(A) Human naive CD4⁺ T cells cultured under Tfh conditions in the presence or absence of P2X channel blockers (oATP, A438079) or the activator BzATP for 5 days. Frequencies of ICOS⁺CXCR5⁺ cells as percentage of CD4⁺ cells are shown as representative contour plots and summary data from 4 experiments. (B) Human total T cells of the different ENTPD1 SNP genotypes were cultured under Tfh conditions with indicated blocking antibody for 5 days. Frequencies of ICOS CXCR5⁺ cells as percentage of CD4⁺ cells are shown as contour plots for an individual typing AG for the ENTPD1 SNP (left); fold increases of ICOS⁺CXCR5⁺ T cell frequencies due to CD39 or CD73 blocking are compared for AA versus AG/GG donors (right). (C) Human naive CD4⁺ cells were activated with anti-CD3/anti-CD28 beads and in parallel transduced with Ctrl or ENTPD1-expressing lentivirus. On day 1.5, cells were enriched for successfully transduced GFP⁺ cells and then cultured on anti-CD3–coated plates in the presence of isotype control or anti-CD73 antibodies under Tfh condition for a total of 5 days. Results are shown as representative contour plots (left) and data from 3 experiments (right). (D) Human naive CD4⁺ cells were cultured under Tfh conditions with indicated small molecules for 5 days; cells were analyzed by flow cytometry. Representative contour plots and data from 5 experiments are shown. Data are shown as mean ± SEM and were compared by 2-tailed unpaired t test (A–C) or 1-way ANOVA with post hoc Tukey’s test (D). *P < 0.05, **P ≤ 0.01; ***P ≤ 0.001. NS, not significant.