Decreased surface expression of CXCR4 and CD40L in stimulated UCB CD4⁺ T cells. CD4⁺ T cells were purified from each UCB and AB sample, stimulated for 20 hours and analyzed by flow cytometry for surface expression of (A) CXCR4 and (B) CD40L. Representative histograms of 4 UCB and 4 adults are shown.