Blocking of CD70⁺ decreases proliferation and IFN-γ secretion in donor T cells. (A) Schematic view of the proliferation assay performed on day 14 patient PBMCs (n = 6; 5 MUD and 1 sibling donor) after allo-HSCT and stimulated with recipient patient’s T-cell–depleted pretransplant PBMCs in the presence/absence of anti-human CD70 antibody. (B-C) Percentage of CFSE-CD8⁺ T cells (B) and CFSE-CD4⁺ T cells (C) measured after 5 days with no stimulation (unstim), in a mixed lymphocyte reaction (MLR) with isotype control, and in MLR with anti-CD70 antibody. (E) Schematic view of the IFN-γ secretion assay performed on day 14 PBMCs from allogeneic transplant patients (n = 6; 5 MUD and 1 sibling donor) in the presence/absence of anti-CD70 antibody. (E) IFN-γ secretion measured by ELISPOT for the various direct stimulation methods measured PBMCs of 6 patients who underwent allo-HSCT in the presence/absence of CD70 antibody. (F) Frequency (mean) of IFN-γ SFC per 1 × 10⁶ PBMCs after 5 days of stimulation followed by an overnight ELISPOT as indicated (n = 6; ∗P < .05). Statistical comparisons were made using 1-way ANOVA with Tukey multiple comparison test: ns, not significant; ∗P < .05; ∗∗P < .01. CFSE, Carboxyfluorescein succinimidyl ester; mab, monoclonal antibody; MUD, Matched Unrelated Donor.