IMMU-03. TUMOR NECROSIS FACTOR OVERCOMES IMMUNE EVASION IN P53-MUTANT MEDULLOBLASTOMA. (23rd April 2019) - Garancher, Alexandra
Abstract: Many immunotherapies act by enhancing the ability of T cells to kill tumor cells. But T cell killing depends on recognition of antigens presented by Class I MHC (MHC-I) on the tumor cell surface; if a tumor lacks MHC-I, it cannot be recognized by T cells. To study the efficacy of immunotherapy for Group 3 medulloblastoma, we have used mouse models driven by overexpression of M yc and dominant negative p 53 ("MP tumors"), or by overexpression of M yc and G fi1 ("MG tumors"). While MP tumors grow in immunocompetent mice, MG tumors don't grow, due to T-cell rejection. To understand this difference, we analyzed expression of immunoregulatory molecules, and found that MP tumors completely lack surface MHC-I. Mechanistically, this is because two key proteins required for MHC-I trafficking – TAP1 and ERAP1 – are targets of p53; since MP tumors lack functional p53, they also lack TAP1 and ERAP1, and surface MHC-I. These studies suggest that p53 plays a critical role in determining immunogenicity, and that p53-mutant tumors are resistant to immune attack. To overcome this resistance, we treated tumor cells with agents that regulate MHC-1. We found that low doses of tumor necrosis factor alpha (TNF) can rescue expression of ERAP, TAP and MHC-I on MP tumor cells. In vivo, TNF prolongs survival of tumor-bearing mice, and markedly augments the efficacy of immune checkpoint inhibitors. These results raise the possibility that TNF could be used prior to immunotherapy to render tumors more sensitive to T cell attack.