Dual Blockade of ICOS and CD28 with Acazicolcept (ALPN-101) Reveals Non-Redundant Roles of T Cell Co-Stimulation Pathways in Inflammatory Arthritis

OBJECTIVE

CD28 and inducible T cell costimulator (ICOS) appear to play non-redundant roles in T cell activation and adaptive immunity. Acazicolcept (ALPN-101), an Fc fusion protein of a human variant ICOS Ligand (ICOSL) domain designed to inhibit both CD28 and ICOS costimulation, was characterized for therapeutic potential in inflammatory arthritis in vitro and in vivo.

METHODS

Acazicolcept was compared to inhibitors of either the ICOS or CD28 pathways (abatacept and belatacept [CTLA-4-Ig], prezalumab [anti-ICOSL mAb]) in vitro, in receptor binding and signaling assays, and in a collagen-induced arthritis (CIA) model. Acazicolcept was also compared in cytokine and/or gene expression assays of PBMC from healthy donors or rheumatoid arthritis (RA) or psoriatic arthritis (PsA) patients, stimulated with artificial antigen presenting cells (aAPC) expressing CD28 and ICOS ligands.

RESULTS

Acazicolcept bound CD28 and ICOS, prevented ligand binding, and inhibited human T cell functional interactions, matching or exceeding the activity of CD28 or ICOS costimulatory single pathway inhibitors tested individually or in combination. Acazicolcept administration reduced disease in the CIA model significantly and more potently than abatacept. Acazicolcept also inhibited pro-inflammatory cytokine production from stimulated PBMC in co-cultures with aAPC and demonstrated unique impacts on gene expression distinct from those induced by abatacept, prezalumab, or a combination of both.

CONCLUSION

Both CD28 and ICOS signaling play critical roles in inflammatory arthritis. Therapeutic agents such as acazicolcept that co-inhibit both ICOS and CD28 signaling may mitigate inflammation and/or disease progression in RA and PsA more effectively than inhibitors of either pathway alone. This article is protected by copyright. All rights reserved.

Systemic Administration of Acazicolcept, a Dual CD28 and Inducible T cell Costimulator Inhibitor, Ameliorates Experimental Autoimmune Uveitis

Purpose

Combined inhibition of CD28 and inducible T cell costimulator (ICOS) pathways with acazicolcept (ALPN-101) represents a potential new treatment for uveitis. Here, we evaluate preclinical efficacy using experimental autoimmune uveitis (EAU) in Lewis rats.

Methods

Efficacy was tested in 57 Lewis rats treated with either systemic (subcutaneous) or local (intravitreal) administration of acazicolcept and compared to treatment with a matched Fc-only control or corticosteroid. Impact of treatment on uveitis was assessed using clinical scoring, optical coherence tomography (OCT), and histology. Ocular effector T cell populations were determined using flow cytometry, and multiplex ELISA used to measure aqueous cytokine concentrations.

Results

When compared to Fc control treatment, systemic acazicolcept led to statistically significant decreases in clinical score (P < 0.01), histologic score (P < 0.05), and number of ocular CD45+ cells (P < 0.01). Number of ocular CD4+ and CD8+ T cells expressing IL-17A+ and IFNγ+ were also decreased with statistical significance (P < 0.01). Similar results were achieved with corticosteroids. Intravitreal acazicolcept decreased inflammation scores when compared to untreated fellow eyes and to Fc control treated eyes, although not statistically significant. Systemic toxicity, measured by weight loss, occurred in the corticosteroid-treated, but not in the acazicolcept-treated animals.

Conclusions

Systemic treatment with acazicolcept statistically significantly suppressed EAU. Acazicolcept was well-tolerated without the weight loss associated with corticosteroids. Acazicolcept may be an effective alternative to corticosteroids for use in treating autoimmune uveitis. Additional studies are needed to clarify the optimal dose and route for use in humans.

Translational Relevance

We show that T cell costimulatory blockade could be an effective mechanism for treating uveitis.

Povetacicept, an Enhanced Dual APRIL/BAFF Antagonist that Modulates B Lymphocytes and Pathogenic Autoantibodies for the Treatment of Lupus and Other B Cell-Related Autoimmune Diseases

OBJECTIVE

Dysregulated APRIL/BAFF signaling is implicated in the pathogenesis of multiple autoimmune diseases, including SLE and LN. A high affinity APRIL/BAFF antagonist was developed to overcome the clinical limitations of existing B cell inhibitors.

METHODS

A variant of TACI-Fc generated by directed evolution showed enhanced binding for both APRIL and BAFF and was designated povetacicept (ALPN-303). Povetacicept was compared to WT TACI-Fc and related molecules in vitro and in vivo.

RESULTS

Povetacicept inhibited APRIL and BAFF more effectively than all evaluated forms of WT TACI-Fc, and selective APRIL and BAFF inhibitors, in cell-based reporter assays and primary human B cell assays, mediating potent suppression of B cell proliferation, differentiation, and immunoglobulin secretion. In mouse immunization models, povetacicept significantly reduced serum Ig titers and antibody-secreting cells more effectively than anti-CD20 mAb, WT TACI-Fc, or APRIL and BAFF inhibitors. In the NZB/W lupus nephritis model, povetacicept significantly enhanced survival and suppressed proteinuria, anti-double stranded DNA antibody titers, blood urea nitrogen, glomerulonephritis, and renal Ig deposition. In the bm12 lupus model, povetacicept significantly reduced splenic plasmablasts, T_FH , and germinal center B cells. In non-human primates, povetacicept was well-tolerated and exhibited high serum exposure and significantly decreased serum IgM, IgA, and IgG levels after a single dose.

CONCLUSION

Enhanced APRIL and BAFF inhibition by povetacicept leads to greater inhibition of B cell populations critical for autoantibody production versus WT TACI-Fc and CD20-, APRIL-, or BAFF-selective inhibitors. Potent, dual inhibition by povetacicept has the potential to significantly improve clinical outcomes in autoantibody-related autoimmune diseases. This article is protected by copyright. All rights reserved.

Dose escalation of davoceticept, a conditional CD28 costimulator and dual checkpoint inhibitor, in advanced malignancies (NEON-1)

2560

Background: Strong preclinical rationale supports combining checkpoint inhibition (CPI) with T cell costimulatory agonists, particularly of CD28, a critical T cell costimulatory molecule recognized as a key target of checkpoint inhibition. Davoceticept (ALPN-202) is a variant CD80 vIgD-Fc fusion that mediates PD-L1-dependent CD28 costimulation and inhibits the PD-L1 and CTLA-4 checkpoints. It has demonstrated superiority to CPI-only therapies in multiple tumor models in vitro and in vivo, while demonstrating favorable preclinical safety. Methods: This is an open-label dose escalation and expansion study of davoceticept in adults with advanced solid tumors or lymphoma (NCT04186637). Patients with cancers refractory to standard therapies including CPIs, or cancers without available standard or curative therapy are eligible. Dose escalation studied two dose schedules, Q1W and Q3W. Objectives include safety and tolerability, PK, PD and preliminary anticancer activity. Disease assessments are evaluated by RECIST v1.1 for solid tumors. A prior presentation discussed the first 5 cohorts of the Q1W schedule; this presentation updates progress in dose escalation, including the Q3W schedule. Results: As of January 2022, 57 adults with various advanced solid tumors, most commonly colorectal and pancreatic, received davoceticept monotherapy, which was well tolerated through 10 mg/kg Q3W. It demonstrated dose-dependent PK and target saturation. Immune-related AEs (irAEs), occurred in 20/57 (35%), mostly of the skin, endocrine and gastrointestinal systems. All but 4 of the irAE were grade 1-2. Only one DLT (chronic active gastritis grade 3) was observed at 3 mg/kg Q3W. Among 48 evaluable patients, unconfirmed partial responses were observed in 2 (colorectal and renal cell). Stable disease, at first scan at 6 weeks, was observed in 23 (48%); 11 (23%) demonstrated volume reduction (target lesion ΔSLD < 0%); 2 had SD for > 6 months, and 1 had an ongoing SD at 8 months. At doses above 0.1 mg/kg, ex vivo analyses showed agonism of T cell CD28, and flow cytometry demonstrated increased circulating activated (ICOS+), proliferating (Ki-67+) and central memory T cells, and reduced regulatory T cells, consistent with CD28 engagement. Conclusions: Davoceticept was well tolerated at doses capable of engaging CD28 costimulation in vivo, with early signs of activity and peripheral immune activation in a largely treatment-refractory, non-immunogenic tumor population. These findings support an additive benefit of combining CD28 agonism with checkpoint inhibition and identify biologically active dose regimens of davoceticept for subsequent single agent development, and provide further rationale for combination study. Expansion cohorts, including cutaneous melanoma and PD-L1-positive cancers, are planned, and a combination study with pembrolizumab has initiated (NCT04920383). Clinical trial information: NCT04186637.

