A Phase 2 Trial of Sibeprenlimab in Patients with IgA Nephropathy.

BACKGROUND: A proliferation-inducing ligand (APRIL) is implicated in the pathogenesis of IgA nephropathy. Sibeprenlimab is a humanized IgG2 monoclonal antibody that binds to and neutralizes APRIL. METHODS: In this phase 2, multicenter, double-blind, randomized, placebo-controlled, parallel-group trial, we randomly assigned adults with biopsy-confirmed IgA nephropathy who were at high risk for disease progression, despite having received standard-care treatment, in a 1:1:1:1 ratio to receive intravenous sibeprenlimab at a dose of 2, 4, or 8 mg per kilogram of body weight or placebo once monthly for 12 months. The primary end point was the change from baseline in the log-transformed 24-hour urinary protein-to-creatinine ratio at month 12. Secondary end points included the change from baseline in the estimated glomerular filtration rate (eGFR) at month 12. Safety was also assessed. RESULTS: Among 155 patients who underwent randomization, 38 received sibeprenlimab at a dose of 2 mg per kilogram, 41 received sibeprenlimab at a dose of 4 mg per kilogram, 38 received sibeprenlimab at a dose of 8 mg per kilogram, and 38 received placebo. At 12 months, the geometric mean ratio reduction (±SE) from baseline in the 24-hour urinary protein-to-creatinine ratio was 47.2±8.2%, 58.8±6.1%, 62.0±5.7%, and 20.0±12.6% in the sibeprenlimab 2-mg, 4-mg, and 8-mg groups and the placebo group, respectively. At 12 months, the least-squares mean (±SE) change from baseline in eGFR was -2.7±1.8, 0.2±1.7, -1.5±1.8, and -7.4±1.8 ml per minute per 1.73 m2 in the sibeprenlimab 2-mg, 4-mg, and 8-mg groups and the placebo group, respectively. The incidence of adverse events that occurred after the start of administration of sibeprenlimab or placebo was 78.6% in the pooled sibeprenlimab groups and 71.1% in the placebo group. CONCLUSIONS: In patients with IgA nephropathy, 12 months of treatment with sibeprenlimab resulted in a significantly greater decrease in proteinuria than placebo. (Funded by Visterra; ENVISION ClinicalTrials.gov number, NCT04287985; EudraCT number, 2019-002531-29.).

Telitacicept as a BLyS/APRIL dual inhibitor for autoimmune disease.

The pathogenic roles for B cells in autoimmunity include produce pathogenic autoantibodies and modulate immune responses via the production of cytokines and chemokines. The B lymphocyte stimulator BLyS (also known as B-cell-activating factor, BAFF) and APRIL (a proliferation-inducing ligand) are critical factors in the maintenance of the B-cell pool and humoral immunity, namely BLyS modulates the differentiation and maturation of immature B cell, while APRIL modulates the function and survival of long-lived plasma cell, which plays a prominent role in the pathogenesis of autoimmune diseases. Telitacicept is a novel recombinant fusion protein of both the ligand-binding domain of the TACI receptor and the Fc component of human IgG and which is a BLyS/APRIL dual inhibitor. Moreover, telitacicept was developed by Remegen Co., Ltd. in China and is approved to treat systemic lupus erythematosus in China. We review the rationale, clinical evidence, and future perspectives of telitacicept for the treatment of autoimmune disease.HighlightThe B lymphocyte stimulator BLyS (also known as B-cell-activating factor, BAFF) and APRIL (a proliferation-inducing ligand), members of tumor necrosis factor (TNF) family, and which are critical factors in the maintenance of the B-cell pool and humoral immunity.BAFF and APRIL are implicated in the pathogenesis of several human autoimmune diseases with autoreactive B-cell involvement, and targeting both is beneficial for the treatment of autoimmune diseases.Telitacicept is a novel recombinant fusion protein of both the ligand-binding domain of the TACI receptor and the Fc component of human IgG, as a BLyS/APRIL dual inhibitor and which has been approved by National Medical Products Administration (MNPA) for the treatment of patients with SLE in China.With more clinical trials underway, telitacicept may also be approved for the treatment of other autoimmune diseases in the future.

