KIR B donors improve the outcome for AML patients given reduced intensity conditioning and unrelated donor transplantation

The role and novel use of natural killer cells in graft-versus-leukemia reactions after allogeneic transplantation

Allogeneic hematopoietic cell transplantation (HCT) has transformed over the past several decades through enhanced supportive care, reduced intensity conditioning (RIC), improved human leukocyte antigen (HLA) typing, and novel graft-versus-host disease (GVHD)-prevention and treatment strategies. Most notably, the implementation of post-transplantation cyclophosphamide (PTCy) has dramatically increased the safety and availability of this life-saving therapy. Given reductions in nonrelapse mortality (NRM) with these advances, the HCT community has placed even greater emphasis on developing ways to reduce relapse - the leading cause of death after HCT. When using RIC HCT, protection from relapse relies predominantly on graft-versus-leukemia (GVL) reactions. Donor lymphocyte infusion (DLI), adoptive cellular therapy, checkpoint inhibition, and post-HCT maintenance strategies represent approaches under study that aim to augment or synergize with the GVL effects of HCT. Optimizing donor selection algorithms to leverage GVL represents another active area of research. Many of these strategies seek to harness the effects of T cells, which for decades were felt to be the primary mediators of GVL and the focus of investigation in relapse reduction. However, there is growing interest in capitalizing on the ability of natural killer (NK) cells to yield potent anti-tumor effects. A potential advantage of NK cell-based approaches over T cell-mediated is the potential to reduce NRM in addition to relapse. By decreasing infection, without increasing the risk of GVHD, NK cells may mitigate NRM, while still yielding relapse reduction through identification and clearance of cancer cells. Most T cell-focused relapse-prevention strategies must weigh the benefits of relapse reduction against the increased risk of NRM from GVHD. In contrast, NK cells have the potential to reduce both, potentially tipping the scales significantly in favor of survival. Here, we will review the role of NK cells in GVL, optimization of NK cell match or mismatch, and burgeoning areas of research in NK cell therapy such as adoptive transfer and chimeric antigen receptor (CAR) NK cells.

Donor KIR2DL1 Allelic Polymorphism Influences Posthematopoietic Progenitor Cell Transplantation Outcomes in the T Cell Depleted and Reduced Intensity Conditioning Setting

The majority of established KIR clinical assessment algorithms used for donor selection for hematopoietic progenitor cell transplantation (HPCT) evaluate gene content (presence/absence) of the KIR gene complex. In comparison, relatively little is known about the impact of KIR allelic polymorphism. By analyzing donors of T cell depleted (TcD) reduced intensity conditioning (RIC) HPCT, this study investigated the influence on post-transplant outcome of 2 polymorphic residues of the inhibitory KIR2DL1. The aim of this study was to expand upon existing research into the influence of KIR2DL1 allelic polymorphism upon post-transplant outcome. The effects of allele groups upon transplant outcomes were investigated within a patient cohort using a defined treatment protocol of RIC with TcD. Using phylogenetic data, KIR2DL1 allelic polymorphism was categorized into groups on the basis of variation within codons 114 and 245 (positive or negative for the following groups: KIR2DL1*002/001g, KIR2DL1*003, KIR2DL1*004g) and the identification of null alleles. The influence of these KIR2DL1 allele groups in hematopoietic progenitor cell transplantation (HPCT) donors was assessed in the post-transplant data of 86 acute myelogenous leukemia patients receiving RIC TcD HPCT at a single center. KIR2DL1 allele groups in the donor significantly impacted upon 5-year post-transplant outcomes in RIC TcD HPCT. Donor KIR2DL1*003 presented the greatest influence upon post-transplant outcomes, with KIR2DL1*003 positive donors severely reducing 5-year post-transplant overall survival (OS) compared to those receiving a transplant from a KIR2DL1*003 negative donor (KIR2DL1*003 pos versus neg: 27.0% versus 60.0%, P = .008, pc = 0.024) and disease-free survival (DFS) (KIR2DL1*003 pos versus neg: 23.5% versus 60.0%, P = .004, pc = 0.012), and increasing 5-year relapse incidence (KIR2DL1*003 pos versus neg: 63.9% versus 27.2%, P = .009, pc = 0.027). KIR2DL1*003 homozygous and KIR2DL1*003 heterozygous grafts did not present significantly different post-transplant outcomes. Donors possessing the KIR2DL1*002/001 allele group were found to significantly improve post-transplant outcomes, with donors positive for the KIR2DL1*004 allele group presenting a trend towards improvement. KIR2DL1*002/001 allele group (KIR2DL1*002/001g) positive donors improved 5-year OS (KIR2DL1*002/001g pos versus neg: 56.4% versus 27.2%, P = .009, pc = 0.024) and DFS (KIR2DL1*002/001g pos versus neg: 53.8% versus 25.5%, P = .018, pc = 0.036). KIR2DL1*004 allele group (KIR2DL1*004g) positive donors trended towards improving 5-year OS (KIR2DL1*004g pos versus neg: 53.3% versus 35.5%, P = .097, pc = 0.097) and DFS (KIR2DL1*004g pos versus neg: 50.0% versus 33.9%, P = .121, pc = 0.121), and reducing relapse incidence (KIR2DL1*004g pos versus neg: 33.1% versus 54.0%, P = .079, pc = 0.152). The presented findings suggest donor selection algorithms for TcD RIC HPCT should consider avoiding KIR2DL1*003 positive donors, where possible, and contributes to the mounting evidence that KIR assessment in donor selection algorithms should reflect the conditioning regime protocol used.

Increased donor inhibitory KIR are associated with reduced GVHD and improved survival following HLA-matched unrelated donor HCT in paediatric acute leukaemia

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell-mediated effects after haematopoietic stem cell transplantation (HCT). Previous work has shown that accounting for known KIR-KIRL interactions may identify donors with optimal NK cell-mediated alloreactivity in the adult transplant setting. Paediatric acute leukaemia patients were retrospectively analysed, and KIR-KIRL combinations and maximal inhibitory KIR ligand (IM-KIR) scores were determined. Clinical outcomes were examined using a series of graphs depicting clinical events and endpoints. The graph methodology demonstrated that prognostic variables significant in the occurrence of specific clinical endpoints remained significant for relevant downstream events. KIR-KIRL combinations were significantly predictive for reduced grade 3-4 aGVHD likelihood, in patients transplanted with increased inhibitory KIR gene content and IM-KIR = 5 scores. Improvements were also observed in associated outcomes for both ALL and AML patients, including relapse-free survival, GRFS and overall survival. This study demonstrates that NK cell KIR HLA interactions may be relevant to the paediatric acute leukaemia transplant setting. Reduction in aGVHD suggests KIR effects may extend beyond NK cells. Moving forward clinical trials utilizing donors with a higher iKIR should be considered for URD HCT in paediatric recipients with acute leukaemia to optimize clinical outcomes.

