STATUS OF A SUBJECT

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U. S. Application No. 62/337,263, filed May 16, 2016. This application is incorporated herein by reference in its entirety.

STATEMENT REGARDING SEQUENCE LISTING

The Sequence Listing associated with this application is provided in text format in lieu of a paper copy, and is hereby incorporated by reference into the

specification. The name of the text file containing the Sequence Listing is

IMBC_009_01WO_SeqList_ST25.txt. The text file is 8 KB, was created on May 16, 2017, and is being submitted electronically via EFS-Web.

BACKGROUND

The compositions and methods of the invention relate generally to detection of biomarkers for the monitoring of immune status. In particular, the invention relates to compositions and methods for detection of B cell-activating factor (BAFF) for the monitoring of immune status of a subject.

The immune system is a system of many biological structures and processes within a subject that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from a subject' s own healthy tissue. Therefore, proper functioning of the immune system requires that all components of the immune system work in a coordinated manner to neutralize pathogens. An impairment of a subject' s immune system leads to infections by opportunistic pathogens that may eventually prove to be fatal.

Conversely, a hyperactive immune system (e.g., in autoimmune diseases) causes the immune system to attack a subject' s normal tissues as if they were foreign organisms. The overall efficiency (i.e., normal, hyperactive, or impaired) of a subject's immune system is referred to as the subject's immune status.

The immune system can be classified into subsystems - innate immunity and adaptive immunity. Defense against pathogens is mediated by the early reactions of innate immunity and the later responses of adaptive immunity. There are two types of adaptive immune responses, called cell-mediated immunity (mediated by T cells) and humoral immunity (mediated by B cells).

B cells or B lymphocytes are a type of white blood cell of the lymphocyte subtype. They function in the humoral immunity component of the adaptive immune system by secreting antibodies. Additionally, B cells present antigens (they are also classified as professional antigen-presenting cells (APCs)) and secrete cytokines. In mammals, B cells mature to plasma cells in the bone marrow.

An important factor in the survival, proliferation, normal development, and maturation of B cells is B-cell activating factor (BAFF). BAFF is a 285-amino-acid type II transmembrane protein that belongs to the superfamily of 19 known Tumor Necrosis Factor (TNF) ligands. This cytokine is expressed in B cell lineage cells, and acts as a potent B cell activator. BAFF has also been shown to play a role in B-cell proliferation and as a specific immunity response enhancer. BAFF is expressed as a membrane-bound type II transmembrane protein on various cell types including monocytes, dendritic cells and bone marrow stromal cells. The transmembrane form of BAFF can be cleaved from the membrane, generating a soluble BAFF polypeptide. Soluble BAFF levels in blood are related closely to the number of circulating B-cells. The homotrimeric soluble form of BAFF binds to and activates the BAFF Receptor (BAFF-R). Signaling through BAFF-R stimulates B lymphocytes to undergo proliferation. (For a review, see Rihacek et al, 2015).

Currently, an objective test to determine the immune status of a subject is not available, and the existence of a disease or infection is determined by a physician's observation of the subject's physical symptoms {e.g., body temperature or physical discomfort such as pain). However, such observations are subjective and can vary from one physician to another. Furthermore, a rapid and reliable determination of a subject' s response to treatment is also currently not available, and would be greatly facilitated by a test that could reliably monitor a subject's immune status at different time points during the course of a treatment regimen. Therefore, there is a need in the art to design a fast, reproducible, inexpensive, and reliable test that can indicate the immune status of a subject.

The present inventors have now surprisingly found that levels of BAFF polypeptide or a fragment thereof in a biological sample (e.g., serum) of a subject correlate with the subject's overall immune status. The present inventors have found that an increased amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject compared to BAFF polypeptide or a fragment thereof in a control biological sample obtained from a normal healthy subject is indicative of an impaired immune system as indicated by a reduction in their immunoglobulin levels, while a decreased amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject compared to amounts of BAFF polypeptide or a fragment thereof in a biological sample obtained from a normal healthy subject indicates that the subject is suffering from an infection or a disease.

BRIEF SUMMARY

In accordance with the purpose of this invention, as embodied and broadly described herein, this invention generally provides compositions and methods for reliably and reproducibly monitoring the immune status of a subject. The levels of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject can be detected and/or measured and compared against a baseline or control to reliably and reproducibly monitor the immune status of the subject.

In various embodiments, a method of monitoring immune status of a subject is provided. In some embodiments, a method of monitoring immune status of a subject, comprises: (a) detecting an amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from the subject; and (b) comparing the amount of BAFF polypeptide or fragment thereof detected in (a) to a predetermined cut-off value or to an amount detected in a control serum or plasma sample, wherein an increased amount of BAFF polypeptide or fragment in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample is indicative of an impaired immune system, wherein the biological sample is a serum or plasma sample.

In other embodiments, a method of monitoring immune status of a subject, comprises: (a) detecting an amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from the subject; and (b) comparing the amount of BAFF polypeptide or fragment thereof detected in (a) to a predetermined cut-off value or to an amount detected in a control serum or plasma sample, wherein a decreased amount of BAFF polypeptide or fragment in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample indicates that the subject is suffering from or at higher risk to develop an infection or a disease, wherein the biological sample is a serum or plasma sample.

In additional embodiments, a method of monitoring immune status of a subject, comprises: (a) detecting an amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from the subject; and (b) comparing the amount of BAFF polypeptide or fragment thereof detected in (a) to a predetermined cut-off value or to an amount detected in a control serum or plasma sample, wherein an increased amount of BAFF polypeptide or fragment in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample is indicative of an impaired immune system, and a decreased amount of BAFF polypeptide or fragment in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample indicates that the subject is at risk of or suffering from an infection or a disease, wherein the biological sample is a serum or plasma sample.

In other aspects, a kit for monitoring immune status of a subject is provided. In certain embodiments, the kit for monitoring immune status of a subject, comprising a reagent suitable for determining levels of BAFF polypeptide or a fragment thereof in a biological sample obtained from the subject, wherein the biological sample is a serum or plasma sample.

In other aspects, a method of monitoring response to a treatment of a subject is provided. In some embodiments, the method of monitoring response to a treatment of a subject comprises: (a) detecting an amount of BAFF polypeptide or a fragment thereof in a biological sample, obtained from the subject a time point prior to start of the treatment; (b) detecting an amount of BAFF polypeptide or a fragment thereof in the biological sample, obtained from the subject a time point subsequent to start of the treatment; and (c) comparing the amount of BAFF polypeptide or a fragment thereof detected in (a) to the amount of BAFF polypeptide or a fragment thereof detected in (b), wherein an increased amount of BAFF polypeptide or a fragment thereof detected in (b) as compared to the amount of BAFF polypeptide or a fragment thereof detected in (a) indicates that the subject is responding to treatment, and wherein a decreased or unchanged amount of BAFF polypeptide or a fragment thereof detected in (b) as compared to the amount of BAFF polypeptide or a fragment thereof detected in (a) indicates that the subject is not responding to treatment, wherein the biological sample is a serum or plasma sample.

In some embodiments, the biological sample includes, without limitation, cells in culture, cell supernatants, cell lysates, serum, plasma, urine, cerebral spinal fluid, biological fluid, and tissue samples. In certain embodiments, the biological sample is a serum sample. In some embodiments, the biological sample is a plasma sample. In other embodiments, the biological sample is supernatant obtained from culture of the subject's bone marrow mononuclear cells. In yet other embodiments, the biological sample is supernatant obtained from culture of the subject's peripheral blood mononuclear cells.

In some embodiments, the BAFF fragment is a cleaved BAFF polypeptide.

In some embodiments, the cleaved BAFF polypeptide is a soluble form of the BAFF polypeptide. In additional embodiments, BAFF polypeptide or a fragment thereof comprises the amino acid sequence of SEQ ID NO: 1. In yet other embodiments, the BAFF polypeptide or a fragment thereof comprises an amino acid sequence having at least about 20% identity, at least about 30% identity, at least about 40% identity, at least about 50% identity, at least about 60% identity, at least about 70% identity, at least about 75% identity, at least about 80% identity, at least about 90% identity, at least about 95% identity, at least about 96% identity, at least about 97% identity, at least about 98% identity, or at least about 99% identity with SEQ ID NO: 1.

In additional embodiments, the BAFF polypeptide or a fragment thereof is detected using a detection system selected from the group consisting of: western blot assay, immunohistochemistry, enzyme-linked immunosorbent assay (ELISA),

radioimmunoassay (RIA), enzyme immunoassay (EIA), fluorescence immunoassay (FIA), luminescence immunoassay (LIA), lateral flow assay, or strip assay. In some

embodiments, the detection system is an ELISA assay. In other embodiments, the detection system is a lateral flow assay.

In some embodiments, the detection is performed using an antibody specific for soluble BAFF polypeptide or a fragment thereof. In certain embodiments, the antibody specific for soluble BAFF polypeptide or a fragment thereof is a monoclonal antibody. In other embodiments, the antibody specific for soluble BAFF polypeptide or a fragment thereof is a polyclonal antibody.

In some aspects, the impaired immune system is the result of an immunodeficiency disease. In some embodiments, the immunodeficiency disease includes, but is not limited to, Acquired Immune Deficiency Syndrome (AIDS), Ataxia

telangiectasia, Chediak Higashi Syndrome, Common Variable Immune Deficiency

(CVID), Combined Immunodeficiency Disease, Complement deficiencies, DiGeorge Syndrome, Hypogammaglobulinemia, Job Syndrome, Leukocyte Adhesion Deficiency, Panhypogammaglobulinemia, X-linked Agammaglobulinemia Disease (Bruton's disease), Congenital Agammaglobulinemia, Selective Deficiency of IgA, Wiskott Aldrich

Syndrome, Chronic Granulomatous Disease, Severe Combined Immunodeficiency Disease, Hyper Immunoglobulin E Syndrome (Job's Syndrome), Hyper IgM Syndrome, X-linked agammaglobulinemia (XLA), Crohn's disease, Thymoma, immunodeficiencies associated with mutations in the LRBA gene (encoding the lipopolysaccharide-responsive and beigelike anchor protein), or immunodeficiencies associated with phosphatidylinositol 3 -kinase δ (PI3KD).

