Alloreactive killer cells: hindrance and help for haematopoietic transplants

KIR genotype and haplotype repertoire in Kuwaiti healthy donors, hematopoietic cell transplant recipients and healthy family members

The gene complex located on chromosome 19q13.4 encodes the Killer-cell Immunoglobulin-like Receptors (KIRs), which exhibit remarkable polymorphism in both gene content and sequences. Further, the repertoire of KIR genes varies within and between populations, creating a diverse pool of KIR genotypes. This study was carried out to characterize KIR genotypes and haplotypes among 379 Arab Kuwaiti individuals including 60 subjects from 20 trio families, 49 hematopoietic cell transplantation (HCT) recipients and 270 healthy Kuwaiti volunteer HCT donors. KIR Genotyping was performed by a combination of reverse sequence specific oligonucleotide probes (rSSO) and/or Real Time PCR. The frequencies of KIR genes in 270 healthy Kuwaiti volunteer donors were compared to previously reported frequencies in other populations. In addition, we compared the differences in KIR repertoire of patients and healthy donors to investigate the reproducibility of previously reported significant differences between patients with hematological malignancies and healthy donors. The observed frequencies in our cohort volunteer HCT donors was comparable to those reported in neighboring Arab populations. The activating genes KIR2DS1, KIR2DS5 and KIR3DS1 and the inhibitory gene KIR2DL5 were significantly more frequent in patients compared to healthy donors, however, none of the previously reported differences were reproducible in our Kuwaiti cohort. This report is the first description of KIR gene carrier frequency and haplotype characterization in a fairly large cohort of the Kuwaiti population, which may have implications in KIR based HCT donor selection strategies.

Cellular Therapy Advances in Chronic Lymphocytic Leukemia and Richter's Syndrome

Over the past 10 years, there have been great treatment advances for chronic lymphocytic leukemia (CLL) with the development of small molecule inhibitors. However, there remains an area of unmet need for patients who progress on novel therapies. The development of cellular therapies in CLL has been hindered by CLL induced immunosuppression. Fortunately, recent progress in various methods in immunomodulation may help overcome this limitation in CLL. These advances have spurred ongoing interest in the development of cellular therapies for CLL, including chimeric antigen receptor (CAR) T cell therapies, bi-specific antibodies, and use of natural killer cells. These novel treatment modalities may hold promise for patients with refractory, and potentially transformed disease. Here, we discuss the development of CAR-T cell therapy in CLL and the impact of combining CAR-T and small molecule inhibitors on treatment outcomes, the evolving role of bi-specific antibodies and natural killer cells, and comment on the use of cellular therapies for Richter's syndrome.

Improved hematopoietic stem cell transplantation upon inhibition of natural killer cell-derived interferon-gamma

Hematopoietic stem cell transplantation (HSCT) is a frequent therapeutic approach to restore hematopoiesis in patients with hematologic diseases. Patients receive a hematopoietic stem cell (HSC)-enriched donor cell infusion also containing immune cells, which may have a beneficial effect by eliminating residual neoplastic cells. However, the effect that donor innate immune cells may have on the donor HSCs has not been deeply explored. Here, we evaluate the influence of donor natural killer (NK) cells on HSC fate, concluded that NK cells negatively affect HSC frequency and function, and identified interferon-gamma (IFNγ) as a potential mediator. Interestingly, improved HSC fitness was achieved by NK cell depletion from murine and human donor infusions or by blocking IFNγ activity. Thus, our data suggest that suppression of inflammatory signals generated by donor innate immune cells can enhance engraftment and hematopoietic reconstitution during HSCT, which is particularly critical when limited HSC numbers are available and the risk of engraftment failure is high.

Natural Killer Cell Responses during Human γ-Herpesvirus Infections

Herpesviruses are main sculptors of natural killer (NK) cell repertoires. While the β-herpesvirus human cytomegalovirus (CMV) drives the accumulation of adaptive NKG2C-positive NK cells, the human γ-herpesvirus Epstein–Barr virus (EBV) expands early differentiated NKG2A-positive NK cells. While adaptive NK cells support adaptive immunity by antibody-dependent cellular cytotoxicity, NKG2A-positive NK cells seem to preferentially target lytic EBV replicating B cells. The importance of this restriction of EBV replication during γ-herpesvirus pathogenesis will be discussed. Furthermore, the modification of EBV-driven NK cell expansion by coinfections, including by the other human γ-herpesvirus Kaposi sarcoma-associated herpesvirus (KSHV), will be summarized.

Effective Murine Model Induction for Niche Study in Immune Cells Against Leukemia

Murine models have become powerful tools in leukemia research for investigating interactions between blast cells niche factors. In the tumor microenvironment, immune cells are one of the most important niche factors, capable of mounting dynamic innate or adoptive responses against leukemic cells. Acute myeloid leukemia (AML) is a systemic cancer accompanied by immune disruption. In order to exploit the enhanced activity of immune cells in AML treatment, the use of syngeneic mouse models is necessary. Studies of crosstalk between cancer blast cells and immune cells in syngeneic mouse models are beneficial, as the absence of immune functions in syngeneic models enables focus on cancer-associated immune reactions. Once AML is induced, innate and adoptive immune cells respond differently, ultimately resulting in suppression of the immune cells. Murine AML models are commonly induced by intravenous or subcutaneous injection of C1498 cells. Despite the popularity of murine models, they have not yet resulted in the elucidation of distinct differences in immune cells by the injection method. Here, we investigated the frequency of immune cells and survival rate of mice with AML induced using both injection methods.

