Genetically Determined Strength of Natural Killer Cells is Enhanced by Adaptive HLA class I Admixture in East Asians

AbstractHuman natural killer (NK) cells are essential for controlling infection, cancer and fetal development. NK cell functions are modulated by interactions between polymorphic inhibitory killer cell immunoglobulin-like receptors (KIR) and polymorphic HLA-A, -B and -C ligands expressed on tissue cells. All HLA-C alleles encode a KIR ligand and contribute to reproduction and immunity. In contrast, only some HLA-A and -B alleles encode KIR ligands and they focus on immunity. By high-resolution analysis of KIR and HLA-A, -B and -C genes, we show that the Chinese Southern Han are significantly enriched for interactions between inhibitory KIR and HLA-A and -B. This enrichment has had substantial input through population admixture with neighboring populations, who contributed HLA class I haplotypes expressing the KIR ligands B*46:01 and B*58:01, which subsequently rose to high frequency by natural selection. Consequently, over 80% of Southern Han HLA haplotypes encode more than one KIR ligand. Complementing the high number of KIR ligands, the Chinese Southern Han KIR locus combines a high frequency of genes expressing potent inhibitory KIR, with a low frequency of those expressing activating KIR. The Southern Han centromeric KIR region encodes strong, conserved, inhibitory HLA-C specific receptors, and the telomeric region provides a high number and diversity of inhibitory HLA-A and -B specific receptors. In all these characteristics, the Southern Han represent other East Asians, whose NK cell repertoires are thus enhanced in quantity, diversity and effector strength, likely through natural selection for resistance to endemic viral infections.

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Adaptive Admixture of HLA class I Allotypes Enhanced Genetically Determined Strength of Natural Killer Cells in East Asians

Molecular Biology and Evolution ◽

10.1093/molbev/msab053 ◽

2021 ◽

Author(s):

Zhihui Deng ◽

Jianxin Zhen ◽

Genelle F Harrison ◽

Guobin Zhang ◽

Rui Chen ◽

...

Keyword(s):

Natural Killer ◽

High Frequency ◽

Nk Cell ◽

Killer Cell ◽

Hla Class I ◽

Class I ◽

Telomeric Region ◽

East Asians ◽

Cell Functions ◽

Specific Receptors

Abstract Human natural killer (NK) cells are essential for controlling infection, cancer and fetal development. NK cell functions are modulated by interactions between polymorphic inhibitory killer cell immunoglobulin-like receptors (KIR) and polymorphic HLA-A, -B and -C ligands expressed on tissue cells. All HLA-C alleles encode a KIR ligand and contribute to reproduction and immunity. In contrast, only some HLA-A and -B alleles encode KIR ligands and they focus on immunity. By high-resolution analysis of KIR and HLA-A, -B and -C genes, we show that the Chinese Southern Han are significantly enriched for interactions between inhibitory KIR and HLA-A and -B. This enrichment has had substantial input through population admixture with neighboring populations, who contributed HLA class I haplotypes expressing the KIR ligands B*46:01 and B*58:01, which subsequently rose to high frequency by natural selection. Consequently, over 80% of Southern Han HLA haplotypes encode more than one KIR ligand. Complementing the high number of KIR ligands, the Chinese Southern Han KIR locus combines a high frequency of genes expressing potent inhibitory KIR, with a low frequency of those expressing activating KIR. The Southern Han centromeric KIR region encodes strong, conserved, inhibitory HLA-C specific receptors, and the telomeric region provides a high number and diversity of inhibitory HLA-A and -B specific receptors. In all these characteristics, the Chinese Southern Han represent other East Asians, whose NK cell repertoires are thus enhanced in quantity, diversity and effector strength, likely augmenting resistance to endemic viral infections.

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High-Resolution Analysis Identifies High Frequency of KIR-A Haplotypes and Inhibitory Interactions of KIR With HLA Class I in Zhejiang Han

Frontiers in Immunology ◽

10.3389/fimmu.2021.640334 ◽

2021 ◽

Vol 12 ◽

Author(s):

Sudan Tao ◽

Yanmin He ◽

Katherine M. Kichula ◽

Jielin Wang ◽

Ji He ◽

...

