into account in the analysis. A non supervised PAM 2 classes statistical analysis is performed.

2.2 Results

All individual patients included in the validation step were analyzed without knowing to which group they belong (tolerant or chronic rejection) .

For each patient, two cross validation (CV) probabilities (comprised between 0 and 1) were calculated, corresponding respectively to the probability, calculated based on their expression profile on the dedicated microarray, that said patient belong to either the tolerant group, or the group of patients in chronic rejection.

The CV probabilities of the 6 tolerant patients and the 8 patients in chronic rejection are plotted in Figure 1, either with Table 1 and Table 2 genes (Figure IA) or with only Table 1 genes (Figure IB) . Moreover, the mean probability to accurately identify a tolerant subject within the tolerant group (P _to i) and a patient in chronic rejection in the chronic rejection group (P _CR ) , as well as the mean value of these two probabilities (P) , were calculated and are displayed in Figure 1.

Results, which are summarized in Figure 1, show that the dedicated microarrays have a high predictive

diagnostic value, since the probability to identify a tolerant patient (Ptoi) is superior to 0.75, with or without Table 2 genes, while the probability to identify a patient in chronic rejection (P _CR ) is superior to 0.90, with or without Table 2 genes.

Overall, the probability to correctly identify the phenotype of an individual subject (P) is superior to 0.80, with or without Table 2 genes.