In some embodiments, the infection includes, but is not limited to, a viral infection, a bacterial infection, a prion infection, or a fungal infection. In some

embodiments, the disease includes, but is not limited to, autoimmune diseases including, without limitations, Systemic Lupus Erythematosus (SLE), Multiple Sclerosis (MS), Hashimoto's thyroiditis, rheumatoid arthritis, or diabetes mellitus type 1. In other embodiments, the disease includes genetic diseases such as cancer including, but not limited to, myeloma, lymphoma, or leukemia. In some aspects, the myeloma is multiple myeloma (MM). In other aspects, the lymphoma is non-Hodgkin lymphoma (NHL). In other embodiments, the leukemia is chronic lymphocytic leukemia (CLL).

In some embodiments, a kit for monitoring immune status of a subject is provided. In certain aspects, the kit for monitoring immune status of a subject comprises a reagent suitable for determining levels of BAFF polypeptide or a fragment thereof in a biological sample obtained from the subject, wherein the biological sample is a serum or plasma sample.

In some embodiments, the kit comprises an antibody that specifically binds soluble BAFF polypeptide or fragment thereof. In certain embodiments, the antibody that specifically binds soluble BAFF polypeptide or fragment thereof is a monoclonal antibody. In other embodiments, the antibody that specifically binds soluble BAFF polypeptide or fragment thereof is a polyclonal antibody.

In some aspects, the kit comprises a detection system selected from the group consisting of: ELISA assay, RIA assay, EIA assay, FIA assay, LIA assay, lateral flow assay, or strip assay. In some embodiments, the kit comprises an ELISA assay. In other embodiments, the kit comprises a lateral flow assay. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the disclosed method and compositions and together with the description, serve to explain the principles of the disclosed methods.

Figure 1 shows that B cell maturation antigen (BCMA) and BAFF form complexes in vitro. A, Detecting recombinant mouse BAFF (rmBAFF)- recombinant human BCMA (rhBCMA) complexes in vitro. B, Detecting mouse BAFF (mBAFF;

derived from SCID plasma)-rhBCMA complexes in vitro.

Figure 2 shows that BCMA and BAFF form complexes in vitro. A, rhBCMA-Fc injected into C57 Bl/6 mice binds mouse BAFF, forming human BCMA (hBCMA)-mBAFF complexes. B, hBCMA-mBAFF complexes were detected in severe combined immune deficient (SCID) mice dosed with hBCMA-Fc (top panel) and BAFF levels in these mice following formation of hBCMA-mBAFF complexes (bottom panel). C, hBCMA-mBAFF complexes were detected as early as day 1 in C57 Bl/6 mice dosed with rhBCMA-Fc. Negative controls include samples of mBAFF, hlgG and rhBCMA. Absorbance was determined by a microplate spectrophotometer with KC Junior software. Data are presented as means ± SEM, obtained from two independent

experiments and samples were analyzed twice.

Figure 3 shows that plasma human BCMA levels correlate with human MM tumor volume and BAFF-BCMA complexes are found in SCID mice bearing these tumors: In SCID mice bearing the A, LAG -l, B, LAGK-2 and C, LAG κ-1 A human MM xenografts. D, Human BCMA (from human MM tumors growing in SCID mice) binds mouse BAFF in mouse plasma and forms hBCMA-mBAFF complexes. D, In the plasma from mice bearing these three human MM xenografts, the levels of BCMA in the plasma correlate with the amount of BAFF-BCMA complex formation.

Figure 4 shows that severe combined immunodeficiency (SCID) mice bearing human multiple myeloma (MM) xenografts show reduced plasma BAFF levels. A, Decrease in plasma BAFF levels in mice implanted with the human MM tumor LAG -l when compared to SCID mice without MM tumors (day 14: P = 0.0143; day 21 : P = 0.0002; and day 28: P = 0.0008). B, Decrease in plasma BAFF levels in mice implanted with the human MM tumor LAGK-2 when compared to SCID mice without MM tumor (day 14: ^ = 0.0015; day 21 : P < 0.0001; day 28: P < 0.0001; and day 35: P < 0.0001). Results presented are group means ± SEM (n = 4-5 mice/group) from two independent experiments.

Figure 5 shows that increasing concentrations of rhBCMA interfere with mouse BAFF detection (A) and human BAFF detection (B), with the highest concentration of BCMA used being similar to concentrations found in MM patients. C, Using RT-PCR, no differences in BAFF mRNA levels were detected in SCID mice with or without human MM xenografts.

Figure 6 shows that sera of MM patients contain hBCMA-hBAFF complexes. BCMA-BAFF complexes in serum of MM patients were detected using anti- human BAFF capture antibody and anti-hBCMA detection antibody.

Figure 7 shows that serum BAFF levels are reduced in MM patients with active disease compared to healthy donors. Determination of serum BAFF levels from 31 patients with active MM (13 with progressive disease (PD) and 18 untreated) versus healthy donors (n = 11) shows reduced BAFF levels in the MM patients (436.0 pg/mL) compared to healthy donors (837.5 pg/mL).

Figure 8 shows serum BAFF levels are increased in MM patients in complete remission (CR) compared to healthy donors. Determination of serum BAFF levels from 15 patients with active MM versus healthy donors (n = 11) shows increased BAFF levels in the MM patients (1395.0 pg/mL) compared to healthy donors (837.5 pg/mL).

Figure 9 shows that serum BAFF levels can be used to monitor multiple myeloma. Serum BAFF levels are reduced in MM patients with active disease compared to healthy donors, and increased in MM patients in complete remission (CR) compared to healthy donors.

Figure 10 shows that serum B cell maturation antigen (BCMA) levels are inversely related to serum BAFF levels in MM patients.

Figure 1 1 shows flow cytometric analysis of serum BAFF (sBAFF; 500 ng/mL) binding to Raji cells (A) in the presence of rhBCMA (3.0 μg/mL, A, top row, third column) and serum from MM patients with progressive disease (PD) with a high level of serum BCMA (0.75 μg/mL, A, top row, second column) or complete remission (CR) with a low level (0.02 μg/mL, A, bottom row, second column) or a healthy subject (also 0.02 μg/mL, A, bottom row, first column). Both rhBCMA and serum from the MM patient with PD with a high level of serum BCMA markedly reduced BAFF binding to Raji B-cells, and addition of anti-BCMA blocking antibody restored BAFF binding. In contrast, minimal reduction in BAFF binding occurred in the presence of serum from the healthy subject (A, bottom row, first column) or MM patient in CR (A, bottom row, second column) both with low serum BCMA levels. B, This same experiment was duplicated using an additional human B-cell line, TB94, and similar results were obtained. Flow cytometric analysis was performed using a Beckman-Coulter FC500 cytometer with Cytomics CXP software. Each data point represents one individual MM patient' s serum sample.

DETAILED DESCRIPTION

Currently, an objective test to determine the immune status of a subject is not available, and the existence of a disease or infection is determined by a physician' s observation of the subject' s physical symptoms (e.g., body temperature or physical discomfort such as pain). However, such observations are subjective and can vary from one physician to another. Furthermore, a rapid and reliable determination of a subject' s response to treatment is also currently not available, and would be greatly facilitated by a test that could reliably monitor a subject's immune status at different time points during the course of a treatment regimen. The present inventors have found that levels of BAFF polypeptide or a fragment thereof correlate with the overall immune status of a subject. The present inventors have found that an increased amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject compared to BAFF polypeptide or a fragment thereof in a control biological sample obtained from a normal healthy subject is indicative of an impaired immune system, while a decreased amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject compared to amounts of BAFF polypeptide or a fragment thereof in a biological sample obtained from a normal healthy subject indicates that the subject is suffering or is at higher risk to suffer from an infection or an immune deficiency-related disease.

In various embodiments, methods for reliably monitoring the immune status of a subject are provided. Concentrations of BAFF polypeptide or a fragment thereof in a biological sample (e.g., a subject's sera) is detected and/or measured and compared against a baseline or control to reliably monitor the immune status of a subject. Without wishing to be bound to a particular theory, it is believed that because lower levels of BAFF polypeptide or a fragment thereof were detected in biological samples of subjects having active disease compared to biological samples of subjects having indolent disease, whereas higher levels of BAFF polypeptide or a fragment thereof were detected in biological samples of subjects having impaired immune systems compared to biological samples of normal healthy subjects, levels of soluble BAFF polypeptide or a fragment thereof can be used to reliably monitor the immune status of a subject.

In various other embodiments, methods for reliably monitoring the response of a subject to treatments targeted to improve the immune status of the subject are provided. Levels of soluble BAFF polypeptide or a fragment thereof are used to monitor the response of a subject to treatments targeted to improve the immune status of a subject. Without wishing to be bound to a particular theory, it is believed that because levels of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject correlated with the immune status of the subject, the levels of BAFF polypeptide or a fragment thereof in the biological sample can be determined at different times point subsequent to start of the treatment and compared to an initial time point prior to start of the treatment to monitor the response of a subject to treatments targeted to improve the immune status of the subject.

The practice of the invention will employ, unless indicated specifically to the contrary, conventional methods of chemistry, biochemistry, organic chemistry, molecular biology, microbiology, recombinant DNA techniques, genetics, immunology, and cell biology that are within the skill of the art, many of which are described below for the purpose of illustration. Such techniques are explained fully in the literature. See, e.g., Sambrook, et al, Molecular Cloning: A Laboratory Manual (3rd Edition, 2001);

Sambrook, et al, Molecular Cloning: A Laboratory Manual (2nd Edition, 1989); Maniatis et al, Molecular Cloning: A Laboratory Manual (1982); Ausubel et al, Current Protocols in Molecular Biology (John Wiley and Sons, updated July 2008); Short Protocols in Molecular Biology: A Compendium of Methods from Current Protocols in Molecular Biology, Greene Pub. Associates and Wiley-Interscience; Glover, DNA Cloning: A

Practical Approach, vol. I & II (IRL Press, Oxford, 1985); Anand, Techniques for the Analysis of Complex Genomes, (Academic Press, New York, 1992); Transcription and Translation (B. Hames & S. Higgins, Eds., 1984); Perbal, A Practical Guide to Molecular Cloning (1984); and Harlow and Lane, Antibodies, (Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1998).

