The KIR locus comprises centromeric (Cen) and telomeric (Tel) gene content motifs. (A) The organization of genes in the KIR locus. The centromeric and telomeric regions are separated by a unique recombination site (RS) sequence that can function to reassort the centromeric and telomeric gene motifs. The gene content of the common motifs is shown. The conserved framework genes are shaded gray, B haplotype genes are blue, and A haplotype genes are red. (B) Groups used for the Cen and Tel analysis on the basis of the content of the inhibitory (L-long) or activating (S-short) KIR genes, and their frequencies among donors in the AML and ALL cohorts. (C) KIR B–content score and the frequency of donors in each group. The KIR B–content score is calculated by adding the number of Cen-B and/or Tel-B motifs in each genotype.