Harnessing NK Cells for Cancer Treatment

In the last years, natural killer (NK) cell-based immunotherapy has emerged as a promising therapeutic approach for solid tumors and hematological malignancies. NK cells are innate lymphocytes with an array of functional competences, including anti-cancer, anti-viral, and anti-graft-vs.-host disease potential. The intriguing idea of harnessing such potent innate immune system effectors for cancer treatment led to the development of clinical trials based on the adoptive therapy of NK cells or on the use of monoclonal antibodies targeting the main NK cell immune checkpoints. Indeed, checkpoint immunotherapy that targets inhibitory receptors of T cells, reversing their functional blocking, marked a breakthrough in anticancer therapy, opening new approaches for cancer immunotherapy and resulted in extensive research on immune checkpoints. However, the clinical efficacy of T cell-based immunotherapy presents a series of limitations, including the inability of T cells to recognize and kill HLA-I^neg tumor cells. For these reasons, new strategies for cancer immunotherapy are now focusing on NK cells. Blockade with NK cell checkpoint inhibitors that reverse their functional block may overcome the limitations of T cell-based immunotherapy, mainly against HLA-I^neg tumor targets. Here, we discuss recent anti-tumor approaches based on mAb-mediated blocking of immune checkpoints (either restricted to NK cells or shared with T cells), used either as a single agent or in combination with other compounds, that have demonstrated promising clinical responses in both solid tumors and hematological malignancies.

Allogeneic dendritic cells induce potent antitumor immunity by activating KLRG1+CD8 T cells

The graft-versus-leukemia effect reminds us to observe the allogeneic cell elicited anti-tumor immune responses. Here we immunized recipient B6 mice with different types of allogenic leukocytes and found that vaccination with allogenic dendritic cells (alloDC) elicited the most efficient protection against broad-spectrum tumors. The recipient lymphocytes were analyzed and the data showed that CD8 T cells increased significantly after immunization and expressed effector memory T cell marker KLRG1. Functional evaluation demonstrated that these KLRG1⁺CD8 T cells could kill tumor cells in vitro and in vivo in Granzyme B- and Fas/FasL-dependent manners with no tumor antigen specificity, and tend to migrate into tumor sites by high expression of heparanase. Adoptive transfer of these cells could provide antitumor protection against tumors. AlloDC could also treat mice with residual tumors and combination of anti-PD1 antibody could enhance this effects. Together, our study showed that alloDC-immunization could induce potent antitumor effect through the expansion of KLRG1⁺CD8 T cells, which can work as both preventive and therapeutic tumor vaccines.

Restoring Natural Killer Cell Immunity against Multiple Myeloma in the Era of New Drugs

Transformed plasma cells in multiple myeloma (MM) are susceptible to natural killer (NK) cell-mediated killing via engagement of tumor ligands for NK activating receptors or “missing-self” recognition. Similar to other cancers, MM targets may elude NK cell immunosurveillance by reprogramming tumor microenvironment and editing cell surface antigen repertoire. Along disease continuum, these effects collectively result in a progressive decline of NK cell immunity, a phenomenon increasingly recognized as a critical determinant of MM progression. In recent years, unprecedented efforts in drug development and experimental research have brought about emergence of novel therapeutic interventions with the potential to override MM-induced NK cell immunosuppression. These NK-cell enhancing treatment strategies may be identified in two major groups: (1) immunomodulatory biologics and small molecules, namely, immune checkpoint inhibitors, therapeutic antibodies, lenalidomide, and indoleamine 2,3-dioxygenase inhibitors and (2) NK cell therapy, namely, adoptive transfer of unmanipulated and chimeric antigen receptor-engineered NK cells. Here, we summarize the mechanisms responsible for NK cell functional suppression in the context of cancer and, specifically, myeloma. Subsequently, contemporary strategies potentially able to reverse NK dysfunction in MM are discussed.

NKp46 expression on NK cells as a prognostic and predictive biomarker for response to allo-SCT in patients with AML

NKp46 is a major determinant of natural killer (NK) cell function and it is implicated in tumor immune surveillance in acute myeloid leukemia (AML). The purpose of this study was to investigate the prognostic significance of NKp46 expression in an independent cohort of patients with AML, and to investigate the impact of NKp46 on clinical outcome after allogeneic stem cell transplantation (allo-SCT).

NKp46 expression was assessed at diagnosis on NK cells by flow cytometry (N = 180 patients). Clinical outcome was evaluated with regard to NKp46 expression. Patients with NKp46^high phenotype at diagnosis had better progression-free survival (PFS) and overall survival (OS) than patients with NKp46^low phenotype (74.3% vs. 46.6%, p = 0.014; 82.6% vs. 57.1%, p = 0.010, respectively). In multivariate analysis, high NKp46 was an independent factor for improved OS (HR = 0.409, p = 0.010) and PFS (HR = 0.335, p = 0.011). Subgroup analysis revealed that allo-SCT had a favorable impact on PFS in patients with NKp46^high phenotype (p = 0.025). By contrast, allo-SCT did not impact PFS in patients with low NKp46 expression (p = 0.303).

In conclusion, we validate the prognostic value of NKp46 expression at diagnosis in AML. However, the prognostic value of NKp46 expression is limited to patients treated with allo-SCT, thus suggesting that NKp46 status may be predictive for allo-SCT responsiveness.

Zinc-Induced Polymerization of Killer-Cell Ig-like Receptor into Filaments Promotes Its Inhibitory Function at Cytotoxic Immunological Synapses

The inhibitory function of killer cell immunoglobulin-like receptors (KIR) that bind HLA-C and block activation of human natural killer (NK) cells is dependent on zinc. We report that zinc induced the assembly of soluble KIR into filamentous polymers, as detected by electron microscopy, which depolymerized after zinc chelation. Similar KIR filaments were isolated from lysates of cells treated with zinc, and membrane protrusions enriched in zinc were detected on whole cells by scanning electron microscopy and imaging mass spectrometry. Two independent mutations in the extracellular domain of KIR, away from the HLA-C binding site, impaired zinc-driven polymerization and inhibitory function. KIR filaments formed spontaneously, without the addition of zinc, at functional inhibitory immunological synapses of NK cells with HLA-C(+) cells. Adding to the recent paradigm of signal transduction through higher order molecular assemblies, zinc-induced polymerization of inhibitory KIR represents an unusual mode of signaling by a receptor at the cell surface.

Maternal microchimerism in health and disease

Circulating maternal cells transfer to the fetus during pregnancy, where they may integrate with the fetal immune and organ systems, creating a state of maternal microchimerism (MMc). MMc can persist throughout the child's life, and it has been implicated in the triggering or perpetuation of chronic inflammatory autoimmune diseases, in the context of specific major histocompatibility genes. Correlative data in humans have now been tested in animal model systems. Results suggest that maternal-fetal tolerance may have health implications far beyond the time of pregnancy and into the child's life.