All publications, patents and patent applications cited herein are hereby incorporated by reference in their entirety.

A. Definitions

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred embodiments of compositions, methods and materials are described herein. For the purposes of the present invention, the following terms are defined below.

The articles "a," "an," and "the" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

As used herein, the term "about" or "approximately" refers to a quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length that varies by as much as 30, 25, 20, 25, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 % to a reference quantity, level, value, number, frequency, percentage, dimension, size, amount, weight or length. In particular embodiments, the terms "about" or "approximately" when preceding a numerical value indicates the value plus or minus a range of 15%, 10%, 5%, or 1%.

Throughout this specification, unless the context requires otherwise, the words "comprise", "comprises" and "comprising" will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements. By "consisting of is meant including, and limited to, whatever follows the phrase "consisting of." Thus, the phrase "consisting of indicates that the listed elements are required or mandatory, and that no other elements may be present. By "consisting essentially of is meant including any elements listed after the phrase, and limited to other elements that do not interfere with or contribute to the activity or action specified in the disclosure for the listed elements. Thus, the phrase "consisting essentially of indicates that the listed elements are required or mandatory, but that no other elements are optional and may or may not be present depending upon whether or not they affect the activity or action of the listed elements.

Reference throughout this specification to "one embodiment," "an embodiment," "embodiment," "a particular embodiment," "a related embodiment," "a certain embodiment," "an additional embodiment," "some embodiments," "certain embodiments," "other embodiments," "additional embodiments," "Further embodiments," or "a further embodiment" or combinations thereof means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the foregoing phrases in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As used herein, the term "BAFF" or "BAFF polypeptide" is intended to generically refer to both the wild-type and variant B-cell activation factor, unless specifically denoted otherwise. BAFF polypeptides are encoded by the BAFF gene. As it is commonly used in the art, the term "gene" is intended to refer to the genomic region encompassing 5' untranslated region(s) (UTR), exons, introns, and 3' UTR. Individual segments may be specifically referred to, e.g., promoter, coding region, etc. Combinations of such segments that provide for a complete BAFF protein may be referred to generically as a protein coding sequence.

The terms "BAFF" or "BAFF polypeptide" or "soluble BAFF polypetide" are used interchangeably and encompass an amino acid sequence encoded by an open reading frame (ORF) of a known BAFF polynucleotide, including the full-length native polypeptide and fragments thereof, particularly biologically active fragments and/or fragments corresponding to functional domains, e.g., a region or domain having biological activity, etc; antigenic fragments thereof, and including fusions of the subject polypeptides to other proteins or parts thereof. The amino acid sequence of BAFF polypeptide has been disclosed. {See e.g., Schnieder et al, J. Exp. Med. 189(11)2: 1747-17564, 1999; Karpusas et al, J. Mol. Biol, 315(5): 1145-1154 (2002). The BAFF polypeptides of the invention can be isolated from a variety of sources, such as from human tissue types or biological samples such as serum, plasma, bone, marrow, or tissue.

As used herein, the term "fragment thereof refers to a portion of the full- length native BAFF polypeptide. In some embodiments, the BAFF fragment is a cleaved BAFF polypeptide. In some embodiments, the cleaved BAFF polypeptide is a soluble form of the BAFF polypeptide. In some embodiments, the BAFF polypeptide or a fragment thereof comprises an amino acid sequence having at least about 20% identity, at least about 30% identity, at least about 40% identity, at least about 50% identity, at least about 60% identity, at least about 70% identity, at least about 75% identity, at least about 80%) identity, at least about 90% identity, at least about 95% identity, at least about 96% identity, at least about 97% identity, at least about 98% identity, or at least about 99% identity with the full-length native BAFF polypeptide.

As used herein, the term "immune status" of a subject refers to the efficiency of the subject's immune system. As such, the immune status of a subject indicates whether the subject's immune system is normal, impaired (for e.g., if the subject is afflicted with an immune deficiency disease), or hyperactive (for e.g., if the subject is afflicted with a disease, an autoimmune disease, or an illness) compared to a normal healthy subject.

The term "immune system" refers to a system of many biological structures and processes within an organism that protects against disease.

The following are non-limiting embodiments of polynucleotides: a gene or gene fragment, exons, introns, mRNA, tRNA, rRNA, ribozymes, cDNA, recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence, isolated RNA of any sequence, nucleic acid probes, and primers. A nucleic acid molecule may also comprise modified nucleic acid molecules, such as methylated nucleic acid molecules and nucleic acid molecule analogs. Analogs of purines and pyrimidines are known in the art. Nucleic acids may be naturally occurring, e.g., DNA or RNA, or may be synthetic analogs, as known in the art. Such analogs may be preferred for use as probes because of superior stability under assay conditions. Modifications in the native structure, including alterations in the backbone, sugars or heterocyclic bases, have been shown to increase intracellular stability and binding affinity. Among useful changes in the backbone chemistry are phosphorothioates; phosphorodithioates, where both of the non-bridging oxygens are substituted with sulfur; phosphoroamidites; alkyl phosphotriesters and boranophosphates. Achiral phosphate derivatives include 3'-0'-5'-S-phosphorothioate, 3'- S-5'-0-phosphorothioate, 3'-CH2-5'-0-phosphonate and 3'- H-5'-0-phosphoroamidate. Peptide nucleic acids replace the entire ribose phosphodiester backbone with a peptide linkage.

The terms "polypeptide" and "protein", used interchangeably herein, refer to a polymeric form of amino acids of any length, which can include coded and non-coded amino acids, chemically or biochemically modified or derivatized amino acids, and polypeptides having modified peptide backbones. In various embodiments, BAFF polypeptides are contemplated for use within diagnostic, prognostic, or monitoring compositions and methods disclosed herein. The term includes fusion proteins, including, but not limited to, fusion proteins with a heterologous amino acid sequence, fusions with heterologous and homologous leader sequences, with or without N-terminal methionine residues; immunologically tagged proteins; and the like.

A "substantially isolated" or "isolated" substance is one that is substantially free of its associated surrounding materials in nature. By substantially free is meant at least 50%, preferably at least 70%, more preferably at least 80%, and even more preferably at least 90% free of the materials with which it is associated in nature. As used herein, an "isolated" can refer to polynucleotides, polypeptides, cells, samples, and antibodies.

Hybridization reactions can be performed under conditions of different "stringency". Conditions that increase stringency of a hybridization reaction are widely known and published in the art. See, for example, Sambrook et al. (1989). Examples of relevant conditions include (in order of increasing stringency): incubation temperatures of 25° C, 37° C, 50° C. and 68° C; buffer concentrations of lOxSSC, 6xSSC, l SSC, 0.1 x SSC (where SSC is 0.15 M NaCl and 15 mM citrate buffer) and their equivalents using other buffer systems; formamide concentrations of 0%, 25%, 50%, and 75%; incubation times from 5 minutes to 24 hours; 1, 2, or more washing steps; wash incubation times of 1, 2, or 15 minutes; and wash solutions of 6xSSC, l xSSC, O. l xSSC, or deionized water. Examples of stringent conditions are hybridization and washing at 50° C. or higher and in 0.1 x SSC (9 mM NaCl/0.9 mM sodium citrate). The term "target cell" includes an individual cell, cell from a biological sample, or cell culture. Target cells include progeny of a single target cell, and the progeny may not necessarily be completely identical (in morphology or in total DNA complement) to the original parent cell due to natural, accidental, or deliberate mutation and/or change. In particular embodiments, target cells include multiple myeloma, chronic lymphocytic leukemia, lymphoma, or Waldenstrom's macroglobulinemia tumor cells, bone marrow or peripheral blood mononuclear cells, B-cells, or plasma cells.

The detection systems of the invention are based, in part, on the ability of a binding agent to bind soluble BAFF polypeptide or a fragment thereof. Generally, the invention contemplates the use of a binding agent that specifically binds soluble BAFF polypeptide or a fragment thereof, resulting in the formation of a detectable complex of soluble BAFF polypeptide or a fragment thereof and binding agent. In some embodiments, the invention utilizes two binding agents, a capture binding agent and a detection binding agent, both of which bind to soluble BAFF polypeptide or a fragment thereof, resulting in the formation of a ternary complex comprising capture binding agent, soluble BAFF polypeptide, and detection binding agent.

Any of a variety of binding agents may be used, including, for example, polypeptides, sugars, and nucleic acids. In yet other embodiments, the invention further includes the use of an additional binding agent that binds to the detection binding agent. Such an additional binding agent may be useful, e.g., in detecting bound detection binding agent. Accordingly, one example of such an additional binding agent is antibodies specific for a fragment of an antibody, e.g., an F _c fragment, which may be detectably labeled and, therefore used to detect bound detection binding agent, and are particularly useful when the detection binding agent is not itself easily amenable to labeling. In certain embodiments, the binding agent is an antibody specific for bacteria.