Keyword(s):

High Resolution ◽

High Frequency ◽

Killer Cell ◽

Hla Class I ◽

Class I ◽

Gene Copy ◽

Human Populations ◽

Telomeric Region ◽

Cell Functions ◽

Hla Class I Molecules

Killer cell immunoglobulin-like receptors (KIR) interact with human leukocyte antigen (HLA) class I molecules, modulating critical NK cell functions in the maintenance of human health. Characterizing the distribution and characteristics of KIR and HLA allotype diversity across defined human populations is thus essential for understanding the multiple associations with disease, and for directing therapies. In this study of 176 Zhejiang Han individuals from Southeastern China, we describe diversity of the highly polymorphic KIR and HLA class I genes at high resolution. KIR-A haplotypes, which carry four inhibitory receptors specific for HLA-A, B or C, are known to associate with protection from infection and some cancers. We show the Chinese Southern Han from Zhejiang are characterized by a high frequency of KIR-A haplotypes and a high frequency of C1 KIR ligands. Accordingly, interactions of inhibitory KIR2DL3 with C1+HLA are more frequent in Zhejiang Han than populations outside East Asia. Zhejiang Han exhibit greater diversity of inhibitory than activating KIR, with three-domain inhibitory KIR exhibiting the greatest degree of polymorphism. As distinguished by gene copy number and allele content, 54 centromeric and 37 telomeric haplotypes were observed. We observed 6% of the population to have KIR haplotypes containing large-scale duplications or deletions that include complete genes. A unique truncated haplotype containing only KIR2DL4 in the telomeric region was also identified. An additional feature is the high frequency of HLA-B*46:01, which may have arisen due to selection pressure from infectious disease. This study will provide further insight into the role of KIR and HLA polymorphism in disease susceptibility of Zhejiang Chinese.

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Preclinical characterization of 1-7F9, a novel human anti–KIR receptor therapeutic antibody that augments natural killer–mediated killing of tumor cells

Blood ◽

10.1182/blood-2009-02-206532 ◽

2009 ◽

Vol 114 (13) ◽

pp. 2667-2677 ◽

Cited By ~ 234

Author(s):

Francois Romagné ◽

Pascale André ◽

Pieter Spee ◽

Stefan Zahn ◽

Nicolas Anfossi ◽

...

Keyword(s):

Monoclonal Antibody ◽

Natural Killer ◽

Tumor Cells ◽

Nk Cell ◽

Hla Class I ◽

Therapeutic Antibody ◽

Class I ◽

Therapeutic Window ◽

Target Cells ◽

Term Survival

Abstract Inhibitory-cell killer immunoglobulin-like receptors (KIR) negatively regulate natural killer (NK) cell–mediated killing of HLA class I–expressing tumors. Lack of KIR-HLA class I interactions has been associated with potent NK-mediated antitumor efficacy and increased survival in acute myeloid leukemia (AML) patients upon haploidentical stem cell transplantation from KIR-mismatched donors. To exploit this pathway pharmacologically, we generated a fully human monoclonal antibody, 1-7F9, which cross-reacts with KIR2DL1, -2, and -3 receptors, and prevents their inhibitory signaling. The 1-7F9 monoclonal antibody augmented NK cell–mediated lysis of HLA-C–expressing tumor cells, including autologous AML blasts, but did not induce killing of normal peripheral blood mononuclear cells, suggesting a therapeutic window for preferential enhancement of NK-cell cytotoxicity against malignant target cells. Administration of 1-7F9 to KIR2DL3-transgenic mice resulted in dose-dependent rejection of HLA-Cw3–positive target cells. In an immunodeficient mouse model in which inoculation of human NK cells alone was unable to protect against lethal, autologous AML, preadministration of 1-7F9 resulted in long-term survival. These data show that 1-7F9 confers specific, stable blockade of KIR, boosting NK-mediated killing of HLA-matched AML blasts in vitro and in vivo, providing a preclinical basis for initiating phase 1 clinical trials with this candidate therapeutic antibody.

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Analysis of natural killer cells in TAP2-deficient patients: expression of functional triggering receptors and evidence for the existence of inhibitory receptor(s) that prevent lysis of normal autologous cells

Blood ◽

10.1182/blood.v99.5.1723 ◽

2002 ◽

Vol 99 (5) ◽

pp. 1723-1729 ◽

Cited By ~ 47

Author(s):

Massimo Vitale ◽

Jacques Zimmer ◽

Roberta Castriconi ◽

Daniel Hanau ◽

Lionel Donato ◽

...