Donor KIR genotype based outcome prediction after allogeneic stem cell transplantation: no land in sight

Optimizing natural killer (NK) cell alloreactivity could further improve outcome after allogeneic hematopoietic cell transplantation (alloHCT). The donor's Killer-cell Immunoglobulin-like Receptor (KIR) genotype may provide important information in this regard. In the past decade, different models have been proposed aiming at maximizing NK cell activation by activating KIR-ligand interactions or minimizing inhibitory KIR-ligand interactions. Alternative classifications intended predicting outcome after alloHCT by donor KIR-haplotypes. In the present study, we aimed at validating proposed models and exploring more classification approaches. To this end, we analyzed samples stored at the Collaborative Biobank from HLA-compatible unrelated stem cell donors who had donated for patients with acute myeloid leukemia (AML) or myelodysplastic neoplasm (MDS) and whose outcome data had been reported to EBMT or CIBMTR. The donor KIR genotype was determined by high resolution amplicon-based next generation sequencing. We analyzed data from 5,017 transplants. The median patient age at alloHCT was 56 years. Patients were transplanted for AML between 2013 and 2018. Donor-recipient pairs were matched for HLA-A, -B, -C, -DRB1, and -DQB1 (79%) or had single HLA mismatches. Myeloablative conditioning was given to 56% of patients. Fifty-two percent of patients received anti-thymocyte-globulin-based graft-versus-host disease prophylaxis, 32% calcineurin-inhibitor-based prophylaxis, and 7% post-transplant cyclophosphamide-based prophylaxis. We tested several previously reported classifications in multivariable regression analyses but could not confirm outcome associations. Exploratory analyses in 1,939 patients (39%) who were transplanted from donors with homozygous centromeric (cen) or telomeric (tel) A or B motifs, showed that the donor cen B/B-tel A/A diplotype was associated with a trend to better event-free survival (HR 0.84, p=.08) and reduced risk of non-relapse mortality (NRM) (HR 0.65, p=.01). When we further dissected the contribution of B subtypes, we found that only the cen B01/B01-telA/A diplotype was associated with a reduced risk of relapse (HR 0.40, p=.04) while all subtype combinations contributed to a reduced risk of NRM. This exploratory finding has to be validated in an independent data set. In summary, the existing body of evidence is not (yet) consistent enough to recommend use of donor KIR genotype information for donor selection in routine clinical practice.

Systematic evaluation of donor-KIR/recipient-HLA interactions in HLA-matched hematopoietic cell transplantation for AML

ABSTRACT

In acute myeloid leukemia (AML), donor natural killer cell killer immunoglobulin-like receptors (KIR) and recipient HLA interactions may contribute to the graft-versus-leukemia effect of allogeneic hematopoietic cell transplantation (HCT). Analyses of individual KIR/HLA interactions, however, have yielded conflicting findings, and their importance in the HLA-matched unrelated donor (MUD) setting remains controversial. We systematically studied outcomes of individual donor-KIR/recipient-HLA interactions for HCT outcomes and empirically evaluated prevalent KIR genotypes for clinical benefit. Adult patients with AML (n = 2025) who received HCT with MUD grafts in complete remission reported to the Center for International Blood and Marrow Transplantation were evaluated. Only the donor-2DL2+/recipient-HLA-C1+ pair was associated with reduced relapse (hazard ratio [HR], 0.79; 95% confidence interval [CI], 0.67-0.93; P = .006) compared with donor-2DL2-/recipient-HLA-C1+ pair. However, no association was found when comparing HLA-C groups among KIR-2DL2+-graft recipients. We identified 9 prevalent donor KIR genotypes in our cohort and screened them for association with relapse risk. Genotype 5 (G5) in all recipients and G3 in Bw4+ recipients were associated with decreased relapse risk (HR, 0.52; 95% CI, 0.35-0.78; P = .002; and HR, 0.32; 95% CI, 0.14-0.72; P = .006; respectively) and G2 (HR 1.63, 95% CI, 1.15-2.29; P = .005) with increased relapse risk in C1-homozygous recipients, compared with other patients with the same ligand. However, we could not validate these findings in an external data set of 796 AML transplants from the German transplantation registry. Neither a systematic evaluation of known HLA-KIR interactions nor an empiric assessment of prevalent KIR genotypes demonstrated clinically actionable associations; therefore, these data do not support these KIR-driven strategies for MUD selection in AML.

A retrospective analysis to evaluate if KIR B haplotype donors associate with a reduced risk of relapse in patients with haematological malignancies following haploidentical transplantation at the Blood and Bone Marrow Transplant Unit at Hammersmith Hospital ICHNHST

Relapse is a major cause of treatment failure in haploidentical haematopoietic progenitor cell transplant (HPCT) with PTCy. Natural killer cells suppress graft versus host disease and mediate the graft versus leukaemia effect, driven by killer cell immunoglobulin-like receptors (KIRs). Emerging research suggests that donor KIR genotype may influence graft outcome in haploidentical transplants with varying impacts between patient cohorts. This study investigates whether donors with greater KIR B motifs associate with outcomes such as greater relapse-free survival (RFS), overall survival (OS), nonrelapse mortality (NRM), acute graft versus host disease (GvHD) and infection. The study cohort included 98 haploidentical donor-recipient (D/R) pairs (myeloablative n = 37, RIC n = 61) with various haematological malignancies, receiving primary T-cell replete haploidentical HSCT with PTCγ. Following KIR SSO genotyping, donors are categorised into neutral (n = 63) or better and best (n = 35), based on KIR B motif content. Kaplan-Meier and Cox regression survival functions are performed to investigate associations with outcomes. Our results show that the better and best category has significantly poorer RFS (p = 0.013; hazard ratio [HR] 3.16, 95% CI 1.21-8.24: p = 0.018). The greater risk of relapse associated with poorer OS (p = 0.011; HR 2.24, 95% CI 1.18-4.24: p = 0.01) in the better and best category. The competing KIR receptor-ligand and missing licensing proof models failed to predict transplant outcomes. Here, we show neutral donors associate with favourable outcomes in T-cell replete haplo-HPCT with PTCγ after categorisation using the KIR B content model, due to the increased risk of relapse associated with the use of better and best donors.