Impact of B-Cell-Targeted Therapies on Cardiovascular Disease.

Atherosclerosis is a lipid-driven chronic inflammatory disease that is modulated by many immune cell subsets, including B cells. Therefore, targeting the inflammatory component of cardiovascular disease represents a promising therapeutic strategy. In the past years, immunotherapy has revolutionized the treatment of autoimmunity and cancer. Many of these clinically used strategies target B cells. Given the multifaceted role of B cells in atherogenesis, it is conceivable that B-cell-directed therapies can modulate disease development. Here, we review clinically available B-cell-targeted therapies and the possible benefits or detrimental effects on cardiovascular disease.

A Proliferation Inducing Ligand (APRIL) targeted antibody is a safe and effective treatment of murine IgA nephropathy.

IgA nephropathy (IgAN) is the most prevalent primary chronic glomerular disease for which no safe disease-specific therapies currently exist. IgAN is an autoimmune disease involving the production of autoantigenic, aberrantly O-glycosylated IgA1 and ensuing deposition of nephritogenic immune complexes in the kidney. A Proliferation Inducing Ligand (APRIL) has emerged as a key B-cell-modulating factor in this pathogenesis. Using a mouse anti-APRIL monoclonal antibody (4540), we confirm both the pathogenic role of APRIL in IgAN and the therapeutic efficacy of antibody-directed neutralization of APRIL in the grouped mouse ddY disease model. Treatment with 4540 directly translated to a reduction in relevant pathogenic mechanisms including suppressed serum IgA levels, reduced circulating immune complexes, significantly lower kidney deposits of IgA, IgG and C3, and suppression of proteinuria compared to mice receiving vehicle or isotype control antibodies. Furthermore, we translated these findings to the pharmacological characterization of VIS649, a highly potent, humanized IgG2κ antibody targeting and neutralizing human APRIL through unique epitope engagement, leading to inhibition of APRIL-mediated B-cell activities. VIS649 treatment of non-human primates showed dose-dependent reduction of serum IgA levels of up to 70%. A reduction of IgA+, IgM+, and IgG+ B cells was noted in the gut-associated mucosa of VIS649-treated animals. Population-based modeling predicted a favorable therapeutic dosing profile for subcutaneous administration of VIS649 in the clinical setting. Thus, our data highlight the potential therapeutic benefit of VIS649 for the treatment of IgAN.

A proliferation-inducing ligand (APRIL) induced hyper-production of IgA from tonsillar mononuclear cells in patients with IgA nephropathy.

IgA nephropathy (IgAN) is a tonsil-related disease. We previously showed that oligodeoxynucleotides with CpG (CpG-ODN) and B-cell activation factor (BAFF) are involved in hyperproduction of IgA from tonsillar mononuclear cells of patients with IgAN (IgAN-TMCs). In this study, we focused on a proliferation-inducing ligand (APRIL), homologous to BAFF. IgAN-TMCs produced more APRIL than non IgAN-TMCs in the presence of both CpG-ODN and control-ODN. TLR9 expression was higher in B-cells of IgAN-TMCs, and treatment with CpG-ODN enhanced transmembrane activator and CAML interactor (TACI) expression. IgA production from IgAN-TMCs was inhibited by APRIL neutralization antibody or TACI blocking antibody, and enhanced by co-treatment of APRIL and CpG-ODN. Serum APRIL levels were higher in patients with IgAN, and decreased after tonsillectomy. These findings suggest that APRIL is involved in the hyperproduction of IgA from IgAN-TMCs, and that CpG-ODN enhanced APRIL-induced IgA production by increasing TACI expression on B-cells of IgAN-TMCs.

A mouse model of systemic lupus erythematosus responds better to soluble TACI than to soluble BAFFR, correlating with depletion of plasma cells.

