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 (2019)

BackgroundALPN-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.MethodsA 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.ResultsALPN-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 < 0.01 by Mantel-Cox log rank test). Notably, single dose (100 µg) administration of ALPN-101 resulted in similar protection from disease as repeat dosing of 100 µg belatacept. The observed serum exposure of ALPN-101 in the GvHD model was 45% lower than that of normal mice. The trough concentrations of ALPN-101 were 60-80% lower than those of belatacept at the same dose level. Flow cytometric analysis of blood and serum cytokine analyses at end of study demonstrated ALPN-101 suppressed activation and expansion of transferred human T cells and cytokine production, and no acute cytokine release was observed at any point in the study. In contrast, serum inflammatory cytokines and activated human T cells expressing ICOS were readily detectable in the belatacept-treated mice. While most of the transferred human T cells initially expressed CD28 and just ∼15% were ICOS+, the activated T cells remaining in the saline- or belatacept-treated mice at termination/end of study were >80% ICOS+ (Fig 2).ConclusionALPN-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. 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. 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. 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 < 0.01 by Mantel-Cox log rank test). Notably, single dose (100 µg) administration of ALPN-101 resulted in similar protection from disease as repeat dosing of 100 µg belatacept. The observed serum exposure of ALPN-101 in the GvHD model was 45% lower than that of normal mice. The trough concentrations of ALPN-101 were 60-80% lower than those of belatacept at the same dose level. Flow cytometric analysis of blood and serum cytokine analyses at end of study demonstrated ALPN-101 suppressed activation and expansion of transferred human T cells and cytokine production, and no acute cytokine release was observed at any point in the study. In contrast, serum inflammatory cytokines and activated human T cells expressing ICOS were readily detectable in the belatacept-treated mice. While most of the transferred human T cells initially expressed CD28 and just ∼15% were ICOS+, the activated T cells remaining in the saline- or belatacept-treated mice at termination/end of study were >80% ICOS+ (Fig 2). 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.