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.