Immune modulation of the breast tumor microenvironment by targeting CD40

While immunotherapy has revolutionized the treatment of several cancers, most patients with triple negative breast cancer (TNBC) do not respond to this approach. Thus, new ways to mobilize the immune system to fight TNBC are needed. Antibodies targeting CD40 can stimulate antigen-presenting cells (APCs), which drive anti-tumor T-cell responses. However, other anti-CD40 antibodies have shown modest clinical activity, coupled with severe toxicities. We re-engineered the Fc portion of a human anti-CD40 antibody to enhance its binding to FcRIIB (an inhibitory receptor, expressed on APCs) which resulted in a 25-fold increased potency. In parallel, we generated a transgenic mouse model that expresses human CD40 and human Fc Receptors, while lacking murine CD40 and murine Fc Receptors. This mouse model allows evaluating the activity of CD40-targeting antibodies designed for the clinic (with a human IgG Fc), in an immunocompetent setting. The engineered antibody proved efficacious and safe both in our transgenic mice inoculated orthotopically with TNBC, and in patients treated in our Phase1 clinical trial (NCT04059588). The antibody led not only to primary tumor clearance, but also to an abscopal effect and to formation of a long-term immune memory. Using adoptive cell transfer, depletion studies, and multi-parameter staining of tumors and lymph nodes - we identified the immune sub-populations that mediate the effect of anti-CD40 antibodies. Out study enhances our understanding of breast cancer immunobiology and support the translation of CD40-targeting antibodies to the clinic for the treatment of patients with TNBC.