Mismatch Repair Protein Deficiency Is a Risk Factor for Aberrant Expression of HLA Class I Molecules: A Putative "Adaptive Immune Escape" Phenomenon.

Accumulating evidence indicates that immune checkpoint inhibition-mediated cancer immunotherapies greatly improve the prognosis of certain types of cancer. This approach is now becoming a standard therapy, joining surgery, radiotherapy, and chemotherapy. Because the costs of antibody drugs are now a socioeconomic burden in many countries, an urgent need in cancer immunotherapy is the identification of relevant biomarkers that can predict therapy efficacy. Recent studies have reported that colorectal adenocarcinoma with hereditary or sporadic deficiency in mismatch repair (MMR) proteins has high antigenicity and that detection of these proteins could be a promising way to estimate clinical response. In this study of 135 patients with colorectal cancer, we used immunohistochemistry to investigate the correlation between deficiency in MMR proteins and expression of human leukocyte antigen (HLA) class I molecules, a prerequisite of cytotoxic T-cell-based immunotherapy. Interestingly, MMR protein deficiency was an independent risk factor for the impaired expression of HLA class I molecules (odds ratio (OR)=10.44, 95% confidence interval (CI)=3.15-34.62, p<0.001), suggesting the existence of a putative entity that we have named "adaptive immune escape". Moreover, our results might provide a potential novel biomarker for the selection of patients who would respond to cancer immunotherapies. At the same time, the results suggest that we have to overcome the impaired expression of HLA class I molecules to further improve the cure rate of cancer immunotherapies.