Abstract 2768: Potentiating the action of antibody-dependent cell-mediated cytotoxicity with immunocytokines

Intact antibodies in the IgG format typically display only moderate in vivo activity against solid tumor masses, when their mechanism of action relies on antibody-dependent cellular cytotoxicity (ADCC). The therapeutic activity is mainly limited by the lack of immune effector cells (and most notably NK cells) in the neoplastic mass. Our group had previously reported that the therapeutic activity of Rituximab and other intact immunoglobulins could be strongly potentiated by the antibody-based targeted delivery of interleukin-2 (IL2) to the tumor environment. The combination regimen induced complete remissions of established localized lymphomas and provided long-lasting protection from disseminated lymphoma, in mouse models that featured functional NK cells. In this study, we examined the ADCC activity of TA99, a monoclonal antibody which specifically recognizes gp75, a conserved tumor-associated antigen over-expressed in both murine and human melanoma cells. In a preventive setting TA99 in murine IgG2a format completely inhibited the formation of lung metastases in mice, which had been injected intravenously with B16F10 melanoma cells. However, when the B16F10 melanoma tumor was grown subcutaneously in immunocompetent mice, the ADCC activity was not potent enough to eradicate the pre-established tumors and only a modest tumor growth inhibition was observed. A microscopic tissue distribution analysis revealed that TA99-IgG2a had selectively accumulated in the tumor mass compared to normal organs and that NK cells within the neoplastic lesions were scarce. In order to increase NK cell density at the tumor site and potentiate ADCC activity, we developed fusion proteins of the TA99 antibody with murine TNFα, IL2 and IL12. The antibody-cytokine fusion proteins were used alone and in combination with TA99-IgG2a. Combination treatment led to a marked increase of anti-cancer activity against established subcutaneous tumors. Our findings indicate that the targeted delivery of certain pro-inflammatory cytokines to the tumor site potentiates the anti-cancer properties of intact antibodies, enhancing their ability to induce ADCC. Citation Format: Patrizia Murer, Jonathan D. Kiefer, Louis Plüss, Dario Neri. Potentiating the action of antibody-dependent cell-mediated cytotoxicity with immunocytokines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13