The term "binds specifically," in the context of antibody binding, refers to high avidity and/or high affinity binding of an antibody to a specific polypeptide i.e., epitope of a BAFF polypeptide or a fragment thereof. Antibody binding to an epitope on a specific polypeptide (also referred to herein as "an epitope") is preferably stronger than binding of the same antibody to any other epitope, particularly those which may be present in molecules in association with, or in the same sample, as the specific polypeptide of interest, e.g., binds more strongly to a specific epitope on the soluble BAFF polypeptide than to a different BAFF epitope or non-BAFF epitope. Antibodies which bind specifically to a polypeptide of interest may be capable of binding other polypeptides at a weak, yet detectable, level (e.g., 10% or less, 5% or less, 1% or less of the binding shown to the polypeptide of interest). Such weak binding, or background binding, is readily discernible from the specific antibody binding to the compound or polypeptide of interest, e.g. by use of appropriate controls. In general, antibodies used in compositions and methods of the invention which bind to a specific BAFF polypeptide or a fragment thereof with a binding affinity of 10 ⁷ moles/L or more, preferably 10 ⁸ moles/L or more are said to bind specifically to the specific BAFF polypeptide. In general, an antibody with a binding affinity of 10 ⁶ moles/L or less is not useful in that it will not bind an antigen at a detectable level using conventional methodology currently used.

In some embodiments, the affinity of specific binding of a BAFF binding agent to soluble BAFF polypeptide or a fragment thereof is about 2 times greater than background binding, about 5 times greater than background binding, about 10 times greater than background binding, about 20 times greater than background binding, about 50 times greater than background binding, about 100 times greater than background binding, or about 1000 times greater than background binding or more.

In other embodiments, the affinity of specific binding is between about 2 to about 1,000 times greater than background binding, between about 2 to 500 times greater than background binding, between about 2 to about 100 times greater than background binding, between about 2 to about 50 times greater than background binding, between about 2 to about 20 times greater than background binding, between about 2 to about 10 times greater than background binding, between about 5 to about 100 times greater than background binding, between about 5 to about 50 times greater than background binding, between about 5 to about 20 times greater than background binding, between about 10 to about 100 times greater than background binding, between about 10 to about 50 times greater than background binding, between about 50 to about 500 times greater than background binding, or any intervening range of affinity.

Accordingly, specific binding occurs between a binding agent and soluble

BAFF polypeptide or a fragment thereof where there is an interaction between the two which produces a bound complex having the characteristics of an antibody/antigen or enzyme/substrate interaction. In some embodiments, specific binding is characterized when one member of a pair substantially binds to a particular species and to no other species within the family of compounds to which the corresponding member of the binding member belongs. In other embodiments, specific binding is characterized when one member of a pair substantially binds to one or more particular species and to no other species within the family of compounds to which the corresponding member of the binding member belongs. In yet other embodiments, specific binding is characterized when one member of a pair substantially binds to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more particular species and to no other species within the family of compounds to which the corresponding member of the binding member belongs.

Generally speaking, the binding affinity of a binding agent of the invention (A) to soluble BAFF polypeptide or a fragment thereof (B) can be generally expressed by the chemical equilibrium constant Kd resulting from the following reaction: [A] +[B]- [AB]. The chemical equilibrium constant Kd is then given by: Kd=[A]x[B]/[AB].

Whether the binding of a binding agent is specific or not can be judged from the difference between the binding affinity (Kd value) of the binding agent to soluble BAFF polypeptide or a fragment thereof, versus the binding to another polypeptide.

Kd values and differences in Kd values can be measured using, for example, in vitro or in vivo binding assays and/or assays on other materials such as a polystyrene microtitre plate or a specialized surface in an analytical biosensor. In some embodiments, the difference between the Kd value of a binding agent to soluble BAFF polypeptide or a fragment thereof, versus the binding to an undesired polypeptide is about 2-fold, about 3- fold, about 4-fold, about 5-fold, about 6-fold, about 7-fold, about 8-fold, about-9 fold, about 10-fold, about 20-fold, about 50-fold, about 100-fold, about 1000-fold, or more.

In other embodiments, the Kd value is less than 10 ⁴ M, less than 10 ⁵ M, less than 10 ⁶ M, less than 10 ⁷ M, less than 10 ⁸ M, less than 10 ⁹ M, less than 10 ¹⁰ M and could be 10 ¹¹ M, less than 10 ¹² M, less than 10 ¹³ M, less than 10 ¹⁴ M, less than 10 ¹⁵ M or less.

In other aspects, the Kd value is between about 10 ⁴ M and about 10 ¹⁵ M, between about 10 ⁴ M and about 10 ¹² M, between about 10 ⁴ M and about 10 ¹⁰ M, between about 10 ⁶ M and about 10 ¹⁵ M, between about 10 ⁶ M and about 10 ¹² M, between about 10 ⁶ M and about 10 ¹⁰ M, between about 10 ⁸ M and about 10 ¹⁵ M, between about 10 ⁸ M and about 10 ¹² M, between about 10 ⁸ M and about 10 ¹⁰ M, between about 10 ⁷ M and about 10 ¹⁰ M, or any intervening range of affinity.

The term "antibody" herein is used in the broadest sense and specifically covers monoclonal antibodies, polyclonal antibodies, multispecific antibodies (e.g., bispecific antibodies) formed from at least two intact antibodies, and antibody fragments so long as they exhibit the desired biological activity.

The term "monoclonal antibody" as used herein refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies comprising the population are identical except for possible naturally occurring mutations that can be present in minor amounts.

In some embodiments, the monoclonal antibody is an anti-BAFF

monoclonal antibody. In other embodiments, the monoclonal antibody specifically recognizes an epitope present in a fragment of the soluble BAFF polypeptide.

Monoclonal antibodies are highly specific, being directed against a single antigenic site. Furthermore, in contrast to conventional (polyclonal) antibody preparations which typically include different antibodies directed against different determinants (epitopes), each monoclonal antibody is directed against a single determinant on the antigen. In addition to their specificity, the monoclonal antibodies are advantageous in that they are synthesized by the hybridoma culture, uncontaminated by other immunoglobulins. The modifier "monoclonal" indicates the character of the antibody as being obtained from a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by any particular method. For example, the monoclonal antibodies to be used in accordance with the present invention may be made by the hybridoma method first described by Kohler et al, Nature, 256: 495 (1975), or may be made by recombinant DNA methods (see, e.g., U.S. Pat. No. 4,816,567). The "monoclonal antibodies" may also be isolated from phage antibody libraries using the techniques described in Clackson et al, Nature, 352: 624-628 (1991) and Marks et al, J. Mol. Biol., 222: 581-597 (1991), for example.

The monoclonal antibodies herein specifically include "chimeric" antibodies (immunoglobulins) in which a portion of the heavy and/or light chain is identical with or homologous to corresponding sequences in antibodies derived from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain (s) is identical with or homologous to corresponding sequences in antibodies derived from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity (U.S. Pat. No.

4,816,567; Morrison et al., Proc. Natl. Acad. Sci. USA, 81 : 6851-6855 (1984)). Methods of making chimeric antibodies are known in the art.

"Humanized" forms of non-human (e.g., murine) antibodies are chimeric immunoglobulins, immunoglobulin chains or fragments thereof (such as Fv, Fab, Fab', F (ab') 2 or other antigen-binding subsequences of antibodies) which contain minimal sequence derived from non-human immunoglobulin.

For the most part, humanized antibodies are human immunoglobulins (recipient antibody) in which residues from a complementarity-determining region (CDR) of the recipient are replaced by residues from a CDR of a non-human species (donor antibody) such as mouse, rat or rabbit having the desired specificity, affinity, and capacity. In some instances, Fv framework region (FR) residues of the human immunoglobulin are replaced by corresponding non-human residues. Furthermore, humanized antibodies may comprise residues which are found neither in the recipient antibody nor in the imported CDR or framework sequences. These modifications are made to further refine and maximize antibody performance. In general, the humanized antibody will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the hypervariable loops correspond to those of a non-human

immunoglobulin and all or substantially all of the FR regions are those of a human immunoglobulin sequence although the FR regions may include one or more amino acid substitutions that improve binding affinity. The number of these amino acid substitutions in the FR is typically no more than 6 in the H chain, and no more than 3 in the L chain. The humanized antibody optimally also will comprise at least a portion of an

immunoglobulin constant region (Fc), typically that of a human immunoglobulin. For further details, see Jones et al, Nature, 321 : 522-525 (1986); Reichmann et al., Nature, 332: 323-329 (1988); and Presta, Curr. Op. Struct. Biol, 2: 593-596 (1992). The humanized antibody includes a PRIMATIZED antibody wherein the antigen-binding region of the antibody is derived from an antibody produced by, e.g., immunizing macaque monkeys with the antigen of interest. Methods of making humanized antibodies are known in the art.

Human antibodies can also be produced using various techniques known in the art, including phage-display libraries. Hoogenboom and Winter, J. Mol. Biol, 227: 381 (1991); Marks et al, J. Mol. Biol, 222: 581 (1991). The techniques of Cole et al. and Boerner et al. are also available for the preparation of human monoclonal antibodies. Cole et al, Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, p. 77 (1985); Boerner et al., J. Immunol, 147(1): 86-95 (1991).

"Functional fragments" of the binding antibodies of the invention are those fragments that retain binding to antigen with substantially the same affinity as the intact full chain molecule from which they are derived. An "isolated" antibody is one which has been identified and separated and/or recovered from a component of its natural environment. Contaminant components of its natural environment are materials which would interfere with diagnostic or therapeutic uses for the antibody, and may include enzymes, hormones, and other proteinaceous or nonproteinaceous solutes. In preferred embodiments, the antibody will be purified (1) to greater than about 95% by weight of antibody as determined by the Lowry method, and most preferably more than about 99% by weight, (2) to a degree sufficient to obtain at least 15 residues of N-terminal or internal amino acid sequence by use of a spinning cup sequenator, or (3) to homogeneity by SDS-PAGE under reducing or nonreducing conditions using Coomassie blue or, preferably, silver stain. Isolated antibody includes the antibody in situ within recombinant cells since at least one component of the antibody's natural environment will not be present. Ordinarily, however, isolated antibody will be prepared by at least one purification step.

