To understand how HLA-I levelsin tumors are associated with the tumor microenvironment (TME), weapplied xCell analysis21 on transcriptomedata to characterize all tumor samples with different cell type features(Figure S7a) and then identified cell typesthat are significantly affected by HLA-I RNA and protein expression.Among 64 different cell-type signatures, HLA-I is positively associatedwith CD8 T cells, CD4 T cells, dendritic cells, macrophages, and Bcells in most cancer types, and the associations were observed onboth RNA and protein levels (Figure 4A and Figure S7b). Here, CD4 is linked to cancer.