Tumor recognition is a key factor in checkpoint inhibitors (CPI) efficacy and acquired resistance. Lack or loss of tumor antigens expression or inefficient presentation prevents tumor cell recognition by T cells, inhibiting CPI anti-cancer effect. Naptumomab estafenatox (Nap) is a tumor-targeted superantigen (TTS) protein that increases tumor recognition by both coating tumor cells with bacterial-derived superantigens (SAg) as well as selectively expanding T cells lineages that can recognize it. Nap consists of a genetically engineered SAg, staphylococcal enterotoxin A (SEA/E-120), linked to a fragment antigen binding (Fab) moiety directed to the 5T4 oncofetal tumor-associated antigen expressed on many tumors. Here we present new pre-clinical results of synergistic anti-tumor effect of Nap (or its murine equivalent TTS) with anti-PD1, under conditions which mimic poor tumor recognition. In vitro studies with Nap investigated the effect of co-culturing SAg activated T cells with HCC827 NSCLC or MDA-MB 231 Triple-Negative Breast Cancer cells. Co-cultures of T cells with either cancer cell line resulted in an increase in tumor staining for PDL1, which was further elevated in the presence of Nap, probably due to increase in IFNγ secretion. The viability of HCC827 or MDA-MB-231 cells co-cultured with the SAg activated T cells was examined in the presence or absence of the PD1 inhibitor, Nap or the combination. Anti-PD1 alone had no effect on T cell mediated cytotoxicity, whereas Nap induced a significant cytotoxic effect, with the combination of anti-PD1 plus Nap producing the most significant reduction in tumor cell viability. Similar to the in vitro studies, the in vivo mouse studies using low immunogenic tumor models showed limited or no effect of anti-PD1 monotherapy. Although TTS alone increased T cells activation and infiltration into the tumor, the combination with anti-PD1 was significantly more effective in increasing serum cytokines, increasing the CD8:CD4 ratio in the tumor, reducing tumor burden and prolonging median survival. In summary, our studies show that combination of anti-PD1 with tumor-targeted superantigens overcomes the limited effect of anti-PD1 monotherapy in low immunogenic tumor models in vitro and in vivo. This novel combination may offer clinical benefit for CPI unresponsive patients, particularly in cases where tumor recognition is lost or restricted. Clinical phase 1-2 trials are planned with the combination of naptumomab estafenatox and anti-PD1/PDL1 blockade.

Citation Format: Meir Azulay, Sveta Lifshits, Adam Fridman, Gunnar Hedlund, Marie Törngren, Michal Shahar. Naptumomab Estafenatox induces T cell recognition, turning anti-PD-1 unresponsive "cold" tumors into "hot" responsive tumors [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 Suppl):Abstract nr 2712.