Comparison of ICOSLG, PDCD1, and PD-1 expression in CD37⁺and CD37⁻DLBCL. (A) CD37 positivity was associated with significantly higher levels of ICOSLG in GCB-DLBCL. (B) CD37 loss correlated with PDCD1 (PD-1) upregulation in ABC-DLBCL. (C) In p50^high (≥20% nuclear expression) DLBCL, CD37 loss correlated with PD-1 upregulation in both GCB- and ABC-DLBCL. (D-E) CD37 loss in DLBCL correlated with significantly higher levels of PD-1 receptor expression on both cytotoxic and helper T cells. (F) The ABC subtype had significantly higher CD274 (PD-L1) levels compared with the GCB subtype, which was more apparent in the CD37⁻ DLBCL subset.