CD28 Costimulatory Pathway Research Articles

Non-Redundant Roles of T Cell Costimulation Pathways in Inflammatory Arthritis Revealed by Dual Blockade of ICOS and CD28 with Acazicolcept (ALPN-101).

CD28 and inducible T cell costimulator (ICOS) appear to have nonredundant roles in T cell activation and adaptive immunity. We undertook this study to characterize in vitro and in vivo the therapeutic potential of acazicolcept (ALPN-101), an Fc fusion protein of a human variant ICOS ligand (ICOSL) domain designed to inhibit both CD28 and ICOS costimulation, in inflammatory arthritis. Acazicolcept was compared in vitro with inhibitors of either the CD28 or ICOS pathways (abatacept and belatacept [CTLA-4Ig], prezalumab [anti-ICOSL monoclonal antibody]) in receptor binding and signaling assays, and in a collagen-induced arthritis (CIA) model. Acazicolcept was also compared in cytokine and gene expression assays of peripheral blood mononuclear cells (PBMCs) from healthy donors or rheumatoid arthritis (RA) or psoriatic arthritis (PsA) patients stimulated with artificial antigen-presenting cells (APCs) expressing CD28 and ICOS ligands*. 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 significantly reduced disease in the CIA model and more potently than abatacept. Acazicolcept also inhibited proinflammatory cytokine production from stimulated PBMCs in cocultures with artificial APCs and demonstrated unique effects on gene expression distinct from those induced by abatacept, prezalumab, or a combination of both. Both CD28 and ICOS signaling play critical roles in inflammatory arthritis. Therapeutic agents such as acazicolcept that coinhibit both ICOS and CD28 signaling may mitigate inflammation and/or disease progression in RA and PsA more effectively than inhibitors of either pathway alone.

Activated CTLA-4-independent immunosuppression of Treg cells disturbs CTLA-4 blockade-mediated antitumor immunity.

Combination therapy with anti-cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and anti-programmed death-1 (PD-1) monoclonal antibodies (mAbs) has dramatically improved the prognosis of patients with multiple types of cancer, including renal cell carcinoma (RCC). However, more than half of RCC patients fail to respond to this therapy. Regulatory T cells (Treg cells) are a subset of highly immunosuppressive CD4+ T cells that promote the immune escape of tumors by suppressing effector T cells in the tumor microenvironment (TME) through various mechanisms. CTLA-4 is constitutively expressed in Treg cells and is regarded as a key molecule for Treg-cell-mediated immunosuppressive functions, suppressing antigen-presenting cells by binding to CD80/CD86. Reducing Treg cells in the TME with an anti-CTLA-4 mAb with antibody-dependent cellular cytotoxicity (ADCC) activity is considered an essential mechanism to achieve tumor regression. In contrast, we demonstrated that CTLA-4 blockade without ADCC activity enhanced CD28 costimulatory signaling pathways in Treg cells and promoted Treg-cell proliferation in mouse models. CTLA-4 blockade also augmented CTLA-4-independent immunosuppressive functions, including cytokine production, leading to insufficient antitumor effects. Similar results were also observed in human peripheral blood lymphocytes and tumor-infiltrating lymphocytes from patients with RCC. Our findings highlight the importance of Treg-cell depletion to achieve tumor regression in response to CTLA-4 blockade therapies.

Mycobacterium tuberculosis impedes CD40-dependent notch signaling to restrict Th17 polarization during infection

SummaryEarly Th17 responses are necessary to provide protection against Mycobacterium tuberculosis (Mtb). Mtb impedes Th17 polarization by restricting CD40 co-stimulatory pathway on dendritic cells (DCs). We previously demonstrated that engaging CD40 on DCs increased Th17 responses. However, the molecular mechanisms that contributed to Th17 polarization were unknown. Here, we identify the Notch ligand DLL4 as necessary for Th17 polarization and demonstrate that Mtb limits DLL4 on DCs to prevent optimal Th17 responses. Although Mtb infection induced only low levels of DLL4, engaging CD40 on DCs increased DLL4 expression. Antibody blockade of DLL4 on DCs reduced Th17 polarization in vitro and in vivo. In addition, we show that the Mtb Hip1 protease attenuates DLL4 expression on lung DCs by impeding CD40 signaling. Overall, our results demonstrate that Mtb impedes CD40-dependent DLL4 expression to restrict Th17 responses and identify the CD40-DLL4 pathways as targets for developing new Th17-inducing vaccines and adjuvants for tuberculosis.

The Expression of CD28 and Its Synergism on the Immune Response of Flounder (Paralichthys olivaceus) to Thymus-Dependent Antigen.

