893 ATG-101, a novel PD-L1/4–1BB bispecific antibody, augments anti-tumor immunity through immune checkpoint inhibition and PDL1-directed 4–1BB activation

Background Programmed death-ligand 1 (PD-L1) and programmed cell death protein 1(PD-1) blockade therapy has revolutionized the treatment landscape of malignancies. However, only a minority patients are anticipated to experience deep durable response. In addition, successful therapeutic agonism 4-1BB, promising co-stimulatory immunologic target, been limited by major safety concerns hepatotoxicity or suboptimal agonistic potency. ATG-101, novel PD-L1/4-1BB bispecific antibody, was designed activate 4-1BB positive T cells in PDL1-crosslinking dependent manner effectively treat tumors without on-target-off-tumor liver toxicity (figure 1). Methods ATG-101 developed introducing lower affinity scFv into human IgG1 PD-L1 monoclonal antibody. The N297A mutation on CH2 abolishes binding capacity most Fc?Rs but retains Fc?Rn. A series vitro vivo studies were performed evaluate potency, specific mechanism action. Results simultaneous binds with higher PD-L1, potently activates when crosslinked cells. Upon crosslinking, also PD1+TIM3+ exhausted vitro, suggesting potential reversing T-cell dysfunction exhaustion shows potent anti-tumor activities various animal models, including h4-1BB humanized mice bearing MC38 colon cancer, PD(L)1 insensitive B16F10 melanoma EL4 lymphoma, no body weight loss observed. To efficacy progressing after anti-PD(L)1 treatment, treated anti-PDL1 initially achieve tumor growth inhibition, half switched upon disease progression, other continuing anti-PD-L1 treatment. induced inhibition regression anti-PDL1-resistant prolonged survival. Flow cytometry multiplex IHC staining samples from control suggest that increases infiltration, proliferation activation CD8+ 2), infiltration natural killer CD8+/Treg ratio TILs. 4-week GLP study cynomolgus monkey, up 100mg/kg repeated doses well tolerated Abstract 893 Figure conditionally (A) Mechanism action (B) Exhausted CD3+T cultured anti-CD3/CD28 beads for 6 days. percentage terminally (PD-1+Tim-3+) progenitor (PD-1+Tim-3-) increased Day6 (C) With presence cells, IL2 INF-? secretion 2 Potent ATG-101. Representative curve individual PBS (black), 10mpk atezolizumab (Atezo) (red) 13mpk progression (red-green); arrow indicates day switching Atezo ATG-101; all (black, n=6), (red, n=14), before (red-green, n=14) ; Survival data mouse shown (B); (D) images collected (B). (E) Quantitative analysis TILs (D). Compared group atezo-only group, significantly microenvironment. MHCII: APC Cells, CD4+ CD8-: Helper CD4- CD8+: Cytotoxic CD8- F4/80- PDL1+: Tumor Cells. Conclusions demonstrated significant activity models those anti Good PK/PD properties preclinical models. phase I, multicenter, dose-escalating clinical trial evaluating solid hematologic malignancies is ongoing. Ethics Approval protocol any amendment(s) procedures involving care use animals this reviewed approved Institutional Animal Care Use Committee (IACUC) CrownBio Innostar prior execution an AUP number IACUC approval each study. During study, conducted accordance regulations Association Assessment Accreditation Laboratory (AAALAC).All following protocol. NO.:2004-12-1465, 2004-12-1000; number: IACUC-2021-M-003