High CD4⁺T-cell infiltration, a favorable prognostic factor in cHL, is associated with antitumor effects induced by PD-1 blockade therapy. (A) OS and PFS according to CD4⁺ T-cell infiltration. The survival of 76 patients with cHL who received first-line standard chemotherapy (doxorubicin, bleomycin, vinblastine, and dacarbazine) was examined. The cohort was divided by a cutoff value (high, CD4 ≥425, vs low, <425) determined by the ROC curve. **P < .01. (B-C) Representative staining pictures for MHC-II and CD4 (B) and computed tomographic imaging (C) in patients with cHL who received anti-PD-1 mAb (nivolumab). IHC was conducted on FFPE sections (3 µm thick). Patient CCC-43 (64-year-old male) received nivolumab monotherapy as fourth-line therapy. He achieved a partial response after 8 cycles of nivolumab (arrowheads), and his performance status improved from 3 to 2. Patient CCC-66 (56-year-old male) received nivolumab monotherapy as fourth-line therapy and achieved a PR after 8 cycles of nivolumab (arrowheads).