The terms "detectably labeled antibody" refers to an antibody (or antibody fragment which retains binding specificity for soluble BAFF polypeptide or a fragment thereof), having an attached detectable label. The detectable label is normally attached by- chemical conjugation, but where the label is a polypeptide, it could alternatively be attached by genetic engineering techniques. Methods for production of detectably labeled proteins are well known in the art. Detectable labels may be selected from a variety of such labels known in the art, including, but not limited to, haptens, radioisotopes, fluorophores, paramagnetic labels, enzymes (e.g., horseradish peroxidase), or other moieties or compounds which either emit a detectable signal (e.g., radioactivity, fluorescence, color) or emit a detectable signal after exposure of the label to its substrate. Various detectable label/substrate pairs (e.g., horseradish peroxidase/diaminobenzidine, avidin/streptavidin, luciferase/luciferin)), methods for labeling antibodies, and methods for using labeled antibodies are well known in the art (see, for example, Harlow and Lane, eds. (Antibodies: A Laboratory Manual (1988) Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.)). In one technique, an immunogen comprising the polypeptide is initially injected into any of a wide variety of mammals (e.g., mice, rats, rabbits, sheep or goats). Polyclonal antibodies specific for the polypeptide may then be purified from such antisera by, for example, affinity chromatography using the polypeptide coupled to a suitable solid support. In some embodiments, the antibody is an anti-BAFF polyclonal antibody. In other embodiments, the antibody is polyclonal antibody that recognizes the soluble BAFF polypeptide. In yet other embodiments, the antibody is polyclonal antibody that recognizes a fragment of the soluble BAFF polypeptide.

A "biological sample" encompasses a variety of sample types obtained from an individual and can be used in a diagnostic or monitoring assay. The definition encompasses blood and other liquid samples of biological origin, solid tissue samples such as a biopsy specimen or tissue cultures or cells derived there from and the progeny thereof. The definition also includes samples that have been manipulated in any way after their procurement, such as by treatment with reagents, solubilization, or enrichment for certain components, such as polynucleotides. The term "biological sample" encompasses a clinical sample, and also includes, without limitation, cells in culture, cell supernatants, cell lysates, serum, plasma, urine, cerebral spinal fluid, biological fluid, and tissue samples. The sample may be pretreated as necessary by dilution in an appropriate buffer solution or concentrated, if desired. Any of a number of standard aqueous buffer solutions, employing one of a variety of buffers, such as phosphate, Tris, or the like, preferably at physiological pH can be used. Biological samples can be derived from patients using well known techniques such as venipuncture, lumbar puncture, fluid sample such as saliva or urine, or tissue biopsy and the like.

As used herein, the terms "correlated with" or "associated with" refer to the levels of soluble BAFF polypeptide or a fragment thereof in a biological sample of a subject that has a statistically significant correlation with a physiologic state, e.g., disease status or extent of the disease, response to treatment, and survival. The strength of the correlation between levels of soluble BAFF polypeptide or a fragment thereof and the presence or absence of a particular physiologic state may be determined by a statistical test of significance. Methods for determining the strength of a correlation between the expression level of a differentially-expressed gene and a particular physiologic state by assigning a statistical score to the correlation are reviewed in Holloway et al. (2002) Nature Genetics Suppl. 32:481-89, Churchill (2002) Nature Genetics Suppl. 32:490-95, Quackenbush (2002) Nature Genetics Suppl. 32: 496-501; Slonim (2002) Nature Genetics Suppl. 32:502-08; and Chuaqui et al. (2002) Nature Genetics Suppl. 32:509-514; each of which is herein incorporated by reference in its entirety.

A "conjugate" refers to any molecule, e.g., antibody bound or joined covalently or non-covalently to another molecule, e.g., a hapten, small molecule, or label, including fusion proteins and as well as molecules that contain both amino acid or protein portions and non-protein portions. Conjugates may be synthesized by a variety of techniques known in the art including, for example, solid phase synthesis, solution phase synthesis, organic chemical synthetic techniques or a combination of these techniques. The choice of synthesis will depend upon the particular molecule to be generated.

The terms "individual," "subject," and "patient," used interchangeably herein, refer to a mammal, including, but not limited to, murines, simians, humans, mammalian farm animals, mammalian sport animals, and mammalian pets. In some embodiments, the subject is a human subject.

The term "mammal" refers to any animal classified as a mammal, including humans, domestic and farm animals, and zoo, sports, or pet animals, such as dogs, horses, cats, cows, etc. In some embodiments, the mammal herein is human.

B. Methods of Monitoring of Immune Status of a Subject

The present inventors have discovered that soluble BAFF polypeptide levels or levels of a fragment thereof correlate with the immune status of a subject. As such,

BAFF polypeptide levels or levels of a fragment thereof are increased in biological samples obtained from subjects with impaired immune systems, and decreased in biological samples obtained from subjects suffering from an infection or disease. Accordingly, particular embodiments of the invention provide methods for the monitoring the immune status of a subject as well as monitoring the response of the subject to treatment, based upon the level of BAFF polypeptide or a fragment thereof in a biological sample obtained from a patient, including, e.g., a patient's bloodstream, serum, bone marrow, or tissue at different time points. A variety of methods of determining soluble BAFF polypeptide levels are known and available in the art. In certain embodiments, these involve the use of a BAFF binding agent, such as an antibody that binds with specificity to soluble BAFF polypeptide. As discussed elsewhere herein, there are a variety of assay formats known to those of ordinary skill in the art and suitable for using a binding agent to detect polypeptide markers in a sample. E.g., ELISA assays, lateral flow assays, etc.; see also, Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, 1988.

In general, a condition leading to impairment of the immune system is monitored by the presence of at least about 2-fold, at least about 5-fold, at least about 10- fold, at least about 20-fold, at least about 50-fold, at least about 100-fold, at least about 1000-fold, or higher levels of soluble BAFF polypeptide or a fragment thereof as compared to those in a normal control subject. In general, an infective or disease state is monitored by the presence of at least about 2-fold, at least about 5-fold, at least about 10- fold, at least about 20-fold, at least about 50-fold, at least about 100-fold, at least about 1000-fold, or lower levels of solubleBAFF polypeptide or a fragment thereof as compared to those in a normal control subject.

In some embodiments, methods of monitoring immune status of a subject comprise: (a) detecting an amount of BAFF polypeptide or a fragment thereof in a biological sample, e.g., serum, obtained from a subject; and (b) comparing the amount of BAFF polypeptide or fragment thereof detected in (a) to a predetermined cut-off value or to an amount detected in a control serum or plasma sample, wherein an increased amount of BAFF polypeptide or a fragment thereof in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample is indicative of an impaired immune system, and a decreased amount of BAFF polypeptide or a fragment thereof in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample indicates that the subject is at higher risk of or is suffering from an infection or a disease, wherein the biological sample is a serum or plasma sample.

In other embodiments, methods of monitoring immune status of a subject comprise: (a) detecting an amount of BAFF or a fragment thereof in a biological sample, e.g., serum, obtained from a subject; and (b) comparing the amount of BAFF polypeptide or a fragment thereof detected in (a) to a predetermined cut-off value or to an amount detected in a control serum or plasma sample, wherein a decreased amount of BAFF polypeptide or a fragment thereof in the biological sample of the subject as compared to the predetermined cut-off value or amount in the control serum or plasma sample is indicative of an impaired immune system, wherein the biological sample is a serum or plasma sample.

In yet other embodiments, methods of monitoring immune status of a subject comprise: (a) detecting an amount of BAFF polypeptide or a fragment thereof in a biological sample obtained from a subject at an initial time point; (b) detecting an amount of BAFF polypeptide or a fragment thereof in the biological sample obtained from the subject at a later time point; and (c) comparing the amount of BAFF polypeptide or a fragment thereof detected in (a) to the amount of BAFF polypeptide or a fragment thereof detected in (b), wherein an increased amount of BAFF polypeptide or a fragment thereof detected in (b) as compared to the amount of BAFF polypeptide or a fragment thereof detected in (a) indicates that the subject is responding to treatment, and wherein a decreased or unchanged amount of BAFF polypeptide or a fragment thereof detected in (b) as compared to the amount of BAFF polypeptide or a fragment thereof detected in (a) indicates that the subject is not responding to treatment, wherein the biological sample is a serum or plasma sample. In some embodiments, the immune status of a subject may be determined by (a) contacting a biological sample obtained from a subject with a BAFF binding agent; (b) detecting in the sample a level of soluble BAFF polypeptide or a fragment thereof that binds to the binding agent; and (c) comparing the level of soluble BAFF polypeptide or a fragment thereof with a predetermined cut-off value or with the value obtained from a normal control subject. In certain embodiments, the cut-off value for the detection of impairment of the immune system and/or an infection or disease state is the average mean signal obtained when the immobilized antibody is incubated with samples from patients not suffering from an immune system impairment and not suffering from an infection or disease state.

In various embodiments, the biological sample includes, without limitation, cells in culture, cell supernatants, cell lysates, serum, plasma, urine, cerebral spinal fluid, biological fluid, and tissue samples. In certain embodiments, the biological sample is supernatant obtained from a culture of the subject's cells. In some aspects, the cells are the subject's bone marrow mononuclear cells. In other aspects, the cells are the subject's peripheral blood mononuclear cells.

In particular embodiments, detection involves measuring BAFF mRNA levels present in the biological sample. In some embodiments, detection is performed using one or more nucleic acid primers specific for BAFF DNA or mRNA. In other embodiments, detection involves determining soluble BAFF polypeptide levels present in the biological sample. In certain embodiments, detection is performed using an antibody specific for soluble BAFF polypeptide or a fragment thereof.