Davoceticept (ALPN-202), a PD-L1-dependent CD28 costimulator and dual checkpoint inhibitor, in combination with pembrolizumab in patients with advanced malignancies (NEON-2)

TPS2683

Background: Despite successes with checkpoint inhibition (CPI) in a wide range of tumors, most demonstrate primary or acquired resistance, warranting better therapeutic strategies. PD-1 is now recognized to effect much of its benefit by disinhibiting CD28 signaling – a mechanism expected to require intra-tumoral engagement of CD28 by its ligands CD80/CD86. Davoceticept (ALPN-202), a variant CD80 vIgD-Fc fusion protein, was engineered to provide tumor localizing PD-L1-dependent CD28 agonism, while inhibiting PD-L1 and CTLA-4. Davoceticept has demonstrated superiority to CPI-only therapies in both in vitro and in vivo tumor models, while also demonstrating additional benefit in combination with targeted PD-1 axis blockade (Lewis et al. (2019) J Immunother Cancer 7(S1): P467). The benefit appeared at least additive in models of poorly immunogenic tumors, suggesting the possibility of meaningful clinical benefit where CPI therapeutic efficacy is limited, such as noninflamed tumors. Single agent safety and tolerability of davoceticept has been demonstrated along with pharmacodynamic evidence of CD28 engagement with immune checkpoint inhibition (Moser et al. (2021) J Clin Oncol 39(s15): 2547). Methods: NEON-2 is an open-label dose escalation and expansion study of davoceticept combined with pembrolizumab in adults with advanced solid tumors or lymphoma that was initiated in June 2021 (NCT04920383). Eligibility includes tumors where single agent PD-(L)1 antagonists are SOC, are refractory or resistant to standard therapies (including approved CPIs), or have no standard or curative therapy. The study employs a standard 3+3 dose escalation design with two schedules, Q1W and Q3W of davoceticept. Pembrolizumab is given per label at 400 mg IV Q6W. Objectives include evaluation of safety and tolerability, identification of the recommended phase 2 dose(s) (RP2D), PK, PD, exploratory predictive biomarker analysis (i.e., PD-L1, CD28, CD80 and CD86 expression, as well as immunophenotyping of immune cell populations on treatment) and preliminary anticancer activity of davoceticept in combination with pembrolizumab. Disease assessments are evaluated by RECIST v1.1 for solid tumors or by Lugano Classification for lymphoma. Efficacy endpoints include ORR, duration of response and disease control rate. Once the RP2D combination is identified, tumor-specific expansion cohorts of ̃ 30- 35 patients will be performed, including histologies that have not been demonstrated to be CPI responsive, as well as those where CPIs are approved SOC. The 0.1 mg/kg cohorts have been completed without DLT. Enrollment to the 0.3 mg/kg cohorts began in September 2021. Clinical trial information: NCT04920383.

The engineered CD80 variant fusion therapeutic davoceticept combines checkpoint antagonism with conditional CD28 costimulation for anti-tumor immunity

Despite the recent clinical success of T cell checkpoint inhibition targeting the CTLA-4 and PD-1 pathways, many patients either fail to achieve objective responses or they develop resistance to therapy. In some cases, poor responses to checkpoint blockade have been linked to suboptimal CD28 costimulation and the inability to generate and maintain a productive adaptive anti-tumor immune response. To address this, here we utilize directed evolution to engineer a CD80 IgV domain with increased PD-L1 affinity and fuse this to an immunoglobulin Fc domain, creating a therapeutic (ALPN-202, davoceticept) capable of providing CD28 costimulation in a PD-L1-dependent fashion while also antagonizing PD-1 - PD-L1 and CTLA-4–CD80/CD86 interactions. We demonstrate that by combining CD28 costimulation and dual checkpoint inhibition, ALPN-202 enhances T cell activation and anti-tumor efficacy in cell-based assays and mouse tumor models more potently than checkpoint blockade alone and thus has the potential to generate potent, clinically meaningful anti-tumor immunity in humans.

Acazicolcept (ALPN-101), a dual ICOS/CD28 antagonist, demonstrates efficacy in systemic sclerosis preclinical mouse models

Background

Uncontrolled immune response with T cell activation has a key role in the pathogenesis of systemic sclerosis (SSc), a disorder that is characterized by generalized fibrosis affecting particularly the lungs and skin. Costimulatory molecules are key players during immune activation, and recent evidence supports a role of CD28 and ICOS in the development of fibrosis. We herein investigated the efficacy of acazicolcept (ALPN-101), a dual ICOS/CD28 antagonist, in two complementary SSc-related mouse models recapitulating skin fibrosis, interstitial lung disease, and pulmonary hypertension.

Methods

Expression of circulating soluble ICOS and skin-expressed ICOS was investigated in SSc patients. Thereafter, acazicolcept was evaluated in the hypochlorous acid (HOCL)-induced dermal fibrosis mouse model and in the Fra-2 transgenic (Tg) mouse model. In each model, mice received 400 μg of acazicolcept or a molar-matched dose of an Fc control protein twice a week for 6 weeks. After 6 weeks, skin and lung were evaluated.

Results

ICOS was significantly increased in the sera from SSc patients and in SSc skin biopsies as compared to samples from healthy controls. Similar body weight changes were observed between Fc control and acazicolcept groups in both HOCL and Fra-2 Tg mice suggesting a good tolerance of acazicolcept treatment. In mice challenged with HOCL, acazicolcept induced a significant decrease in dermal thickness, collagen content, myofibroblast number, and inflammatory infiltrates characterized by B cells, T cells, neutrophils, and macrophages. In the Fra-2 Tg mouse model, acazicolcept treatment reduced lung collagen content, fibrillar collagen, histological fibrosis score, and right ventricular systolic pressure (RVSP). A reduction in frequency of CD4+ and T effector memory cells and an increase in the percentage of CD4+ T naïve cells in spleen and lung of acazicolcept-treated Fra-2 Tg mice was observed as compared to Fc control-treated Fra-2 Tg mice. Moreover, acazicolcept reduced CD69 and PD-1 expression on CD4+ T cells from the spleen and the lung. Target engagement by acazicolcept was demonstrated by blockade of CD28 and ICOS detection by flow cytometry in treated mice.

Conclusions

Our results confirm the importance of costimulatory molecules in inflammatory-driven fibrosis. Our data highlight a key role of ICOS and CD28 in SSc. Using complementary models, we demonstrated that dual ICOS/CD28 blockade by acazicolcept decreased dermal and pulmonary fibrosis and alleviated pulmonary hypertension. These results pave the way for subsequent research on ICOS/CD28-targeted therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02709-2.

Abstract 1740: Engineered variant domain fusion proteins provide checkpoint inhibition and tumor antigen dependent CD28 costimulation resulting in potent anti-tumor immunity

Introduction: Checkpoint inhibition (CPI) has been shown to be an effective anti-tumor therapy, but CPI alone is frequently insufficient to control tumor growth, and costimulatory signals may also be required to produce clinically significant anti-tumor responses. PD1-PDL1 are established CPI targets and TMIGD2 is an inhibitory receptor expressed on T cells that is engaged by its cognate ligand HHLA2 on tumor cells, leading to inhibition of T cell responses. Novel biologics combining CD28 costimulation and CPI may yield promising tumor antigen-specific therapeutic candidates.

Methods: Variants of CD86 with increased CD28 affinity were engineered using our directed evolution platform. PD1 and TMIGD2 variants were also engineered for increased affinity to PDL1 and HHLA2, respectively. Fusion proteins were generated including either PD1 or TMIGD2 domains, an effectorless Fc domain, and an engineered CD86 domain to generate proteins to provide target-dependent costimulation (TDC) and evaluated in multiple in vitro T cell stimulation assays. Costimulatory effects were confirmed by evaluating T cell proliferation, cytokine release, and tumor cell killing. Fusion proteins were also tested in vivo in a mouse tumor model using MC38 cells expressing human PDL1 or HHLA2, and in a humanized tumor model where an HPV+ squamous cell carcinoma cell line expressing either PDL1 or HHLA2 was implanted into NSG mice. Tumor-bearing NSG mice were given primary human T cells expressing an HPV peptide-specific TCR, with or without the corresponding fusion protein, and tumor growth was measured over time.

Results: PD1-CD86 and TMIGD2-CD86 TDC proteins enhanced T cell costimulation in multiple in vitro T cell response assays, and costimulation was dependent on target cell lines expressing PDL1 or HHLA2, respectively. There was no effect on T cell responses if the target cells did not express the relevant target protein. PD1 and TMIGD2 domains alone had little effect on T cell responses, indicating these TDC proteins were driving enhanced responses. PD1-CD86 and TMIGD2-CD86 TDC proteins enhanced anti-tumor responses in vivo in a syngeneic MC38 implantation model only when MC38 cells expressed human PDL1 or HHLA2, respectively. Both proteins also enhanced antitumor responses in a humanized tumor implantation system using an HPV+ tumor cell line expressing the corresponding target antigen in the presence of human T cells expressing an HPV-specific TCR, but failed to control tumor growth when tumor cells lacked expression of the target protein.