Recipient expression of ligands for donor inhibitory KIRs enhances NK-cell function to control leukemic relapse after haploidentical transplantation

Natural killer (NK) cells that express self-HLA-specific receptors (where HLA is human leukocyte antigen) are "licensed" and more readily activated than unlicensed cells; therefore, NK-cell licensing could influence the antileukemia effects of NK cells following haploidentical stem cell transplantation (haplo-SCT). In this study, we compared the functionality of reconstituting NK cells, based on CD107α expression and interferon-γsecretion, in a cohort of 29 patients that expressed (n = 8) or lacked (n = 21) class I human leukocyte antigens for donor inhibitory killer cell immunoglobulin-like receptors (KIRs) following T-cell-replete haplo-SCT. We also addressed whether recipient expression of class I ligands for donor inhibitory KIRs could predict relapse occurrence in another cohort of 188 patients. A longitudinal analysis indicated that patients presenting class I for all donor inhibitory KIRs showed more capable functional NK effector cells when tested against class I negative K562 cells and primary leukemic cells within 3 months of transplantation. The lowest 7-year relapse incidence was observed when donor KIRs were ligated by recipient class I (n = 60) compared with donor-host partnerships where donor KIR(+) cells were ligated by donor, but not recipient class I (n = 86, p = 0.026) or KIRs that were ligated by neither donor nor recipient class I (n = 42, p = 0.043). This study suggests that haplo-SCT recipients presenting class I for donor inhibitory KIRs promote NK-cell licensing, leading to decreased relapse rates.

Donor-derived natural killer cells infused after human leukocyte antigen-haploidentical hematopoietic cell transplantation: a dose-escalation study

The doses of donor-derived natural killer (NK) cells that can be given safely after human leukocyte antigen (HLA)-haploidentical hematopoietic cell transplantation (HCT) remain to be defined. Forty-one patients (ages 17 to 75 years) with hematologic malignancy underwent HLA-haploidentical HCT after reduced-intensity conditioning containing busulfan, fludarabine, and antithymocyte globulin. Cell donors (ages 7 to 62 years) underwent growth factor-mobilized leukapheresis for 3 to 4 days. Cells collected on the first 2 to 3 days were used for HCT, whereas those collected on the last day were CD3-depleted and cultured into NK cells using human interleukins-15 and -21. These NK cells were then infused into patients twice at 2 and 3 weeks after HCT at an escalating doses of .2 × 10(8) cells/kg of body weight (3 patients), .5 × 10(8) cells/kg (3 patients), 1.0 × 10(8) cells/kg (8 patients), and ≥ 1.0 × 10(8) cells/kg or available cells (27 patients). At all dose levels, no acute toxicity was observed after NK cell infusion. After HLA-haploidentical HCT and subsequent donor NK cell infusion, when referenced to 31 historical patients who had undergone HLA-haploidentical HCT after the same conditioning regimen but without high-dose NK cell infusion, there was no significant difference in the cumulative incidences of major HCT outcomes, including engraftment (absolute neutrophil count ≥ 500/μL, 85% versus 87%), grade 2 to 4 acute graft-versus-host disease (GVHD, 17% versus 16%), moderate to severe chronic GVHD (15% versus 10%), and transplantation-related mortality (27% versus 19%). There was, however, a significant reduction in leukemia progression (74% to 46%), with post-transplantation NK cell infusion being an independent predictor for less leukemia progression (hazard ratio, .527). Our findings showed that, when given 2 to 3 weeks after HLA-haploidentical HCT, donor-derived NK cells were well tolerated at a median total dose of 2.0 × 10(8) cells/kg. In addition, they may decrease post-transplantation progression of acute leukemia.

Tumor-primed NK cells: waiting for the green light

The functional impairment of natural killer (NK) cells has been frequently reported in cancer studies. As one of the central components of host anti-tumor immunity, NK cells exert cellular cytotoxicity against tumor cells, and secrete a cytokine milieu to inhibit tumor progression and enable the recruitment of other immune cells to the tumor site. The unlocking of the full functional potential of NK cells requires successful progression through discrete activation stages that are tightly regulated by a complex array of signaling molecules. Target cell susceptibility to NK cell-mediated killing is dependent on the intensity and specific combination of ligand expression for NK cell receptors. Tumor cells utilize numerous strategies for evading NK cells, including the downregulation of important NK cell-activating ligands. Here, we review key studies on NK cell activation requirements, and argue, based on our findings from NK cell-tumor interactions, that the altered characteristics of tumor-associated NK cells are indicative of unmet signaling requirements for full NK cell activation, rather than NK cell dysfunction in cancer.

Fludarabine and 2-Gy TBI is superior to 2 Gy TBI as conditioning for HLA-matched related hematopoietic cell transplantation: a phase III randomized trial

The risks and benefits of adding fludarabine to a 2-Gy total body irradiation (TBI) nonmyeloablative regimen are unknown. For this reason, we conducted a prospective randomized trial comparing 2-Gy TBI alone, or in combination with 90 mg/m(2) fludarabine (FLU/TBI), before transplantation of peripheral blood stem cells from HLA-matched related donors. Eighty-five patients with hematological malignancies were randomized to be conditioned with TBI alone (n = 44) or FLU/TBI (n = 41). All patients had initial engraftment. Two graft rejections were observed, both in the TBI group. Infection rates, nonrelapse mortality, and graft-versus-host disease (GVHD) were similar between groups. Three-year overall survival was lower in the TBI group (54% versus 65%; hazard ratio [HR], .57; P = .09), with higher incidences of relapse/progression (55% versus 40%; HR, .55; P = .06), relapse-related mortality (37% versus 28%; HR, .53; P = .09), and a lower progression-free survival (36% versus 53%; HR, .56; P = .05). Median donor T cell chimerism levels were significantly lower in the TBI group at days 28 (61% versus 90%; P < .0001) and 84 (68% versus 92%; P < .0001), as was NK cell chimerism on day 28 (75% versus 96%; P = .0005). In conclusion, this randomized trial demonstrates the importance of fludarabine in augmenting the graft-versus-tumor effect by ensuring prompt and durable high-level donor engraftment early after transplantation.

