B2M and cancer: To gain insights into the immune cell subsets that are involved in immune responses to HLA-class-I-negative MMR-d cancers, we used data of The Cancer Genome Atlas (TCGA) and studied the transcriptomic changes associated with the genomic loss of B2M in three cohorts of individuals with MMR-d cancer in colon adenocarcinoma (COAD; n = 50 (B2MWT), n = 7 (B2MMUT)), stomach adenocarcinoma (STAD; n = 48 (B2MWT) and n = 12 (B2MMUT)), and endometrium carcinoma (UCEC; n = 118 (B2MWT) and n = 4 (B2MMUT)).