The TNF family cytokines B-cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL) support plasma cell survival. It is known that inhibitors of BAFF only (BAFFR-Fc) or BAFF and APRIL (TACI-Fc) administered early enough in an NZB/NZW F1 mouse model of systemic lupus erythematosus (SLE) ameliorate clinical outcomes, pointing to a pathogenic role of BAFF. In the present study, TACI-Fc administrated at a later stage of disease, after onset of autoimmunity, decreased the number of bone marrow plasma cells and slowed down further formation of autoantibodies. TACI-Fc prevented renal damage during a 12-week treatment period regardless of autoantibody levels, while BAFFR-Fc did not despite a similar BAFF-blocking activity in vivo. TACI-Fc also decreased established plasma cells in a T-dependent hapten/carrier immunization system better than single inhibitors of BAFF or APRIL, and sometimes better than combined single inhibitors with at least equivalent BAFF and APRIL inhibitory activities. These results indicate that TACI-Fc can prevent symptoms of renal damage in a mouse model of SLE when BAFFR-Fc cannot, and point to a plasticity of plasma cells for survival factors. Targeting plasma cells with TACI-Fc might be beneficial to prevent autoantibody-mediated damages in SLE.

The role of APRIL - A proliferation inducing ligand - In autoimmune diseases and expectations from its targeting.

Autoimmunity occurs when an adaptive immune response is directed against a self-antigen. As such, autoimmune reactions associated with the production of autoantibodies are common. These autoantibodies may either be pathogenic by inducing the initial damage to self, or exacerbate the reaction secondarily to the initial damage. In both cases, the pathway(s) leading to exposure of the immune system to the self-antigen inducing the production of autoantibodies is largely unknown. The latter is largely complicating the setting of putative prophylactic treatments. As a consequence, one possible way to control these diseases is to eliminate the cells producing antibodies. We will see that this approach is not yet part of any treatment in autoimmunity. Indeed, all the currently available non-specific immunosuppressive treatments do not target directly quiescent antibody-producing plasma cells. However, treatments aimed at depleting precursors of plasma cells, mature B-lymphocytes and/or antigen-experienced B cells not yet fully differentiated into plasma cells, are emerging. Such strategies were recently proven to be highly successful in several autoimmune disorders by two independent ways. The first way is by induction of B-cell cytotoxicity with an antibody directed against the surface antigen CD20. The second way is by antagonism of a key B-cell survival factor, the B-cell activation factor from the TNF superfamily (BAFF). In the present review, we will focus on the current knowledge regarding the role of a molecule related to BAFF, a proliferation-inducing ligand (APRIL), in autoimmune diseases, which acts on antibody-producing plasma cells. We will discuss expectations deriving from APRIL targeting in autoimmune diseases.

A proliferation inducing ligand (APRIL) promotes IL-10 production and regulatory functions of human B cells.

B cells may have a negative regulatory role, mainly mediated by interleukin 10 (IL-10). We recently showed that regulatory B-cell functions are impaired in patients with rheumatoid arthritis (RA) and that mice transgenic for a proliferation-inducing ligand (APRIL) are protected against collagen-induced arthritis. We aimed to explore the effect of APRIL on human B-cell IL-10 production, in healthy subjects and in patients with RA. The IL-10 production of B-cell was greater with APRIL than with BLyS or control medium, in a dose dependent manner. TACI expression was greater in IL-10 producing B cells (B10) than non-IL-10-producing B cells whereas BAFF-R expression was lower. TNF-α and IFN-γ secretion of T-cells were decreased by APRIL-stimulated B cells. APRIL stimulated STAT3 and STAT3 inhibition decreased B10 cells. APRIL also promoted B10 cells in RA patients. In conclusion, APRIL but not BLyS promotes IL-10 production by CpG-activated B cells and enhances the regulatory role of B cells on T cells. B10 cells in RA patients are responsive to APRIL, which suggests a possible therapeutic application of APRIL to expand B10 cells. This could also explain the difference of clinical efficacy observed between belimumab and atacicept in RA.

Targeting the BLyS-APRIL signaling pathway in SLE.

The B lymphocyte stimulator (BLyS)-A PRoliferation-Inducing Ligand (APRIL) signaling pathway has an important role in the selection, maturation and survival of B cells and plays a significant role in the pathogenesis of systemic lupus erythematosus (SLE). The inhibition of BLyS, a survival factor for transitional and mature B cells, has recently proven to be successful in large phase III clinical trials that led to the approval of an anti-BLyS monoclonal antibody (belimumab) for the treatment of SLE. Yet, there is currently a need to both understand better the mechanisms of action of belimumab in SLE and better define the subsets of patients that are more likely to respond to the drug.