A mathematical model of natural killer cell activity

Natural killer (NK) cells are capable of lysing their target cells with the help of perforin. The application of these cells for immunotherapy requires the estimation of their potency for the purpose of validation and batch-to-batch comparison. Cytotoxicity measurements have been carried out at only a few effector target ratios, therefore, allowing only semiquantitative assessment at best. By using a novel approach of varying the effector target ratio continuously and careful analysis of the experimental data after the reactions, we have achieved a precision necessary for constructing a mathematical model of cytotoxic reaction. Curve-fitting to experimental data indicates that NK cell cytotoxicity follows the law of mass action and fits the model of a single ligand-receptor interaction. The method allows to use the value of half-maximal lysis to describe the potency of cytotoxic NK cells numerically.

Positive C4d immunostaining of placental villous syncytiotrophoblasts supports host-versus-graft rejection in villitis of unknown etiology

ABSTRACT Chronic villitis of unknown etiology (VUE) occurs in 5% of placentas submitted to pathology and is characterized by lymphohistiocytic infiltration of chorionic villi. VUE is associated with fetal growth restriction, preterm birth, and recurrent pregnancy loss. Accumulating evidence indicates that VUE may represent a host-versus-graft reaction analogous to transplant rejection. Pathologists routinely screen for antibody-mediated rejection in transplant biopsies by immunostaining for C4d, which highlights the recognition of donor cells by the host immune system. Since the hemochorial placenta is bathed in maternal blood, we hypothesized that cases of VUE may show C4d deposition onto villous syncytiotrophoblasts (STB). Chronic villitis was diagnosed in 82 of 1986 (4%) singleton placentas submitted to our department from 2007 through 2011. Forty randomly selected cases were gestational age-matched with 40 negative controls. Patient charts were reviewed and representative placental sections were immunostained for C4d. A positive C4d result was defined as circumferential immunostaining of the STB around at least one villous, or strong staining of fetal endothelial cells in the chorionic plate or stem villi. Our data indicate that VUE usually occurs in the 3rd trimester (37 ± 0.5 weeks) and is associated with significantly reduced placental weight (P  =  0.006). Positive C4d staining of STB was more common in VUE (35/40, 88%) compared with negative controls (2/40, 5%) (P < 0.0001). It was also more common in multiparous (35/66, 53%) than primiparous (2/14, 14%) women (P < 0.01). Although the precise mechanism remains to be determined, our data support the hypothesis that VUE may represent host-versus-graft rejection by the mother.

HLA-C matching status does not affect rituximab-mediated antibody-dependent cellular cytotoxicity by allogeneic natural killer Cells

Risk of leukemia relapse after T cell-depleted hematopoietic stem cell transplantation is lower in the "HLA-C mismatched" recipient-donor combinations. This might be attributable to increased natural killing by allogeneic NK cells carrying a KIR that does not bind to HLA-C on target cells (HLA-C-uncoupled KIR). Considering a new strategy of allogeneic NK cell transfer with rituximab to treat B-cell lymphomas, however, it is unknown whether the HLA-C matching status also affects rituximab-mediated antibody-dependent cellular cytotoxicity (ADCC). To address this issue, we investigated the levels of ADCC by purified NK cells carrying an HLA-C-uncoupled KIR, where the NK cell donors had either matched or mismatched HLA-C combination with target cells. Purified NK cells carrying an HLA-C-uncoupled KIR consistently showed enhanced ADCC against target cells when NK cell donors had an HLA-C-mismatch. When NK cell donors did not have an HLA-C mismatch, it was inconsistent whether HLA-C-uncoupled KIR caused ADCC enhancement. When the levels of ADCC by whole NK cells were compared, there were substantial differences among the donors regardless of the HLA-C matching status. Subjects with HLA-C mismatch may not have an advantage when cytoimmunotherapy using allogeneic NK cells is considered in combination with rituximab.

Membrane-bound IL-21 promotes sustained ex vivo proliferation of human natural killer cells

NK cells have therapeutic potential for a wide variety of human malignancies. However, because NK cells expand poorly in vitro, have limited life spans in vivo, and represent a small fraction of peripheral white blood cells, obtaining sufficient cell numbers is the major obstacle for NK-cell immunotherapy. Genetically-engineered artificial antigen-presenting cells (aAPCs) expressing membrane-bound IL-15 (mbIL15) have been used to propagate clinical-grade NK cells for human trials of adoptive immunotherapy, but ex vivo proliferation has been limited by telomere shortening. We developed K562-based aAPCs with membrane-bound IL-21 (mbIL21) and assessed their ability to support human NK-cell proliferation. In contrast to mbIL15, mbIL21-expressing aAPCs promoted log-phase NK cell expansion without evidence of senescence for up to 6 weeks of culture. By day 21, parallel expansion of NK cells from 22 donors demonstrated a mean 47,967-fold expansion (median 31,747) when co-cultured with aAPCs expressing mbIL21 compared to 825-fold expansion (median 325) with mbIL15. Despite the significant increase in proliferation, mbIL21-expanded NK cells also showed a significant increase in telomere length compared to freshly obtained NK cells, suggesting a possible mechanism for their sustained proliferation. NK cells expanded with mbIL21 were similar in phenotype and cytotoxicity to those expanded with mbIL15, with retained donor KIR repertoires and high expression of NCRs, CD16, and NKG2D, but had superior cytokine secretion. The mbIL21-expanded NK cells showed increased transcription of the activating receptor CD160, but otherwise had remarkably similar mRNA expression profiles of the 96 genes assessed. mbIL21-expanded NK cells had significant cytotoxicity against all tumor cell lines tested, retained responsiveness to inhibitory KIR ligands, and demonstrated enhanced killing via antibody-dependent cell cytotoxicity. Thus, aAPCs expressing mbIL21 promote improved proliferation of human NK cells with longer telomeres and less senescence, supporting their clinical use in propagating NK cells for adoptive immunotherapy.