CD28 is well known as a critical T-cell costimulatory receptor involved in T cell activation by binding to its ligands. In this study, CD28 was cloned, and its expression profiles were characterized in flounder (Paralichthys olivaceus); variations of CD28+ cells after being stimulated with different types of antigens and the function of the CD28 costimulatory pathway on T-cell activation were investigated in vitro. fCD28 consists of four exons and three introns, and the full-length cDNA of fCD28 was 675-bp encoded 224 amino acids. The conserved motif (121TFPPPF126) binding to the CD80/86 ligand exists in the Ig-superfamily homology domain. The high expression of fCD28 is in gills, PBLs, head kidney, and spleen. CD28+ cells were co-localized with CD4+ T lymphocytes but not on IgM+ B lymphocyte cells. Moreover, the expression of CD28 was significantly varied in flounder after being stimulated by keyhole limpet hemocyanin (KLH) at both the transcriptional and cellular levels, while no significant differences were observed between lipopolysaccharide (LPS) stimulation and the control group. Notably, treatment of PBLs cultured in vitro with CD28 molecule-specific antibody (anti-CD28 Abs) and PHA produced more cell colonies and stimulated the proliferation of cultured leukocytes compared to PHA stimulation alone and the control group, and a higher level of IL-2 was detected in the culture medium. Meanwhile, anti-CD28 Abs increased the percent of CD28+ cells (10.41 ± 1.35%), CD4+ T lymphocytes (18.32 ± 2.15%), and CD28+/CD4+ double-positive cells (6.24 ± 1.52%). This effect also resulted in significant variations in the genes of cell membrane-bound molecules, cytokines, and related signaling pathways in cultured leukocytes, with significant changes in the genes of interleukin-2 (IL-2) and nuclear factor of activated T cells (NFAT) in the early stages of culture, and the expression of other molecules increased over time. These results proved the localization of the CD28 molecule on T lymphocytes in flounder, and anti-CD28 may act as the B7 ligand involved in T cell activation after antigen stimulation. These data provide a basis for a more in-depth study of the mechanism of the CD28 costimulatory pathway in T cell activation.

Innate and Adaptive Immunity in Giant Cell Arteritis.

Autoimmune diseases can afflict every organ system, including blood vessels that are critically important for host survival. The most frequent autoimmune vasculitis is giant cell arteritis (GCA), which causes aggressive wall inflammation in medium and large arteries and results in vaso-occlusive wall remodeling. GCA shares with other autoimmune diseases that it occurs in genetically predisposed individuals, that females are at higher risk, and that environmental triggers are suspected to beget the loss of immunological tolerance. GCA has features that distinguish it from other autoimmune diseases and predict the need for tailored diagnostic and therapeutic approaches. At the core of GCA pathology are CD4+ T cells that gain access to the protected tissue niche of the vessel wall, differentiate into cytokine producers, attain tissue residency, and enforce macrophages differentiation into tissue-destructive effector cells. Several signaling pathways have been implicated in initiating and sustaining pathogenic CD4+ T cell function, including the NOTCH1-Jagged1 pathway, the CD28 co-stimulatory pathway, the PD-1/PD-L1 co-inhibitory pathway, and the JAK/STAT signaling pathway. Inadequacy of mechanisms that normally dampen immune responses, such as defective expression of the PD-L1 ligand and malfunction of immunosuppressive CD8+ T regulatory cells are a common theme in GCA immunopathology. Recent studies are providing a string of novel mechanisms that will permit more precise pathogenic modeling and therapeutic targeting in GCA and will fundamentally inform how abnormal immune responses in blood vessels lead to disease.

309 - Alpn-101 (ICOSL vIgD-Fc), a Dual Antagonist of the ICOS and CD28 Costimulatory Pathways, for Treatment of Steroid Refractory Acute GVHD (aGVHD): Case Report

309 - Alpn-101 (ICOSL vIgD-Fc), a Dual Antagonist of the ICOS and CD28 Costimulatory Pathways, for Treatment of Steroid Refractory Acute GVHD (aGVHD): Case Report

<i>Mycobacterium tuberculosis</i> Impedes CD40-Dependent Notch Signaling to Restrict Th <sub>17</sub> Polarization During Infection