Conclusions: Tumor antigen-specific antitumor therapy can be achieved with fusion proteins that combine engineered CPI and CD28 costimulatory domains. Such novel biologics may provide promising approaches to enhancing the efficacy of CPI monotherapies and to address checkpoint inhibitor-resistant tumors.

Citation Format: Steven D. Levin, Mark F. Maurer, Chelsea Gudgeon, Siddarth Chandrasekaran, Daniel Ardourel, Daniel Demonte, Joseph Kuijper, Martin Wolfson, Logan Garrett, Kayla N. Kleist, Sherri Mudri, Hieu Nguyen, Michelle Seaberg, Rachel Wang, Jing Yang, Katherine E. Lewis, Stacey R. Dillon, Mark Rixon, Stanford L. Peng. Engineered variant domain fusion proteins provide checkpoint inhibition and tumor antigen dependent CD28 costimulation resulting in potent anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1740.

ICOSL+ plasmacytoid dendritic cells as inducer of graft-versus-host disease, responsive to a dual ICOS/CD28 antagonist

Acute graft-versus-host disease (aGVHD) remains a major complication of allogeneic hematopoietic cell transplantation (HCT). CD146 and CCR5 are proteins that mark activated T helper 17 (Th17) cells. The Th17 cell phenotype is promoted by the interaction of the receptor ICOS on T cells with ICOS ligand (ICOSL) on dendritic cells (DCs). We performed multiparametric flow cytometry in a cohort of 156 HCT recipients and conducted experiments with aGVHD murine models to understand the role of ICOSL⁺ DCs. We observed an increased frequency of ICOSL⁺ plasmacytoid DCs, correlating with CD146⁺CCR5⁺ T cell frequencies, in the 64 HCT recipients with gastrointestinal aGVHD. In murine models, donor bone marrow cells from ICOSL-deficient mice compared to those from wild-type mice reduced aGVHD-related mortality. Reduced aGVHD resulted from lower intestinal infiltration of pDCs and pathogenic Th17 cells. We transplanted activated human ICOSL⁺ pDCs along with human peripheral blood mononuclear cells into immunocompromised mice and observed infiltration of intestinal CD146⁺CCR5⁺ T cells. We found that prophylactic administration of a dual human ICOS/CD28 antagonist (ALPN-101) prevented aGVHD in this model better than did the clinically approved belatacept (CTLA-4-Fc), which binds CD80 (B7-1) and CD86 (B7-2) and interferes with the CD28 T cell costimulatory pathway. When started at onset of aGVHD signs, ALPN-101 treatment alleviated symptoms of ongoing aGVHD and improved survival while preserving antitumoral cytotoxicity. Our data identified ICOSL⁺-pDCs as an aGVHD biomarker and suggest that coinhibition of the ICOSL/ICOS and B7/CD28 axes with one biologic drug may represent a therapeutic opportunity to prevent or treat aGVHD.

IL-31 transgenic mice show reduced allergen-induced lung inflammation

Interleukin-31 (IL-31) is a Th2 cell-derived cytokine that has been closely linked to pruritic skin inflammation. More recently, enhanced IL-31 serum levels have also been observed in patients with allergic rhinitis and allergic asthma. Therefore, the main aim of this study was to unravel the contribution of IL-31 to allergen-induced lung inflammation. We analyzed lung inflammation in response to the timothy grass (Phleum pratense) pollen allergen Phl p 5 in C57BL/6 wild-type (wt) mice, IL-31 transgenic (IL-31tg) mice, and IL-31 receptor alpha-deficient animals (IL-31RA-/- ). IL-31 and IL-31RA levels were monitored by qRT-PCR. Cellular infiltrate in bronchoalveolar lavage fluid (BALF) and lung tissue inflammation, mucus production as well as epithelial thickness were measured by flow cytometry and histomorphology. While allergen challenge induced IL-31RA expression in lung tissue of wt and IL-31tg mice, high IL-31 expression was exclusively observed in lung tissue of IL-31tg mice. Upon Phl p 5 challenge, IL-31tg mice showed reduced numbers of leukocytes and eosinophils in BALF and lung tissue as well as diminished mucin expression and less pronounced epithelial thickening compared to IL-31RA-/- or wt animals. These findings suggest that the IL-31/IL-31RA axis may regulate local, allergen-induced inflammation in the lungs.

Abstract LB-085: ALPN-202 combines checkpoint inhibition with conditional T cell costimulation to overcome T cell suppression by M2c macrophages and improve the durability of engineered T cell anti-tumor responses

Background: Despite significant clinical benefit of checkpoint inhibitors (CPI) in some settings, unfortunately, the majority of patients still fail to respond and/or develop resistance. This is likely due to a complex set of factors including, but not limited to, the presence of immunosuppressive myeloid cells and/or T cell exhaustion due to chronic TCR activation in the absence of sufficient costimulation. ALPN-202, a variant CD80 vIgD™-Fc fusion protein that mediates PD-L1-dependent CD28 costimulation and blocks PD-L1 and CTLA-4, was designed to overcome several of these suppressive mechanisms. The objective of these studies was to measure effects of ALPN-202 on the suppression of T cell activation by M2c macrophages and to determine in vivo effects of ALPN-202 on T cell exhaustion in an adoptively transferred human TCR transgenic tumor model. Methods: M2c macrophages differentiated from primary monocytes with M-CSF and IL-10 were cocultured for 72hr with T cells, anti-CD3 and a titration of ALPN-202, anti-PD-1, anti-PD-L1, or anti-CTLA-4 antibodies. Cytokine concentrations in the culture media were measured at 24 and 72 hrs, and T cells and macrophages characterized at 72 hrs by flow cytometry. To measure its anti-tumor activity and effect on T cell exhaustion in vivo, ALPN-202 was evaluated in a humanized model using anti-HPV E6 TCR-transduced human T cells transferred into immunodeficient NSG mice bearing HPV+ SCC152 squamous cell tumors stably expressing PD-L1. Tumor volume was measured twice weekly and on day 38 tumors were harvested, digested, and intratumoral T cells characterized for expression of exhaustion markers. Results: In the in vitro coculture assay, ALPN-202 increased T cell proliferation and production of IL-2, IFNγ, TNFα, GM-CSF, IL-6, and IL-21 significantly more potently than CPI alone. Additionally, the M2c macrophages in the presence of ALPN-202 displayed a dose-dependent elevation of MHC II, CD80, and CD86, indicative of a more pro-inflammatory, M1-like phenotype. In the SCC152 tumor model, ALPN-202 induced a more robust anti-tumor response than CPI while the intratumoral T cells expressed lower levels of exhaustion markers. Conclusions: As a dual checkpoint inhibitor and conditional CD28-costimulator, ALPN-202 induced robust and selective T cell costimulation in vitro which overcame M2c macrophage-mediated suppression more potently than CPI alone. Intriguingly, not only were T cells vigorously activated, but M2c macrophages transitioned to a more M1-like proinflammatory phenotype. In a humanized tumor model, ALPN-202 treatment resulted in potent anti-tumor activity with reduced signs of T cell exhaustion in the TME. The data suggest that by combining CD28 costimulation with CPI, ALPN-202 may provide a more robust and persistent anti-tumor T cell response compared to CPI alone.

Citation Format: Mark F. Maurer, Siddarth Chandrasekaran, Katherine Lewis, Sherri Mudri, Kayla Kleist, Fariha Ahmed-Qadri, Chelsea Gudgeon, Steven D. Levin, Stacey R. Dillon, Kristine M. Swiderek, Stanford L. Peng. ALPN-202 combines checkpoint inhibition with conditional T cell costimulation to overcome T cell suppression by M2c macrophages and improve the durability of engineered T cell anti-tumor responses [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-085.

Novel Immunomodulatory Proteins Generated via Directed Evolution of Variant IgSF Domains

Immunoglobulin superfamily member (IgSF) proteins play a significant role in regulating immune responses with surface expression on all immune cell subsets, making the IgSF an attractive family of proteins for therapeutic targeting in human diseases. We have developed a directed evolution platform capable of engineering IgSF domains to increase affinities for cognate ligands and/or introduce binding to non-cognate ligands. Using this scientific platform, ICOSL domains have been derived with enhanced binding to ICOS and with additional high-affinity binding to the non-cognate receptor, CD28. Fc-fusion proteins containing these engineered ICOSL domains significantly attenuate T cell activation in vitro and in vivo and can inhibit development of inflammatory diseases in mouse models. We also present evidence that engineered ICOSL domains can be formatted to selectively provide costimulatory signals to augment T cell responses. Our scientific platform thus provides a system for developing therapeutic protein candidates with selective biological impact for treatments of a wide array of human disorders including cancer and autoimmune/inflammatory diseases.