Diversity of killer cell immunoglobulin-like receptor genes in Southern Turkey

Killer cell immunoglobulin-like receptors (KIRs) are a family of inhibitory and activating receptors expressed by natural killer (NK) cells and regulate NK cells' activity. KIR genes are highly polymorphic markers, characterized by a wide diversity, and can therefore be considered as good population genetic markers. The aim of this study was to determine KIR gene frequencies, ratios of haplotypes and genotypes in Southern Turkey and also to compare the data with other worldwide populations studied previously. The study group consisted of 200 non-related individuals from Southern Turkey. The percentage of each KIR gene in the population group was determined by direct counting. Differences between populations in the distribution of each KIR gene and genotype profile were estimated by two-tailed Fisher Exact test. The most frequent non-framework KIR genes detected in Southern Turkey population were: KIR 2DL1 (97%), KIR 3DL1 (91%), KIR 2DS4 (92%) and the pseudogene 2DP1 (96%). Fourty different genotypes were found in 200 subjects and AA1 genotype was the most frequent (27%). Among 40 different genotypes, ten of these were described for the first time in this study and were added to the database ( http://www.allelefrequencies.net ) numerized as genotype ID from 400 to 409. Gene frequencies and found genotypes demonstrated similarity of Southern Turkey's KIR repertoire with the KIR repertoires of Middle East and European population. High variability seen in KIR genome in this region is thought to be formed as a result of migration and settlement of different civilizations in this region and heterogenity formed in time.

Confinement of activating receptors at the plasma membrane controls natural killer cell tolerance

Natural killer (NK) cell tolerance to self is partly ensured by major histocompatibility complex (MHC) class I-specific inhibitory receptors on NK cells, which dampen their reactivity when engaged. However, NK cells that do not detect self MHC class I are not autoreactive. We used dynamic fluorescence correlation spectroscopy to show that MHC class I-independent NK cell tolerance in mice was associated with the presence of hyporesponsive NK cells in which both activating and inhibitory receptors were confined in an actin meshwork at the plasma membrane. In contrast, the recognition of self MHC class I by inhibitory receptors "educated" NK cells to become fully reactive, and activating NK cell receptors became dynamically compartmentalized in membrane nanodomains. We propose that the confinement of activating receptors at the plasma membrane is pivotal to ensuring the self-tolerance of NK cells.

Exploiting T cells specific for human minor histocompatibility antigens for therapy of leukemia

Minor histocompatibility (H) antigens are major targets of a graft-versus-leukemia (GVL) effect mediated by donor CD8(+) and CD4(+) T cells following allogeneic hematopoietic cell transplantation (HCT) between human leukocyte antigen identical individuals. In the 15 years since the first molecular characterization of human minor H antigens, significant strides in minor H antigen discovery have been made as a consequence of advances in cellular, genetic and molecular techniques. Much has been learned about the mechanisms of minor H antigen immunogenicity, their expression on normal and malignant cells, and their role in GVL responses. T cells specific for minor H antigens expressed on leukemic cells, including leukemic stem cells, can be isolated and expanded in vitro and infused into allogeneic HCT recipients to augment the GVL effect to prevent and treat relapse. The first report of the adoptive transfer of minor H antigen-specific T-cell clones to patients with leukemic relapse in 2010 illustrates the potential for the manipulation of alloreactivity for therapeutic benefit. This review describes the recent developments in T-cell recognition of human minor H antigens, and efforts to translate these discoveries to reduce leukemia relapse after allogeneic HCT.

Exploiting T cells specific for human minor histocompatibility antigens for therapy of leukemia

Minor histocompatibility (H) antigens are major targets of a graft-versus-leukemia (GVL) effect mediated by donor CD8(+) and CD4(+) T cells following allogeneic hematopoietic cell transplantation (HCT) between human leukocyte antigen identical individuals. In the 15 years since the first molecular characterization of human minor H antigens, significant strides in minor H antigen discovery have been made as a consequence of advances in cellular, genetic and molecular techniques. Much has been learned about the mechanisms of minor H antigen immunogenicity, their expression on normal and malignant cells, and their role in GVL responses. T cells specific for minor H antigens expressed on leukemic cells, including leukemic stem cells, can be isolated and expanded in vitro and infused into allogeneic HCT recipients to augment the GVL effect to prevent and treat relapse. The first report of the adoptive transfer of minor H antigen-specific T-cell clones to patients with leukemic relapse in 2010 illustrates the potential for the manipulation of alloreactivity for therapeutic benefit. This review describes the recent developments in T-cell recognition of human minor H antigens, and efforts to translate these discoveries to reduce leukemia relapse after allogeneic HCT.

Innate or adaptive immunity? The example of natural killer cells

Natural killer (NK) cells were originally defined as effector lymphocytes of innate immunity endowed with constitutive cytolytic functions. More recently, a more nuanced view of NK cells has emerged. NK cells are now recognized to express a repertoire of activating and inhibitory receptors that is calibrated to ensure self-tolerance while allowing efficacy against assaults such as viral infection and tumor development. Moreover, NK cells do not react in an invariant manner but rather adapt to their environment. Finally, recent studies have unveiled that NK cells can also mount a form of antigen-specific immunologic memory. NK cells thus exert sophisticated biological functions that are attributes of both innate and adaptive immunity, blurring the functional borders between these two arms of the immune response.

Suicide gene therapy for graft-versus-host disease

In allogeneic hematopoietic stem cell transplantation, donor-derived T cells are key players for early immune reconstitution and efficient engraftment, as well as the graft-versus-leukemia and graft-versus-infection effects. However, a severe and quite common life-threatening complication is the development of graft-versus-host disease, during which the alloreactive donor T cells attack the host. Controlling graft-versus-host disease while preserving the benefits of graft-versus-leukemia still constitutes a challenge. A promising approach for the control of graft-versus-host disease is suicide gene therapy, which involves the ex vivo genetic modification of donor T cells with a suicide gene that allows for the selective elimination of the cells in vivo if graft-versus-host disease occurs. This article presents an overview of such approaches with special reference to lessons learned from previous clinical experiences, as well as a discussion of critical factors in suicide gene therapy.