Early Th17 responses are necessary to provide protection against Mycobacterium tuberculosis (Mtb). However, we previously demonstrated that Mtb restricts Th17 polarization and that engaging the CD40 costimulatory pathway on dendritic cells (DCs) enhances Th17 responses and augments Mtb control. Defining the molecular mechanisms that limit Th17 polarization during Mtb infection will facilitate the design of TB vaccination strategies that induce protective Th17 immunity. Here, we identify the Notch ligand, Delta-like ligand 4 (DLL4), as necessary for Th17 polarization and demonstrate that Mtb limits DLL4 signaling on DCs to prevent optimal Th17 responses. While Mtb infection induced only low levels of Dll4 mRNA in DCs, exogenously engaging CD40 on Mtb-infected DCs enhanced Dll4 expression and led to high frequencies of DLL4+ and DLL4+ Jagged1+ DCs. Antibody blockade of DLL4 on DCs reduced Th17 polarization but did not affect Th1 polarization. DLL4 was also required for inducing multifunctional CXCR3+ CCR6+ CD4 T cells co-expressing IL-17, IL-22 and IFN-γ in the lungs of mice, and DLL4-dependent Th17 responses inversely correlated with Mtb lung burdens. Additionally, we show that the Mtb Hip1 protease attenuates DLL4 expression on lung DCs by impeding CD40 signaling. Overall, our results demonstrate that Mtb impedes CD40-dependent Notch ligand signaling to restrict Th17 responses and identify the CD40-DLL4 pathways as targets for developing new Th17-inducing vaccines and adjuvants for TB.

Tumor-targeted CD28 bispecific antibodies enhance the antitumor efficacy of PD-1 immunotherapy.

Monoclonal antibodies that block the programmed cell death 1 (PD-1) checkpoint have revolutionized cancer immunotherapy. However, many major tumor types remain unresponsive to anti-PD-1 therapy, and even among responsive tumor types, most of the patients do not develop durable antitumor immunity. It has been shown that bispecific antibodies activate T cells by cross-linking the TCR/CD3 complex with a tumor-specific antigen (TSA). The class of TSAxCD3 bispecific antibodies have generated exciting results in early clinical trials. We have recently described another class of "costimulatory bispecifics" that cross-link a TSA to CD28 (TSAxCD28) and cooperate with TSAxCD3 bispecifics. Here, we demonstrate that these TSAxCD28 bispecifics (one specific for prostate cancer and the other for epithelial tumors) can also synergize with the broader anti-PD-1 approach and endow responsiveness-as well as long-term immune memory-against tumors that otherwise do not respond to anti-PD-1 alone. Unlike CD28 superagonists, which broadly activate T cells and induce cytokine storm, TSAxCD28 bispecifics display little or no toxicity when used alone or in combination with a PD-1 blocker in genetically humanized immunocompetent mouse models or in primates and thus may provide a well-tolerated and "off the shelf" combination approach with PD-1 immunotherapy that can markedly enhance antitumor efficacy.

P156 ALPN-101, A FIRST-IN-CLASS DUAL ICOS/CD28 ANTAGONIST, DEMONSTRATES EFFICACY IN PATIENT-DERIVED PBMC IN VITRO AND IN AN IN VIVO T CELL TRANSFER MODEL OF CHRONIC INFLAMMATORY BOWEL DISEASE (IBD)

T cell costimulation has been strongly implicated in the pathogenesis of IBD, yet CD28 costimulatory pathway inhibitors (e.g. abatacept, CTLA4-Fc) have not proven clinically efficacious, implicating an alternative costimulatory pathway. ICOS is a costimulatory receptor highly related to CD28, upregulated upon T cell activation and mediating costimulatory signals in post-activation T cells - suggesting ICOS may be more relevant in active disease. In contrast, CD28 predominates in naïve T cells and is less critical in activated, effector and/or memory T cells. ALPN-101 is an Fc fusion protein of a human inducible T cell costimulator ligand (ICOSL) variant immunoglobulin domain (vIgDTM) engineered to inhibit simultaneously the CD28 and ICOS pathways. It has been shown to have potent in vitro immunosuppressive activity and in vivo efficacy in models of disease for which implication of CD28 and ICOS has been reported (e.g. aGvHD, inflammatory arthritis, Sjögren’s, lupus, MS). Its safety, tolerability, and dose-dependent pharmacokinetics/dynamics are under study in a Ph1 healthy volunteer study. Here, we evaluate ALPN-101 in vitro using PBMC from Crohn’s and ulcerative colitis patients demonstrating superior suppression of T cell activation and cytokine release and show its efficacy to both prevent and treat disease in a mouse T cell transfer model of chronic colitis.

P156 ALPN-101, A FIRST-IN-CLASS DUAL ICOS/CD28 ANTAGONIST, DEMONSTRATES EFFICACY IN PATIENT-DERIVED PBMC IN VITRO AND IN AN IN VIVO T CELL TRANSFER MODEL OF CHRONIC INFLAMMATORY BOWEL DISEASE (IBD)

