(209g) Noncovalently Anchoring Cytokines to Intratumorally Administered Particles Safely Boost Anti-Tumor Immunity

Preclinical studies have shown that immunostimulatory cytokines elicit anti-tumor immune responses, but their clinical use is limited by severe immune-related adverse events upon systemic administration. Conventional delivery methods, including tethering cytokines to soluble macromolecules, or intratumorally (i.t.) administration of free cytokines or cytokine-loaded nanoparticles fail to enhance cytokine retention in tumors, and inevitably overstimulates immune cells in healthy tissues. Herein, we report a facile strategy for noncovalently anchoring commercially available Fc-fused cytokines (Fc = fragment crystallizable domain) to the surface of particles decorated with Fc-binding peptide (Figure 1). Injection of such particles into tumors resulted in prolonged tumor retention of cytokines with minimal systemic toxicity, and more importantly, the retention time was particle-size dependent. The 1-µm particles surface-decorated with FcBP showed longer i.t. retention of Fc-fused molecules over 1 week than did smaller particles. Moreover, such particle-anchored IL-12 and IL-15 have minimal systemic exposure, thereby eliciting anti-tumor immunity while eliminating systemic toxicity caused by circulating free cytokines. Furthermore, i.t.-administered PS particle surfaces can initiate anti-tumor immunity in immune-excluded tumors such as 4T1 and B16F10 tumor models, increase infiltration of both innate and adaptive immune cells, and produce robust systemic anti-tumor responses without systemic toxicity. Rechallenge studies in a 4T1 breast tumor model demonstrated that our combination therapy generated durable anti-tumor immune memory to control disseminated metastases. Intratumoral cell analysis showed that the decreased production of inhibitory checkpoint receptors—including TIM-3, LAG-3, and TIGIT—and a reduced ratio between terminally and progenitor exhausted CD8+ cells contributed to improved proliferation and polyfunctionality of CD8+ TILs in mice that received the combination therapy. Our results suggest that IL-12 and IL-15 signaling could help reinvigorate exhausted CD8+ T cells toward ICB antibody-responsive states, thereby generating durable anti-tumor immunity and immune memory. Lastly, the potent combination of the particle-anchored cytokines and immune-checkpoint blockade (ICB) antibodies safely improved overall survival in another two transgenic tumor models, MMTV-PyMT and braf/pten transgenic tumor models.