Abstract P1-20-03: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Dillon SR, Evans LS, Rickel E, Lewis KE, Swanson R, Levin SD, Wolfson M, Peng SL, Swiderek KM. Withdrawn [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-20-03.

Abstract 4550: CD80 vIgD-Fc proteins combine checkpoint antagonism and costimulatory signaling for potent antitumor immunity

Introduction: PD-1 pathway antagonists have revealed the importance of checkpoint pathways in regulating antitumor immunity, but an existing immune response is generally required for clinical efficacy. Specific T cell costimulation through CD28 is central to this process, but the CD28 ligands CD80 and CD86 are often poorly expressed in the tumor microenvironment, accounting for a second important mechanism of immune evasion by tumors. In contrast, PD-L1 expression has been found extensively in multiple tumor cell types. Therapeutics that combine PD-L1/PD-1 antagonism coupled with PD-L1 dependent CD28 agonism may therefore provide a more potent, yet safe immunotherapeutic approach.

Experimental Procedures: The variant Ig Domain (vIgD)TM platform has generated a diversity of human CD80 variants using yeast display affinity maturation and selections against all three CD80 counterstructures CD28, CTLA-4, and PD-L1. CD80 vIgDs were produced in a mammalian expression system as recombinant Fc fusion proteins (CD80 vIgD-Fc proteins) and their binding properties were quantified by flow cytometry. Functional activity was determined in vitro by assessing responses from human primary T cells or an IL-2-luciferase Jurkat T cell reporter line stimulated with PD-L1-expressing artificial antigen presenting cells (aAPCs). In vitro human T cell cytotoxicity assays with a human PD-L1-expressing tumor line were also performed. Antitumor activity was assessed in vivo with mice implanted with human PD-L1 transduced MC38 tumors.

Data Summary: The human CD80 IgV fragment was found to be optimal for high affinity PD-L1 and CD28 binding. A large panel of CD80 vIgD-Fc proteins demonstrated a range of binding towards CD28, PD-L1, and/or CTLA-4, and CD80 vIgD-Fc proteins with high affinity for PD-L1 antagonized the PD-L1/PD-1 interaction. Some CD80 vIgD-Fc proteins agonized CD28 in a PD-L1 dependent fashion with increased luciferase activity in the Jurkat reporter assay as well as increased cytokine production by primary human T cells when stimulated with a PD-L1 expressing aAPC in vitro. The same candidates also showed specific killing of human PD-L1 expressing tumor cells in vitro compared to the parental tumor line lacking PD-L1 expression. Importantly, selected CD80 vIgD-Fc proteins caused significant tumor reduction in the MC38 in vivo tumor model.

Conclusion: Engineered CD80 vIgD-Fc proteins that deliver a localized CD28 costimulatory signal to T cells while simultaneously antagonizing the inhibitory PD-L1/PD-1 pathway may provide a transformative mechanism of action to drive potent, tolerable antitumor immunity. Preclinical development of therapeutic candidates is under way.

Citation Format: Ryan Swanson, Mark F. Maurer, Chris L. Navas, Chelsea J. Gudgeon, Joseph L. Kuijper, Martin Wolfson, Katherine E. Lewis, Stacey R. Dillon, Steve D. Levin, Michael G. Kornacker. CD80 vIgD-Fc proteins combine checkpoint antagonism and costimulatory signaling for potent antitumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4550.

Interleukin-21 combined with PD-1 or CTLA-4 blockade enhances antitumor immunity in mouse tumor models

Recent advances in cancer treatment with checkpoint blockade of receptors such as CTLA-4 and PD-1 have demonstrated that combinations of agents with complementary immunomodulatory effects have the potential to enhance antitumor activity as compared to single agents. We investigated the efficacy of immune-modulatory interleukin-21 (IL-21) combined with checkpoint blockade in several syngeneic mouse tumor models. After tumor establishment, mice were administered recombinant mouse IL-21 (mIL-21) alone or in combination with blocking monoclonal antibodies against mouse PD-1 or CTLA-4. In contrast to monotherapy, IL-21 enhanced antitumor activity of mCTLA-4 mAb in four models and anti-PD-1 mAb in two models, with evidence of synergy for one or both of the combination treatments in the EMT-6 and MC38 models. The enhanced efficacy was associated with increased intratumoral CD8+ T cell infiltrates, CD8+ T cell proliferation, and increased effector memory T cells, along with decreased frequency of central memory CD8+ T cells. In vivo depletion of CD8+ T cells abolished the antitumor activities observed for both combination and monotherapy treatments, further supporting a beneficial role for CD8+ T cells. In all studies, the combination therapies were well tolerated. These results support the hypothesis that the combination of recombinant human IL-21 with CTLA-4 or PD-1 monoclonal antibodies could lead to improved outcomes in cancer patients.

Novel immunomodulatory proteins generated via directed evolution of variant IgSF domains

The immunoglobulin superfamily (IgSF) is a large, diverse family of proteins expressed on immune cells that have been extensively targeted for treatment of cancers and autoimmune diseases. Most of the therapeutic strategies targeting this family have focused on high affinity antibodies that bind a single receptor. Moreover, wild-type IgSF receptors typically exhibit low affinities for their counter-structures, limiting their utility in therapeutic modulation of immune responses. We have developed a novel variant Ig domain (vIgD™) platform using directed evolution and yeast display to affinity mature human IgSF extracellular domains. In this platform, libraries of mutagenized IgSF domains were selected for enhanced or altered affinity to specific recombinant proteins. Fc fusion proteins incorporating these evolved immunomodulatory IgSF domains were then tested in vitro for their ability to either agonize or antagonize T cell responses. Multiple novel vIgD™ fusion proteins have been generated that significantly attenuate T cell activation in vitro as assessed by proliferation and cytokine production. Lead molecules also exhibited in vivo efficacy in the human PBMC-NSG™ GVHD mouse model. Efficacy in vitro and in vivo was superior to wild-type IgSF domains due to the induced alterations in affinity for cognate ligand and through specifically directed changes in their ability to bind additional counter-structures. Our results demonstrate that vIgDs™ can be developed to acquire unique biochemical properties that significantly enhance therapeutic utility as immunomodulatory agents. This vIgD™ therapeutic platform has broad potential to enhance the activity of biologics in treatment of both autoimmune disease and cancer.

IL-31-Driven Skin Remodeling Involves Epidermal Cell Proliferation and Thickening That Lead to Impaired Skin-Barrier Function

Interleukin-31 (IL-31) is a type 2 helper T-cell-derived cytokine that has recently been shown to cause severe inflammation and tissue remodeling in multiple chronic diseases of the skin and lungs. IL-31 is upregulated in allergic and inflammatory diseases, including atopic dermatitis, asthma, cutaneous T-cell lymphomas, and allergic rhinitis, as well as autoimmune diseases such as systemic erythematosus. Overexpression of IL-31 in T cells causes severe inflammation, with histological features similar to skin lesions of patients with atopic dermatitis. However, the molecular mechanisms involved in IL31-driven pathological remodeling in skin diseases remain largely unknown. Here, we studied the role of IL-31 in skin damage as a result of intradermal administration of recombinant IL-31 into mice. Notably, IL-31 was sufficient to increase epidermal basal-cell proliferation and thickening of the epidermal skin layer. Our findings demonstrate a progressive increase in transepidermal water loss with chronic administration of IL-31 into the skin. Further, analysis of the skin transcriptome indicates a significant increase in the transcripts involved in epidermal-cell proliferation, epidermal thickening, and mechanical integrity. In summary, our findings demonstrate an important role for IL-31 signaling in epidermal cell proliferation and thickening that together may lead to impaired skin-barrier function in pathological remodeling of the skin.

Th2 Cytokines Augment IL-31/IL-31RA Interactions via STAT6-dependent IL-31RA Expression

Interleukin 31 receptor α (IL-31RA) is a novel Type I cytokine receptor that pairs with oncostatin M receptor to mediate IL-31 signaling. Binding of IL-31 to its receptor results in the phosphorylation and activation of STATs, MAPK, and JNK signaling pathways. IL-31 plays a pathogenic role in tissue inflammation, particularly in allergic diseases. Recent studies demonstrate IL-31RA expression and signaling in non-hematopoietic cells, but this receptor is poorly studied in immune cells. Macrophages are key immune-effector cells that play a critical role in Th2-cytokine-mediated allergic diseases. Here, we demonstrate that Th2 cytokines IL-4 and IL-13 are capable of up-regulating IL-31RA expression on both peritoneal and bone marrow-derived macrophages from mice. Our data also demonstrate that IL-4Rα-driven IL-31RA expression is STAT6 dependent in macrophages. Notably, the inflammation-associated genes Fizz1 and serum amyloid A (SAA) are significantly up-regulated in M2 macrophages stimulated with IL-31, but not in IL-4 receptor-deficient macrophages. Furthermore, the absence of Type II IL-4 receptor signaling is sufficient to attenuate the expression of IL-31RA in vivo during allergic asthma induced by soluble egg antigen, which may suggest a role for IL-31 signaling in Th2 cytokine-driven inflammation and allergic responses. Our study reveals an important counter-regulatory role between Th2 cytokine and IL-31 signaling involved in allergic diseases.