Abstract Background T cell costimulation has been strongly implicated in the pathogenesis of IBD, yet CD28 costimulatory pathway inhibitors (e.g. abatacept, CTLA4-Fc) have not proven clinically efficacious, implicating an alternative costimulatory pathway. ICOS is a costimulatory receptor highly related to CD28, upregulated upon T cell activation and mediating costimulatory signals in post-activation T cells - suggesting ICOS may be more relevant in active disease. In contrast, CD28 predominates in naïve T cells and is less critical in activated, effector and/or memory T cells. ALPN-101 is an Fc fusion protein of a human inducible T cell costimulator ligand (ICOSL) variant immunoglobulin domain (vIgDTM) engineered to inhibit simultaneously the CD28 and ICOS pathways. It has been shown to have potent in vitro immunosuppressive activity and in vivo efficacy in models of disease for which implication of CD28 and ICOS has been reported (e.g. aGvHD, inflammatory arthritis, Sjögren’s, lupus, MS). Its safety, tolerability, and dose-dependent pharmacokinetics/dynamics are under study in a Ph1 healthy volunteer study. Here, we evaluate ALPN-101 in vitro using PBMC from Crohn’s and ulcerative colitis patients demonstrating superior suppression of T cell activation and cytokine release and show its efficacy to both prevent and treat disease in a mouse T cell transfer model of chronic colitis. Methods Primary cell assays were performed with PBMC stimulated with K562 cells (CD80+, CD86+, ICOSL+, anti-CD3 (OKT3) +) to evaluate suppression of cytokine release and compare to single pathway inhibition. ALPN-101 was assessed in the CD4+CD45RBhigh T cell-induced colitis model either singly dosed on Day 0 or 14 or repeat dosed 2x/week starting at Day 0 or 14 through Day 41, respectively. Serum cytokine and flow analysis of blood was performed throughout the study. Clinical presence of colitis was assessed using a disease activity index based on weight loss and stool consistency. At end of study, colons were measured and assessed histologically. Results ALPN-101 suppressed cytokine release (IFNγ, IL-2) from healthy or IBD patient PBMCs superior to single pathway inhibitors. In vivo, preventively or therapeutically, a single dose of ALPN-101 was efficacious to significantly improve multiple colitis readouts. Repeat dosing completely prevented onset of colitis. ALPN-101-treated mice gained weight and had colon weight-to-length ratios similar to the no-colitis cohort and demonstrated significant suppression of T cells and pro-inflammatory cytokines (e.g. TNFα, IL-12/23, IL-6). Conclusion Dual pathway inhibitor ALPN-101 is superior to single pathway inhibition in human in vitro and mouse in vivo translational studies and may be a novel therapeutic candidate for the treatment of IBD. Clinical trials for ALPN-101 in multiple inflammatory diseases are planned and underway. Consistent with clinical findings, histological analysis confirms efficacy of ALPN-101 in reducing colitis. All ALPN-101 treated groups had lower histological scores compared to the Fc control treated group (B). Mice treated from Day 0 to the end of the study had no pathological colon findings (C), 4/12 mice treated from Day 14 to end of study had no signs of colitis (D). None of the mice in these groups had their muscularis layer of colon affected by inflammation. Mice treated with a single dose at day 0 or day 14 had milder colitis than Fc control-treated mice, although the differences were not statistically significant.

An Open Label Study of Alpn-101, a First-in-Class Dual CD28/ICOS Antagonist, in Subjects with Steroid-Resistant or Steroid-Refractory Acute Graft Versus Host Disease (aGVHD)

