Notably, several immune cell subtypes were found to increase BC risk, including naive CD4+ T cells (OR = 1.091, 95% CI = 1.029–1.156; P = .003) and HLA-DR on CD14+ monocytes (OR = 1.084, 95% CI = 1.020–1.151; P = .008). Here, CD4 is linked to breast cancer.