Flow and mass cytometry revealed relevant associations between certain WBC subtypes and ICI efficacy, such as high baseline T regulatory cells (Tregs) (FoxP3+CD4+ T cells) associating with ipilimumab (anti‐CTLA‐4) efficacy [22] and classical (CD14+CD16−) monocytes associating with anti‐PD1 efficacy in melanoma [27]. Here, CTLA4 is linked to melanoma.