CD4 and Merkel cell skin cancer: In fact, approximately half of the PD-1+ TILs were CD4+ (Teff or Treg), which is consistent with studies of archival HNSCC, ovarian cancer, and Hodgkin lymphoma FFPE specimens studied by IHC/IF; [27, 30–32] and melanoma, renal cell carcinoma, and MCC specimens studied by flow cytometry [33–35].