Donor natural killer cell allorecognition of missing self in haploidentical hematopoietic transplantation for acute myeloid leukemia: challenging its predictive value

Persuading natural killer cells to eliminate bad B cells

Clinical trials are underway infusing T cells genetically modified to be specific for B-cell malignancies using a chimeric antigen receptor (CAR) to redirect specificity for CD19. However, issues remain about whether the CAR can provide a fully competent application signal and whether other lymphocytes with lytic capacity can target CD19(+) tumors.

Natural killer cell immunotherapy for cancer: a new hope

Recently there has been a substantial gain in our understanding of the role NK-cells play in mediating innate host immune responses. Although NK cells have long been known to mediate antigen independent tumor cytotoxicity, the therapeutic potential of NK cell-based immunotherapy has yet to be realized. Manipulating the balance between inhibitory and activating NK receptor signals, sensitization of tumor target cells to NK cell-mediated apoptosis, and recent discoveries in NK-cell receptor biology have fueled translational research that has led to clinical trials investigating a number of novel methods to potentiate NK cytotoxicity against human malignancies.

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.

Separating graft-versus-leukemia from graft-versus-host disease in allogeneic hematopoietic stem cell transplantation

Routine methods to maximize the graft-versus-leukemia (GvL) activity of allogeneic hematopoietic stem cell transplantation (HSCT) without the detrimental effects of graft-versus-host disease (GvHD) are lacking. Depletion or inhibition of alloreactive T cells is partially effective in preventing GvHD, but usually leads to decreased GvL activity. The current model for the pathophysiology of acute GvHD describes a series of immune pathways that lead to activation of donor T cells and inflammatory cytokines responsible for tissue damage in acute GvHD. This model does not account for how allotransplant can lead to GvL effects without GvHD, or how the initial activation of donor immune cells may lead to counter-regulatory effects that limit GvHD. In this review, we will summarize new findings that support a more complex model for the initiation of GvHD and GvL activities in allogeneic HSCT, and discuss the potential of novel strategies to enhance GvL activity of the transplant.

Genetic and antibody-mediated reprogramming of natural killer cell missing-self recognition in vivo

Natural killer (NK) cells are lymphocytes of the innate immune system able to recognize and kill tumors lacking self-MHC class I molecules. This "missing-self" recognition is mediated by the lack of engagement of MHC class I-specific inhibitory NK cell receptors that include the killer cell Ig-like receptors (KIR) in humans and Ly49 molecules in mice. A promising immunotherapeutic strategy against MHC class I(+) cancer cells is to block NK cell inhibitory receptors using monoclonal antibodies (mAb). However, interactions between MHC class I molecules and their inhibitory receptors are also required for the acquisition of NK cell functional competence, a process referred as to "education." In addition, inhibitory receptors are involved in self-tolerance on educated NK cells. Here, we developed a preclinical mouse model in which all NK cells are educated by a single transgenic inhibitory receptor, human KIR2DL3, through the engagement with its HLA-Cw3 ligand. This approach revealed that NK cells could be reprogrammed to control the development of mouse syngenic tumors in vivo. Moreover, in vivo anti-KIR mAb treatment induced the killing of HLA(+) target cells without breaking self-tolerance. Finally, the long-term infusion of anti-KIR mAb neither abolished NK cell education nor tumor cell recognition. Therefore, these results strongly support the use of inhibitory receptor blockade in cancer patients.

Immunotherapy for pediatric cancer

Improvements in adult cancer survivorship can be achieved from behavioral changes and adopting screening programs. Yet, these approaches cannot be readily applied to lower the morbidity and mortality from childhood cancers. Rather, pediatric oncologists must rely on procedures and therapies to treat, rather than prevent malignancies. The systematic application of chemotherapy, radiation therapy, and surgery has led to remarkable advances in survival but these improvements have come at a cost. Children routinely receive chemotherapy agents that were designed decades ago, and these drugs have predictable side effects that result in the loss of potential for long-term survivors. The advent of targeted applications of immune-based therapies offers children with cancer a new class of oncolytic therapies that may be used to treat disease refractory to conventional approaches and lessen the toxicity of current treatment regimens without compromising remission. This review explores how 3 components of the immune system--T cells, natural killer (NK) cells, and antibodies--can be used for therapy of pediatric malignancies.