Targeting KIR as a novel approach to improve CAR-NK cell function

Chimeric antigen receptor (CAR) NK cells are demonstrating promising activity in clinical trials and possess a favorable safety profile compared to CAR-T cells. The Killer cell Immunoglobulin-like Receptors (KIR) have a critical role in the control of NK cell function, and recently, this family of activating and inhibitory receptors have been targeted to improve CAR-NK function. These strategies include the utilisation of inhibitory KIR to reduce trogocytosis-associated NK cell fratricide, the downregulation of inhibitory KIR on CAR-NK cells to alleviate HLA mediated suppression, the selection of CAR-NK cell donors enriched for activating KIR, and the use of activating KIR intracellular domains within novel CAR constructs. These pre-clinical studies demonstrate the potential utility of targeting the KIR to improve CAR-NK cell efficacy and patient outcomes.

Crosstalk of Mast Cells and Natural Killer Cells with Neurons in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major comorbidity of cancer. Multiple clinical interventions have been studied to effectively treat CIPN, but the results have been disappointing, with no or little efficacy. Hence, understanding the pathophysiology of CIPN is critical to improving the quality of life and clinical outcomes of cancer patients. Although various mechanisms of CIPN have been described in neuropathic anti-cancer agents, the neuroinflammatory process involving cytotoxic/proinflammatory immune cells remains underexamined. While mast cells (MCs) and natural killer (NK) cells are the key innate immune compartments implicated in the pathogenesis of peripheral neuropathy, their role in CIPN has remained under-appreciated. Moreover, the biology of proinflammatory cytokines associated with MCs and NK cells in CIPN is particularly under-evaluated. In this review, we will focus on the interactions between MCs, NK cells, and neuronal structure and their communications via proinflammatory cytokines, including TNFα, IL-1β, and IL-6, in peripheral neuropathy in association with tumor immunology. This review will help lay the foundation to investigate MCs, NK cells, and cytokines to advance future therapeutic strategies for CIPN.

Prospects and Advances in Adoptive Natural Killer Cell Therapy for Unmet Therapeutic Needs in Pediatric Bone Sarcomas

Malignant bone tumors are aggressive tumors, with a high tendency to metastasize, that are observed most frequently in adolescents during rapid growth spurts. Pediatric patients with malignant bone sarcomas, Ewing sarcoma and osteosarcoma, who present with progressive disease have dire survival rates despite aggressive therapy. These therapies can have long-term effects on bone growth, such as decreased bone mineral density and reduced longitudinal growth. New therapeutic approaches are therefore urgently needed for targeting pediatric malignant bone tumors. Harnessing the power of the immune system against cancer has improved the survival rates dramatically in certain cancer types. Natural killer (NK) cells are a heterogeneous group of innate effector cells that possess numerous antitumor effects, such as cytolysis and cytokine production. Pediatric sarcoma cells have been shown to be especially susceptible to NK-cell-mediated killing. NK-cell adoptive therapy confers numerous advantages over T-cell adoptive therapy, including a good safety profile and a lack of major histocompatibility complex restriction. NK-cell immunotherapy has the potential to be a new therapy for pediatric malignant bone tumors. In this manuscript, we review the general characteristics of osteosarcoma and Ewing sarcoma, discuss the long-term effects of sarcoma treatment on bones, and the barriers to effective immunotherapy in bone sarcomas. We then present the laboratory and clinical studies on NK-cell immunotherapy for pediatric malignant bone tumors. We discuss the various donor sources and NK-cell types, the engineering of NK cells and combinatorial treatment approaches that are being studied to overcome the current challenges in adoptive NK-cell therapy, while suggesting approaches for future studies on NK-cell immunotherapy in pediatric bone tumors.

Clinical impact of KIR haplotypes in 10/10 HLA-matched unrelated donor-recipient pairs undergoing allogeneic hematopoietic stem cell transplantation

To evaluate the impact of killer immunoglobulin-like receptor (KIR) genotyping in allogeneic hematopoietic stem cell transplantation for myeloid disorders at our institution, retrospective KIR genotyping was performed on 77 patients and their 10/10 matched unrelated donors. In a multivariate model including donor age, HLA-DPB1 permissiveness, and presence of donor KIR B/x, an association with overall survival was observed (p = .047). Within the model, increasing donor age increased risk (RR 1.03 [1.00-1.06]/year, p = .046), while donor KIR and HLA-DPB1 permissiveness were not associated with risk (RR 0.51 [0.26-1.03] and RR 0.68 [0.34-1.36]). Grouping recipients by conditioning regimen or limiting the analysis to recipients of peripheral blood stem cells, no association between donor KIR and survival or relapse was identified. No significant associations were observed between overall survival, relapse, grade III-IV acute, or chronic graft versus host disease and presence of KIR B (B/x), quantity of donor KIR B haplotype motifs, or centromeric KIR type (all p > .05).

Human natural killer cells: Form, function, and development

Human natural killer (NK) cells are innate lymphoid cells that mediate important effector functions in the control of viral infection and malignancy. Their ability to distinguish "self" from "nonself" and lyse virally infected and tumorigenic cells through germline-encoded receptors makes them important players in maintaining human health and a powerful tool for immunotherapeutic applications and fighting disease. This review introduces our current understanding of NK cell biology, including key facets of NK cell differentiation and the acquisition and execution of NK cell effector function. Further, it addresses the clinical relevance of NK cells in both primary immunodeficiency and immunotherapy. It is intended to provide an up-to-date and comprehensive overview of this important and interesting innate immune effector cell subset.