Natural killer cell-enriched donor lymphocyte infusions from A 3-6/6 HLA matched family member following nonmyeloablative allogeneic stem cell transplantation

Infusing natural killer (NK) cells following transplantation may allow less infections and relapse with little risk of acute graft-versus-host disease (aGVHD). We delivered 51 total NK cell-enriched donor lymphocyte infusions (DLIs) to 30 patients following a 3-6/6 HLA matched T cell-depleted nonmyeloablative allogeneic transplant. The primary endpoint of this study was feasibility and safety. Eight weeks following transplantation, donor NK cell-enriched DLIs were processed using a CD56(+) selecting column with up to 3 fresh infusions allowed. Toxicity, relapse, and survival were monitored. T cell phenotype, NK cell functional recovery, and KIR typing were assessed for association with outcomes. Fourteen matched and 16 mismatched transplanted patients received a total of 51 NK cell-enriched DLIs. Selection resulted in 96% (standard deviation [SD] 8%) purity and 83% (SD 21%) yield in the matched setting and 97% (SD 3%) purity and 77% (SD 24%) yield in the mismatched setting. The median number of CD3(-) CD56(+) NK cells infused was 10.6 (SD 7.91) x 10(6) cells/kg and 9.21 (SD 5.6) x 10(6) cells/kg, respectively. The median number of contaminating CD3(+)CD56(-) T cells infused was .53 (1.1) x 10(6) and .27 (.78) x 10(6) in the matched and mismatched setting, respectively. Only 1 patient each in the matched (n = 14) or mismatched (n = 16) setting experienced severe aGVHD with little other toxicity attributable to the infusions. Long-term responders with multiple NK cell-enriched infusions and improved T cell phenotypic recovery had improved duration of responses (p = .0045) and overall survival (OS) (P = .0058). A 1-step, high-yield process is feasible, and results in high doses of NK cells infused with little toxicity. NK cell-enriched DLIs result in improved immune recovery and outcomes for some. Future studies must assess whether the improved outcomes are the direct result of the high doses and improved NK cell function or other aspects of immune recovery.

Extending killer Ig-like receptor function: from HLA class I recognition to sensors of microbial products

Killer Ig-like receptors (KIRs) are human natural killer (NK) receptors that recognize allotypic determinants of human leukocyte antigen (HLA) class I. Inhibitory KIRs discriminate normal cells from tumour or virus-infected cells that have lost or reduced HLA class I expression. Donor NK cell "alloeffector" responses are exploited in haploidentical haematopoietic stem cell transplantation to treat leukaemia. NK cells also express several toll-like receptors (TLRs) that increase NK cell cytotoxicity and cytokine release in response to ligands. Surprisingly, KIR3DL2 binds the TLR ligand CpG-oligodexynucleotides, and together, they are co-internalized and translocated to TLR9-rich early endosomes. This novel KIR-associated function offers clues to understanding the NK cell response to microbial infection, and extends the role played by KIRs in immune defence.

Distribution of killer cell immunoglobulin-like receptor genes and 2DS4 alleles in the Chinese Han population

Killer cell immunoglobulinlike receptors (KIRs) are a diverse family of receptors on natural killer cells. The KIR2DS4-deleted variant differs from the normal KIR2DS4 sequence by a 22-bp deletion in exon 5, which causes a frame shift, yielding a truncated KIR2DS4 protein with loss of the transmembrane and cytoplasmic domains of the full-length KIR2DS4 protein. A sequence-based testing and TOPO TA cloning system identifying and distinguishing alleles of the KIR2DS4 gene was established. The method was applied to 150 Chinese Han individuals: 75 patients who received T-depleted hematopoietic stem cells transplantation and their unrelated donors, establishing frequencies of 2DS4 allele and KIR gene within the local population. A majority (139) of the 150 samples (92.7%) were positive for KIR2DS4. The ratio of deleted to nondeleted versions of KIR2DS4 was approximately 1:2. Three KIR2DS4 novel alleles were identified. Forty-four percent individuals carried two group A haplotypes. The 17 KIR gene loci were found in 21.3%-100% in the population. Our findings suggest that the Chinese Han population is distinct in KIR gene frequencies and 2DS4 allele frequencies in comparison with some other populations.

Generation of donor natural killer cells from CD34(+) progenitor cells and subsequent infusion after HLA-mismatched allogeneic hematopoietic cell transplantation: a feasibility study

Post transplant infusion of donor-type natural killer (NK) cells has been shown to have an anti-leukemia-enhancing effect without evoking GVHD in murine hematopoietic cell transplantation (HCT) models. Here, we tested 14 patients (age, 23-65 years), 12 with acute leukemia and 2 with myelodysplastic syndrome, who underwent HLA-mismatched HCT and subsequently received donor NK cell infusions. Cell donors (age, 16-51 years), comprising seven siblings, five offspring, and two mothers of the patients, underwent growth factor-mobilized leukapheresis for 3-5 days. Cells collected on the first 2-4 days were used for HCT, whereas those collected on the last day were CD34 selected by magnetic-activated cell sorting (median, 2.22 x 10(6) cells/kg; range, 0.29-5.66). Donor NK cells were generated from the CD34(+) cells by ex vivo cell culture over a 6-week period (median, 9.28 x 10(6) cells/kg; range, 0.33-24.50; CD122/CD56(+) 64%; CD3(+) 1.0%; and viability 88%). There were no signs of acute toxicity in patients infused with these cells 6-7 weeks post transplant. Overall, one and five patients developed acute and chronic GVHD during post transplant period, respectively. These results showed that clinical-grade donor NK cell production from CD34(+) cells is feasible.

Loss of mismatched HLA in leukemia after stem-cell transplantation

BACKGROUND

Transplantation of hematopoietic stem cells from partially matched family donors is a promising therapy for patients who have a hematologic cancer and are at high risk for relapse. The donor T-cell infusions associated with such transplantation can promote post-transplantation immune reconstitution and control residual disease.

METHODS

We identified 43 patients who underwent haploidentical transplantation and infusion of donor T cells for acute myeloid leukemia or myelodysplastic syndrome and conducted post-transplantation studies that included morphologic examination of bone marrow, assessment of hematopoietic chimerism with the use of short-tandem-repeat amplification, and HLA typing. The genomic rearrangements in mutant variants of leukemia were studied with the use of genomic HLA typing, microsatellite mapping, and single-nucleotide-polymorphism arrays. The post-transplantation immune responses against the original cells and the mutated leukemic cells were analyzed with the use of mixed lymphocyte cultures.