Keyword(s):

Nk Cells ◽

Natural Killer ◽

Antigen Processing ◽

Nk Cell ◽

Hla Class I ◽

Surface Expression ◽

Class I ◽

Inhibitory Receptor ◽

Surface Receptors ◽

Hla Class I Molecules

Natural killer (NK) cells are characterized by the ability to kill cells that lack HLA class I molecules while sparing autologous normal (HLA class I+) cells. However, patients with transporter-associated antigen processing (TAP) deficiency, though displaying strong reductions of HLA class I surface expression, in most instances do not experience NK-mediated autoimmune phenomena. A possible mechanism by which TAP−/− NK cells avoid autoreactivity against autologous HLA class I–deficient cells could be based on either quantitative or qualitative defects of surface receptors involved in NK cell triggering. In this study we show that NK cells derived from 2 patients with TAP2−/− express normal levels of all known triggering receptors. As revealed by the analysis of polyclonal and clonal NK cells, these receptors display normal functional capabilities and allow the killing of a panel of NK-susceptible targets, including autologous B-LCLs. On the other hand, TAP2−/− NK cells were unable to kill either allogeneic (HLA class I+) or autologous (HLA class I− ) phytohemagglutinin (PHA) blasts even in the presence of anti-HLA class I monoclonal antibody. These data suggest that TAP2−/− NK cells express still unknown inhibitory receptor(s) capable of down-regulating the NK cell cytotoxicity on binding to surface ligand(s) expressed by T cell blasts. Functional analyses, both at the polyclonal and at the clonal level, are consistent with the concept that the putative inhibitory receptor is expressed by virtually all TAP2−/− NK cells, whereas it is present only in rare NK cells from healthy persons. Another possibility would be that TAP2−/− NK cells are missing a still unidentified triggering receptor involved in NK cell-mediated killing of PHA blasts.

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HLA upregulation during dengue virus infection suppresses the natural killer cell response

10.1101/698803 ◽

2019 ◽

Author(s):

Julia L. McKechnie ◽

Davis Beltran ◽

Arcelys Pitti ◽

Lisseth Saenz ◽

Ana B. Araúz ◽

...

Keyword(s):

Dengue Virus ◽

Nk Cells ◽

Natural Killer ◽

Cell Response ◽

Nk Cell ◽

Hla Class I ◽

Denv Infection ◽

Class I ◽

Hla Class I Molecules

AbstractDengue virus (DENV) is the most prevalent mosquito-borne virus in the world and a major cause of morbidity in the tropics and subtropics. Upregulation of HLA class I molecules has long been considered a feature of DENV infection, yet this has not been evaluated in the setting of natural infection. Natural killer (NK) cells, an innate immune cell subset critical for mounting an early response to viral infection, are inhibited by self HLA class I, suggesting that upregulation of HLA class I during DENV infection could dampen the NK cell response. Here we addressed whether upregulation of HLA class I molecules occurs during in vivo DENV infection and, if so, whether this suppresses the NK cell response. We found that HLA class I expression was indeed upregulated during acute DENV infection across multiple cell lineages in vivo. To better understand the role of HLA class I upregulation, we infected primary human monocytes, a major target of DENV infection, in vitro. Upregulation of total HLA class I is dependent on active viral replication and is mediated in part by cytokines and other soluble factors induced by infection, while upregulation of HLA-E occurs in the presence of replication-incompetent virus. Importantly, blocking DENV-infected monocytes with a pan-HLA class I Fab nearly doubles the frequency of degranulating NK cells, while blocking HLA-E does not significantly improve the NK cell response. These findings demonstrate that upregulation of HLA class I during DENV infection suppresses the NK cell response, potentially contributing to disease pathogenesis.

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Bortezomib Down-Regulates HLA Class I and Enhances Natural Killer Cell Mediated Lysis of Myeloma.

Blood ◽

10.1182/blood.v108.11.3498.3498 ◽

2006 ◽

Vol 108 (11) ◽

pp. 3498-3498

Author(s):

Jumei Shi ◽

Tarun K. Garg ◽

Rachel E. Kellum ◽

Susann M. Szmania ◽

Bart Barlogie ◽

...