A sensory neuron-expressed IL-31 receptor mediates T helper cell-dependent itch: Involvement of TRPV1 and TRPA1

BACKGROUND

Although the cytokine IL-31 has been implicated in inflammatory and lymphoma-associated itch, the cellular basis for its pruritic action is yet unclear.

OBJECTIVE

We sought to determine whether immune cell-derived IL-31 directly stimulates sensory neurons and to identify the molecular basis of IL-31-induced itch.

METHODS

We used immunohistochemistry and quantitative real-time PCR to determine IL-31 expression levels in mice and human subjects. Immunohistochemistry, immunofluorescence, quantitative real-time PCR, in vivo pharmacology, Western blotting, single-cell calcium imaging, and electrophysiology were used to examine the distribution, functionality, and cellular basis of the neuronal IL-31 receptor α in mice and human subjects.

RESULTS

Among all immune and resident skin cells examined, IL-31 was predominantly produced by TH2 and, to a significantly lesser extent, mature dendritic cells. Cutaneous and intrathecal injections of IL-31 evoked intense itch, and its concentrations increased significantly in murine atopy-like dermatitis skin. Both human and mouse dorsal root ganglia neurons express IL-31RA, largely in neurons that coexpress transient receptor potential cation channel vanilloid subtype 1 (TRPV1). IL-31-induced itch was significantly reduced in TRPV1-deficient and transient receptor channel potential cation channel ankyrin subtype 1 (TRPA1)-deficient mice but not in c-kit or proteinase-activated receptor 2 mice. In cultured primary sensory neurons IL-31 triggered Ca(2+) release and extracellular signal-regulated kinase 1/2 phosphorylation, inhibition of which blocked IL-31 signaling in vitro and reduced IL-31-induced scratching in vivo.

CONCLUSION

IL-31RA is a functional receptor expressed by a small subpopulation of IL-31RA(+)/TRPV1(+)/TRPA1(+) neurons and is a critical neuroimmune link between TH2 cells and sensory nerves for the generation of T cell-mediated itch. Thus targeting neuronal IL-31RA might be effective in the management of TH2-mediated itch, including atopic dermatitis and cutaneous T-cell lymphoma.

Generation and characterization of human anti-human IL-21 neutralizing monoclonal antibodies

Interleukin-21 (IL-21) is a type I four-helical bundle cytokine that exerts a variety of significant effects on many hematopoietic cells, including T and B lymphocytes and natural killer cells. IL-21 is produced predominantly by CD4+ T cells and natural killer T cells and, when aberrantly overexpressed, appears to play important roles in a wide variety of autoimmune disorders. To generate potential therapeutic reagents capable of inhibiting IL-21 for clinical use, we immunized human immunoglobulin transgenic mice with IL-21 and then identified and cloned a panel of human anti-human IL-21 binding monoclonal antibodies. IL-21 neutralizing and IL-21-binding, non-neutralizing antibodies were assigned to distinct epitope "bins" based on surface plasmon resonance competition studies. The most potent neutralizing antibodies had extremely high (sub pM) affinity for IL-21 and were able to block IL-21 activity in various biological assays using either an IL-21R-transfected pre-B-cell line or primary human B cells, and their neutralizing activity was, in some cases, superior to that of a soluble form of the high affinity heterodimeric IL-21 receptor. Characterization of this panel of IL-21 antibodies provided the basis for the selection of a therapeutic candidate antibody capable of inhibiting IL-21 activity for the treatment of autoimmune and inflammatory diseases.

Serum from patients with SLE instructs monocytes to promote IgG and IgA plasmablast differentiation

Monocytes exposed to serum from SLE patients promote B cell differentiation to IgG and IgA plasmablasts dependent on BAFF and IL-10 or APRIL, respectively.

The development of autoantibodies is a hallmark of systemic lupus erythematosus (SLE). SLE serum can induce monocyte differentiation into dendritic cells (DCs) in a type I IFN–dependent manner. Such SLE-DCs activate T cells, but whether they promote B cell responses is not known. In this study, we demonstrate that SLE-DCs can efficiently stimulate naive and memory B cells to differentiate into IgG- and IgA-plasmablasts (PBs) resembling those found in the blood of SLE patients. SLE-DC–mediated IgG-PB differentiation is dependent on B cell–activating factor (BAFF) and IL-10, whereas IgA-PB differentiation is dependent on a proliferation-inducing ligand (APRIL). Importantly, SLE-DCs express CD138 and trans-present CD138-bound APRIL to B cells, leading to the induction of IgA switching and PB differentiation in an IFN-α–independent manner. We further found that this mechanism of providing B cell help is relevant in vivo, as CD138-bound APRIL is expressed on blood monocytes from active SLE patients. Collectively, our study suggests that a direct myeloid DC–B cell interplay might contribute to the pathogenesis of SLE.

Stromal endothelial cells establish a bidirectional crosstalk with chronic lymphocytic leukemia cells through the TNF-related factors BAFF, APRIL, and CD40L

Chronic lymphocytic leukemia (CLL) is a clonal B cell disorder of unknown origin. Accessory signals from the microenvironment are critical for the survival, expansion, and progression of malignant B cells. We found that the CLL stroma included microvascular endothelial cells (MVECs) expressing BAFF and APRIL, two TNF family members related to the T cell-associated B cell-stimulating molecule CD40L. Constitutive release of soluble BAFF and APRIL increased upon engagement of CD40 on MVECs by CD40L aberrantly expressed on CLL cells. In addition to enhancing MVEC expression of CD40, leukemic CD40L induced cleavases that elicited intracellular processing of pro-BAFF and pro-APRIL proteins in MVECs. The resulting soluble BAFF and APRIL proteins delivered survival, activation, Ig gene remodeling, and differentiation signals by stimulating CLL cells through TACI, BAFF-R, and BCMA receptors. BAFF and APRIL further amplified CLL cell survival by upregulating the expression of leukemic CD40L. Inhibition of TACI, BCMA, and BAFF-R expression on CLL cells; abrogation of CD40 expression in MVECs; or suppression of BAFF and APRIL cleavases in MVECs reduced the survival and diversification of malignant B cells. These data indicate that BAFF, APRIL, and CD40L form a CLL-enhancing bidirectional signaling network linking neoplastic B cells with the microvascular stroma.

IL-31 expression by inflammatory cells is preferentially elevated in atopic dermatitis

Interleukin-31 (IL-31) is a recently discovered cytokine expressed in many human tissues, and predominantly by activated CD4(+) T cells. IL-31 signals through a heterodimeric receptor consisting of IL-31 receptor alpha (IL-31RA) and oncostatin M receptor beta (OSMR). Earlier studies have shown involvement of IL-31 and its receptor components IL-31RA and OSMR in atopic dermatitis, pruritus and Th2-weighted inflammation at the mRNA level. The aim of this study was to investigate IL-31 protein expression in skin of such conditions. Immunohistochemical staining for IL-31, IL-31RA and OSMR was performed in formalin-fixed paraffin-embedded biopsy specimens. IL-31 expression was increased in the inflammatory infiltrates from skin biopsies taken from subjects with atopic dermatitis, compared with controls (p ≤ 0.05). IL-31, IL-31RA and OSMR protein immunoreactivity was not increased in biopsies from subjects with other Th2-weighted and pruritic skin diseases. Our results confirm, at the protein level, the relationship between IL-31 expression and atopic dermatitis. Our results do not support a general relationship between expression of IL-31/IL-31R and pruritic or Th2-mediated diseases.

Toll-like receptor 9, transmembrane activator and calcium-modulating cyclophilin ligand interactor, and CD40 synergize in causing B-cell activation

BACKGROUND

B cells receive activating signals from T cells through CD40, from microbial DNA through Toll-like receptor (TLR) 9, and from dendritic cells through transmembrane activator and calcium-modulating cyclophilin ligand interactor (TACI). TLR9 and CD40 ligation augment TACI-driven B-cell activation, but only the mechanism of synergy between CD40 and TACI has been explored. Synergy between CD40 and TLR9 in B-cell activation is controversial.

OBJECTIVE

We sought to examine the mechanisms by which TLR9 modulates CD40- and TACI-mediated activation of B cells and to determine whether all 3 receptors synergize to activate B cells.

METHODS

Naive murine B cells and human PBMCs were stimulated with combinations of anti-CD40, CpG, and a proliferation inducing ligand in the presence of IL-4. Proliferation was measured by means of tritiated thymidine incorporation. Immunoglobulin production was measured by means of ELISA. Class-switch recombination (CSR) was examined by measuring mRNA for germline transcripts, activation-induced cytidine deaminase (AICDA), and mature immunoglobulin transcripts. Plasma cell differentiation was examined by using syndecan-1/CD138 staining and mRNA expression of B lymphocyte-induced maturation protein 1 (Blimp-1).