Background: Cluster of differentiation 28 (CD28) and inducible T cell costimulator (ICOS) provide costimulatory signals required for optimal T cell activation when bound to their respective ligands, CD80 (B7-1) and CD86 (B7-2), and ICOS ligand (ICOSL). CD28 is involved in initiation of the pathogenic process in GVHD and recent studies suggest therapeutic utility of CD28 pathway inhibitors for prophylaxis and treatment. However, CD28 pathway inhibition alone appears insufficient to control established disease in most patients. In this context, it is recognized that following initial activation, CD28 is often down-regulated while ICOS, its most closely related family member, is upregulated, providing additional T cell costimulation that may sustain GVHD including gastrointestinal manifestations (Adom D et al. Blood. 2018; 132:355). In murine models of aGVHD, combined blockade of CD28 and ICOS was significantly superior to isolated blockade of the CD28 or ICOS pathways alone. ALPN-101 is an Fc fusion protein of a human ICOSL variant immunoglobulin domain (vIgDTM) designed to inhibit both the CD28 and ICOS costimulatory pathways. Nonclinical studies of ALPN-101 demonstrate high affinity binding to CD28 and ICOS, potent inhibition of T cell activation, and suppression of disease activity in a human xenogeneic model of GVHD in mice, after only a single dose (Dillon SR et al. Blood. 2018; 132:2037). ALPN-101 is in development as a novel and potentially transformative approach for GVHD. A first-in-human study of ALPN-101 in healthy subjects is ongoing. This clinical study will assess the safety, efficacy, pharmacokinetics (PK), and pharmacodynamics (PD) of ALPN-101 in subjects with aGVHD. Study Design and Methods: Adults with Grade II-IV aGVHD per Mount Sinai Acute GVHD international Consortium (MAGIC) criteria (Harris et al. 2016) that is resistant or refractory to glucocorticoids will receive a single intravenous dose of ALPN-101. This study will be conducted in two parts including dose escalation and dose expansion. Dose escalation will proceed by using an accelerated titration design. Thereafter, a selected dose level(s) will be evaluated in an expansion cohort of 10 subjects; if ≥ 25% (n=3) subjects achieve response, 15 additional subjects will be enrolled (Simon two-stage design). Background Therapy:At the investigator's discretion, subjects may continue therapies administered for prophylaxis, continue or increase glucocorticoids, and/or add another salvage therapy. Responders will be considered for glucocorticoid taper. Endpoints: Safety will be assessed based on the incidence, severity, and seriousness of adverse events. Efficacy endpoints include the objective response rate, duration of response, failure-free survival, event-free survival, non-relapse mortality, malignancy relapse/progression, overall survival, and glucocorticoid use. The incidence and titer of anti-drug antibodies will be assessed. Serum concentrations of ALPN-101 will be measured and PK parameters will be estimated. PD endpoints include target saturation and immunophenotyping of circulating leucocytes, and may include quantification of circulating cytokines, immunoglobulins, acute phase reactants, and soluble forms of the targeted pathway receptor, evaluation of changes in mRNA expression in circulating leucocytes, evaluation of risk alleles, and correlates of response. Disclosures Yang: Alpine immune sciences: Employment, Equity Ownership. Hillson:Alpine Immune Sciences: Employment, Equity Ownership. Manjarrez:Alpine Immune Sciences: Employment, Equity Ownership. Wiley:Alpine Immune Sciences: Employment, Equity Ownership. Means:Alpine Immune Sciences: Employment, Equity Ownership. Dillon:Alpine Immune Sciences: Employment, Equity Ownership. Peng:Alpine Immune Sciences: Employment, Equity Ownership.

Tumor suppression of novel anti-PD-1 antibodies mediated through CD28 costimulatory pathway.

Classical antagonistic antibodies (Abs) targeting PD-1, such as pembrolizumab and nivolumab, act through blockade of the PD-1-PDL-1 interaction. Here, we have identified novel antagonistic anti-PD-1 Abs not blocking the PD-1-PDL-1 interaction. The nonblocking Abs recognize epitopes on PD-1 located on the opposing face of the PDL-1 interaction and overlap with a newly identified evolutionarily conserved patch. These nonblocking Abs act predominantly through the CD28 coreceptor. Importantly, a combination of blocking and nonblocking Abs synergize in the functional recovery of antigen-specific exhausted CD8 T cells. Interestingly, nonblocking anti-PD-1 Abs have equivalent antitumor activity compared with blocker Abs in two mouse tumor models, and combination therapy using both classes of Abs enhanced tumor suppression in the mouse immunogenic tumor model. The identification of the novel nonblocker anti-PD-1 Abs and their synergy with classical blocker Abs may be instrumental in potentiating immunotherapy strategies and antitumor activity.

Correlation of CD28 expression on CD8+ T cells with prognosis in advanced lung adenocarcinomas and squamous cell carcinomas.

e14185 Background: Programmed death-1 (PD-1)-targeted therapies that treat non-small cell lung cancer (NSCLC) to salvage exhausted CD8 T cells depends on CD28 costimulatory pathway. However, the prognostic values of CD8+CD28+ T and CD8+CD28- T in advanced NSCLC and the impact of histological type on them remains unclear. Methods: Of 232 advanced NSCLC patients, 101 treatment-naïve individuals were eligible and included in our study. Flow cytometry was used to evaluate CD8+CD28+ T, CD8+CD28- T, CD4+CD25hi T, B, natural killer, γδT, and natural killer T cells in patients’ peripheral blood. Results: Multivariate analysis showed that increased levels of CD8+CD28+ T cells independently predicted favorable overall survival (OS) [hazard ratio (HR): 0.59, 95% confidence interval (CI): 0.28-0.93, P = 0.034] and progression-free survival (PFS) (HR: 0.60, 95%CI: 0.27-0.98, P = 0.033) in ADs but not in SCCs. In addition, high levels of CD8+CD28- T cells independently predicted unfavorable OS (HR: 1.57, 95%CI: 1.13-3.34, P = 0.039) and PFS (HR: 2.08, 95%CI: 1.02-4.23, P = 0.043) in SCCs but not in ADs. ADs had higher levels of CD4+CD25hi T and CD8+CD28- T, and lower NK (all P < 0.05) cell counts than SCCs. Conclusions: The prognostic values of peripheral CD8+CD28+ and CD8+CD28- T cells in advanced NSCLC patients differ depending on histological type. These results could help refine the CD28-dependent PD-1-targeted therapies for advanced NSCLC with ADs and SCCs.

