Differential CD40L expression in different CD4 T cells compartments in carriers and recipients post-HSCT. (A) Representative flow cytometry plot demonstrating CD40L expression in different CD4 T-cell immune compartments at baseline and after stimulation; CD40L expression in cTfh cells is increased when compared with total CD4 of CD40L carriers and minimal expression of CD40L in Tregs. (B-C) Fold change in CD40L expression in cTfh, CXCR5⁺PD1-memory CD4, Tregs, and non-Treg CD4 cells relative to CD40L expression in total CD4 cells in healthy donors (HD), CD40L carriers, and recipients after HSCT. One-way analysis of variance with multiple comparison test was used for calculating the significant differences between groups. *P < .05; **P < .01; ***P < .001; ****P < .0001; ns, not significant.