In certain embodiments, a sample generating a signal that is statistically stronger than the predetermined cut-off value is considered positive for an infection or disease condition, whereas a sample generating a signal that is statistically weaker than the predetermined cut-off value is considered positive for an impaired immune system. In certain embodiments, the sample generates a signal that is up to about two standard deviations, up to about three standard deviations, up to about five standard deviations, up to about ten standard deviations, up to about twenty standard deviations, up to about thirty standard deviations, up to about forty standard deviations, up to about fifty standard deviations, up to about sixty standard deviations, up to about seventy standard deviations, up to about eighty standard deviations, up to about ninety standard deviations, or up to about hundred standard deviations above the predetermined cut-off. In other embodiments, the sample generates a signal that is up to about two standard deviations, up to about three standard deviations, up to about five standard deviations, up to about ten standard deviations, up to about twenty standard deviations, up to about thirty standard deviations, up to about forty standard deviations, up to about fifty standard deviations, up to about sixty standard deviations, up to about seventy standard deviations, up to about eighty standard deviations, up to about ninety standard deviations, or up to about hundred standard deviations below the predetermined cut-off.

In other embodiments, the cut-off value is determined using a Receiver Operator Curve, according to the method of Sackett et al, Clinical Epidemiology: A Basic Science for Clinical Medicine, Little Brown and Co., 1985, p. 106-7. Briefly, in these embodiments, the cut-off value may be determined from a plot of pairs of true positive rates {i.e., sensitivity) and false positive rates (100%-specificity) that correspond to each possible cut-off value for the diagnostic test result. The cut-off value on the plot that is the closest to the upper left-hand corner {i.e., the value that encloses the largest area) is the most accurate cut-off value, and a sample generating a signal that is higher than the cut-off value determined by this method may be considered positive. Alternatively, the cut-off value may be shifted to the left along the plot, to minimize the false positive rate, or to the right, to minimize the false negative rate. In general, a sample generating a signal that is higher than the cut-off value determined by this method is considered positive for an infection or disease condition, whereas a sample generating a signal that is three standard deviations below the predetermined cut-off value is considered positive for an impaired immune system. In some embodiments, the assay involves the use of a BAFF binding agent immobilized on a solid support to bind to and remove the BAFF polypeptide or a fragment thereof from the remainder of the sample. The bound BAFF polypeptide may then be detected using a detection reagent that contains a reporter group and specifically binds to the binding agent/polypeptide complex. Such detection reagents may comprise, for example, a binding agent that specifically binds to the soluble BAFF polypeptide or a fragment thereof, or an antibody or other agent that specifically binds to the binding agent, such as an anti-immunoglobulin, protein G5 protein A or a lectin. In some embodiments, the BAFF detection reagent, e.g., antibody, is bound to biotin which recognizes and specifically binds a streptavidin or avidin binding agent.

In certain embodiments, the assay is performed in a lateral flow or strip test format, as discussed elsewhere herein, wherein the BAFF binding agent, e.g., antibody, is immobilized on a membrane, such as nitrocellulose. In the lateral flow test, soluble BAFF polypeptides or a fragment thereof within the sample bind to the immobilized binding agent as the sample passes through the membrane. A second, labeled binding agent then binds to the BAFF binding agent-polypeptide complex as a solution containing the second binding agent flows through the membrane. The detection of bound second binding agent may then be performed as described above. In the strip test format, one end of the membrane to which BAFF binding agent is bound is immersed in a solution containing the sample. The sample migrates along the membrane through a region containing second binding agent and to the area of immobilized binding agent. Concentration of second binding agent at the area of immobilized antibody indicates the immune status of a subject.

In several embodiments, the invention provides similar methods for determining response of the immune status of a subject to treatment. Since serum BAFF polypeptide levels correlate with the immune status, response to treatment or therapy is monitored by comparing soluble BAFF polypeptide levels in a subject's serum (or other biological sample) at different time points during the course of a treatment regimen. Thus, the present invention provides a rapid and reliable method of monitoring immune status of a subject and response to treatment of immune status, using, for e.g., a serum or plasma sample obtained from the subject's bloodstream. In particular embodiments, the method is practiced by ELISA assay, lateral flow assay, or strip test assay using an antibody specific for soluble BAFF polypeptide or a fragment thereof.

The invention further provides systems and kits for monitoring immune status of a subject, comprising a reagent suitable for determining levels of BAFF polypeptide or a fragment thereof in a biological sample obtained from the subject, wherein the biological sample is a serum or plasma sample. In some embodiments, the kit includes reagents for performing ELISA, lateral flow, or strip test assays such as an antibody specific for soluble BAFF polypeptide or a fragment thereof. Detection systems and kits of the invention are described in further detail below.

C. Detection Systems and Kits

In various embodiments, the present invention provides detection systems and kits for monitoring immune status of a subject. A detection system or kit of the present invention may be used for monitoring immune status of a subject using a biological sample, e.g., serum, of a subject. The diagnostic kit could include the method for the detection of antigen-antibody reaction in addition to the material. The detection method is preferably selected from the group consisting of flow cytometry, immunohistochemistry, and enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), enzyme immunoassay (EIA), fluorescence immunoassay (FIA), luminescence immunoassay (LIA), lateral flow assay, and strip assay. The reactivity of the antigen recognition material could be confirmed using device detecting an enzyme reaction, fluorescence, luminescence, or radiation. In some embodiments, monitoring the immune status of a subject can be performed with a flow cytometry kit, immunohistochemistry kit, ELISA kit or lateral flow or strip kit including the anti-BAFF antibody or an antigen binding fragment thereof.

In some embodiment, monitoring of the immune status of a subject can be performed with a flow cytometry kit, immunohistochemistry kit, ELISA kit or lateral flow or strip kit including an antibody that is specific for soluble BAFF polypeptide or a fragment thereof.

In some embodiments, a kit or system may comprise one or more or all of the following components: 1) one or more standards comprised of one or more of the biomarker(s) of the invention, such as soluble BAFF polypeptide or a fragment thereof; 2) a binding agent, such as an antibody or a plurality of antibodies, that are specific for the biomarker(s) that are to be assayed for using the kit; 3) written instructions; 4) diluents for samples and the standards; 5) a wash buffer; 6) color reagents; 7) stop solution; and 8) a carrier, such as an antibody carrier, for example, a lateral flow device, or a microplate with bound antibody, or polystyrene beads.

In some embodiments, the detection system or kit used to monitor immune status of a subject is a quantitative ELISA (enzyme-linked immunosorbent assay) that determines the concentration or concentrations of the biomarker or biomarker(s) in accordance with methods embodied by the invention. The principle of the assay is to use the quantitative sandwich enzyme immunoassay technique wherein a monoclonal or polyclonal antibody selective for a biomarker is pre-coated onto a carrier such as a microplate into its wells. The standards and sample are then pipetted into the wells and any of the biomarker that is present is bound to this immobilized antibody. Next, the wells are washed with washing buffer, and an enzyme-linked monoclonal or polyclonal antibody that is specific for the biomarker is added to the wells. Washing is again performed, and then a substrate solution is added to the wells. Color subsequently develops in proportion to the amount of polypeptide of the invention that is bound in the first step. The color

development is stopped using a stop solution, and the intensity of the color is measured by a microplate reader.

In other embodiments, the monitoring of the immune status of a subject may be carried out using, for example, a lateral flow assay. Such lateral flow assays have the potential to be a cost-effective, fast, simple, and sensitive method, for instance for on-site screening assays. The lateral flow assay comprises a carrier that allows a lateral flow to occur wherein either the sample or the detection reagent is displaced form one location on the carrier to another. There are many formats of lateral flow assays suitable for use in the methods embodied by the invention, and the skilled person will readily know how to select and optimize a particular format. An example of a lateral flow test strip of the invention comprises, for example, the following components: sample pad; an absorbent pad onto which the test sample is applied; a conjugate or reagent pad that contains antibodies specific to the target analyte and conjugated to colored particles (usually colloidal gold particles, or latex microspheres); a reaction membrane, typically a hydrophobic

nitrocellulose or cellulose acetate membrane onto which anti-target analyte antibodies are immobilized in a line across the membrane as a capture zone or test line (a control zone may also be present, containing antibodies specific for the conjugate antibodies); and a wick or waste reservoir, a further absorbent pad designed to draw the sample across the reaction membrane by capillary action and collect it.

There are a number of variations on lateral flow technology. The capture zone on the membrane may contain immobilized antigens or enzymes depending on the target analyte rather than antibodies. It is also possible to apply multiple capture zones to create a multiplex test. For example, in particular embodiments, test strips able to detect soluble BAFF polypeptide or a fragment thereof and separately in the same sample additional biomarkers of a specific disease, e.g., multiple myeloma, e.g., D2M, IL-6, C- reactive protein, and serum monoclonal protein are contemplated. Lateral flow

immunoassays are simple to use by untrained operators and generally produce a result within 15 minutes. They are very stable and robust, have a long shelf life and do not usually require refrigeration. They are also relatively inexpensive to produce. These features make them ideal for use at the point-of-care and for testing samples in the field, as well as in the laboratory.

While most lateral flow immunoassays are only capable of providing a qualitative result, it is possible to obtain some degree of quantification by measuring the amount of conjugate bound to the capture zone. This can be done using a dedicated reader to measure the intensity of the colored test line. For example, the Neogen Corporation has developed the Accuscan™ lateral flow reader for use with its range of Reveal® assay kits and Charm Sciences also supplies a reader for its Rosa® range of test strips. More sophisticated techniques, such as fluorescent dye labeled conjugates, have also been developed to improve the quantitative potential of lateral flow assays.

A detection system in kit form can include, for example, in an amount sufficient for at least one assay a polyclonal antibody composition or a monoclonal antibody composition that binds soluble B AFF polypeptide or a fragment thereof, as a packaged reagent. Instructions for use of the packaged reagent are also typically included.

A detection system in kit form can also include, for example, a means for combining the test sample with a buffering system (Reagent 1) containing viscosity controllers and stabilizers into a reaction vessel and mixing the solution. A detection system in kit form can also include a means for reading the a parameter of the reaction vessel with sample and buffer, and further means for combining the test sample and buffer mixture with a fluorescence-labeled ligand (Reagent 2) to said biological substance in the reaction vessel, mixing the solution to produce an assay solution. Furthermore, Reagent 2 may be delivered to the reaction vessel without further dilution volume of the assay solution.