Current donor selection strategies for allogeneic hematopoietic cell transplantation

Since the first allogeneic hematopoietic stem cell transplantation (HCT) was performed by Dr. E. Donnall Thomas in 1957, the field has advanced with new stem cell sources, immune suppressive regimens, and transplant protocols. Stem cells may be collected from bone marrow, peripheral or cord blood from an identical twin, a sibling, or a related or unrelated donor, which can be human leukocyte antigen (HLA) matched, mismatched, or haploidentical. Although HLA matching is one of the most important criteria for successful allogeneic HCT (allo-HCT) to minimize graft vs host disease (GVHD), prevent relapse, and improve overall survival, the novel immunosuppressive protocols for GVHD prophylaxis offered improved outcomes in haploidentical HCT (haplo-HCT), expanding donor availability for the majority of HCT candidates. These immunosuppressive protocols are currently being tested with the HLA-matched and mismatched donors to improve HCT outcomes further. In addition, fine-tuning the DPB1 mismatching and discovering the B leader genotype and mismatching may offer further optimization of donor selection and transplant outcomes. While the decision about a donor type largely depends on the patient's characteristics, disease status, and the transplant protocols utilized by an individual transplant center, there are general approaches to donor selection dictated by donor-recipient histocompatibility and the urgency for HCT. This review highlights recent advances in understanding critical factors in donor selection strategies for allo-HCT. It uses clinical vignettes to demonstrate the importance of making timely decisions for HCT candidates.

Donor selection based on NK alloreactivity for patients with hematological malignancies

Natural killer (NK) cells are an important defender against infections and tumors. Their function is regulated by the balance of inhibitory and activating receptors. Among all inhibitory NK receptors: killer immunoglobulin-like receptors (KIR) and CD94/NKG2A recognize human leukocyte antigen (HLA) Class I molecules, allowing NK cells to be 'licensed' to avoid autoreactivity, but be fully functional at the same time. Licensed NK cells can target malignant cells with altered or downregulated/missing 'self' antigens. NK cell attacking malignant cells is one of the mechanisms of graft-versus-leukemia (GVL) effect. Numerous studies have demonstrated that NK cells improve hematopoietic stem cell transplantation (HCT) survival by reducing relapse mortality through GVL effect. Therapeutic strategies, such as adoptive alloreactive NK cell transfer, CAR-NK cells, antibodies against NKG2A and KIR2DL1-3, have been utilized to treat hematological malignancies in HCT. In this review, NK cell functions, NK cell receptors and ligands, as well as common alloreactive NK donor selection algorithms for patients with hematological malignancies in the setting of HCT are discussed. The goal of this review is to provide insights on the controversial results and provide better understanding and resources on how to perform alloreactive donor NK cell selection in HCT.

KIR2DS2 Expression Identifies NK Cells With Enhanced Anticancer Activity

NK cells are promising cellular therapeutics against hematological and solid malignancies. Immunogenetic studies have identified that various activating killer cell Ig-like receptors (KIRs) are associated with cancer outcomes. Specifically, KIR2DS2 has been associated with reduced incidence of relapse following transplant in hematological malignancies and improved outcomes in solid tumors, but the mechanism remains obscure. Therefore, we investigated how KIR2DS2 expression impacts NK cell function. Using a novel flow cytometry panel, we show that human NK cells with high KIR2DS2 expression have enhanced spontaneous activation against malignant B cell lines, liver cancer cell lines, and primary chronic lymphocytic leukemia cells. Surface expression of CD16 was increased on KIR2DS2high NK cells, and, accordingly, KIR2DS2high NK cells had increased activation against lymphoma cells coated with the clinically relevant anti-CD20 Abs rituximab and obinutuzumab. Bulk RNA sequencing revealed that KIR2DS2high NK cells have upregulation of NK-mediated cytotoxicity, translation, and FCGR gene pathways. We developed a novel single-cell RNA-sequencing technique to identify KIR2DS2+ NK cells, and this confirmed that KIR2DS2 is associated with enhanced NK cell-mediated cytotoxicity. This study provides evidence that KIR2DS2 marks a population of NK cells primed for anticancer activity and indicates that KIR2DS2 is an attractive target for NK-based therapeutic strategies.

Practical Considerations and Workflow in Utilizing KIR Genotyping in Transplantation Medicine

This chapter is intended to serve as a practical guide for establishing a workflow using sequence-specific polymorphism PCR (SSP-PCR) for killer cell immunoglobulin-like receptor (KIR) genotyping in a clinical setting, especially in allogeneic hematopoietic stem cell transplantation (HSCT). As clinical evidence accumulates on the application of KIR and HLA genetics to guide donor selection in HSCT, there is an increasing need for KIR genotyping in clinical settings, and thus medical institutes may need to build this capability. Among the various KIR genotyping approaches now available, SSP-PCR methods are well-established and are the most cost-effective and will likely be the method of choice especially when expenses will be passed on to the patient. The protocol described in this chapter developed by Vilches et al. features small amplicon PCR and is suitable for KIR genotyping using FFPE-derived DNA as well as DNA extracted from blood samples. Setting up a laboratory workflow for in-house KIR genotyping is relatively straightforward; in this chapter, considerations for KIR genotyping to guide clinical decisions are discussed.In HSCT, a main objective of KIR genotyping is to apply the genetic analysis to predict donor and recipient combinations that have the most potential to produce NK cell alloresponses either through the missing-self mechanism or by action associated with activating KIR. The desired effects are reduction in acute GVHD and relapse rates and enhancement of overall survival. The information herein may also be useful to clinical laboratories considering the application of KIR genotyping in areas such as solid organ transplantation, NK cell-based treatment in other forms of cancer and autoimmune diseases, humanized antibody treatment, regenerative medicine, and reproductive medicine. Some background knowledge on KIR genetics will be necessary in managing a KIR genotyping platform. This chapter aims to address the main difficulties often encountered by physicians in understanding the KIR system, such as basic aspects of the nomenclature of KIR genes and haplotypes, genotypes, and determining presence/absence of KIR ligands in the patient and donor from the extensively diversified HLA class I allotypes. In describing the workflow, emphasis has been placed on the processes after genotype PCR and gel image acquisition: haplotype inference, generating B content scores, deduction of KIR ligands from HLA typing results, and the emerging algorithms for donor selection based on KIR and HLA genetics.

