CTLA-4–positive cells are present after anti–PD-1 immunotherapy and focally contact HRS cells. Representative mIF images of core tissue biopsy samples from 3 patients with recurrent cHL after anti–PD-1 immunotherapy (A-C), from 1 patient after doxorubicin, bleomycin, vinblastine, and dacarbazine therapy (ABVD) (D), and from 1 patient after SCT (E), and showing the presence of CTLA-4–positive cells, including CTLA-4–positive T cells focally in contact with CD86-positive/PAX5-positive HRS cells. (F) Relapsed cHL cases (n = 18) have a large portion of HRS cells in contact with CTLA-4–positive cells (median, 54%; range, 13%-98%); this is greater (Mann-Whitney U test, P = .11) than the portion of HRS cells in contact with CTLA-4–positive cells among diagnostic cases (n = 20; median, 40%; range, 7%-76%). DAPI, 4′,6-diamidino-2-phenylindole.