RESULTS

TLR9 synergized with CD40 and TACI in driving CSR and inducing IgG(1) and IgE secretion by naive murine B cells and synergized with TACI in driving B-cell proliferation and plasma cell differentiation. All 3 receptors synergized together in driving murine B-cell proliferation, CSR, plasma cell differentiation, and IgG(1) and IgE secretion. TLR9 synergized with CD40 and TACI in driving IgG secretion in IL-4-stimulated human B cells.

CONCLUSION

Signals from TLR9, TACI, and CD40 are integrated to promote B-cell activation and differentiation.

The C104R mutant impairs the function of transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) through haploinsufficiency

BACKGROUND

TNFRSF13B, which encodes transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), is mutated in 10% of patients with common variable immunodeficiency. One of the 2 most common TACI mutations in common variable immunodeficiency, C104R, abolishes ligand binding and is found predominantly in the heterozygous state. The murine TACI mutant C76R is the equivalent of the human TACI mutant C104R.

OBJECTIVE

We sought to define the consequence of the C76R mutation on TACI function in mice that express both wild-type TACI and the murine C76R mutant.

METHODS

Transgenic mice that express murine TACI C76R, the counterpart of human TACI C104R, on the TACI(+/-) B6/129 background (C76R/TACI(+/-) mice) were constructed. Serum immunoglobulins and antibody responses to the type II T-independent antigen trinitrophenylated (TNP)-Ficoll were determined by means of ELISA. B-cell proliferation in response to a proliferation-inducing ligand was determined based on tritiated thymidine incorporation into DNA. IgG1 secretion by B cells in response to a proliferation-inducing ligand plus IL-4 was determined by means of ELISA.

RESULTS

C76R/TACI(+/-) mice had significantly impaired antibody responses to the type II T-independent antigen TNP-Ficoll compared with TACI(+/+) B6/129 control animals, and their B cells were impaired in their capacity to proliferate and secrete IgG1 in response to TACI ligation. Unexpectedly, TACI(+/-) mice had similarly impaired B-cell function as C76R/TACI(+/-) littermates. Impaired TACI function caused by haploinsufficiency was confirmed in TACI(+/-) mice on the C57BL/6 background.

CONCLUSION

These results suggest that the human TACI mutant C104R might impair TACI function in heterozygotes through haploinsufficiency.

B-lymphocyte stimulator/a proliferation-inducing ligand heterotrimers are elevated in the sera of patients with autoimmune disease and are neutralized by atacicept and B-cell maturation antigen-immunoglobulin

Introduction

B-lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL) are members of the tumor necrosis factor (TNF) family that regulate B-cell maturation, survival, and function. They are overexpressed in a variety of autoimmune diseases and reportedly exist in vivo not only as homotrimers, but also as BLyS/APRIL heterotrimers.

Methods

A proprietary N-terminal trimerization domain was used to produce recombinant BLyS/APRIL heterotrimers. Heterotrimer biologic activity was compared with that of BLyS and APRIL in a 4-hour signaling assay by using transmembrane activator and CAML interactor (TACI)-transfected Jurkat cells and in a 4-day primary human B-cell proliferation assay. A bead-based immunoassay was developed to quantify native heterotrimers in human sera from healthy donors (n = 89) and patients with systemic lupus erythematosus (SLE; n = 89) or rheumatoid arthritis (RA; n = 30). Heterotrimer levels were compared with BLyS and APRIL homotrimer levels in a subset of these samples.

Results

The recombinant heterotrimers consisted mostly of one BLyS and two APRIL molecules. Heterotrimer signaling did not show any significant difference compared with APRIL in the TACI-Jurkat assay. Heterotrimers were less-potent inducers of B-cell proliferation than were homotrimeric BLyS or APRIL (EC₅₀, nMol/L: BLyS, 0.02; APRIL, 0.17; heterotrimers, 4.06). The soluble receptor fusion proteins atacicept and B-cell maturation antigen (BCMA)-immunoglobulin (Ig) neutralized the activity of BLyS, APRIL, and heterotrimers in both cellular assays, whereas B-cell activating factor belonging to the TNF family receptor (BAFF-R)-Ig neutralized only the activity of BLyS. In human sera, significantly more patients with SLE had detectable BLyS (67% versus 18%; P < 0.0001), APRIL (38% versus 3%; P < 0.0002), and heterotrimer (27% versus 8%; P = 0.0013) levels compared with healthy donors. Significantly more patients with RA had detectable APRIL, but not BLyS or heterotrimer, levels compared with healthy donors (83% versus 3%; P < 0.0001). Heterotrimer levels weakly correlated with BLyS, but not APRIL, levels.

Conclusions

Recombinant BLyS/APRIL heterotrimers have biologic activity and are inhibited by atacicept and BCMA-Ig, but not by BAFF-R-Ig. A novel immunoassay demonstrated that native BLyS/APRIL heterotrimers, as well as BLyS and APRIL homotrimers, are elevated in patients with autoimmune diseases.

The receptor tyrosine kinase MerTK regulates dendritic cell production of BAFF

The MerTK receptor tyrosine kinase is an important negative regulator of dendritic cell function and is required to prevent B cell autoimmunity in vivo. It is not currently known however, if any causal relationship exists between these two aspects of MerTK function. We sought to determine if dendritic cells (DC) from mice lacking MerTK (mertk(- / - ) mice) have characteristics that may aid in the development of B cell autoimmunity. Specifically, we found that mertk(- / - ) mice contain an elevated number of splenic DC, and this population contains an elevated proportion of cells secreting the critical B cell pro-survival factor, B cell activating factor (BAFF). Elevated numbers of BAFF-secreting cells were also detected among mertk(- / - ) bone marrow-derived dendritic cell (BMDC) populations. This was observed in both resting BMDC, and BMDC stimulated with lipopolysaccharide (LPS) or treated with exogenous apoptotic cells. We also found that DC in general have a pro-survival effect on resting B cells in co-culture. However, despite containing more BAFF-secreting cells, mertk(- / - ) BMDC were not superior to C57BL/6 or baff-deficient BMDC at promoting B cell survival. Furthermore, using decoy receptors, we show that DC may promote B cell survival and autoimmunity through a BAFF-and a proliferation-inducing ligand-independent mechanism.

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.

Genetic variation in B-cell-activating factor is associated with an increased risk of developing B-cell non-Hodgkin lymphoma

Elevated B-cell-activating factor (BAFF; TNFSF13B) levels have been found in patients with B-cell malignancies and autoimmune diseases, suggesting that it may play a pathogenic role. We previously found that a single nucleotide polymorphism (SNP) in the TNFSF13B promoter resulted in increased transcription, suggesting that genetic variation in TNFSF13B may influence its expression. We therefore wanted to determine if genetic variation in TNFSF13B is associated with high BAFF levels and non-Hogkin lymphoma (NHL) risk. We genotyped 9 tagSNPs within TNFSF13B in a clinic-based study of 441 NHL cases and 475 matched controls and evaluated the association of individual SNPs with risk of NHL; 3 tagSNPs were significant (P < 0.05). When categorized into low-, moderate-, and high-risk groups based on risk alleles, we found the permutation-corrected odds ratio for the trend to be 1.43 (P = 0.0019) for risk of B-cell NHL, 1.69 (P = 0.0093) for diffuse large B-cell lymphoma, 1.43 (P = 0.029) for follicular lymphoma, and 1.06 (P = 0.21) for chronic lymphocytic leukemia/small lymphocytic lymphoma. The mean serum BAFF level in those who carried the low-risk alleles was 2 ng/mL compared with 4.3 ng/mL in those with the high-risk alleles (P = 0.02). Taken together, our data suggest that genetic variation in the TNFSF13B gene is significantly associated with NHL risk and elevated serum BAFF levels.

Anti-IL-21 monoclonal antibody reduces disease severity and inflammatory cytokines in a murine model of psoriasis and colitis (97.16)

IL-21 plays a role in many autoimmune and inflammatory diseases, including psoriasis and inflammatory bowel disease (IBD). To investigate IL-21 antagonism in disease, we evaluated a neutralizing anti-mouse IL-21 mAb in a CD4+CD25- T cell transfer SCID mouse model of psoriasis and colitis. Mice treated prophylactically with IL-21 mAb had significant reductions in colitis and psoriatic-like skin symptoms compared to mice treated with PBS or isotype control mAb. IL-21 mAb-treated mice had 5-7-fold lower average lesional skin scores, 6-7-fold lower average clinical colitis scores and significant reductions in histological indices of colitis compared to controls. Mice treated with IL-21 mAb also had significantly lower serum IL-6, RANTES, TNF-α, and MIP-1β levels compared to controls, further supporting an anti-inflammatory role for IL-21 mAb. In a delayed dosing study, mice treated with IL-21 mAb starting 12 days after T cell transfer had significant reductions in colitis, with 3.5-4-fold lower average colitis scores than control-treated mice. Dose-related reductions in lesional skin scores were also observed. Efficacy of IL-21 mAb was equivalent to or better than an anti-mouse IL-12/23p40 active control mAb. These results demonstrate that IL-21 mAb reduces psoriasis-like disease and colitis in a murine model and suggest that an anti-human IL-21 mAb may have clinical utility in treatment of psoriasis and IBD.