BAFF/APRIL inhibition decreases selection of naive but not antigen-induced autoreactive B cells in murine systemic lupus erythematosus.

BAFF inhibition is a new B cell-directed therapeutic strategy for autoimmune disease. Our purpose was to analyze the effect of BAFF/APRIL availability on the naive and Ag-activated B cell repertoires in systemic lupus erythematosus, using the autoreactive germline D42 H chain (glD42H) site-directed transgenic NZB/W mouse. In this article, we show that the naive Vκ repertoire in both young and diseased glD42H NZB/W mice is dominated by five L chains that confer no or low-affinity polyreactivity. In contrast, glD42H B cells expressing L chains that confer high-affinity autoreactivity are mostly deleted before the mature B cell stage, but are positively selected and expanded in the germinal centers (GCs) as the mice age. Of these, the most abundant is VκRF (Vκ16-104*01), which is expressed by almost all IgG anti-DNA hybridomas derived from the glD42H mouse. Competition with nonautoreactive B cells or BAFF/APRIL inhibition significantly inhibited selection of glD42H B cells at the late transitional stage, with only subtle effects on the glD42H-associated L chain repertoire. However, glD42H/VκRF-encoded B cells were still vastly overrepresented in the GC, and serum IgG anti-DNA Abs arose with only a slight delay. Thus, although BAFF/APRIL inhibition increases the stringency of negative selection of the naive autoreactive B cell repertoire in NZB/W mice, it does not correct the major breach in B cell tolerance that occurs at the GC checkpoint.

The rationale for BAFF inhibition in systemic lupus erythematosus.

BAFF (B-cell-activating factor) is a critical survival factor for transitional and mature B cells and is a promising therapeutic target for systemic lupus erythematosus (SLE). In 2010-2011, two phase 3 clinical trials showed that the addition of the anti-BAFF antibody belimumab to standard-of-care therapy in patients with moderately active SLE results in a better outcome at 52 weeks than standard-of-care therapy alone. Belimumab has been US Food and Drug Administration approved for the treatment of SLE, and other drugs that target BAFF are now in various stages of clinical testing. This review describes the function of BAFF and its homolog APRIL (a proliferation-inducing ligand) and addresses the rationale for the treatment of SLE with BAFF/APRIL inhibitors.

TACI-Fc gene therapy improves autoimmune sialadenitis but not salivary gland function in non-obese diabetic mice.

OBJECTIVE: Patients with Sjögren's syndrome (SS) show aberrant expression of the B cell-related mediators, B cell-activating factor (BAFF), and a proliferation-inducing ligand (APRIL) in serum and salivary glands (SGs). We studied the biological effect of neutralizing these cytokines by local gene transfer of the common receptor transmembrane activator and CAML interactor (TACI) in an animal model of SS. MATERIAL AND METHODS: A recombinant serotype 2 adeno-associated virus (rAAV2) encoding TACI-Fc was constructed, and its efficacy was tested in the SGs of non-obese diabetic mice. Ten weeks later, SG inflammation was evaluated and serum and SG tissue were analyzed for inflammatory markers including immunoglobulins (Ig) and cytokines. RESULTS: AAV2-TACI-Fc gene therapy significantly reduced the number of inflammatory foci in the SG, owing to a decrease in IgD(+) cells and CD138(+) cells. Moreover, IgG and IgM levels, but not IgA levels, were reduced in the SG. Overall expression of mainly proinflammatory cytokines tended to be lower in AAV2-TACI-Fc-treated mice. Salivary flow was unaffected. CONCLUSION: Although local expression of soluble TACI-Fc reduced inflammation and immunoglobulin levels in the SG, further research will have to prove whether dual blockade of APRIL and BAFF by TACI-Fc can provide a satisfying treatment for the clinical symptoms of patients.

Anticytokine therapy impacting on B cells in autoimmune diseases.