Donor activating killer cell immunoglobulin-like receptors genes correlated with Epstein-Barr virus reactivation after haploidentical haematopoietic stem cell transplantation

Natural killer (NK) cells exert anti-viral effects after haematopoietic stem cell transplantation (HSCT). The balance between inhibition and activation of NK cells determined by the inherited repertoire of killer cell immunoglobulin-like receptors (KIR) genes may influence Epstein-Barr virus (EBV) reactivation after transplantation. To evaluate the relative contributions of KIR genotypes to EBV reactivation, we prospectively enrolled 300 patients with malignant haematological disease who were suitable for haploidentical HSCT. Univariate analysis showed that donors with KIR2DS1, KIR2DS3 or KIR3DS1 genes were associated with an increased risk of EBV reactivation [hazard ratio (HR) 1·86, 95% confidence interval (CI) 1·19-2·9, P = 0·0067; HR 1·78, 95% CI 1·07-2·97, P = 0·027; HR 1·86, 95% CI 1·19-2·91, P = 0·0065 respectively]. Multivariate analysis revealed that the presence of KIR2DS1, KIR2DS3 or KIR3DS1 genes was associated with increased EBV reactivation after HSCT. This effect was more evident in the absence of the cognate ligands for the corresponding activating receptors. Our present data firstly showed that donors with activating KIR genes, specifically activating KIR2DS1, KIR2DS3 and KIR3DS1, had an increased risk of EBV reactivation. Precaution for patients whose donors carry activating genes will help prevent EBV reactivation and improve patient prognosis after HSCT.

Key Activating and Inhibitory Ligands Involved in the Mobilization of Natural Killer Cells for Cancer Immunotherapies

Natural killer (NK) cells are the most potent arm of the innate immune system and play an important role in immunity, alloimmunity, autoimmunity, and cancer. NK cells recognize “altered-self” cells due to oncogenic transformation or stress due to viral infection and target to kill them. The effector functions of NK cells depend on the interaction of the activating and inhibitory receptors on their surface with their cognate ligand expressed on the target cells. These activating and inhibitory receptors interact with major histocompatibility complex I (MHC I) expressed on the target cells and make decisions to mount an immune response. NK cell immune response includes cytolytic activity and secretion of cytokines to help with the ongoing immune response. The advancement of our knowledge on the expression of inhibitory and activating molecules led us to exploit these molecules in the treatment of cancer. This review discusses the importance of activating and inhibitory receptors on NK cells and their clinical importance in cancer immunotherapy.

Effect of Donor NKG2D Polymorphism on Relapse after Haploidentical Transplantation with Post-Transplantation Cyclophosphamide

NKG2D-mediated cytotoxicity is regulated by the single nucleotide polymorphism rs1049174, and its antitumor effect has been observed in various clinical settings. There are no previously published data on the influence of donor rs1049174 polymorphism on HLA-haploidentical allogeneic hematopoietic cell transplantation using post-transplantation cyclophosphamide (PTCy-haplo). We aimed to investigate the effect of donor NKG2D gene polymorphism on PTCy-haplo recipients. We retrospectively reviewed 91 consecutive PTCy-haplo recipients at our institution, and genotyped rs1049174 of the NKG2D gene in both donors and patients. In the patients who received PTCy without antithymocyte globulin (ATG) as graft-versus-host disease prophylaxis, the 2-year cumulative incidence of relapse/progression (RI) of PTCy-haplo from rs1049174 CC donors was lower than that from rs1049174 CG/GG donors (25.0% versus 52.4%; P = .041), and rs1049174 CC donors were associated with a decreased risk of relapse/progression (adjusted hazard ratio, 0.2; 95% confidence interval, 0.0 to 0.6; P = .007). Furthermore, a beneficial effect of rs1049174 CC donor on OS and RI was observed in non-acute myelogenous leukemia patients. This study demonstrates that receipt of PTCy-haplo from rs1049174 CC donors was associated with a decreased risk of relapse/progression in the patients who underwent PTCy-haplo without ATG. Future large-scale validation studies are needed to test the significance of donor NKG2D polymorphism in the development of a new donor selection algorithm for PTCy-haplo. © 2021 American Society for Transplantation and Cellular Therapy. Published by Elsevier Inc.

Influence of Killer Immunoglobulin-Like Receptors and Somatic Mutations on Transplant Outcomes in Acute Myeloid Leukemia

Natural killer (NK) cells are regulated by killer immunoglobulin-like receptor (KIR) interactions with human leukocyte antigen class I ligands. Various models of NK cell alloreactivity have been associated with outcomes after allogeneic hematopoietic cell transplant (alloHCT), but results have varied widely. We hypothesized that somatic mutations in acute myeloid leukemia (AML) in the context of KIR profiles may further refine their association with transplant outcomes. In this single-center, retrospective, observational study, 81 AML patients who underwent matched-related donor alloHCT were included. Post-HCT outcomes were assessed based on mutational status and KIR profiles with the Kaplan-Meier method and log-rank test. On multivariable analysis those with any somatic mutations and C1/C2 heterozygosity had less acute graft-versus-host disease (GvHD) (hazard ratio [HR], 0.32; 95% confidence interval [CI], 0.14-0.75; P = .009), more relapse (HR, 3.02; 95% CI, 1.30-7.01; P = .010), inferior relapse-free survival (RFS; (HR, 2.22; 95% CI, 1.17-4.20; P = .014), and overall survival (OS; HR, 2.21; 95% CI, 1.17-4.20; P = .015), whereas those with a missing KIR ligand had superior RFS (HR, 0.53; 95% CI, 0.30-0.94; P = .031). The presence of a somatic mutation and donor haplotype A was also associated with less acute GvHD (HR, 0.38; 95% CI, 0.16-0.92; P = .032), more relapse (HR, 2.72; 95% CI, 1.13-6.52; P = .025), inferior RFS (HR, 2.11; 95% CI, 1.07-4.14; P = .030), and OS (HR, 2.20; 95% CI, 1.11-4.38; P = .024). Enhanced NK cell alloreactivity from more KIR activating signals (donor B haplotype) and fewer inhibitory signals (recipient missing KIR ligand or C1 or C2 homozygosity) may help mitigate the adverse prognosis associated with some AML somatic mutations. These results may have implications for improving patient risk stratification prior to transplant and optimizing donor selection.