RESULTS

In 5 of 17 patients with leukemia relapse after haploidentical transplantation and infusion of donor T cells, we identified mutant variants of the original leukemic cells. In the mutant leukemic cells, the HLA haplotype that differed from the donor's haplotype had been lost because of acquired uniparental disomy of chromosome 6p. T cells from the donor and the patient after transplantation did not recognize the mutant leukemic cells, whereas the original leukemic cells taken at the time of diagnosis were efficiently recognized and killed.

CONCLUSIONS

After transplantation of haploidentical hematopoietic stem cells and infusion of donor T cells, leukemic cells can escape from the donor's antileukemic T cells through the loss of the mismatched HLA haplotype. This event leads to relapse.

Human acute myeloid leukemia CD34+CD38- stem cells are susceptible to allorecognition and lysis by single KIR-expressing natural killer cells

The concept of tumor immunosurveillance has raised prospects for natural killer cell-based immunotherapy of human cancer. The cure of acute myeloid leukemia may depend on eradication of leukemic stem cells, the self-renewing component of leukemia. Whether natural killer cells can recognize and lyse leukemic stem cells is not known. To develop strategies that effectively target acute myeloid leukemia-leukemic stem cells, we investigated anti-leukemic effects of human alloreactive single KIR(+) natural killer cells. Natural killer effectors with KIR specificity mismatched with respect to HLA class I allotype of target cells effectively recognized acute myeloid leukemia-leukemic stem cells defined phenotypically as CD34(+)CD38(-), while healthy bone marrow-derived CD34(+)CD38(-) hematopoietic stem cells were spared, as demonstrated by cytotoxicity and hematopoietic colony-forming assays. The HDAC inhibitor valproic acid increased the activating NKG2D ligand-dependent lysis of acute myeloid leukemia-CD34(+)CD38(-) leukemic stem cells. These results show that alloreactive natural killer cells have the potential to detect and target leukemic stem cells, and thus to improve the treatment outcome in acute myeloid leukemia.

What is the role for donor natural killer cells after nonmyeloablative conditioning?

We investigated the impacts of the tempo of early (days 14, 28, and 42) donor T cell and natural killer (NK) cell engraftment, missing recipient killer cell immunoglobulin-like receptor (KIR) ligands, and numbers of donor inhibitory and activating KIR genes on hematopoietic cell transplantation (HCT) outcomes in 282 patients with hematologic malignancies given nonmyeloablative conditioning. Modeling chimerism levels as a continuous linear variable, we found that high early donor T cell chimerism was significantly associated with acute graft-versus-host disease (aGVHD) (P = .01), whereas high donor NK cell chimerism levels had no such association (P = .38). Conversely, high donor NK cell chimerism levels were significantly associated with low relapse risk (P = .0009), whereas no significant association was seen with high donor T cell chimerism (P = .10). The qualitative associations between donor T cell and NK cell chimerism levels and GVHD and relapse did not change after adjustment for the presence of recipient KIR ligands or numbers of donor inhibitory or activating KIR genes. Our data indicate that prompt engraftment of donor NK cells correlated with lessened risks of relapse, but not with GVHD, whereas the converse was true for T cells.

Effects of activating NK cell receptor expression and NK cell reconstitution on the outcomes of unrelated donor hematopoietic cell transplantation for hematologic malignancies

Inhibitory NK cell receptors are recognized as important determinants of NK cell activity in hematopoietic cell transplantation (HCT). The role of activating receptors and their acquisition after HCT is less certain. Therefore, we comprehensively evaluated both inhibitory and activating receptors in 59 patients receiving unrelated donor HCT. NK cell numbers normalized quickly relative to B and T cells; however, the expression of both inhibitory and activating isoforms of killer immunoglobulin-like receptors (KIRs) was delayed. Most NK cells expressed an immature phenotype during the first 6 months post-HCT; however, we found high expression of activating NKp46 and NKp44 natural cytotoxicity receptors (NCRs), and cytotoxicity was preserved. Early reconstituting NK cells from unmanipulated grafts showed lower cytotoxicity than those from T-cell-depleted grafts. Differences in NK cell reconstitution had significant effects on clinical outcomes. Patients whose NK cells reconstituted earlier had better survival and lower relapse rates. The best survival group was recipients who possessed HLA-C2 but their donor lacked the cognate-activating KIR2DS1. Collectively, our data underscore the clinical relevance of reconstituting NK cells and their activating KIRs and NCRs. In addition to NK cell quantification and genotyping, comprehensive assessment of NK cell functions and phenotypes, including activating receptors, is essential.

What are the most important donor and recipient factors affecting the outcome of related and unrelated allogeneic transplantation?

Several recipient and donor risk factors affect outcome after transplantation with allogeneic hematopoietic stem cells. The most important recipient risk factors are patient age, comorbidity, performance status, cytomegalovirus (CMV) status, and disease considerations, such as diagnosis, stage, and cytogenetic risk. Prior chemotherapy regimens, patient race, and IL10 promoter polymorphism also appear to have some impact, but to a lesser extent. The most important donor factor is the level of HLA mismatch. Donor gender, relation, age, and KIR genotype also affect outcome. Donor CMV serology, parity, and race do not appear to affect outcome. These factors must all be considered in relation to one another when selecting whether to recommend patients for transplant.

