A Phase 2 Trial of KIR-Mismatched Unrelated Donor Transplantation Using in Vivo T Cell Depletion with Antithymocyte Globulin in Acute Myelogenous Leukemia: Children's Oncology Group AAML05P1 Study.

Patients with acute myelogenous leukemia (AML) who undergo killer immunoglobulin-like receptor (KIR)-mismatched haploidentical hematopoietic stem cell transplantation (HSCT) have improved survival. Children's Oncology Group AAML05P1 is a prospective phase 2 trial of unrelated donor (URD) HSCT in which KIR typing of donors was available to the treating physician at donor selection, aiming to determine feasibility (defined as the ability to obtain donor samples from URDs and obtain KIR data before transplantation) of prospective selection of KIR-mismatched donors and effect on outcomes. Patients age ≤30 years with high-risk AML at presentation or relapsed AML were eligible; the study accrued 90 evaluable patients. After enrollment, as many as 5 potential URD samples were KIR-typed (including gene expression) in a central laboratory and results reported to the treating physician, who made the final donor selection. Cases were categorized as KIR-matched or KIR-mismatched using different published strategies. Overall survival (OS), disease-free survival (DFS), and relapse did not differ significantly by KIR mismatch status. Acute graft-versus-host disease (GVHD) was significantly lower in recipients of KIR-mismatched stem cells (35% versus 60%; P = .027). We examined DFS according to time to natural killer (NK) receptor recovery after HSCT. NK p44 recovery was significantly associated with KIR mismatch and with decreased DFS and increased relapse risk in multivariate Cox analysis (P = .006 and .009, respectively). We show that prospective selection of URD according to KIR type was feasible, acute GVHD was reduced, but survival did not differ using any model of KIR mismatch. However, the study enrolled mostly matched transplants, so ligand-ligand mismatch was rare, and thus the sample size was insufficient to determine potential benefit according to this model. Cord blood recipients demonstrated a trend toward improved DFS with KIR mismatch, but the study was not powered to detect a difference in this small subset of patients. Our data suggest that recovery of NK receptor expression might influence DFS after HSCT.

Impact of Natural Killer Cell-Associated Factors on Acute Leukemia Outcomes after Haploidentical Hematopoietic Stem Cell Transplantation with αß T Cell Depletion in a Pediatric Cohort.

The technique of αß T cell depletion (αßTCD) is a well-established method of hematopoietic stem cell transplantation (HSCT) for children with acute leukemia owing to the low rates of graft-versus-host disease and nonrelapse mortality (NRM). The graft-versus-leukemia effect is generally ascribed to natural killer (NK) cells conserved within the graft. It is not known whether NK-related factors affect the outcome of αßTCD HSCT, however. The aim of this retrospective study was to explore the impact of NK alloreactivity (based on donor-recipient killer immunoglobulin-like receptor [KIR] mismatch), graft NK cell dose, and blood NK cell recovery on day +30 post-HSCT on the incidences of leukemia relapse and NRM. The pediatric acute leukemia cohort comprised 295 patients who underwent their first HSCT from a haploidentical donor in complete remission. During post hoc analysis, the total cohort was divided into subcohorts by diagnosis (acute lymphoblastic leukemia [ALL]/acute myeloid leukemia [AML]), NK alloreactivity prediction (KIR match/KIR mismatch), graft NK cell dose (less than versus greater than the median value), and blood NK cell recovery on day +30 post-HSCT (less than versus greater than the median value). We also investigated the influence of serotherapy (antithymocyte globulin [ATG] group) versus abatacept + tocilizumab combination [aba+toci] group) on relapse risk in the context of KIR mismatch. The risks of relapse and NRM were calculated by the cumulative risk method, and groups were compared using the Gray test. Multivariate analysis revealed no apparent impact of predicted NK alloreactivity or any other studied NK cell-related factors for the entire cohort. For patients with AML, a significantly higher relapse risk associated with high NK cell graft content on the background of no predicted KIR mismatch (P = .002) was shown. Multivariate analysis confirmed this finding (P = .018); on the other hand, for the KIR-mismatched patients, there was a trend toward a lower risk of relapse associated with high NK cell dose. The use of ATG was associated with a trend toward reduced relapse risk (P = .074) in the AML patients. There was no significant impact of NK-related factors in the ALL patients. Overall, the evaluated NK-related factors did not show a clear and straightforward correlation with the key outcomes of HSCT in our cohort of children with acute leukemia. In practice, the data support prioritization of KIR-mismatched donors for patients with AML. Importantly, a potential interaction of KIR ligand mismatch and NK cell content in the graft was identified. Indirect evidence suggests that additional cellular constituents of the graft could influence the function of NK cells after HSCT and affect their role as graft-versus-leukemia effectors.