Alpn-101, a Dual ICOS/CD28 Antagonist, Demonstrates Potent and Dose-Dependent Suppression of Graft Vs. Host Disease (GvHD) in a Human/NSG Mouse Xenograft Model, with Activity Superior to CD28 or ICOS Single Pathway Antagonists

Background ALPN-101 (ICOSL vIgD-Fc) is an Fc fusion protein of a human ICOSL variant immunoglobulin domain (vIgD™) designed to simultaneously inhibit the ICOS and CD28 costimulatory pathways. ICOS and CD28 bind ICOSL and CD80/CD86, respectively, and play critical roles in T cell activation and adaptive immunity. ALPN-101 has demonstrated preliminary efficacy in a model of graft versus host disease (GvHD) (2018 BMT abstract #244). Here we examined its efficacy, exposure, and pharmacodynamics in preparation for upcoming clinical studies. Methods A dose ranging study was conducted with 20, 100, or 500 µg ALPN-101 administered to NSG™ mice engrafted with human PBMC, and compared to belatacept, an approved CTLA-4-Fc protein CD28 pathway inhibitor. Mice were monitored for clinical signs of GvHD, inflammatory cytokines, and phenotype of the transferred cells. Pharmacokinetic analyses were also performed. Results ALPN-101 inhibited T cell activation in the GvHD model with all dose regimens tested (Fig 1). Significantly enhanced survival and reduced disease scores were observed in mice treated with ALPN-101 compared to mice treated with belatacept (i.e. 100% vs. 40% survival at Day 42, respectively; p 80% ICOS+ (Fig 2). Conclusion ALPN-101 is a potent dual ICOS/CD28 T cell antagonist capable–even with a single dose–of inhibiting lethal inflammatory processes with superior efficacy vs continuous CD28 or ICOS single pathway inhibition despite lower PK exposure, likely attributable to superior control of ICOS+ T cells which otherwise escape single pathway blockade. ALPN-101 is thus a promising novel therapeutic candidate for GvHD, and upcoming clinical trials will explore its therapeutic potential in GVHD and other inflammatory diseases.

Dexamethasone-induced immunosuppression: mechanisms and implications for immunotherapy

BackgroundCorticosteroids are routinely utilized to alleviate edema in patients with intracranial lesions and are first-line agents to combat immune-related adverse events (irAEs) that arise with immune checkpoint blockade treatment. However, it is not known if or when corticosteroids can be administered without abrogating the efforts of immunotherapy. The purpose of this study was to evaluate the impact of dexamethasone on lymphocyte activation and proliferation during checkpoint blockade to provide guidance for corticosteroid use while immunotherapy is being implemented as a cancer treatment.MethodsLymphocyte proliferation, differentiation, and cytokine production were evaluated during dexamethasone exposure. Human T cells were stimulated through CD3 ligation and co-stimulated either directly by CD28 ligation or by providing CD80, a shared ligand for CD28 and CTLA-4. CTLA-4 signaling was inhibited by antibody blockade using ipilimumab which has been approved for the treatment of several solid tumors. The in vivo effects of dexamethasone during checkpoint blockade were evaluated using the GL261 syngeneic mouse intracranial model, and immune populations were profiled by flow cytometry.ResultsDexamethasone upregulated CTLA-4 mRNA and protein in CD4 and CD8 T cells and blocked CD28-mediated cell cycle entry and differentiation. Naïve T cells were most sensitive, leading to a decrease of the development of more differentiated subsets. Resistance to dexamethasone was conferred by blocking CTLA-4 or providing strong CD28 co-stimulation prior to dexamethasone exposure. CTLA-4 blockade increased IFNγ expression, but not IL-2, in stimulated human peripheral blood T cells exposed to dexamethasone. Finally, we found that CTLA-4 blockade partially rescued T cell numbers in mice bearing intracranial gliomas. CTLA-4 blockade was associated with increased IFNγ-producing tumor-infiltrating T cells and extended survival of dexamethasone-treated mice.ConclusionsDexamethasone-mediated T cell suppression diminishes naïve T cell proliferation and differentiation by attenuating the CD28 co-stimulatory pathway. However, CTLA-4, but not PD-1 blockade can partially prevent some of the inhibitory effects of dexamethasone on the immune response.

Donor-Derived Regulatory Dendritic Cell Infusion Maintains Donor-Reactive CD4+CTLA4hi T Cells in Non-Human Primate Renal Allograft Recipients Treated with CD28 Co-Stimulation Blockade.