Relevance of Polymorphic KIR and HLA Class I Genes in NK-Cell-Based Immunotherapies for Adult Leukemic Patients

Simple Summary

Immunotherapies are promising approaches to curing different acute leukemias. Natural killer (NK) cells are lymphocytes that are efficient in the elimination of leukemic cells. NK-cell-based immunotherapies are particularly attractive, but the landscape of the heterogeneity of NK cells must be deciphered. This review provides an overview of the polymorphic KIR and HLA class I genes that modulate the NK cell repertoire and how these markers can improve the outcomes of patients with acute leukemia. A better knowledge of these genetic markers that are linked to NK cell subsets that are efficient against hematological diseases will optimize hematopoietic stem-cell donor selection and NK immunotherapy design.

Abstract

Since the mid-1990s, the biology and functions of natural killer (NK) cells have been deeply investigated in healthy individuals and in people with diseases. These effector cells play a particularly crucial role after allogeneic hematopoietic stem-cell transplantation (HSCT) through their graft-versus-leukemia (GvL) effect, which is mainly mediated through polymorphic killer-cell immunoglobulin-like receptors (KIRs) and their cognates, HLA class I ligands. In this review, we present how KIRs and HLA class I ligands modulate the structural formation and the functional education of NK cells. In particular, we decipher the current knowledge about the extent of KIR and HLA class I gene polymorphisms, as well as their expression, interaction, and functional impact on the KIR⁺ NK cell repertoire in a physiological context and in a leukemic context. In addition, we present the impact of NK cell alloreactivity on the outcomes of HSCT in adult patients with acute leukemia, as well as a description of genetic models of KIRs and NK cell reconstitution, with a focus on emergent T-cell-repleted haplo-identical HSCT using cyclosphosphamide post-grafting (haplo-PTCy). Then, we document how the immunogenetics of KIR/HLA and the immunobiology of NK cells could improve the relapse incidence after haplo-PTCy. Ultimately, we review the emerging NK-cell-based immunotherapies for leukemic patients in addition to HSCT.

KIR Receptors as Key Regulators of NK Cells Activity in Health and Disease

Natural killer (NK) cells are part of the cellular immune response. They target mainly cancer and virally infected cells. To a high extent cytotoxic activity of NK cells is regulated inter alia by signals from killer immunoglobulin-like receptors (KIR). The major histocompatibility complex (MHC) class I molecules are important ligands for KIR receptors. Binding of ligands (such as MHC I) to the KIR receptors has the important role in solid organ or hematopoietic cell transplantation. Of note, the understanding of the relationship between KIR and MHC receptors may contribute to the improvement of transplant results. Donor-recipient matching, which also includes the KIR typing, may improve monitoring, individualize the treatment and allow for predicting possible effects after transplantation, such as the graft-versus-leukemia effect (GvL) or viral re-infection. There are also less evident implications of KIR/MHC matching, such as with pregnancy and cancer. In this review, we present the most relevant literature reports on the importance of the KIR/MHC relationship on NK cell activity and hematopoietic stem cell transplantation (HSCT)/solid organ transplantation (SOT) effects, the risk of allograft rejection, protection against post-transplant cytomegalovirus (CMV) infection, pregnancy complications, cancer and adoptive therapy with NK cells.

Increased donor inhibitory KIR with known HLA interactions provide protection from relapse following HLA matched unrelated donor HCT for AML

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell-mediated graft versus leukemia effect (GVL) after hematopoietic cell transplant (HCT) for AML. Accounting for known KIR-KIRL interactions may identify donors with optimal NK cell-mediated alloreactivity and GVL. A retrospective study of 2359 donor-recipient pairs (DRP) who underwent unrelated donor (URD) HCT for AML was performed. KIR-KIRL combinations were determined and associations with clinical outcomes examined. Relapse risk was reduced in DRP with both higher inhibitory KIR-KIRL (iKIR) and missing KIRL (mKIR) scores, with HR 0.86 (P = 0.01) & HR 0.84 (P = 0.02) respectively. The iKIR and mKIR score components were summed to give a maximal inhibitory KIR ligand (IM-KIR) score for each donor, which if it was 5, as opposed to <5, was also associated with a lower relapse risk, SHR 0.8 (P = 0.004). All IM = 5 donors possess KIR Haplotype B/x. Transplant-related mortality was increased among those with IM-KIR = 5, HR, 1.32 (P = 0.01). In a subset analysis of those transplanted with 8/8 HLA-matched DRP, anti-thymocyte globulin recipients with IM-KIR = 5, had a lower relapse rate HR, 0.61 (p = 0.001). This study demonstrates that HLA-matched unrelated donors with the highest inhibitory KIR content confer relapse protection, albeit with increased TRM. These donors all have KIR haplotype B. Clinical trials utilizing donors with a higher iKIR content in conjunction with novel strategies to reduce TRM should be considered for URD HCT in recipients with AML to optimize clinical outcomes.

Prospective KIR genotype evaluation of hematopoietic cell donors is feasible with potential to benefit patients with AML

Donor KIR and recipient HLA combinations that minimize inhibition and favor activation of the NK repertoire are associated with improved outcomes after allogeneic hematopoietic cell transplantation (HCT) in patients with myeloid neoplasia. We prospectively evaluated a weighted donor ranking algorithm designed to prioritize HLA-compatible unrelated donors (URDs) with weak inhibitory KIR3DL1/HLA-Bw4 interaction, followed by donors with nontolerized activating KIR2DS1, and finally those with KIR centromeric B haplotype. During donor evaluation, we performed KIR genotyping and ranked 2079 URDs for 527 subjects with myelodysplastic syndrome (MDS) or acute myelogenous leukemia (AML). Among all patients, 394 (75%) had at least 1 KIR-advantageous donor, and 263 (50%) underwent HCT. In patients with AML, KIR3DL1 weak inhibition provided protection from relapse. Compared with KIR3DL1-Weak Inhibiting donors, KIR3DL1-Noninteracting donors were associated with increased risk of relapse (HR, 2.97; 95% CI, 1.33-6.64; P = .008) and inferior event-free survival (EFS; HR, 2.14; 95% CI, 1.16-3.95; P = .015). KIR3DL1-Strong Inhibiting donors were associated with HR, 1.65 (95% CI, 0.66-4.08; P = .25) for AML relapse and HR, 1.6 (95% CI, 0.81-3.17; P = .1) for EFS when compared with the use of KIR3DL1-weak inhibiting donors. Donor KIR2DS1/HLA-C1 status and centromeric KIR haplotype-B content were not associated with decreased risk of AML relapse. There was no benefit to KIR-based donor selection in patients with MDS. This study demonstrates that donor KIR typing is feasible, and prioritization of donors with certain KIR3DL1 genotypes may confer a protection from relapse after HCT in patients with AML.