PURPOSE OF REVIEW: To evaluate the impact of particular anticytokine therapies able to indirectly target B cells with emphasis on the tumor necrosis factor (TNF) family members, B cell activating factor/B lymphocyte stimulator (BAFF/BLyS) and a proliferation-inducing ligand (APRIL). RECENT FINDINGS: Although blockade of TNF/lymphotoxin by etanercept has been shown to have an impact on memory B cells, recent studies of inhibiting the TNF family members BAFF/BlyS or simultaneously blocking BAFF/BlyS and APRIL in rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) clearly demonstrated biologic activity, including reductions of immunoglobulin levels. However, clear evidence of clinical activity by any of the compounds interfering with BAFF/BLys or APRIL has not yet been shown. SUMMARY: Although anticytokine therapies mainly blocking signaling pathways of innate immunity, that is TNF-alpha, have shown efficacy in the treatment of arthritides and have partial effects on memory B cells, current studies evaluate effects on adaptive immunity by blocking BAFF/BlyS and/or APRIL which indirectly act on B and plasma cells.

BAFF: a local and systemic target in autoimmune diseases.

BAFF (B lymphocyte activating factor of the tumour necrosis factor family) is a vital homeostatic cytokine for B cells that helps regulate both innate and adaptive immune responses. Increased serum levels of BAFF are found in a number of different autoimmune diseases, and BAFF is found in inflammatory sites in which there is lymphoid neogenesis. BAFF antagonism has been used in several autoimmune disease models, resulting in B cell depletion, decreased activation of T cells and dendritic cells (DC) and a reduction in the overall inflammatory burden. BAFF, through its interaction with BAFF-R, is required for survival of late transitional, marginal zone and mature naive B cells, all of which are depleted by BAFF blockade. Through their interactions with TACI (transmembrane activator and calcium modulator and cyclophilin ligand interactor) and BCMA (B cell maturation protein), BAFF and its homologue APRIL (a proliferation-inducing ligand), support the survival of at least some subsets of plasma cells; blockade of both cytokines results in a decrease in serum levels of immunoglobulin (Ig)G. In contrast, neither BAFF nor APRIL is required for the survival or reactivation of memory B cells or B1 cells. BAFF also helps DC maturation and interleukin (IL)-6 release and is required for proper formation of a follicular dendritic cell (FDC) network within germinal centres, although not for B cell affinity maturation. The clinical efficacy of BAFF blockade in animal models of autoimmunity may be caused both by the decline in the number of inflammatory cells and by the inhibition of DC maturation within target organs. Blockade of BAFF and its homologue APRIL are being explored for human use; several Phase I and II clinical trials of BAFF inhibitors for autoimmunity have been completed and Phase III trials are in progress.

APRIL and TACI interact with syndecan-1 on the surface of multiple myeloma cells to form an essential survival loop.

BLyS and APRIL share two receptors - transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) and B-cell maturation antigen (BCMA) - and BLyS binds to a third receptor, BAFF-R. We previously reported that TACI gene expression is a good indicator of a BLyS-binding receptor in human multiple myeloma cell lines (HMCLs), unlike BCMA, which is expressed by all HMCLs or BAFF-R which is typically not expressed by late-stage B cells. We hypothesised a link between APRIL and TACI through syndecan-1, similar to the situation reported for FGF and FGFR. We observed very strong binding of APRIL, but not BLyS, at the surface of all syndecan-1(+) HMCLs and primary multiple myeloma cells (MMC). All syndecan-1(+) HMCLs and MMC could also bind TACI-Fc, but not BCMA-Fc or BAFF-R-Fc molecules. Binding of APRIL or TACI-Fc was abrogated by heparin or cell pretreatment with heparitinase, which cleaves heparan sulfate chains. The growth factor activity of APRIL on MMC was also inhibited by heparin. Our data identify syndecan-1 as a co-receptor for APRIL and TACI at the cell surface of MMC, promoting the activation of an APRIL/TACI pathway that induces survival and proliferation in MMC.

Targeting of BAFF and APRIL for autoimmunity and oncology.

