707 IL12 Fc-fusions engineered for reduced potency and extended half-life exhibit strong anti-tumor activity and improved therapeutic index compared to wild-type IL12 agents

Background Interleukin-12 (IL12) is a proinflammatory cytokine that induces differentiation of Th1 cells and increased cytotoxicity T NK cells. Stimulation by IL12 leads to production IFNγ an inflammatory tumor microenvironment critical for anti-tumor responses. Studies in mice revealed can dramatically shrink syngeneic tumors, however human clinical studies resulted severe toxicity small therapeutic window, limiting response rates. Prior work at Xencor demonstrated reduced-potency IL15/IL15Rα-Fc fusion proteins exhibited superior index (TI) non-human primates (NHP) reducing receptor-mediated clearance. Applying similar principles IL12, we created heterodimeric Fc-fusions (IL12-Fc) with reduced potency improve TI. Methods heterodimer two subunits, so engineered IL12-Fc fusions fusing the IL12p35 subunit one side (and inactive) Fc domain, IL12p40 other side. These were tuned optimal activity introducing amino acid substitutions putative receptor-interface positions screening reductions vitro potency. In was assessed on PBMCs measuring signaling STAT4 phosphorylation assay mixed-lymphocyte reaction (MLR). vivo huPBMC-NSG-DKO huCD34+ MCF7 xenograft models. Surrogate mouse potency-reduced evaluated Tolerability pharmacodynamic NHP. Results An series created, variants had up 10,000-fold reduction MLR compared wild-type IL12-Fc. Anti-tumor achieved as single-agents combination anti-PD1, weaker maintaining higher dose levels. Analysis peripheral lymphocytes indicated numbers well activation CD8+ Increased expression immune checkpoints including PD1 also observed. serum 200-fold increases improved tolerability greater selectivity tumors spleen less IL10 NHP, exposure slower, more sustained accumulation IP10, gradual dose-dependent peak response, margination Conclusions Potency-reduced retain strong activity, while potentially overcoming safety issues related narrow TI associated or agents.