Haplotype Motif-Based Models for KIR-Genotype Informed Selection of Hematopoietic Cell Donors Fail to Predict Outcome of Patients With Myelodysplastic Syndromes or Secondary Acute Myeloid Leukemia

Results from registry studies suggest that harnessing Natural Killer (NK) cell reactivity mediated through Killer cell Immunoglobulin-like Receptors (KIR) could reduce the risk of relapse after allogeneic Hematopoietic Cell Transplantation (HCT). Several competing models have been developed to classify donors as KIR-advantageous or disadvantageous. Basically, these models differ by grouping donors based on distinct KIR–KIR–ligand combinations or by haplotype motif assignment. This study aimed to validate different models for unrelated donor selection for patients with Myelodysplatic Syndromes (MDS) or secondary Acute Myeloid Leukemia (sAML). In a joint retrospective study of the European Society for Blood and Marrow Transplantation (EBMT) and the Center for International Blood and Marrow Transplant Research (CIBMTR) registry data from 1704 patients with secondary AML or MDS were analysed. The cohort consisted mainly of older patients (median age 61 years) with high risk disease who had received chemotherapy-based reduced intensity conditioning and anti-thymocyte globulin prior to allogeneic HCT from well-matched unrelated stem cell donors. The impact of the predictors on Overall Survival (OS) and relapse incidence was tested in Cox regression models adjusted for patient age, a modified disease risk index, performance status, donor age, HLA-match, sex-match, CMV-match, conditioning intensity, type of T-cell depletion and graft type. KIR genes were typed using high-resolution amplicon-based next generation sequencing. In univariable and multivariable analyses none of the models predicted OS and the risk of relapse consistently. Our results do not support the hypothesis that optimizing NK-mediated alloreactivity is possible by KIR-genotype informed selection of HLA-matched unrelated donors. However, in the context of allogeneic transplantation, NK-cell biology is complex and only partly understood. KIR-genes are highly diverse and current assignment of haplotype motifs based on the presence or absence of selected KIR genes is over-simplistic. As a consequence, further research is highly warranted and should integrate cutting edge knowledge on KIR genetics, and NK-cell biology into future studies focused on homogeneous groups of patients and treatment modalities.

Dual effects of natural killer cells in transplantation for leukemia

Natural killer (NK) cells were originally considered to belong to the innate immune system to play a protective role against tumor cells and viral infections. In human, they can recognize self and non-self HLA class 1 as their ligand. So, analyzing the outcomes of allogeneic hematopoietic stem cell transplantation is a good opportunity to know the antitumor effects and regulatory effects of NK cells through HLA class 1 matching and mismatching of donor and recipient. In this review, I looked back on the main analysis results of the past transplants, summarized our reports consisting of many cases in a single ethnic, and showed that NK cells might work oppositely depending on the type of leukemia. New treatment strategies based on these concepts may offer individualized treatment options and ultimately increase offer the possibility of a cure for patients with leukemia.

Centromeric KIR AA Individuals Harbor Particular KIR Alleles Conferring Beneficial NK Cell Features with Implications in Haplo-Identical Hematopoietic Stem Cell Transplantation

We have recently shown a broad disparity of Natural Killer (NK) cell responses against leukemia highlighting good and bad responders resting on the Killer cell Immunoglobulin-like Receptors (KIR) and HLA genetics. In this study, we deeply studied KIR2D allele expression, HLA-C recognition and functional effect on NK cells in 108 blood donors in combining high-resolution KIR allele typing and multicolor flow cytometry. The KIR2DL1*003 allotype is associated with centromeric (cen) AA motif and confers the highest NK cell frequency, expression level and strength of KIR/HLA-C interactions compared to the KIR2DL1*002 and KIR2DL1*004 allotypes respectively associated with cenAB and BB motifs. KIR2DL2*001 and *003 allotypes negatively affect the frequency of KIR2DL1⁺ and KIR2DL3⁺ NK cells. Altogether, our data suggest that cenAA individuals display more efficient KIR2DL alleles (L1*003 and L3*001) to mount a consistent frequency of KIR2DL⁺ NK cells and to confer an effective NK cell responsiveness. The transposition of our in vitro observations in the T-replete haplo-identical HSCT context led us to observe that cenAA HSC grafts limit significantly the incidence of relapse in patients with myeloid diseases after T-replete haplo-identical HSCT. As NK cells are crucial in HSCT reconstitution, one could expect that the consideration of KIR2DL1/2/3 allelic polymorphism could help to refine scores used for HSC donor selection.

Selection of allogeneic hematopoietic cell transplant donors to optimize natural killer cell alloreactivity

Natural killer (NK) cells are potent mediators of the graft versus leukemia phenomenon critical to the success of allogeneic hematopoietic cell transplantation. Central to calibrating NK effector function via their interaction with class I human leukocyte antigens are the numerous inhibitory killer Ig-like receptors (KIR). The KIR receptors are encoded by a family of polymorphic genes, whose expression is largely stochastic and uninfluenced by human leukocyte antigens genotype. These features provide the opportunity to select hematopoietic cell donors with favorable KIR genotypes that confer enhanced protection from relapse via NK-mediated graft versus leukemia. Over the last 2 decades, a large body of work has emerged examining the use of KIR genotyping to stratify potential donors based on anticipated NK alloreactivity. Overall, these results support KIR-based donor selection for patients undergoing allogeneic hematopoietic cell transplantation for a diagnosis of acute myelogenous leukemia. Despite this, the underlying factors that control NK cell responsiveness are not completely understood, and opportunities remain to refine donor selection using NK cell receptor genotyping. In this review, we will summarize the relevant findings with respect to KIR genotyping as a selection parameter for allogeneic hematopoietic cell donors and address practical considerations with respect to KIR-based selection of donors for patients with myeloid neoplasia.

