In HLA-nonidentical bone marrow transplantation, we studied the characteristics of donor NK cells, recipient leukemia cells, and the cytokine environment that predict the antileukemia effects of allogeneic NK cells. We found that the risk of relapse in pediatric patients with hematologic malignancies was best predicted by a model taking into consideration the presence of inhibitory killer cell Ig-like receptors (KIRs) on the donor’s NK cells and the absence of corresponding KIR ligand in the recipient’s HLA repertoire (a receptor-ligand model). The risk of relapse was prognosticated less precisely by the Perugia donor-recipient KIR ligand-ligand mismatch model or by a natural cytotoxicity model. In contrast to the ligand-ligand model, we found that the new receptor-ligand model was accurate when analysis was applied to patients with lymphoid malignancy. These findings corroborate our observations that the recipient’s KIR repertoire, which was derived from highly purified, HLA-disparate CD34+ cells, resumed a donor-specific pattern within 3 mo of transplantation, but did not correlate evidently with the donor or recipient ligand repertoire. In an in vitro assay and an in vivo mouse model, human NK cell cytotoxicity toward human leukemia cells with 11q23 chromosomal rearrangement increased with the number of receptor-ligand mismatch pairs or prestimulation with IL-12 and IL-18. These findings provide new insights into the determinants of antileukemia effects of allogeneic NK cells and therapeutic strategies.

The repertoire of killer Ig-like receptors (KIRs) can be determined at the level of DNA, RNA, or surface protein expression for selection of blood stem cell donors. We compared genotyping and phenotyping of the four inhibitory KIRs that are important in transplantation for leukemia in 73 unrelated persons. In 5 (7%) of the 68 individuals in whom the KIR2DL1 gene was present and in 10 (15%) of the 67 in whom KIR3DL1 was present, the corresponding receptor was not expressed by NK cells, as determined by flow cytometry analysis. In contrast, one or both allelic forms of KIR2DL2/KIR2DL3 were expressed by a high proportion of NK cells in all 73 individuals. However if both KIR2DL2 and KIR2DL3 genes were present, KIR2DL3 was preferentially expressed, as transcripts of KIR2DL2 was not detectable by RT-PCR in 42% of these individuals. In total, repertoire assessment for the four KIRs by genotyping vs phenotyping was not in complete agreement in 18 (25%) of the 73 individuals. Furthermore, among the samples that tested positive for the expression of a certain KIR gene, the levels of transcripts and surface expression varied considerably as measured by both real-time quantitative PCR and flow cytometry analysis. Extension of this comparative analysis to include all 12 KIR family members showed that KIR2DL3 and KIR3DL2 were the only genes whose transcripts were consistently detectable. These results caution the use of genotyping alone for donor selection or leukemia-relapse prognostication because some KIRs may be expressed at a very low level.

Key Points HLA-DRB1*07:01 is associated with asparaginase hypersensitivity and anti-asparaginase antibodies. HLA-DRB1 alleles that confer high-affinity binding to asparaginase epitopes lead to a higher frequency of hypersensitivity.

Summary. Natural killer (NK) cell alloreactivity resulting from killer immunoglobulin‐like receptor (KIR) ligand incompatibility improves outcomes in patients receiving extensively T‐cell‐depleted bone marrow (BM) grafts. Patients with KIR ligand incompatibility are at risk for donor T‐cell alloreactivity. We investigated the relative significance of NK‐cell and T‐cell alloreactivity in 105 paediatric patients who received a minimally T‐cell‐depleted human leucocyte antigen‐non‐identical BM transplantation. Donor NK‐cell incompatibility did not improve patient outcome [engraftment, graft‐versus‐host disease (GVHD), relapse or overall survival]. In contrast, donor T‐cell incompatibility was a risk factor for acute GVHD, chronic GVHD and death. Thus, T‐cell alloreactivity dominated that of NK cells in minimally T‐cell‐depleted grafts.

Summary The main obstacles to successful haploidentical haematopoietic stem cell transplantation from a mismatched family member donor are delayed immune reconstitution, vulnerability to infections and severe graft‐versus‐host disease (GvHD). We designed a reduced‐intensity conditioning regimen that excluded total body irradiation and anti‐thymocyte globulin in order to expedite immune reconstitution after a CD3‐depleted haploidentical stem cell transplant. This protocol was used to treat 22 paediatric patients with refractory haematological malignancies. After transplantation, 91% of the patients achieved full donor chimaerism. They also showed rapid recovery of CD3+ T‐cells, T‐cell receptor (TCR) excision circle counts, TCRβ repertoire diversity and natural killer (NK)‐cells during the first 4 months post‐transplantation, compared with those results from a group of patients treated with a myeloablative conditioning regimen. The incidence and extent of viremia were limited and no lethal infection was seen. Only 9% of patients had grade 3 acute GvHD, while 27% patients had grade 1 and another 27% had grade 2 acute GvHD. This well‐tolerated regimen appears to accelerate immune recovery and shorten the duration of early post‐transplant immunodeficiency, thereby reducing susceptibility to viral infections. Rapid T‐cell reconstitution, retention of NK‐cells in the graft and induction of low grade GvHD may also enhance the potential anti‐cancer immune effect.