Alloreactivity versus C2 missing target in case of expression of KIR2DS2. Case no. 9 was characterized by C2 KIR-ligand mismatch, because the patient expressed HLA-A*0201,*2402, -B*4001,*5101 (Bw6/Bw4), -C*0102,*0304 (C1), while the donor expressed HLA-A*02,*04, -B*40,*44 (Bw6/Bw4), -C*03,*02 (C1/C2). Thus KIR2DL1 represents the relevant inhibitory KIR. KIR2DS2 was found to be present by KIRtyping analysis, but no mAb can discriminate it from its inhibitory counterparts, KIR2DL2/3, which were also present. Dot plots (A) using 11PB6 (recognizing here KIR2DL1 only) followed by anti–IgG1-PE in combination with CH-L (anti-KIR2DL2/L3/S2), AZ158 (anti-KIR3DL1/2), and Z199 (anti-NKG2A), followed by anti-IgG2b/2a-FITC, are not completely informative to assess the size of the alloreactive subset. Activated NK-cells derived from the donor and the recipient (3 months after HSCT) are shown. (B) Cytolytic activity of activated NK cell populations derived from the donor (filled symbols) and from the recipient at the third month after HSCT (open symbols) was tested against patient leukemia blasts (CD10⁺ ALL, squares) and BM15 B-EBV cell line (Bw4⁺ and C1⁺) expressing the homozygous haplotype HLA-A*0101, -B*4901 (Bw4), -C*0701 (C1) (circles) at different E:T ratios as indicated. (C) representative NK cell clones, derived from the donor (no. 9D) and the recipient (no. 9R), characterized by KIR expression of either KIR2DL1 alone (9D-10 and 9R-129 clones) or KIR2DL1 in combination with KIR2DS2 (9D-6 and 9R-31 clones), were tested against patient leukemia blasts (■) or BM15 (□) at E:T ratio of 10:1. 9R-129 (D) and 9R-31 (E) were tested against 221-Cw4 and 221-Cw3 cell transfectants in the absence (□) or in the presence of anti-KIR2DL1 (HP-3E4, ), anti-KIR2DS2 (GL-183, ▫), or anti-HLA-I (a mixture of A6-136 and 6A4, ■) mAb, at E:T ratio of 5:1. Representative experiments are shown; the SD of the mean of the triplicates was less than 5%.