Major histocompatibility complex class 1 (MHC1) loss among patients with glioblastoma (GBM).

Abstract

e14523 Background: Immune evasion represents a hallmark behavior of cancer and may occur through many mechanisms. Among these, intact tumor antigen presentation at the cell surface is a fundamental prerequisite to achieving successful adaptive immunotherapy. The loss of MHC1 expression due to molecular events, including mutation, deletion, or epigenetic silencing of B2M is commonly acquired during immunotherapy. On the other hand, molecular events affecting antigen presentation machinery may be present prior to immunotherapy administration. Among these, TP53 mutations causing loss of ERAP1 and TAP1 expression compromise transport of MHC1 molecules from the endoplasmic reticulum to the cell surface and mutant peptide integration into the HLA context resulting in absent antigen presentation. Thus far, clinical trials of PD-1/L1 agents have failed to demonstrate a benefit for GBM patients and responses are seen only among a minority. Hence, we set out to assess the integrity of MHC1 expression by using immunohistochemistry. Methods: Immunohistochemical (IHC) stains for HLA, B and C were developed and validated with internal controls. Staining intensity and location (membrane-bound or cytoplasmic) was evaluated semi-quantitatively. The first 10 consecutive patients with GBM who were referred for neoepitope vaccine were evaluated. Results: Absent staining was seen among 6/10, negligible, or faint staining was present in 2, and only 2 tumors demonstrated intact membrane-bound expression. Conclusions: In addition to low tumor mutation burden and an immunosuppressive tumor microenvironment, MHC1 loss is a frequent event among patients with GBM, and may be a dominant cause of immunotherapy failure for as many as 80% of patients. Thus, development of strategies to reverse this loss may be an essential component of successful adaptive immunotherapy for this disease. These data suggest that routine assessment of MHC1 should become a component of eligibility checking for GBM patients being considered for an MHC-restricted approaches. [Table: see text]