Keyword(s):

Natural Killer ◽

Cell Function ◽

Nk Cell ◽

Treated Patient ◽

Hla Class I ◽

Class I ◽

Down Regulation ◽

Myeloma Cells ◽

Bortezomib Treatment

Abstract Introduction: Immunotherapy with Natural Killer (NK) cells may eradicate residual chemotherapy-resistant myeloma (MM) after a state of minimal residual disease has been achieved by autologous stem cell supported high-dose chemotherapy. NK cell activity is regulated by Killer Immunoglobulin-Like Receptors (KIRs). The principal inhibitory ligands of KIRs are HLA Class I molecules (-C and -Bw4) expressed by target cells. NK cells lyse tumor cells that do not display such inhibitory KIR-ligands (KIR-L), such as the K562 cell line. The proteasome is responsible for the generation of peptides that bind to and stabilize Class I molecules at the cell surface. We hypothesized that treatment of MM cells with the proteasome inhibitor bortezomib results in the down-regulation of Class I and thereby sensitizes MM to NK cell mediated lysis. Methods: MM cell lines and primary MM cells were treated with concentrations of bortezomib easily achievable in vivo. The objectives were to determine a) the optimal concentration of bortezomib to down-regulate Class I, b) the time to maximum down-regulation of Class I, and c) a bortezomib concentration that increases NK-mediated MM killing without affecting NK cell function. Results: We found that down-regulation of Class I post-bortezomib treatment of the MM cell line, JJN3, and primary MM cells was dose and time dependent. Bortezomib at 10–20nM down-regulated HLA-class I by 63% compared to untreated control cells with maximal down-regulation at 24hrs (Fig.1a). Bortezomib treatment of primary MM cells greatly increased sensitivity to NK cell-mediated lysis, compared to controls (6% vs. 61%) at an E:T ratio of 20:1 (Fig.1b). These bortezomib concentrations did not affect NK cell function. Conclusions: We observed that bortezomib down-regulates Class I and enhances the sensitivity of MM to NK cell-mediated lysis. Our findings have clear therapeutic implications for MM and other NK cell-sensitive malignancies. Figure 1a. Bortezomib down-regulates HLA-class I expression on patient myeloma cells. Figure 1a. Bortezomib down-regulates HLA-class I expression on patient myeloma cells. Figure 1b. Increased killing of bortezomib-treated patient myeloma by NK in vitro. Figure 1b. Increased killing of bortezomib-treated patient myeloma by NK in vitro.

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Carfilzomib Enhances Natural Killer Cell-Mediated Lysis of Myeloma Linked with Decreasing Expression of HLA Class I

Blood ◽

10.1182/blood.v126.23.1854.1854 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1854-1854

Author(s):

Jumei Shi ◽

Guang Yang ◽

Yuanyuan Kong ◽

Minjie Gao ◽

Yi Tao ◽

...

Keyword(s):

Multiple Myeloma ◽

Nk Cells ◽

Natural Killer ◽

Hematological Malignancies ◽

Nk Cell ◽

Killer Cell ◽

Hla Class I ◽

Class I ◽

Dependent Manner ◽

Down Regulation

Abstract Multiple myeloma (MM) is a malignant disorder characterized by uncontrolled monoclonal plasma cell proliferation. It accounts for 10% of all hematological malignancies and causes 15-20% of deaths from hematological malignancies. Although new therapies were introduced and overall survival of MM was improved in the last 10 years, MM still remains an incurable disease due to drug resistance. Natural killer (NK) cell-based treatments are promising therapies for multiple myeloma (MM). Carfilzomib (CFZ), a second-generation proteasome inhibitor, is used to treat patients with MM who are refractory or intolerant to both bortezomib and lenalidomide (or thalidomide). In this study, we determined that CFZ treatment enhanced the sensitivity of MM cells to NK cell-mediated lysis. Here, we report that CFZ decreased the expression of human leukocyte antigen (HLA) class I on MM cell lines and primary MM cells, the mean reduction was 47.7 ± 9.4% and 42.8 ± 12.4%, respectively. The down-regulation caused by CFZ occurred in a dose- and time- dependent manner. We compared the cell surface levels of HLA class I on MM cells in the presence or absence of CFZ after acid treatment. CFZ also down-regulated the expression of newly formed HLA class I on MM cells. CD107a expression levels were used to measure NK-cell degranulation. When NK cells were incubated with MM cells with CFZ treatment, the percentage of NK cells expressing CD107a on the surface greatly increased (mean ± SD: 33.6 ± 2.1%, for treated cells vs 16.7 ± 2.3%, for control cells, P < 0.05). We also showed that CFZ augmented NK-cell cytotoxity by a perforin/granzyme-mediated mechanism, because such enhancement was abolished when CMA, but not anti-TRAIL or anti-Fas-L antibodies, was added. Treatment of MM with CFZ significantly sensitized patients' MM cells to NK cell-mediated lysis (mean ± SD: 43.1 ± 6.4%, for treated cells vs 16.1 ± 4.0%, for control cells at effector/target (E/T) ratio of 10:1, n = 9, P < 0.01). Furthermore, the exogenous HLA-C binding peptides, used in the CFZ treated group rescued the down-regulation of HLA-C and reduced NK cell-mediated lysis to a similar level as in the untreated group. Blocking NKG2D, NCRs and TRAIL did not have a significant impact on NK cell lysis of myeloma cells. These implied the enhancement of NK cell-mediated lysis was mainly linked with the decreased expression of HLA class I. Our findings show a novel activity of CFZ as an immunomodulating agent and suggest a possible approach to therapeutically augment NK cell function in MM patients. Disclosures No relevant conflicts of interest to declare.