Increased Expression of BCMA on Systemic Lupus Erythematosus B Cells is Associated with Enhanced Response to CpG (99.43)

BLyS and APRIL are members of the TNF superfamily that regulate B cell survival and autoreactivity, and can exist as homotrimers or BLyS/APRIL heterotrimers (HT). To further understand BLyS and APRIL function in SLE, we examined the expression profiles of their receptors (BAFF-R, TACI and BCMA) and their functional effects on B cell subsets. Whereas BAFF-R expression on SLE B cells was significantly lower compared to its levels on healthy control B cells (MFI of control vs SLE, naïve=1387 vs 929, p=0.002; memory=1290 vs 840, p=0.003), BCMA expression was substantially higher on SLE B cells (MFI of control vs SLE: 18 vs 28, p=0.038). This was most pronounced in the memory B cell subset (MFI of control vs SLE=19 vs 29, p=0.008) but was also evident on certain subsets of CD27- B cells. BCMA+ cells were mostly IgD+ and tended to be larger than BCMA-negative cells, and had higher CD19 and CD86 expression, indicating a greater degree of activation. FACS sorted BCMA+ B cells proliferated and differentiated much more potently than BCMA- B cells following CpG stimulation. CpG mainly induced the proliferation of BCMA+ B cells and increased BCMA expression on total B cells. These findings may help to explain the observed expansion of DNA-reactive SLE B cells in the presence of BLyS, APRIL or HT.

TACI-Ig prevents the development of airway hyperresponsiveness in a murine model of asthma

BACKGROUND

Increased levels of serum IgE are associated with greater asthma prevalence and disease severity. IgE depletion using an anti-IgE monoclonal antibody has met with success in the treatment of moderate-to-severe and severe persistent allergic asthma.

OBJECTIVE

To test whether B cell-targeted therapy is a more effective treatment for airway hyperresponsiveness (AHR) in a murine model compared with IgE-depletion.

METHODS

We delivered soluble mTACI-Ig, a receptor for the B cell survival factors BLyS (B Lymphocyte Stimulator) and APRIL (A PRoliferation-Inducing Ligand), or anti-IgE to allergen-sensitized mice before airway challenge with allergen.

RESULTS

mTACI-Ig treatment reduced circulating mature B cell levels in the blood, while anti-IgE treatment had no effect on B cell counts. Both mTACI-Ig and anti-IgE decreased the levels of total and allergen-specific IgE in the serum. Histopathologic analysis of lungs showed a reduction in disease severity scores for both treatment groups, but results were more pronounced in mTACI-Ig-treated mice. Neutrophil and eosinophil numbers in the bronchoalveolar lavage (BAL) were significantly reduced following mTACI-Ig treatment, but not after anti-IgE delivery. BLyS and APRIL blockade also resulted in a significant decrease in IL-4 and eotaxin mRNA and IL-4 and KC protein levels in total lung homogenates and BAL fluid, respectively. Finally, mTACI-Ig treatment was more effective than anti-IgE treatment in reducing AHR to inhaled antigen.

CONCLUSIONS

Our data demonstrate that delivery of mTACI-Ig is a more effective treatment than anti-IgE mAb in a murine model of AHR.

Serum BLyS levels increase after rituximab as initial therapy in patients with follicular Grade 1 non-Hodgkin lymphoma

Serum B-lymphocyte stimulator (BLyS) levels are elevated in a subset of non-Hodgkin lymphoma (NHL) patients, particularly those with a family history of B-cell malignancies or a polymorphism in the BLyS gene. BLyS promotes growth of malignant B-cells and increased serum BLyS levels are associated with a poor clinical outcome. In this study, BLyS levels were measured before and after 4 weekly doses of rituximab in 30 patients with previously untreated follicular Grade 1 NHL. A significant increase was seen in the serum levels of BLyS (P = 0.0001) after rituximab therapy. The increase was independent of genetic variability in the BLyS gene.

Cutting edge: the dependence of plasma cells and independence of memory B cells on BAFF and APRIL

Memory B (B(MEM)) cells and long-lived bone marrow plasma cells (BM-PCs) persist within local environmental survival niches that afford cellular longevity. However, the factors supporting B(MEM) cell survival within the secondary lymphoid organs and allowing BM-PC persistence in the bone marrow remain poorly characterized. We report herein that long-lived B(MEM) cell survival and function are completely independent of BAFF (B cell-activating factor of the TNF family) or APRIL (a proliferation-inducing ligand). Thus, B(MEM) cells represent the only mature B2 lineage subset whose survival is independent of these ligands. We have previously shown that the TNFR family member receptor BCMA (B cell maturation Ag) is a critical survival receptor for BM-PC survival in vivo. We identify in this study the ligands critical for BM-PC survival and show that either BAFF or APRIL supports the survival of BM-PCs in vivo. These data define the BAFF/APRIL-dependent and -independent components of long-lived humoral immunity.

Phase I clinical study of atacicept in patients with relapsed and refractory B-cell non-Hodgkin's lymphoma

PURPOSE

B-lymphocyte stimulator and a proliferation-inducing ligand regulate B-cell homeostasis and immunoglobulin production and are overexpressed in B-cell malignancies. Atacicept (TACI-Ig), a recombinant fusion protein that inhibits both B-lymphocyte stimulator and a proliferation-inducing ligand, may be a novel treatment for B-cell malignancies.

EXPERIMENTAL DESIGN

A phase 1, open-label, dose-escalation study of atacicept in patients with relapsed or refractory B-cell lymphoma was done. Atacicept was given s.c. weekly for 5 weeks to sequential patient cohorts at doses of 2, 4, 7, or 10 mg/kg. Patients responding or with stable disease were eligible for treatment on an extension study for up to 24 weeks or until disease progression.

RESULTS

All patients were heavily pretreated (median number of previous treatments, 5; range, 1-10), and four patients had previously received a stem cell transplant. Four patients were treated at the 2, 4, or 7 mg/kg dose levels, and three patients received 10 mg/kg of atacicept. Atacicept was well tolerated at all doses. Three adverse events with grade 3 severity were reported for one patient, including jaw pain, gastrointestinal hemorrhage, and sepsis; all were considered unrelated to atacicept. Pharmacokinetic results were nonlinear, and treatment with atacicept resulted in dose-dependent decreases in immunoglobulin concentrations. Two patients had stable disease at 8 weeks, entered the extension study, and received additional doses of atacicept with no safety or tolerability concerns.

CONCLUSION

Atacicept at doses of up to 10 mg/kg was well tolerated and showed biological activity by decreasing immunoglobulin concentrations, although tumor responses were not observed.

Hodgkin lymphoma cells express TACI and BCMA receptors and generate survival and proliferation signals in response to BAFF and APRIL

Hodgkin lymphoma (HL) originates from the clonal expansion of malignant Hodgkin and Reed-Sternberg (HRS) cells. These B-cell-derived elements constitute less than 10% of the tumoral mass. The remaining tissue is comprised of an inflammatory infiltrate that includes myeloid cells. Myeloid cells activate B cells by producing BAFF and APRIL, which engage TACI, BCMA, and BAFF-R receptors on the B cells. Here, we studied the role of BAFF and APRIL in HL. Inflammatory and HRS cells from HL tumors expressed BAFF and APRIL. Unlike their putative germinal center B-cell precursors, HRS cells lacked BAFF-R, but expressed TACI and BCMA, a phenotype similar to that of plasmacytoid B cells. BAFF and APRIL enhanced HRS cell survival and proliferation by delivering nonredundant signals via TACI and BCMA receptors through both autocrine and paracrine pathways. These signals caused NF-kappaB activation; Bcl-2, Bcl-xL, and c-Myc up-regulation; and Bax down-regulation, and were amplified by APRIL-binding proteoglycans on HRS cells. Interruption of BAFF and APRIL signaling by TACI-Ig decoy receptor, which binds to and neutralizes BAFF and APRIL, or by small-interfering RNAs targeting BAFF, APRIL, TACI, and BCMA inhibited HRS cell accumulation in vitro and might attenuate HL expansion in vivo.

An APRIL to remember: novel TNF ligands as therapeutic targets

Since their discovery in 1998, the two TNF family members APRIL and BLyS/BAFF have received increasing attention. In addition to regulating normal B-cell development and immune responses, these molecules might be crucial in a diverse set of diseases, including autoimmunity and cancer. Although more has been published about the general biology of BLyS/BAFF than that of APRIL, many recent articles have described novel APRIL biology. Here we focus on APRIL, exploring its normal and pathological functions, and comparing the therapeutic molecules currently under development that target BLyS/BAFF alone, or APRIL and BLyS/BAFF together.