Donor-derived regulatory dendritic cell (DCreg) infusion before transplantation, significantly prolongs renal allograft survival in non-human primates. This is associated with enhanced expression of the immunoregulatory molecules cytotoxic T-lymphocyte-associated antigen (Ag) 4 (CTLA4) and programmed cell death protein 1 (PD1) by host donor-reactive T cells. In rodents and humans, CD28 co-stimulatory pathway blockade with the fusion protein CTLA4:Ig (CTLA4Ig) is associated with reduced differentiation and development of regulatory T cells (Treg). We hypothesized that upregulation of CTLA4 by donor-reactive CD4+ T cells in DCreg-infused recipients treated with CTLA4Ig, might be associated with higher incidences of donor-reactive CD4+ T cells with a Treg phenotype. In normal rhesus monkeys, allo-stimulated CD4+CTLA4hi, but not CD4+CTLA4med/lo T cells exhibited a regulatory phenotype, irrespective of PD1 expression. CTLA4Ig significantly reduced the incidence of CD4+CTLA4hi, but not CD4+CTLA4med/lo T cells following allo-stimulation, associated with a significant reduction in the CD4+CTLA4hi/CD4+CTLA4med/lo T cell ratio. In CTLA4Ig-treated renal allograft recipient monkeys, there was a marked reduction in circulating donor-reactive CD4+CTLA4hi T cells. In contrast, in CTLA4Ig-treated monkeys with DCreg infusion, no such reduction was observed. In parallel, the donor-reactive CD4+CTLA4hi/CD4+CTLA4med/lo T cell ratio was reduced significantly in graft recipients without DCreg infusion, but increased in those given DCreg. These observations suggest that pre-transplant DCreg infusion promotes and maintains donor-reactive CD4+CTLA4hi T cells with a regulatory phenotype after transplantation, even in the presence of CD28 co-stimulation blockade.

Requirement for CD40/CD40L Interactions for Development of Autoimmunity Differs Depending on Specific Checkpoint and Costimulatory Pathways.

CD40/CD40L interactions play a critical role in immunity and autoimmunity. In this study, we sought to understand the requirement for CD40 signaling in the programmed cell death-1 (PD-1) checkpoint and CD28 costimulatory pathways important for maintenance of peripheral tolerance. Blocking either pathway can result in loss of self-tolerance and development of autoimmunity. We found that primary Sjögren’s syndrome (pSS) and autoimmune thyroid diseases (ATDs) that develop spontaneously in CD28-deficient IFN-γ−/− NOD.H-2h4 (CD28−/−) mice required CD40 signaling. Specifically, blockade of CD40L with the anti-CD40L mAb, MR1, inhibited autoantibody production and inflammation in thyroid and salivary gland target tissues. Unexpectedly, however, ATD and pSS in PD-1–deficient IFN-γ−/− NOD.H-2h4 (PD-1−/−) mice developed independently of CD40/CD40L interactions. Treatment with MR1 had no effect and even exacerbated disease development in pSS and ATD, respectively. Most interesting, anti-thyroglobulin and pSS-associated autoantibodies were increased following anti-CD40L treatment, even though MR1 effectively inhibited the spontaneous splenic germinal centers that form in PD-1–deficient mice. Importantly, blockade of the PD-1 pathway by administration of anti–PD-1 mAb in CD28−/− mice recapitulated the PD-1−/− phenotype, significantly impacting the ability of MR1 to suppress ATD and pSS in these mice. These results indicate that there can be different pathways and requirements to autoimmune pathogenesis depending on the availability of specific checkpoint and costimulatory receptors, and an intact PD-1 pathway is apparently required for inhibition of autoimmunity by anti-CD40L.

Selective CD28 Blockade Results in Superior Inhibition of Donor-Specific T Follicular Helper Cell and Antibody Responses Relative to CTLA4-Ig.

Donor-specific antibodies (DSAs) are a barrier to improved long-term outcomes after kidney transplantation. Costimulation blockade with CTLA4-Ig has shown promise as a potential therapeutic strategy to control DSAs. T follicular helper (Tfh) cells, a subset of CD4+ T cells required for optimal antibody production, are reliant on the CD28 costimulatory pathway. We have previously shown that selective CD28 blockade leads to superior allograft survival through improved control of CD8+ T cells relative to CTLA4-Ig, but the impact of CD28-specific blockade on CD4+ Tfh cells is unknown. Thus, we identified and characterized donor-reactive Tfh cells in a murine skin transplant model and then used this model to evaluate the impact of selective CD28 blockade with an anti-CD28 domain antibody (dAb) on the donor-specific Tfh cell-mediated immune response. We observed that the anti-CD28 dAb led to superior inhibition of donor-reactive CXCR5+ PD-1high Tfh cells, CD95+ GL7+ germinal center B cells and DSA formation compared with CTLA4-Ig. Interestingly, donor-reactive Tfh cells differentially upregulated CTLA4 expression, suggesting an important role for CTLA4 in mediating the superior inhibition observed with the anti-CD28 dAb. Therefore, selective CD28 blockade as a novel approach to control Tfh cell responses and prevent DSA after kidney transplantation warrants further study.