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Soluble HLA class I molecules induce natural killer cell apoptosis through the engagement of CD8: evidence for a negative regulation exerted by members of the inhibitory receptor superfamily

Blood ◽

10.1182/blood.v99.5.1706 ◽

2002 ◽

Vol 99 (5) ◽

pp. 1706-1714 ◽

Cited By ~ 55

Author(s):

Grazia Maria Spaggiari ◽

Paola Contini ◽

Roberta Carosio ◽

Marica Arvigo ◽

Massimo Ghio ◽

...

Keyword(s):

Natural Killer ◽

Cell Apoptosis ◽

Fas Ligand ◽

Nk Cell ◽

Killer Cell ◽

Hla Class I ◽

Class I ◽

Inhibitory Receptor ◽

Cell Clones ◽

Soluble Hla

Herein, we show that CD8dull, CD8intermediate, and CD8bright natural killer (NK) cell clones can be identified. Triggering of CD8 with its natural ligand(s), represented by soluble HLA class I (sHLA-I), isolated either from serum of healthy donors or from HLA-I− 721.221 lymphoblastoid cell line transfected with HLA-A2, -Cw4, and -Bw46 alleles, or HLA-G1 leads to NK cell apoptosis. The magnitude of this effect directly correlated with the level of CD8 expression. sHLA-I–induced apoptosis depends on the interaction with CD8, as it was inhibited by masking this molecule with specific monoclonal antibodies (mAbs). Moreover, sHLA-I or CD8 cross-linking with specific mAbs elicited intracellular calcium increases, Fas ligand (FasL) messenger RNA transcription, and FasL secretion, which were needed for delivering the death signal. Indeed, this apoptosis was inhibited by preincubation of NK cell clones with Fas or FasL antagonist mAbs, indicating that the Fas/FasL pathway is involved. Furthermore, members of the inhibitory receptor superfamily, such as CD94/NKG2 complex or killer inhibitory receptors, were shown to exert an inhibitory effect on sHLA-I–mediated apoptosis and secretion of FasL. These findings suggest that interaction between sHLA-I and CD8 evokes an apoptotic signal that is down-regulated by inhibitory receptor superfamily that function as survival receptors in NK cells.

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Natural killer-cell immunoglobulin-like receptors trigger differences in immune response to SARS-CoV-2 infection

PLoS ONE ◽

10.1371/journal.pone.0255608 ◽

2021 ◽

Vol 16 (8) ◽

pp. e0255608

Author(s):

Roberto Littera ◽

Luchino Chessa ◽

Silvia Deidda ◽

Goffredo Angioni ◽

Marcello Campagna ◽

...

Keyword(s):