Novel agents targeting leukemia cells and immune microenvironment for prevention and treatment of relapse of acute myeloid leukemia after allogeneic hematopoietic stem cell transplantation

Relapse remains the worst life-threatening complications after allogeneic hematopoietic stem cell transplantation (allo-HSCT) in patients with acute myeloid leukemia (AML), whose prognosis has been historically dismal. Given the rapid development of genomics and immunotherapies, the interference strategies for AML recurrence have been changing these years. More and more novel targeting agents that have received the U.S. Food and Drug Administration (FDA) approval for de novo AML treatment have been administrated in the salvage or maintenance therapy of post-HSCT relapse. Targeted strategies that regulate the immune microenvironment of and optimize the graft versus leukemia (GVL) effect of immune cells are gradually improved. Such agents not only have been proven to achieve clinical benefits from a single drug, but if combined with classic therapies, can significantly improve the poor prognosis of AML patients who relapse after allo-HSCT. This review will focus on currently available and promising upcoming agents and also discuss the challenges and limitations of targeted therapies in the allogeneic hematopoietic stem cell transplantation community.

Umbilical Cord Blood and iPSC-Derived Natural Killer Cells Demonstrate Key Differences in Cytotoxic Activity and KIR Profiles

Natural killer (NK) cells derived or isolated from different sources have been gaining in importance for cancer therapies. In this study, we evaluate and compare key characteristics between NK cells derived or isolated from umbilical cord blood, umbilical cord blood hematopoietic stem/progenitor cells, peripheral blood, and induced pluripotent stem cells (iPSCs). Specifically, we find CD56⁺ NK cells isolated and expanded directly from umbilical cord blood (UCB56) and NK cells derived from CD34⁺ hematopoietic stem/progenitors in umbilical cord blood (UCB34) differ in their expression of markers associated with differentiation including CD16, CD2, and killer Ig-like receptors (KIRs). UCB56-NK cells also displayed a more potent cytotoxicity compared to UCB34-NK cells. NK cells derived from iPSCs (iPSC-NK cells) were found to have variable KIR expression, with certain iPSC-NK cell populations expressing high levels of KIRs and others not expressing KIRs. Notably, KIR expression on UCB56 and iPSC-NK cells had limited effect on cytotoxic activity when stimulated by tumor target cells that express high levels of cognate HLA class I, suggesting that in vitro differentiation and expansion may override the KIR-HLA class I mediated inhibition when used across HLA barriers. Together our results give a better understanding of the cell surface receptor, transcriptional, and functional differences between NK cells present in umbilical cord blood and hematopoietic progenitor-derived NK cells which may prove important in selecting the most active NK cell populations for treatment of cancer or other therapies.

Inhibitory Receptors and Checkpoints in Human NK Cells, Implications for the Immunotherapy of Cancer

The highly destructive mechanisms by which the immune system faces microbial infections is under the control of a series of inhibitory receptors. While most of these receptors prevent unwanted/excessive responses of individual effector cells, others play a more general role in immunity, acting as true inhibitory checkpoints controlling both innate and adaptive immunity. Regarding human NK cells, their function is finely regulated by HLA-class I-specific inhibitory receptors which allow discrimination between HLA-I⁺, healthy cells and tumor or virus-infected cells displaying loss or substantial alterations of HLA-I molecules, including allelic losses that are sensed by KIRs. A number of non-HLA-specific receptors have been identified which recognize cell surface or extracellular matrix ligands and may contribute to the physiologic control of immune responses and tolerance. Among these receptors, Siglec 7 (p75/AIRM-1), LAIR-1 and IRp60, recognize ligands including sialic acids, extracellular matrix/collagen or aminophospholipids, respectively. These ligands may be expressed at the surface of tumor cells, thus inhibiting NK cell function. Expression of the PD-1 checkpoint by NK cells requires particular cytokines (IL-15, IL-12, IL-18) together with cortisol, a combination that may occur in the microenvironment of different tumors. Blocking of single or combinations of inhibitory receptors unleashes NK cells and restore their anti-tumor activity, with obvious implications for tumor immunotherapy.

Influence of KIR and NK Cell Reconstitution in the Outcomes of Hematopoietic Stem Cell Transplantation

Natural killer (NK) cells play a significant role in immune tolerance and immune surveillance. Killer immunoglobin-like receptors (KIRs), which recognize human leukocyte antigen (HLA) class I molecules, are particularly important for NK cell functions. Previous studies have suggested that, in the setting of hematopoietic stem cell transplantation (HSCT), alloreactive NK cells from the donor could efficiently eliminate recipient tumor cells and the residual immune cells. Subsequently, several clinical models were established to determine the optimal donors who would exhibit a graft-vs. -leukemia (GVL) effect without developing graft-vs. -host disease (GVHD). In addition, hypotheses about specific beneficial receptor-ligand pairs and KIR genes have been raised and the favorable effects of alloreactive NK cells are being investigated. Moreover, with a deeper understanding of the process of NK cell reconstitution post-HSCT, new factors involved in this process and the defects of previous models have been observed. In this review, we summarize the most relevant literatures about the impact of NK cell alloreactivity on transplant outcomes and the factors affecting NK cell reconstitution.

Phenotypic and Functional Characterization of NK Cells in αβT-Cell and B-Cell Depleted Haplo-HSCT to Cure Pediatric Patients with Acute Leukemia

NK cells can exert remarkable graft-versus-leukemia (GvL) effect in HLA-haploidentical hematopoietic stem cell transplantation (haplo-HSCT). Here, we dissected the NK-cell repertoire of 80 pediatric acute leukemia patients previously reported to have an excellent clinical outcome after αβT/B-depleted haplo-HSCT. This graft manipulation strategy allows the co-infusion of mature immune cells, mainly NK and γδT cells, and hematopoietic stem cells (HSCs). To promote NK-cell based antileukemia activity, 36/80 patients were transplanted with an NK alloreactive donor, defined according to the KIR/KIR-Ligand mismatch in the graft-versus-host direction. The analysis of the reconstituted NK-cell repertoire in these patients showed relatively high proportions of mature and functional KIR⁺NKG2A^-CD57⁺ NK cells, including the alloreactive NK cell subset, one month after HSCT. Thus, the NK cells adoptively transfused with the graft persist as a mature source of effector cells while new NK cells differentiate from the donor HSCs. Notably, the alloreactive NK cell subset was endowed with the highest anti-leukemia activity and its size in the reconstituted repertoire could be influenced by human cytomegalovirus (HCMV) reactivation. While the phenotypic pattern of donor NK cells did not impact on post-transplant HCMV reactivation, in the recipients, HCMV infection/reactivation fostered a more differentiated NK-cell phenotype. In this cohort, no significant correlation between differentiated NK cells and relapse-free survival was observed.