Abstract PR-11: Fc-optimized agonistic CD40 antibody induces tumor rejection and systemic antitumor immunity - From the bench to the bedside and back

Abstract While immunotherapy has revolutionized the treatment of several cancer types, some patients do not respond to current therapies. The CD40-CD40L pathway is crucial for activating antigen-presenting cells and initiating antitumor T-cell responses. CD40 is a TNF receptor superfamily member expressed on antigen-presenting cells (APCs, e.g. monocytes and dendritic cells). Several CD40 agonistic antibodies (Abs) have been tested in past clinical trials, however, their efficacy has been limited and accompanied by dose-limiting toxicities (DLT). Thus, CD40 agonism necessitates optimization to allow efficient mobilization of the immune system to fight cancer, while minimizing toxicity. We hypothesize that engagement of CD40 expressed by APCs, will lead to maturation and activation of APCs, enhance antigen presentation and promote recruitment of cytotoxic CD8 T-cells, resulting in tumor elimination. We have previously demonstrated that when the Fc portion of anti-CD40 Abs binds to the inhibitory Fc-Receptor (FcR) FcRIIB, which is expressed on various leukocytes - it provides the necessary crosslinking for CD40 trimerization, promotes CD40 signaling and leads to activation of CD40-expressing APCs. Thus, we engineered the Fc of a human IgG1 anti-CD40 agonistic Ab (clone 2141) by introducing several point mutations (termed herein: the V11 modification) to selectively increase its binding affinity to FcRIIB. To mitigate systemic adverse events - we switched from systemic to in situ administration (injecting the Abs directly into lesions). Finally, we generated an immunocompetent mouse strain that expresses human CD40 and human FcRs, while lacking murine CD40 and murine FcRs (termed herein: hCD40/hFcR mice). We implanted orthotopic murine tumor cells into hCD40/hFcR mice, and treated in situ with the optimized CD40-targeting Ab, 2141-V11. Our findings demonstrate that the Ab leads to the complete elimination of primary tumors. In a bilateral tumor challenge, both tumors fully regress, despite treating only a single tumor. This abscopal effect suggests a robust systemic immune activation, which was supported by an increase in serum cytokine levels such as IFNg, TNFa, IL-15, IL-18, CXCL10, CCL7 and IL-6. Multiplex IHC staining of regressing tumor sections demonstrated formation of tertiary lymphoid structures (TLS). Finally, mice that have rejected the tumors were protected from tumor re-challenge, suggesting durable antitumor immune memory. Following the in vivo findings and pre-clinical toxicology studies in Non-Human Primates, we conducted a Phase I, 3+3 dose escalation trial (n=12), in which 2141-V11 was injected into one/two lesions (NCT04059588). Complete responses (CR) were observed in two patients and stable disease (SD) in six patients, with no DLTs. Moreover, biopsy and serum analyses from treated patients confirmed our in vivo findings (TLS formation and increase in cytokine serum levels). Overall, we show the efficacy and safety of intra-tumoral Fc-optimized CD40 Ab therapy and unveil a potential unique mechanism of action of this immunotherapy. Citation Format: Polina Weitzenfeld, Juan C Osorio, Jeffrey V Ravetch. Fc-optimized agonistic CD40 antibody induces tumor rejection and systemic antitumor immunity - From the bench to the bedside and back [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr PR-11.