Elevated serum B-lymphocyte stimulator levels in patients with familial lymphoproliferative disorders

PURPOSE

Serum B-lymphocyte stimulator (BLyS) levels have been found to be elevated in a number of immune disease models. Therefore, we sought to establish whether BLyS levels were elevated in patients with B-cell lymphoproliferative disorders and to determine whether elevated BLyS levels correlated with clinical characteristics of the disease.

PATIENTS AND METHODS

Specimens were collected from the peripheral blood of individuals diagnosed with B-cell chronic lymphocytic leukemia (B-CLL; n = 70) or from age- and sex-matched patients seen at the same institution (n = 41). Serum BLyS levels were determined by enzyme-linked immunosorbent assay, and sequencing of the BLyS promoter was performed by conventional methods and confirmed by restriction fragment length polymorphism analysis.

RESULTS

We found that elevated BLyS levels were more common in patients with familial B-CLL than individuals with sporadic B-CLL or normal controls. Because of this association, we sequenced the BLyS promoter in patients with B-CLL and normal controls and identified a polymorphic site, -871 C/T. We found that the wild-type sequence was significantly underrepresented in patients with familial B-CLL (4%) compared with patients with sporadic B-CLL (30%; P = .01) or controls (24%; P = .04). Furthermore, using a luciferase reporter under control of the BLyS promoter containing either a C or a T at position -871, we found that the reporter construct containing a T at -871 had a 2.6-fold increase in activity (P = .004).

CONCLUSION

Our data suggest serum BLyS levels are elevated in patients with familial B-CLL and that elevated BLyS levels correlate with the presence of a T at -871 in the BLyS promoter.

B-lymphocyte stimulator (BLyS) stimulates immunoglobulin production and malignant B-cell growth in Waldenstrom macroglobulinemia

Waldenström macroglobulinemia (WM) is a serious and frequently fatal B-cell malignancy associated with an elevated monoclonal IgM protein in the serum. Many of the mechanisms leading to this disease are not yet known. B-lymphocyte stimulator (BLyS) is a TNF family member that is critical for maintenance of normal B-cell development and homeostasis. BLyS is overexpressed in a variety of B-cell malignancies and has been shown to inhibit apoptosis in malignant B cells. It also regulates immunoglobulin secretion by normal B cells. To determine the relevance of BLyS in WM, we examined the role of BLyS in WM patient samples. Malignant B cells were found to bind soluble BLyS and variably express the receptors BAFF-R, TACI, and BCMA. We also found expression of BLyS in bone marrow specimens by immunohistochemistry and elevated serum BLyS levels in patients with WM. BLyS, alone or in combination with cytokines that induce immunoglobulin production, was found to increase IgM secretion by malignant B cells. Furthermore, BLyS was found to increase the viability and proliferation of malignant B cells from WM patients. Due to the role of BLyS in WM, strategies to inhibit BLyS may potentially have therapeutic efficacy in these patients.

Interleukin 31, a cytokine produced by activated T cells, induces dermatitis in mice

T cell-derived cytokines are important in the development of an effective immune response, but when dysregulated they can promote disease. Here we identify a four-helix bundle cytokine we have called interleukin 31 (IL-31), which is preferentially produced by T helper type 2 cells. IL-31 signals through a receptor composed of IL-31 receptor A and oncostatin M receptor. Expression of IL-31 receptor A and oncostatin M receptor mRNA was induced in activated monocytes, whereas epithelial cells expressed both mRNAs constitutively. Transgenic mice overexpressing IL-31 developed severe pruritus, alopecia and skin lesions. Furthermore, IL-31 receptor expression was increased in diseased tissues derived from an animal model of airway hypersensitivity. These data indicate that IL-31 may be involved in promoting the dermatitis and epithelial responses that characterize allergic and non-allergic diseases.

Partial restoration of B cell development in Jak-3(-/-) mice achieved by co-expression of IgH and E(mu)-myc transgenes

Jak-3 is a non-receptor tyrosine kinase that plays an important role in coordinating signals received through a wide range of cytokine receptors, including the IL-7 receptor (IL-7R). Jak-3-deficient mice have a profound block in B cell development at the pro-to-pre-B cell transition and have very few peripheral B cells. This block has been postulated to reflect the inability of Jak-3(-/-) pro-B cells to respond to IL-7. Here we demonstrate that B cell development can be partially restored in Jak-3-deficient mice when they are bred to mice carrying both a rearranged Ig heavy chain (IgH/Igmu) transgene and a c-myc transgene expressed in the B cell lineage. Jak-3(-/-) mice expressing both of these transgenes exhibit significant increases in the number of B cells in the bone marrow and, to a lesser extent, in the spleen. However, very few rescued B cells were detectable in mice greater than 4 months of age. To determine whether resident hyperactivated Jak-3(-/-) peripheral T cells are responsible for the elimination of the rescued B cells in older mice, we bred IgH transgenic (Igmu Tg)/myc Tg/Jak-3(-/-) mice to T cell-deficient (TCRalpha(-/-)) mice. Data from these experiments suggest that the paucity of B cells in older Jak-3(-/-) mice is largely attributable to the lack of Jak-3 in the B cells themselves. Thus, Jak-3 seems to play several important roles in B cells: during development, to enable cell division, Ig gene rearrangement and cell differentiation, and in mature cells, to promote B cell survival in the periphery.

A soluble class II cytokine receptor, IL-22RA2, is a naturally occurring IL-22 antagonist

IL-22 is an IL-10 homologue that binds to and signals through the class II cytokine receptor heterodimer IL-22RA1/CRF2-4. IL-22 is produced by T cells and induces the production of acute-phase reactants in vitro and in vivo, suggesting its involvement in inflammation. Here we report the identification of a class II cytokine receptor designated IL-22RA2 (IL-22 receptor-alpha 2) that appears to be a naturally expressed soluble receptor. IL-22RA2 shares amino acid sequence homology with IL-22RA1 (also known as IL-22R, zcytor11, and CRF2-9) and is physically adjacent to IL-20Ralpha and IFN-gammaR1 on chromosome 6q23.3-24.2. We demonstrate that IL-22RA2 binds specifically to IL-22 and neutralizes IL-22-induced proliferation of BaF3 cells expressing IL-22 receptor subunits. IL-22RA2 mRNA is highly expressed in placenta and spleen by Northern blotting. PCR analysis using RNA from various tissues and cell lines showed that IL-22RA2 was expressed in a range of tissues, including those in the digestive, female reproductive, and immune systems. In situ hybridization revealed the dominant cell types expressing IL-22RA2 were mononuclear cells and epithelium. Because IL-22 induces the expression of acute phase reactants, IL-22RA2 may play an important role as an IL-22 antagonist in the regulation of inflammatory responses.

TACI-Ig neutralizes molecules critical for B cell development and autoimmune disease. impaired B cell maturation in mice lacking BLyS

BLyS and APRIL have similar but distinct biological roles, mediated through two known TNF receptor family members, TACI and BCMA. We show that mice treated with TACI-Ig and TACI-Ig transgenic mice have fewer transitional T2 and mature B cells and reduced levels of circulating immunoglobulin. TACI-Ig treatment inhibits both the production of collagen-specific Abs and the progression of disease in a mouse model of rheumatoid arthritis. In BLyS-deficient mice, B cell development is blocked at the transitional T1 stage such that virtually no mature B cells are present, while B-1 cell numbers are relatively normal. These findings further elucidate the roles of BLyS and APRIL in modulating B cell development and suggest that BLyS is required for the development of most but not all mature B cell populations found in the periphery.

Annexin V binds to positively selected B cells

Recombinant annexin V (rAnV) has been used in flow cytometry to identify cells undergoing apoptosis, based on its ability to bind to phosphatidylserine, a negatively charged lipid normally restricted to the cytoplasmic face of the plasma membrane but externalized early during apoptosis. When we stained murine bone marrow (BM) cells with fluorescently labeled rAnV, we found that a surprisingly large fraction of BM B cells bearing selectable transgenic Ag receptors bind significant amounts of rAnV, but that these cells are not apoptotic. Here, we show that binding of rAnV to developing B cells in normal mice correlates with B cell receptor-dependent selection events at several stages of development within both B-1 and B-2 cell subsets. In fact, nearly all B-1 B cells and splenic marginal zone B cells bind rAnV, suggesting that the externalization of phosphatidylserine occurs once mature B cells are selected through BCR-mediated signaling. However, this plasma membrane alteration is apparently not shared by all lymphocytes, because we did not find a parallel population of rAnV-binding viable T cells in vivo in normal or TCR transgenic mice. We also show that BM stromal cell lines can influence the extent of rAnV binding by viable BM B cells during coculture in vitro. We suggest that rAnV detects a potentially important membrane alteration that occurs as B cells develop in the BM and are readied for export to the peripheral lymphoid organs and again among mature B cells recruited to the marginal zone or the B-1 compartment.