Infusion of haplo-identical killer immunoglobulin-like receptor ligand mismatched NK cells for relapsed myeloma in the setting of autologous stem cell transplantation

Killer immunoglobulin-like receptor (KIR)-ligand mismatched natural killer (NK) cells play a key role in achieving durable remission after haplo-identical transplantation for acute myeloid leukaemia. We investigated the feasibility of transfusing haplo-identical, T-cell depleted, KIR-ligand mismatched NK cells, after conditioning therapy with melphalan and fludarabine, to patients with advanced multiple myeloma (MM) followed by delayed rescue with autologous stem cells. No graft-versus-host disease or failure of autologous stem cells to engraft was observed. There was significant variation in the number of allo-reactive NK cells transfused. However, all NK products containing allo-reactive NK cells killed the NK cell target K562, the MM cell line U266, and recipient MM cells when available. Post NK cell infusion there was a rise in endogenous interleukin-15 accompanied by increasing donor chimaerism. Donor chimaerism was eventually lost, which correlated with the emergence of potent host anti-donor responses indicating that the immunosuppressive properties of the conditioning regimen require further optimization. Further, blocking of inhibitory KIR-ligands with anti-human leucocyte antigen antibody substantially enhanced killing of MM cells thus highlighting the potential for modulating NK/MM cell interaction. Encouragingly, 50% of patients achieved (near) complete remission. These data set the stage for future studies of KIR-ligand mismatched NK cell therapy in the autologous setting.

Role of KIRs and KIR ligands in hematopoietic transplantation

This review focuses on recent research demonstrating the role alloreactive natural killer (NK) cells play in adoptive immunotherapy of leukemia in allogeneic hematopoietic transplantation. For patients with hematologic malignancies and an indication to allogeneic hematopoietic transplantation who do not have a matched sibling donor, unrelated donor, or cord blood transplants are almost always available (as long as the patient's ethnicity is represented in the donor registries). However, up to one half of patients relapse and do not make it to transplant during the time required for the donor search, completion of donor HLA typing, bone marrow harvest, and shipment. Donor-versus-recipient NK cell alloreactivity is effected by a functional repertoire of NK cells which express inhibitory Killer-Cell Immunoglobulin-like Receptor(s) (KIR) for self class I ligand(s), sense missing expression of donor KIR ligand(s) in the recipient and mediate alloreactions. It improves outcomes of HLA haplotype-mismatched ('haploidentical') transplants by controlling acute myeloid leukemia relapse without causing graft-versus-host disease. It is hoped the dramatic improvements afforded by the discovery of the role of NK cell alloreactivity will extend the use of haploidentical transplants, as the donors are, unlike the unrelated, immediately available family members.

Regulation of the NK cell alloreactivity to bone marrow cells by the combination of the host NK gene complex and MHC haplotypes

Host NK cells can reject MHC-incompatible (allogeneic) bone marrow cells (BMCs), suggesting their effective role for graft-vs leukemia effects in the clinical setting of bone marrow transplantation. NK cell-mediated rejection of allogeneic BMCs is dependent on donor and recipient MHC alleles and other factors that are not yet fully characterized. Whereas the molecular mechanisms of allogeneic MHC recognition by NK receptors have been well studied in vitro, guidelines to understand NK cell allogeneic reactivity under the control of multiple genetic components in vivo remain less well understood. In this study, we use congenic mice to show that BMC rejection is regulated by haplotypes of the NK gene complex (NKC) that encodes multiple NK cell receptors. Most importantly, host MHC differences modulated the NKC effect. Moreover, the NKC allelic differences also affected the outcome of hybrid resistance whereby F1 hybrid mice reject parental BMCs. Therefore, these data indicate that NK cell alloreactivity in vivo is dependent on the combination of the host NKC and MHC haplotypes. These data suggest that the NK cell self-tolerance process dynamically modulates the NK cell alloreactivity in vivo.

Hematopoietic SCT from partially HLA-mismatched (HLA-haploidentical) related donors

Hematopoietic SCT from a partially HLA-mismatched (HLA-haploidentical) first-degree relative offers the benefits of rapid and near universal donor availability but also the risks that result from traversing the HLA barrier; namely, graft failure, severe GVHD and prolonged immunodeficiency. Improvements over the last 10 years in conditioning regimens, graft engineering and pharmacological immunoprophylaxis of GVHD have substantially reduced the morbidity and mortality of HLA-haploidentical SCT. Highly immunosuppressive but nonmyeloablative conditioning extends the availability of HLA-haploidentical SCT to elderly hematologic malignancy patients lacking HLA-matched donors and permits recovery of autologous hematopoiesis in the event of graft failure. Current regimens for HLA-haploidentical SCT are associated with a 2-year non-relapse mortality of 20+/-5%, relapse of 35+/-15% and overall survival of 50+/-20%. Major developmental areas include harnessing natural killer cell alloreactivity to reduce the risk of disease relapse and improving immune reconstitution by delayed infusions of lymphocytes selectively depleted of alloreactive cells. Hematologic malignancy patients who lack suitably matched related or unrelated donors can now be treated with HLA-haploidentical related donor or unrelated umbilical cord blood SCT. Future clinical trials will assess the relative risks and benefits of these two graft sources.

Temporal, quantitative, and functional characteristics of single-KIR-positive alloreactive natural killer cell recovery account for impaired graft-versus-leukemia activity after haploidentical hematopoietic stem cell transplantation

In this study, we have characterized reconstitution of the natural killer (NK) cell repertoire after haploidentical CD34(+) selected hematopoietic stem cell transplantation (HSCT) for high-risk hematologic malignancies. Analysis focused on alloreactive single-KIR(+) NK cells, which reportedly are potent antileukemic effectors. One month after HSCT, CD56(bright)/CD56(dim) NK-cell subsets showed inverted ratio and phenotypic features. CD25 and CD117 down-regulation on CD56(bright), and NKG2A and CD62L up-regulation on CD56(dim), suggest sequential CD56(bright)-to-CD56(dim) NK-cell maturation in vivo. Consistently, the functional potential of these maturation intermediates against leukemic blasts was impaired. Mature receptor repertoire reconstitution took at least 3 months. Importantly, at this time point, supposedly alloreactive, single-KIR(+) NK cells were not yet fully functional. Frequency of these cells was highly variable, independently from predicted NK alloreactivity, and below 1% of NK cells in 3 of 6 alloreactive patients studied. In line with these observations, no clinical benefit of predicted NK alloreactivity was observed in the total cohort of 56 patients. Our findings unravel the kinetics, and limits, of NK-cell differentiation from purified haploidentical hematopoietic stem cells in vivo, and suggest that NK-cell antileukemic potential could be best exploited by infusion of mature single-KIR(+) NK cells selected from an alloreactive donor.