As used herein, the term "package" refers to a solid matrix or material such as glass, plastic, paper, foil and the like capable of holding within fixed limits an antibody composition or monoclonal antibody composition. Thus, for example, a package can be a glass vial used to contain milligram quantities of a contemplated polypeptide or it can be a microtiter plate well to which microgram quantities of a contemplated polypeptide or antibody have been operatively affixed.

"Instructions for use" typically include a tangible expression describing the reagent concentration or at least one assay method parameter such as the relative amounts of reagent and sample to be admixed, maintenance time periods for reagent/sample admixtures, temperature, buffer conditions and the like. In particular embodiments, a detection system of the present invention further includes a label or indicating means capable of signaling the formation of a complex containing a polypeptide or antibody molecule of the present invention.

"Complex" as used herein refers to the product of a specific binding reaction such as an antibody-antigen or receptor-ligand reaction. Exemplary complexes are immunoreaction products.

As used herein, the terms "label" and "indicating means" in their various grammatical forms refer to single atoms and molecules that are either directly or indirectly involved in the production of a detectable signal to indicate the presence of a complex. Any label or indicating means can be linked to or incorporated in an expressed protein, polypeptide, or antibody molecule that is part of an antibody or monoclonal antibody composition of the present invention, or used separately, and those atoms or molecules can be used alone or in conjunction with additional reagents such labels are themselves well- known in clinical diagnostic chemistry and constitute a part of this invention only insofar as they are utilized with otherwise novel proteins methods and/or systems.

The labeling means can be a fluorescent labeling agent that chemically binds to antibodies or antigens without denaturing them to form a fluorochrome (dye) that is a useful immunofluorescent tracer. Suitable fluorescent labeling agents are

fluorochromes such as fluorescein isocyanate (FIC), fluorescein isothiocyante (FITC), 5- dimethylamine-l-naphthalenesulfonyl chloride (DANSC), tetramethylrhodamine isothiocyanate (TRITC), lissamine, rhodamine 8200 sulphonyl chloride (RB 200 SC) and the like. A description of immunofluorescence analysis techniques is found in DeLuca, "Immunofluorescence Analysis", in Antibody As a Tool, Marchalonis, et al., eds., John Wiley & Sons, Ltd., pp. 189-231 (1982), which is incorporated herein by reference.

In certain embodiments, the indicating group is an enzyme, such as horseradish peroxidase (HRP), glucose oxidase, or the like. In such cases where the principal indicating group is an enzyme such as HRP or glucose oxidase, additional reagents are required to visualize the fact that a receptor-ligand complex (immunoreactant) has formed. Such additional reagents for HRP include hydrogen peroxide and an oxidation dye precursor such as diaminobenzidine. An additional reagent useful with glucose oxidase is 2,2'-azino-di-(3-ethyl-benzthiazoline-G-sulfonic acid) (ABTS).

In other embodiments, the indicating group is a green fluorescent protein (GFP).

Radioactive elements are also useful labeling agents and are used illustratively herein. An exemplary radiolabeling agent is a radioactive element that produces gamma ray emissions. Elements which themselves emit gamma rays, such as ¹²⁴ I, ¹²⁵ I, ¹²⁸ I, ¹³² I and ⁵¹ Cr represent one class of gamma ray emission-producing radioactive element indicating groups. Particularly preferred is ¹²⁵ I. Another group of useful labeling means are those elements such as ^U C, ¹⁸ F, ¹⁵ 0 and ¹³ N which themselves emit positrons. The positrons so emitted produce gamma rays upon encounters with electrons present in the animal's body. Also useful is a beta emitter, such ^U1 indium or ³ H.

The linking of labels, i.e., labeling of, polypeptides and proteins is well known in the art. For instance, antibody molecules produced by a hybridoma can be labeled by metabolic incorporation of radioisotope-containing amino acids provided as a component in the culture medium. See, for example, Galfre et al., Meth. Enzymol., 73 :3-46 (1981). The techniques of protein conjugation or coupling through activated functional groups are particularly applicable. See, for example, Aurameas, et al, Scand. J. Immunol, Vol. 8 Suppl. 7:7-23 (1978), Rodwell et al, Biotech., 3 :889-894 (1984), and U.S. Pat. No. 4,493,795, which are all incorporated herein by reference.

The detection systems or kits of the present invention can be used in an "ELISA" format to detect, for example, the presence or quantity of soluble BAFF polypeptide or a fragment thereof in a body fluid sample such as the bloodstream, plasma, serum, bone marrow, or tissue, etc. "ELISA" refers to an enzyme-linked immunosorbent assay that employs an antibody or antigen bound to a solid phase and an enzyme-antigen or enzyme-antibody conjugate to detect and quantify the amount of an antigen or antibody present in a sample. Thus, for example, a polypeptide, antibody molecule composition or monoclonal antibody molecule composition of the present invention can be affixed to a solid matrix to form a solid support that comprises a package in the subject diagnostic systems. The reagent is typically affixed to the solid matrix by adsorption from an aqueous medium although other modes of affixation, well known to those skilled in the art, can be used.

Useful solid matrices are also well known in the art. Such materials are water insoluble and include cross-linked dextran; agarose; beads of polystyrene beads about 1 micron to about 5 millimeters in diameter; polyvinyl chloride, polystyrene, cross- linked polyacrylamide, nitrocellulose- or nylon-based webs such as sheets, strips or paddles; or tubes, plates or the wells of a microtiter plate such as those made from polystyrene or polyvinylchloride.

The reagent species, labeled specific binding agent or amplifying reagent of any detection system described herein can be provided in solution, as a liquid dispersion or as a substantially dry power, e.g., in lyophilized form. Where the indicating means is an enzyme, the enzyme's substrate can also be provided in a separate package of a system. A solid support such as the before-described microtiter plate and one or more buffers can also be included as separately packaged elements in this detection assay system.

The packaging materials discussed herein in relation to detection systems are those customarily utilized in diagnostic systems. Such materials include glass and plastic (e.g., polyethylene, polypropylene and polycarbonate) bottles, vials, plastic and plastic-foil laminated envelopes and the like. In some embodiments, a detection system of the present invention is useful for assaying for the presence of soluble BAFF polypeptide or a fragment thereof. In certain embodiments, such a system comprises, in kit form, a package containing an antibody to soluble BAFF polypeptide or a fragment thereof.

All publications, patent applications, and issued patents cited in this specification are herein incorporated by reference as if each individual publication, patent application, or issued patent were specifically and individually indicated to be incorporated by reference. Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to one of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims. The following examples are provided by way of illustration only and not by way of limitation. Those of skill in the art will readily recognize a variety of noncritical parameters that could be changed or modified to yield essentially similar results.

EXAMPLES

Example 1: BCMA and BAFF Form Complexes In Vitro

100 [iL of the anti-mouse BAFF capture antibody was added to 25 μΐ _^ of undiluted plasma from mice with and without MM xenografts. The mixture was vortexed overnight at room temperature (RT). 100 μΐ ννεΐΐ of this solution was added to a 96-well microplate, which was rotated on an orbital rotator overnight at RT. The plates were decanted and washed three times with 200 μΐ _^ wash solution, patted dry and incubated with 200 μΐ _^ blocking solution for 1 hour at RT. The plates were decanted again and washed X 3 with 200 μΐ _^ wash solution and patted dry. The anti-human BCMA detection antibody was diluted in the working concentration using phosphate buffered saline (PBS) and 100 μΐ _^ of this solution added. The plate was rotated overnight at RT, decanted and washed X 3 with 200 μΐ _^ wash solution and patted dry. Next, the streptavidin was prepared to a working concentration in PBS, and 100 μΐ _^ added to the wells for 20 minutes at RT in the dark and decanted, and the plate washed X 3 with 200 μΐ _^ of wash solution, patted dry. Substrate was added atlOO μΕΛνεΙΙ in the dark. After 20 minutes, 50 μΐ _^ of stop solution was added and absorbance at 450 nm was measured.

Recombinant mouse BAFF (rmBAFF)-recombinant human BCMA (rhBCMA) complexes were detected in vitro (Figure 1 A). Varying concentrations of 100: 1 ratio of rhBCMA:rmBAFF were incubated overnight in a 35°C water bath, and their levels were determined using an ELISA against negative controls of rmB AFF and rhBCMA at high standard concentrations (2 ng/ml) using anti-mBAFF capture and anti-hBCMA detection antibodies. The experiment shows that complexes are detected at ratios and concentrations of BCMAto BAFF that typically are present in MM patients. Mouse BAFF (mBAFF; derived from SCID plasma)-rhBCMA complexes were also detected in vitro (Figure IB). Samples that included CB17 SCID plasma and recombinant human BCMA, and IgG were incubated overnight in a 35°C water bath. Negative controls were determined using an ELISA against rmBAFF and rhBCMA at high standard concentrations (2 ng/ml) using anti- mBAFF capture and anti-hBCMA detection antibodies. All samples were run in triplicates and the average ± SEM was graphed. Absorbance was determined by a μθ^ηΐ microplate spectrophotometer with KC Junior software.

Example 2: BCMA and BAFF Complexes Form In Vivo

It was investigated whether BCMA-BAFF complexes form in vivo. Plasma samples from C57 Bl/6 mice injected with rhBCMA-Fc were incubated in wells pre-coated with anti-mBAFF capture antibodies. A polyclonal anti-hBCMA detection antibody was then added. A strong absorbance indicating the presence of rhBCMA-mBAFF complexes was observed in samples collected on days 4 and 6 post-rhBCMA injection (Figure 2A). Only minimal background absorbance was observed in samples from mice injected with the control protein Ig-Fc or from untreated control mice, and antibody cross-reactivity was negative.

Similarly, SCID mice were dosed with rhBCMA-Fc at day 0; animals were bled just prior to its administration, and on post-injection days 1, 2 and 7. Plasma from immune deficient SCID mice contained rhBCMA-mBAFF complexes (Figure 2B; top panel), which could still be detected on days 2 and 7. The corresponding mBAFF level following rhBCMA-Fc treatment is shown in (Figure 2B, bottom panel). rhBCMA-mBAFF complexes were also observed on day 1 in plasma samples from immune competent C57 Bl/6 mice following rhBCMA injection (Figure 2C).

