The G allele of rs4553808 (allele model: p = 0.0452 for G vs. A, OR = 4.63, and 95% CI = 1.04–20.58), the A allele of rs62182595 (allele model: p = 0.0330 for A vs. G, OR = 5.19, and 95% CI = 1.15–23.4), the T allele of rs16840252 (allele model: p = 0.0350 for T vs. C, OR = 5.1, and 95% CI = 1.13–22.98), and the T allele of rs5742909 (allele model: p = 0.0479 for T vs. C, OR = 4.54, and 95% CI = 1.02–20.2) of the CTLA4 gene conferred better protective effects on the development of GVHD in patients with ALL. Here, CTLA4 is linked to acute lymphoblastic leukemia.