CD4 and classic Hodgkin lymphoma: Interestingly, while in the setting of solid tumours the anticancer activity of PD-1 directed CPIs is mediated by the restoration of killer T-cell function, the usual lack of MCH-I expression in cHL makes this mechanism unlikely, turning our attention to CD4+ T-cells and the expression of MHC-II on the surface of HRSC, proven to be a key element in CPI response both by clinical and pathological data.