BLyS and APRIL are tumor necrosis factor superfamily members shown to be important for B-cell development, maturation and survival. Recent data also indicate that these cytokines regulate the survival and maintenance of malignant B-cells in cancer patients. The key role of BlyS/APRIL in the immune system and their potential role in cancers have attracted the attention of basic scientistis and biotechnology companies alike. As a result, the pathways regulated by BLYS and APRIL have been quickly elevated as attractive targets for antibody-based and non-antibody based therapeutics. Exploitation of these pathways has not only given us enormous insights into the basic biology of the APRIL/BLyS system but it has also identified potential clinical candidates for cancer and autoimmunity. As such, multiple biotechnology companies are currently testing various therapeutic candidates in the clinic. This chapter will review BLyS and APRIL functions and discuss alternative therapeutic approaches to target BLyS and APRIL pathways for human malignancies and autoimmunity.

Autoantibody production significantly decreased with APRIL/BLyS blockade in murine chronic rejection kidney transplant model.

Chronic antibody mediated rejection (cAMR) remains a significant barrier to achieving long-term graft survival in kidney transplantation, which results from alloantibody production from B lymphocytes and plasma cells. APRIL (A proliferation-inducing ligand) and BLyS (B lymphocyte stimulator) are critical survival factors for B lymphocytes and plasma cells. Here we describe the results of APRIL/BLyS blockade in a murine cAMR kidney transplant model. c57/B6 mice underwent kidney transplantation with Bm12 kidneys (minor MHC mismatch), a well-described model for chronic rejection where animals cannot make donor specific antibody but rather make antinuclear antibody (ANA). Following transplantation, animals received TACI-Ig (to block APRIL and BLyS) or no treatment. Animals were continued on treatment until harvest 4 weeks following transplant. Serum was analyzed for circulating anti-nuclear autoantibodies using HEp-2 indirect immunofluorescence. Spleen and transplanted kidneys were analyzed via H&E. ANA production was significantly decreased in APRIL/BLyS blockade treated animals (p<0.0001). No significant difference in autoantibody production was found between syngeneic transplant control (B6 to B6) and APRIL/BLyS blockade treated animals (p = 0.90). Additionally, disruption of splenic germinal center architecture was noted in the APRIL/BLyS blockade treated animals. Despite the significant decrease in autoantibody production and germinal center disruption, no significant difference in lymphocyte infiltration was noted in the transplanted kidney. APRIL/BLyS blockade resulted in a significant decrease of autoantibody production and disrupted splenic germinal center formation in a chronic kidney transplant model, however in this model no difference in kidney transplant pathology was seen, which may have to do with the absence of any T cell centric immunosuppression. Regardless, these findings suggest that APRIL/BLyS blockade may play a role in decreasing antibody formation long-term in kidney transplantation. Future investigations will use APRIL/BLyS blockade in conjunction with T lymphocyte depleting agents to determine its efficacy in chronic rejection.

Rational design of a trimeric APRIL-based CAR-binding domain enables efficient targeting of multiple myeloma.

Chimeric antigen receptor (CAR) T cells (CARTs) have shown tremendous potential for the treatment of certain B-cell malignancies, including patients with relapsed/refractory multiple myeloma (MM). Targeting the B-cell maturation antigen (BCMA) has produced the most promising results for CART therapy of MM to date, but not all remissions are sustained. Emergence of BCMA escape variants has been reported under the selective pressure of monospecific anti-BCMA CART treatment. Thus, there is a clinical need for continuous improvement of CART therapies for MM. Here, we show that a novel trimeric APRIL (a proliferation-inducing ligand)-based CAR efficiently targets both BCMA+ and BCMA- MM. Modeled after the natural ligand-receptor pair, APRIL-based CARs allow for bispecific targeting of the MM-associated antigens BCMA and transmembrane activator and CAML interactor (TACI). However, natural ligands as CAR antigen-binding domains may require further engineering to promote optimal binding and multimerization to adequately trigger T-cell activation. We found that using a trimeric rather than a monomeric APRIL format as the antigen-binding domain enhanced binding to BCMA and TACI and CART activity against MM in vitro and in vivo. Dual-specific, trimeric APRIL-based CAR are a promising therapeutic approach for MM with potential for preventing and treating BCMA escape.