Example 3: Plasma human BCMA levels correlate with human MM tumor volume and BAFF-BCMA complexes are found in SCID mice bearing these tumors Human BCMA (hBCMA) levels correlated with increases in tumor volume in human MM xenograft models (Figure 3 A-C). Notably, mBAFF-hBCMA complexes were detected in plasma samples from mice (measured on day 28 post-tumor implantation) containing the three human MM xenografts (Figure 3D). The hBCMA-mBAFF complex levels in the plasma correlate with the amount of BCMA in the plasma in these 3 different human MM xenograft models (Figure 3 A-C). Specifically, LAGK-2 (Figure 3B) had the highest level of plasma BCMA, followed by LAG -l (Figure 3A), and LAGK-1 A (Figure 3C) had the least amount of plasma BCMA; the hBCMA-mBAFF complexes correlated with the amount of BCMA in the plasma of these mice (Figure 3D). Example 4: BAFF levels are significantly lower in SCID mice bearing human MM

It was evaluated whether human B cell maturation antigen (BCMA) produced by MM xenografts affects mouse BAFF plasma levels. Four week-old male CB 17

SCID mice were implanted with human MM tumors (LAGK-2, LAGK-1A or LAG -l) developed from MM patients. Tumors were measured and the formula for an ellipsoid

2

volume was applied (4/3 π x [width/2] x [length/2]). Tumor-bearing mice were dosed with recombinant human BCMA (rhBCMA) and BCMA-BAFF complexes were analyzed in plasma.

Results showed that SCID mice implanted with the human MM tumor LAG -l had lower mouse BAFF (mBAFF) levels (day 14: P = 0.0143; day 21 : P = 0.0002; and day 28: P = 0.0008) when compared with age and sex-matched SCID mice without tumors (Figure 4A). mBAFF was also decreased in plasma collected on days 14, 21, 28, and 35 from mice implanted with LAGK-2 tumors, compared with mice without tumors (P = 0.0015, P < 0.0001, P < 0.0001, and P < 0.0001, respectively; Figure 4B). Similarly, mice bearing LAGK-1A xenografts had significantly lower mBAFF levels when compared to mice without tumors.

When comparing two groups, significance was determined using a Student's t-test. The minimal level of significance was P < 0.05. Statistical significance of differences observed between two or more groups was determined using ANOVA (two-way). Analysis was determined using GraphPad Prism version 4.03 for

Windows, GraphPad Software, San Diego, CA. All in vivo experiments contained 4 or 5 mice per treatment group.

Next, mBAFF was incubated with rhBCMA overnight and an mBAFF ELISA was performed. At the higher and clinically relevant concentration of BCMA found in MM patients (100 ng/ml), rhBCMA inhibited the ability of the anti-mBAFF antibody to detect mBAFF (Figure 5A). In contrast, human IgG at an identical concentration to that of rhBCMA did not interfere with mBAFF detection. Similarly, recombinant human BAFF (rhBAFF) was incubated with rhBCMA overnight and an rhBAFF ELISA was performed. At the clinically relevant concentration of BCMA found in MM patients (100 ng/ml), rhBCMA inhibited the ability of the anti-BAFF antibody to detect rhBAFF. Human IgG at an identical concentration to that of rhBCMA did not interfere with rhBAFF detection (Figure 5B). These results indicate that the decrease in mBAFF levels in MM xenografts was due to the formation of BAFF-BCMA complexes.

The spleens and lymph nodes of human MM-bearing and non-bearing SCID mice were analyzed for mBAFF mRNA levels using RT-PCR. No differences in these levels were detected in either the spleen (Figure 5C) or lymph nodes of mice with or without human MM. These results indicate that the lower mBAFF levels in mice containing human MM xenografts were not from changes in the expression of this gene.

Example 5: Serum BCMA-hBAFF Complexes Are Formed In MM Patient Serum

It was determined if sera from MM patients contained BCMA-hBAFF complexes with a polyclonal anti-human BCMA antibody, using ELISA plates coated with an anti- human BAFF (hBAFF) capture antibody. 25 μΐ _^ of undiluted plasma from MM patients and healthy donors was obtained and vortexed with hBAFF capture antibody overnight at room temperature (RT). 100 [iL/well of this solution was added to a 96-well microplate, which was rotated on an orbital rotator overnight at RT. The plates were decanted and washed three times with 200 μΐ _^ wash solution, patted dry and incubated with 200 μΐ _^ blocking solution for 1 hour at RT. The plates were decanted again and washed X 3 with 200 μΐ _^ wash solution and patted dry. A biotin-labeled anti-human BCMA detection antibody was diluted to the working concentration using phosphate buffered saline (PBS) and 100 μΐ _^ of this solution added. The plate was rotated overnight at RT, decanted and washed X 3 with 200 [iL wash solution and patted dry. Next, 100 μL· of streptavidin was added to the wells for 20 minutes at RT in the dark and decanted, and the plate washed X 3 with 200 μΐ _^ of wash solution, patted dry, and substrate was added at 100 μΐ ννεΐΐ in the dark. After 20 minutes, 50 μΐ _^ of stop solution was added and absorbance was measured at 450 nm. A strong absorbance indicating the presence of BCMA-BAFF complexes was detected in MM patients (Figure 6). These results are consistent with the in vitro binding experiments described in Example 1 above (Figures 5A & B).

Example 6: Serum BAFF Levels Are Reduced in MM Patients With Active Disease

Serum from MM patients and healthy donors was obtained and the serum BAFF levels were analyzed. MM patients (N=31) with active disease have significantly decreased serum BAFF levels (median=436.0 pg/mL) compared to serum BAFF levels

(median=837.5 pg/mL; P = 0.0004) obtained from healthy donors (Figure 7). These results are consistent with the findings in SCID mice, in which animals bearing human MM showed reduced free plasma BAFF levels (Figure 4A & B).

Example 7: BAFF Levels Are Increased in MM Patients Who Have Achieved

Complete Remission

Serum from patients with multiple myeloma (MM) who have achieved complete remission (CR) and healthy donors was obtained and the serum BAFF levels were analyzed. MM patients (N=15) who are in complete remission (CR) show

significantly increased serum BAFF levels (median=1395.0 pg/mLl) compared to serum BAFF levels (median=837.5 pg/mL; P =0.0004) obtained from healthy donors (Figure 8).

Example 8: Serum BCMA Levels Are Inversely Related to Serum BAFF Levels in MM Patients Serum from patients with multiple myeloma (MM) who have achieved complete remission (CR) was obtained and serum BCMA levels and serum BAFF levels were analyzed. Serum BCMA levels were found to be inversely related to the serum BAFF levels in these MM patients (Figure 10). Example 9: MM patient serum and rhBCMA prevent BAFF from binding to Raji or TB94 B-cells

In order to determine if hBCMA present in MM patient serum or rhBCMA- Fc would block BAFF from binding to the surface of B-cells, Raji B-cells were incubated with serum from a healthy subject (0.02 μg/mL) or a MM patient with PD and serum containing high levels of BCMA (0.75 μg/mL) or in CR with low levels of serum BCMA (0.02 μg/mL) or rhBCMA-Fc (3.0 μg/mL) in the presence of rhBAFF (500 ng/mL).

The Raji and TB94 cells were maintained in RPMI 1640 supplemented with 10% fetal bovine serum, 2 mmol/L 1-glutamine, 100 i/u per mL penicillin, 100 μg/mL streptomycin, and essential amino acids in an atmosphere of 5% carbon dioxide (CO2) at 37°C. Five hundred ng/mL BAFF-his-Flag-Tag was pre-incubated with 3.0 μg/mL rhBCMA or serum from a healthy subject (BCMA level 0.02 μg/mL) or a MM patient in complete remission (CR) with a similarly low serum BCMA level (0.02 μg/mL) or with PD with a high serum level (0.75 μg/mL) or control mouse IgG in 1 mL IX PBS at 4°C overnight. Six million Raji or TB94 B-cells were incubated with or without BAFF with or without healthy subject or MM patient serum or rhBCMA for 45 minutes at 37°C. For the blocking experiment, the anti-human BCMA antibody (3.0 μg/mL) was added to rhBCMA or MM serum overnight at 4°C, and this was then cultured with the Raji or TB94 cells. After washing three times, the cells were incubated with either anti-Flag antibody conjugated with FITC or isotype control IgG-FITC for 1 hour at 37°C away from light and then washed three times with PBS. Flow cytometric analysis was performed using a Beckman-Coulter FC500 cytometer with Cytomics CXP software.

Serum from the MM patient with high levels of serum BCMA and rhBCMA-Fc decreased rhBAFF detection on Raji cells from 98.6% to 53.9 % and from 98.6% to 44.2%, respectively (Figure 11 A). An anti-hBCMA blocking antibody added to Raji B-cells incubated with BAFF and either rhBCMA or serum from this MM patient increased BAFF binding back up to 87.1%> and 77.0%, respectively. In contrast, serum from a healthy subject or MM patient in CR with low levels of serum BCMA (both at 0.02 μg/ml) only minimally decreased BAFF binding which is consistent with the low levels of serum BCMA present in healthy subjects and MM patients in CR. In order to confirm that BCMA (from MM serum or rhBCMA) blocks BAFF from binding to the B-cell surface, and that an anti-BCMA antibody restores this binding, the above experiment was performed using an additional human B-cell line, TB94. Similarly, serum from the MM patient with high levels of serum BCMA and rhBCMA-Fc decreased rhBAFF detection on these cells from 94% to 62.1 % and from 98.6% to 48.7%, respectively (Fig. 1 IB). An anti-hBCMA blocking antibody added to TB94-cells incubated with BAFF and either rhBCMA or serum from this MM patient increased BAFF binding back up to 84.8.1% and 79.6%), respectively. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.