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

Refining eligibility criteria of unit selection for myeloablative cord blood transplantation in acute leukemia: Real-world experience of a referral center

The algorithm for cord blood (CB) unit selection is still somewhat ambiguous. We retrospectively analyzed 620 cases of acute leukemia between 2015 and 2020, who were treated with myeloablative single-unit umbilical CB transplantation (UCBT). We found that, when human leukocyte antigen (HLA) mismatch was ≤3/10, CD34⁺ cell dosage <0.83 × 10⁵/kg-considerably lower than prevalent guidelines-was permissible without affecting survival. Moreover, synergy between donor killer-cell immunoglobulin-like receptors (KIR) haplotypes-B and donor-recipient HLA-C mismatch protected against relapse-related mortality. We submit that minimum required CD34⁺ cell dosage can possibly be relaxed to broaden access to UCBT, and donor KIR genotyping should be considered during unit selection.

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.

Immunogenomics of Killer Cell Immunoglobulin-Like Receptor (KIR) and HLA Class I: Coevolution and Consequences for Human Health

Interactions of killer cell immunoglobin-like receptors (KIR) with human leukocyte antigens (HLA) class I regulate effector functions of key cytotoxic cells of innate and adaptive immunity. The extreme diversity of this interaction is genetically determined, having evolved in the ever-changing environment of pathogen exposure. Diversity of KIR and HLA genes is further facilitated by their independent segregation on separate chromosomes. That fetal implantation relies on many of the same types of immune cells as infection control places certain constraints on the evolution of KIR interactions with HLA. Consequently, specific inherited combinations of receptors and ligands may predispose to specific immune-mediated diseases, including autoimmunity. Combinatorial diversity of KIR and HLA class I can also differentiate success rates of immunotherapy directed to these diseases. Progress toward both etiopathology and predicting response to therapy is being achieved through detailed characterization of the extent and consequences of the combinatorial diversity of KIR and HLA. Achieving these goals is more tractable with the development of integrated analyses of molecular evolution, function, and pathology that will establish guidelines for understanding and managing risks. Here, we present what is known about the coevolution of KIR with HLA class I and the impact of their complexity on immune function and homeostasis.

Allele imputation for the killer cell immunoglobulin-like receptor KIR3DL1/S1

Highly polymorphic interaction of KIR3DL1 and KIR3DS1 with HLA class I ligands modulates the effector functions of natural killer (NK) cells and some T cells. This genetically determined diversity affects severity of infections, immune-mediated diseases, and some cancers, and impacts the course of immunotherapies, including transplantation. KIR3DL1 is an inhibitory receptor, and KIR3DS1 is an activating receptor encoded by the KIR3DL1/S1 gene that has more than 200 diverse and divergent alleles. Determination of KIR3DL1/S1 genotypes for medical application is hampered by complex sequence and structural variation, requiring targeted approaches to generate and analyze high-resolution allele data. To overcome these obstacles, we developed and optimized a model for imputing KIR3DL1/S1 alleles at high-resolution from whole-genome SNP data. We designed the model to represent a substantial component of human genetic diversity. Our Global imputation model is effective at genotyping KIR3DL1/S1 alleles with an accuracy ranging from 88% in Africans to 97% in East Asians, with mean specificity of 99% and sensitivity of 95% for alleles >1% frequency. We used the established algorithm of the HIBAG program, in a modification named Pulling Out Natural killer cell Genomics (PONG). Because HIBAG was designed to impute HLA alleles also from whole-genome SNP data, PONG allows combinatorial diversity of KIR3DL1/S1 with HLA-A and -B to be analyzed using complementary techniques on a single data source. The use of PONG thus negates the need for targeted sequencing data in very large-scale association studies where such methods might not be tractable.

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.

Harnessing CD16-Mediated NK Cell Functions to Enhance Therapeutic Efficacy of Tumor-Targeting mAbs

Simple Summary

Natural Killer (NK) cells play a major role in cancer immunotherapy based on tumor-targeting mAbs. NK cell-mediated tumor cell killing and cytokine secretion are powerfully stimulated upon interaction with IgG-opsonized tumor cells, through the aggregation of FcγRIIIA/CD16 IgG receptor. Advances in basic and translational NK cell biology have led to the development of strategies that, by improving mAb-dependent antitumor responses, may overcome the current limitations of antibody therapy attributable to tolerance, immunosuppressive microenvironment, and genotypic factors. This review provides an overview of the immunotherapeutic strategies being pursued to improve the efficacy of mAb-induced NK antitumor activity. The exploitation of antibody combinations, antibody-based molecules, used alone or combined with adoptive NK cell therapy, will be uncovered. Within the landscape of NK cell heterogeneity, we stress the role of memory NK cells as promising effectors in the next generation of immunotherapy with the aim to obtain long-lasting tumor control.

Abstract

Natural killer (NK) cells hold a pivotal role in tumor-targeting monoclonal antibody (mAb)-based activity due to the expression of CD16, the low-affinity receptor for IgG. Indeed, beyond exerting cytotoxic function, activated NK cells also produce an array of cytokines and chemokines, through which they interface with and potentiate adaptive immune responses. Thus, CD16-activated NK cells can concur to mAb-dependent “vaccinal effect”, i.e., the development of antigen-specific responses, which may be highly relevant in maintaining long-term protection of treated patients. On this basis, the review will focus on strategies aimed at potentiating NK cell-mediated antitumor functions in tumor-targeting mAb-based regimens, represented by (a) mAb manipulation strategies, aimed at augmenting recruitment and efficacy of NK cells, such as Fc-engineering, and the design of bi- or trispecific NK cell engagers and (b) the possible exploitation of memory NK cells, whose distinctive characteristics (enhanced responsiveness to CD16 engagement, longevity, and intrinsic resistance to the immunosuppressive microenvironment) may maximize therapeutic mAb antitumor efficacy.

Immune Reconstitution after Haploidentical Donor and Umbilical Cord Blood Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (HCT) is the only potentially curative therapy for a variety of hematologic diseases. However, this therapeutic platform is limited by an initial period when patients are profoundly immunocompromised. There is gradual immune recovery over time, that varies by transplant platform. Here, we review immune reconstitution after allogeneic HCT with a specific focus on two alternative donor platforms that have dramatically improved access to allogeneic HCT for patients who lack an HLA-matched related or unrelated donor: haploidentical and umbilical cord blood HCT. Despite challenges, interventions are available to mitigate the risks during the immunocompromised period including antimicrobial prophylaxis, modified immune suppression strategies, graft manipulation, and emerging adoptive cell therapies. Such interventions can improve the potential for long-term overall survival after allogeneic HCT.