NK cell therapy for hematologic malignancies.

Natural killer (NK) cells are part of the innate immune system and represent the first line of defense against infections and tumors. In contrast to T cells, NK cells do not require prior antigen sensitization to induce cytotoxicity and do not cause graft-versus-host disease. These, along with other advantages, make NK cells an attractive candidate for adoptive cellular therapy. Herein, we describe the mechanisms of NK cell cytotoxicity, which is governed by an intricate balance between various activating and inhibitory receptors, including the killer cell immunoglobulin-like receptors (KIRs). We illustrate the advantages of NK alloreactivity as demonstrated in various types of hematopoietic stem cell transplants (HSCT), such as haploidentical, human leukocyte antigen-matched related or unrelated donor and umbilical cord blood transplant. We elaborate on different models used to predict NK cell alloreactivity in these studies, which are either based on the absence of the ligands for inhibitory KIRs, presence of activating NK cell receptors and KIR genes content in donors, or a combination of these. We will review clinical studies demonstrating anti-tumor efficacy of NK cells used either as a stand-alone immunotherapy or as an adjunct to HSCT and novel genetic engineering strategies to improve the anti-tumor activity of NK cells.

Natural killer cells in malignant hematology: A primer for the non-immunologist.

Natural killer cells were first described over 40years ago, but the last 15years has shown tremendous progress in our understanding of their biology and our ability to manipulate them for clinical therapeutic effect. Despite the increased understanding by clinicians and scientists investigating these cells, their biology remains a confusing subject for many because of the wide array of receptors, complex interactions, multiple models of predicting function, and contradictory data in the literature. While they are microscopically indistinguishable from T cells and share many of the same effector functions, their mechanisms of target recognition are completely distinct from yet complimentary to T cells. In this review we provide a basic understanding of NK cell biology and HLA recognition as compared and contrasted to T cells using a metaphor of border patrol and passports. We conclude with a summary of the evidence for NK cell effects in hematologic malignancies and describe new advances in NK cell immunotherapy aimed at improving these effects.

Cord Blood as a Source of Natural Killer Cells.

Cord blood (CB) offers several unique advantages as a graft source for hematopoietic stem cell transplantation (HSCT). The risk of relapse and graft vs. host disease after cord blood transplantation (CBT) is lower than what is typically observed after other graft sources with a similar degree of human leukocyte antigen mismatch. Natural killer (NK) cells have a well-defined role in both innate and adaptive immunity and as the first lymphocytes to reconstitute after HSCT and CBT, and they play a significant role in protection against early relapse. In this article, we highlight the uses of CB NK cells in transplantation and adoptive immunotherapy. First, we will describe differences in the phenotype and functional characteristics of NK cells in CB as compared with peripheral blood. Then, we will review some of the obstacles we face in using resting CB NK cells for adoptive immunotherapy, and discuss methods to overcome them. We will review the current literature on killer-cell immunoglobulin-like receptors ligand mismatch and outcomes after CBT. Finally, we will touch on current strategies for the use of CB NK cells in cellular immunotherapy.