Desensitization and treatment with APRIL/BLyS blockade in rodent kidney transplant model.

Alloantibody represents a significant barrier in kidney transplant through the sensitization of patients prior to transplant through antibody mediated rejection (ABMR). APRIL BLyS are critical survival factors for mature B lymphocytes plasma cells, the primary source of alloantibody. We examined the effect of APRIL/BLyS blockade via TACI-Ig (Transmembrane activator calcium modulator cyclophilin lig interactor-Immunoglobulin) in a preclinical rodent model as treatment for both desensitization ABMR. Lewis rats were sensitized with Brown Norway (BN) blood for 21 days. Following sensitization, animals were then sacrificed or romized into kidney transplant (G4, sensitized transplant control); desensitization with TACI-Ig followed by kidney transplant (G5, sensitized + pre-transplant TACI-Ig); kidney transplant with post-transplant TACI-Ig for 21 days (G6, sensitized + post-transplant TACI-Ig); desensitization with TACI-Ig followed by kidney transplant post-transplant TACI-Ig for 21 days (G7, sensitized + pre- post-transplant TACI-Ig). Animals were sacrificed on day 21 post-transplant tissues were analyzed using flow cytometry, IHC, ELISPOT, RT-PCR. Sensitized animals treated with APRIL/BLyS blockade demonstrated a significant decrease in marginal zone non-switched B lymphocyte populations (p<0.01). Antibody secreting cells were also significantly reduced in the sensitized APRIL/BLyS blockade treated group. Post-transplant APRIL/BLyS blockade treated animals were found to have significantly less C4d deposition less ABMR as defined by Banff classification when compared to groups receiving APRIL/BLyS blockade before transplant or both before after transplant (p<0.0001). The finding of worse ABMR in groups receiving APRIL/BLyS blockade before both before after transplant may indicate that B lymphocyte depletion in this setting also resulted in regulatory lymphocyte depletion resulting in a worse rejection. Data presented here demonstrates that the targeting of APRIL BLyS can significantly deplete mature B lymphocytes, antibody secreting cells, effectively decrease ABMR when given post-transplant in a sensitized animal model.

APRIL/BLyS Blockade Reduces Donor-specific Antibodies in Allosensitized Mice.

BACKGROUND: Highly sensitized candidates on the transplant waitlist remain a significant challenge, as current desensitization protocols have variable success rates of donor-specific antibody (DSA) reduction. Therefore, improved therapies are needed. A proliferation-inducing ligand (APRIL) and B-lymphocyte stimulator (BLyS) are critical survival factors for B-lymphocytes and plasma cells, which are the primary sources of alloantibody production. We examined the effect of APRIL/BLyS blockade on DSA in a murine kidney transplant model as a possible novel desensitization strategy. METHODS: C57BL/6 mice were sensitized with intraperitoneal (IP) injections of 2 × 10 BALB/c splenocytes. Twenty-one days following sensitization, animals were treated with 100 µg of BLyS blockade (B-cell activating factor receptor-immunoglobulin) or APRIL/BLyS blockade (transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin), administered thrice weekly for an additional 21 days. Animals were then euthanized or randomized to kidney transplant with Control Ig, BLyS blockade, or APRIL/BLyS blockade. Animals were euthanized 7 days posttransplant. B-lymphocytes and DSA of BLyS blockade only or APRIL/BLyS blockade-treated mice were assessed by flow cytometry, immunohistochemistry, and enzyme-linked immunospot. RESULTS: APRIL/BLyS inhibition resulted in a significant reduction of DSA by flow crossmatch compared with controls (P < 0.01). APRIL/BLyS blockade also significantly depleted IgM- and IgG-secreting cells and B-lymphocyte populations compared to controls (P < 0.0001). APRIL/BLyS blockade in transplanted mice also resulted in decreased B-lymphocyte populations; however, no difference in rejection rates were seen between groups. CONCLUSIONS: APRIL/BLyS blockade with transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin significantly depleted B-lymphocytes and reduced DSA in this sensitized murine model. APRIL/BLyS inhibition may be a clinically useful desensitization strategy for sensitized transplant candidates.