Immune Response ◽

Natural Killer ◽

Nk Cell ◽

Severe Disease ◽

Killer Cell ◽

Hla Class I ◽

Class I ◽

Disease Course ◽

Group A ◽

The Impact

Background The diversity in the clinical course of COVID-19 has been related to differences in innate and adaptative immune response mechanisms. Natural killer (NK) lymphocytes are critical protagonists of human host defense against viral infections. It would seem that reduced circulating levels of these cells have an impact on COVID-19 progression and severity. Their activity is strongly regulated by killer-cell immuno-globulin-like receptors (KIRs) expressed on the NK cell surface. The present study’s focus was to investigate the impact of KIRs and their HLA Class I ligands on SARS-CoV-2 infection. Methods KIR gene frequencies, KIR haplotypes, KIR ligands and combinations of KIRs and their HLA Class I ligands were investigated in 396 Sardinian patients with SARS-CoV-2 infection. Comparisons were made between 2 groups of patients divided according to disease severity: 240 patients were symptomatic or paucisymptomatic (Group A), 156 hospitalized patients had severe disease (Group S). The immunogenetic characteristics of patients were also compared to a population group of 400 individuals from the same geographical areas. Results Substantial differences were obtained for KIR genes, KIR haplotypes and KIR-HLA ligand combinations when comparing patients of Group S to those of Group A. Patients in Group S had a statistically significant higher frequency of the KIR A/A haplotype compared to patients in Group A [34.6% vs 23.8%, OR = 1.7 (95% CI 1.1–2.6); P = 0.02, Pc = 0.04]. Moreover, the KIR2DS2/HLA C1 combination was poorly represented in the group of patients with severe symptoms compared to those of the asymptomatic-paucisymptomatic group [33.3% vs 50.0%, OR = 0.5 (95% CI 0.3–0.8), P = 0.001, Pc = 0.002]. Multivariate analysis confirmed that, regardless of the sex and age of the patients, the latter genetic variable correlated with a less severe disease course [ORM = 0.4 (95% CI 0.3–0.7), PM = 0.0005, PMC = 0.005]. Conclusions The KIR2DS2/HLA C1 functional unit resulted to have a strong protective effect against the adverse outcomes of COVID-19. Combined to other well known factors such as advanced age, male sex and concomitant autoimmune diseases, this marker could prove to be highly informative of the disease course and thus enable the timely intervention needed to reduce the mortality associated with the severe forms of SARS-CoV-2 infection. However, larger studies in other populations as well as experimental functional studies will be needed to confirm our findings and further pursue the effect of KIR receptors on NK cell immune-mediated response to SARS-Cov-2 infection.

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Evolution and Immunogenetics of Natural Killer Cell Receptors in Health and Disease

Blood ◽

10.1182/blood.v124.21.sci-25.sci-25 ◽

2014 ◽

Vol 124 (21) ◽

pp. SCI-25-SCI-25

Author(s):

Peter Parham

Keyword(s):

Nk Cells ◽

Natural Killer ◽

Mhc Class I ◽

Nk Cell ◽

Killer Cell ◽

Hla Class I ◽

Class I ◽

Mhc Class I Molecules ◽

Kir Gene ◽

Kir Haplotypes

Abstract Natural killer (NK) cells are phenotypically diverse lymphocytes that contribute to innate immunity, adaptive immunity and placental reproduction. Unlike B and T cells, NK cells do not use rearranging genes to make diverse antigen receptors that are clonally expressed. Instead, NK cells express diverse combinations of a variety of receptors that are encoded by conventional non-rearranging genes. Several of these receptors are specific for conserved and variable determinants of major histocompatibility complex (MHC) class I molecules. In humans, the killer-cell immunoglobulin-like receptors (KIR) are a diverse and polymorphic family of NK-cell receptors that recognize determinants of human leukocyte antigen (HLA)-A, B and C, the polymorphic human MHC class I molecules. HLA-A, B and C are the most polymorphic of human genes, and they correlate with susceptibility to a wide range of diseases and clinical outcomes, including allogeneic hematopoietic cell transplantation (HCT). During NK-cell development, interactions between epitopes of HLA class I and KIR educate the NK cells to recognize the normal expression of these epitopes on healthy cells, and to respond to unhealthy cells in which that expression is perturbed. In the context of HCT, certain types of HLA class I mismatch enable donor-derived NK cells to make an alloreactive and beneficial graft-versus-leukemia response. Although it is likely that all placental mammals have NK cells, only a small minority of these species has a diverse KIR family like that in humans. These comprise the simian primates: New World monkeys, Old World monkeys and the great apes. Under pressure from diverse and rapidly evolving pathogens, both the MHC class I and KIR gene families have been driven to evolve rapidly. Consequently, much of their character is species-specific. This is especially true for the human KIR gene family, which is qualitatively different from that of our closest relatives, the chimpanzees. Whereas chimpanzee KIR haplotype diversity represents variations on a theme of genes encoding robust MHC class I receptors, humans have an even balance between group A KIR haplotypes encoding robust HLA class I receptors and group B KIR haplotypes encoding receptors that, to varying degree, have been subject to natural selection for reduced functional recognition of HLA class I. A balance of A and B is present in all human populations and thus appears essential for the long-term survival and competitiveness of human communities. Whereas the A KIR haplotypes correlate with successful defense against viral infection, maternal B KIR haplotypes correlate with reproductive success and donor B KIR haplotypes improve the outcome of allogeneic HCT as therapy for acute myeloid leukemia. Disclosures No relevant conflicts of interest to declare.

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