Here, Major histocompatibility complex (MHC) molecules were highly expressed in R/R MM samples, whereas MHC-I molecules were not differentially expressed (Figure S2C), suggesting that cancer cells escaped CD8+ T-cell–mediated cytotoxic killing but not NK cell–mediated cytotoxic killing and MHC-II–mediated CD4+ T-cell activation. This evidence concerns the gene CD4 and cancer.