Regulation of human leukocyte antigen class I surface expression through the inhibition of MEK and RET
Claire Oh1*, Elliott Brea1, David Scheinberg1
1Molecular Pharmacology Program, Memorial Sloan Kettering Cancer Center, and Weill Cornell Medicine, New York, New York, 10065
The human major histocompatibility complex I (human leukocyte antigen or HLA) functions in the immune system by binding to peptides of intracellular endogenous proteins and displaying them on the cell surface for recognition by effector T cells. This can result in the killing of infected cells or cancer cells, which display foreign peptides or self-neoantigens, respectively. Tumor associated antigens are targets of some cancer immunotherapies, however the presentation of these antigens on the cell surface can be highly inefficient resulting in extremely low numbers of a tumor specific peptide/MHC epitope displayed for recognition by the T cell receptor (TCR). Therefore, we hypothesized that increasing the number of HLA molecules on the cell surface could increase the numbers of presented epitopes and thereby increase efficacy of T cell based therapies (checkpoint blockade, cell-based, TCR construct-based, or vaccines). A pooled RNAi screen targeting the kinome had been previously performed to determine if they were regulators of HLA surface expression. Major targets of interest that were discovered included the MAPK pathway and MEK. Interestingly, inhibition of pERK was correlated with the upregulation of surface HLA, leading us to hypothesize that targets upstream of the MAPK pathway could be identified that also regulate HLA without negatively impacting T cell function, which might ultimately be combined with the kinase inhibitors. We tested the role of RET on the MHC pathway in various human cell lines. HLA expression was measured through qPCR, western blots, and flow cytometry. Moreover, killing assays were used to determine the effects of these inhibitors on antibody-dependent cell-mediated cytotoxicity directed to MHC in vitro. Down regulation of RET with siRNAs and several small molecule inhibitors resulted in significant upregulation of HLA and antigen processing machinery. The use of pharmacological inhibitors to up-regulate HLA could be a useful adjuvant for T cell based or other peptide/ MHC antigen presentation-dependent therapies.