Costimulatory pathways mediating T-dependent germinal center responses: distinct cellular requirements for CD40 and B7 costimulation

Abstract T cell-dependent (TD) germinal center (GC) and antibody responses require coordinated interactions of T cells with B cells and antigen-presenting dendritic cells (DCs). Although B7 and CD40 costimulatory pathways are critical for these responses, a comprehensive analysis of cell type-specific pathways has been hindered by the absence of models for conditional expression of B7 or CD40. Here we report generation of conditional knockout mice for both B7 and CD40, and the use of these lines together with conditional MHC class II (MHCII) knockouts and bone marrow chimeric strategies, to analyze pathways involved in TD GC and antibody responses. Our results indicate that MHCII-restricted recognition of both DCs and B cells is necessary for generation of antigen-specific TFH cells, GC B cells, and antibody response. Notably, the requirements for expression of B7 and CD40 were distinct, with B7 expression required on DCs but not on B cells, while CD40 was required on B cells but not DCs for generation of TFH cells, antigen-specific GC B cells, and antigen-specific class-switched antibody responses. These findings identify requirements for cell and costimulatory interactions in TD GC and antibody responses and support a unique model in which major costimulatory pathways function through interaction of T cells with distinct cell populations.

PD-L1/CD80 and PD-L1/PD-1 Signaling Reciprocally Regulate Alloreactive CD8+ T Cell Glycolysis, Proliferation, Apoptosis and Gvhd-Inducing Capacity

Graft versus host disease (GVHD) remains the major obstacle for widespread application of allogeneic hematopoietic cell transplantation (HCT), a curative therapy for hematological malignancies. We and others have reported that while sorted CD4+ T cells induce severe acute GVHD, the same numbers of CD8+ T cells induce no acute GVHD. CD8+ T cells can facilitate donor cell engraftment and mediate graft versus leukemia (GVL) effect in the absence of GVHD, but the mechanisms remain largely unknown. Programmed death-ligand 1 (PD-L1) interacts with both CD80 and PD-1. We have recently reported that simultaneous PD-L1/CD80 and PD-L1/PD-1 signaling augments activated alloreactive CD4+ T cell proliferation and apoptosis and ameliorates acute GVHD. However, the impact of this PD-L1-mediated signaling on alloreactive CD8+ T cells has not been investigated. In addition, T cell glycolytic metabolism has been recently reported to be able to regulate acute GVHD, and PD-L1/PD-1 signaling inhibits CD4+ T cell glycolytic flux, but how PD-L1/CD80 modulates T cell metabolism remains unstudied. In the current studies, we evaluated the role of PD-L1/CD80 and PD-L1/PD-1 signaling on alloreactive CD8+ T cell glycolysis, proliferation, apoptosis and GVHD-inducing capacity, using a MHC-mismatched murine HCT model of C57BL/6 (H-2b) donor to BABL/c recipient (H-2d). We have observed the following early (3-5 days) after HCT: 1) In wild-type (WT) recipients, PD-1-/- CD8+ T cells significantly upregulate expression of Glucose Transporter I (Glut1) and exhibit much higher rates of glycolytic flux; PD-1-/- CD8+ T cells also show markedly enhanced proliferation and reduced apoptosis as well as up-regulation of gut tissue homing and chemokine receptors (i.e. α4β7 and CCR9) and induce lethal GVHD, as compared to WT CD8+ T cells that induce little signs of GVHD. 2) In PD-L1-/- recipients, PD-1-/- CD8+ T cells reduce expression of Glut1 and no longer exhibit enhanced glycolytic flux or reduced apoptosis; PD-1-/- CD8+ T cells transplanted into PD-L1-/- recipients also induce little GVHD, similar to WT CD8+ T cells. 3) After injection of anti-PD-L1 mAb (clone 43H12) that specifically blocks PD-L1/CD80 interaction and preserves PD-L1/PD-1 interaction, WT CD8+ T cells in WT recipients show drastically reduced expansion, as compared to control recipients treated with rat-IgG. Blockade of PD-L1/CD80 interaction reduces phosphorylation of key elements in the TCR signaling cascade and CD28 co-stimulatory pathway including ZAP-70, AKT, mTOR and rpS6. Taken together, these studies indicate that 1) PD-L1/CD80 signaling alone augments alloreactive CD8+ T cell expansion and GVHD-inducing capacity; 2) PD-L1/CD80 and PD-L1/PD-1 signaling reciprocally regulate CD8+ T cell glycolysis, proliferation, and apoptosis as well as their GVHD-inducing capacity, and a balance of the two signaling pathways would be required to allow donor CD8+ T cells to facilitate engraftment and mediate GVL effect without causing GVHD. This work was supported by Institutional Funds of The Beckman Research Institute of City of Hope. DisclosuresNo relevant conflicts of interest to declare.