The KIR⁺ NK-cell subset of KIR-KIRL mismatched donors exerts higher cytotoxicity toward pediatric BCP-ALL than the corresponding KIR⁻ subset. (A) Sorted KIR⁺ and KIR⁻ NK cells of the 7 donors characterized in Table 1 were cocultured with NALM-16 or K562 cells as a control to determine the extent of in vitro cytotoxicity (E:T ratio 5:1). (B) Standardization of the data depicted in Figure 2A. Shown is the specific lysis of the KIR⁺ NK-cell subset minus the one of the corresponding KIR⁻ NK-cell subset. Data represent 6 independent experiments with 7 donors performed in triplicates. (C) Interactions of inhibitory KIRs with their cognate ligands determine the extent of NK-cell alloreactivity toward pediatric BCP-ALL. Alloreactivity of sorted KIR⁺ NKAES cells of the donors SNK14B, SNK15B, and SNK20B (KIR-KIRL mismatch), and SNK10P and SNK21BC (KIR-KIRL match) against NALM-16 was determined by in vitro cytotoxicity assays (E:T ratio 2:1) in the presence or absence of the common inhibitory KIR-blocking mAb, IPH2102. Data represent 5 independent experiments performed in triplicates.