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.

Natural killer lysis receptor (NKLR)/NKLR-ligand matching as a novel approach for enhancing anti-tumor activity of allogeneic NK cells

Background

NK cells are key players in anti tumor immune response, which can be employed in cell-based therapeutic modalities. One of the suggested ways to amplify their anti tumor effect, especially in the field of stem cell transplantation, is by selecting donor/recipient mismatches in specific HLA, to reduce the inhibitory effect of killer Ig-like receptors (KIRs). Here we suggest an alternative approach for augmentation of anti tumor effect of allogeneic NK cells, which is founded on profile matching of donor NK lysis receptors (NKLR) phenotype with tumor lysis-ligands.

Methodology/Principal Findings

We show that an NKLR-mediated killing directly correlates with the NKLR expression intensity on NK cells. Considerable donor variability in the expression of CD16, NKp46, NKG2D and NKp30 on circulating NK cells, combined with the stability of phenotype in several independently performed tests over two months, indicates that NKLR-guided selection of donors is feasible. As a proof of concept, we show that melanoma cells are dominantly recognized by three NKLRs: NKG2D, NKp30 and NKp44. Notably, the expression of NKp30 on circulating NK cells among metastatic melanoma patients was significantly decreased, which diminishes their ability to kill melanoma cells. Ex vivo expansion of NK cells results not only in increased amount of cells but also in a consistently superior and predictable expression of NKG2D, NKp30 and NKp44. Moreover, expanded NK cultures with high expression of NKG2D or NKp30 were mostly derived from the corresponding NKG2D^high or NK30^high donors. These NK cultures subsequently displayed an improved cytotoxic activity against melanoma in a HLA/KIR-ligand mismatched setup, which was NKLR-dependent, as demonstrated with blocking anti-NKG2D antibodies.

Conclusions/Significance

NKLR/NKLR-ligand matching reproducibly elicits enhanced NK anti-tumor response. Common NKLR recognition patterns of tumors, as demonstrated here in melanoma, would allow implementation of this approach in solid malignancies and potentially in hematological malignancies, either independently or in adjunction to other modalities.

Clinical and immunologic outcomes following haplocompatible donor lymphocyte infusions

We retrospectively analyzed the characteristics of 16 consecutive pediatric patients who received one or more G-CSF-mobilized donor lymphocyte infusions (DLI) following a T-cell-depleted haplocompatible hematopoietic SCT (HSCT) to enhance immune recovery and/or treat an infection. The median time from HSCT to administration of first DLI was 12 weeks and the median dose of DLI administered was 3 x 10(4)/kg (range, 2.5-6 x 10(4)/kg). The incidence of Grade I-II acute GVHD was 19% (95% confidence interval (CI), 6-44%), and there were no cases of Grade III-IV acute GVHD. Chronic GVHD developed in 13% (95% CI, 2-37%) of patients. In surviving patients who did not undergo a second stem cell infusion, T-cell numbers and function increased to a protective level in a median of 3 months (range, 2-12.5 months) following the first DLI administration. In patients given DLI for treatment of an infection, 75% (95% CI, 46-92%) cleared their infection after a median of 9 weeks (range, 1-27 weeks). In patients with CMV infection, the development of CMV-specific T cells was observed following DLI. The 1-year overall survival following haplocompatible DLI was 71% (95% CI, 59-83%), with a median follow-up of 16 months from the first DLI.

Role of NK and NKT cells in solid organ transplantation

In the context of solid organ transplantation, the exact interactions between the innate and adaptive alloimmune response have not yet been fully explored. In this transplant setting, natural killer (NK) cells have emerged as a particular focus of interest because of their ability to distinguish allogeneic major histocompatibility complex (MHC) antigens and their potent cytolytic activity. Based on this observation and its potential clinical relevance, NK cells have recently been shown to participate in the immune response in both acute and chronic rejection of solid organ allografts. Numerous experimental and clinical studies demonstrate that NK cells determine transplant survival by rejecting an allograft not directly but indirectly by providing bystander effects. In addition, NK cells are influenced by immunosuppressive therapies such as calcineurin inhibitors or steroids. As NK and natural killer T (NKT) cells have also been shown to play a profound role in allograft tolerance induction, this review summarizes the major findings to highlight the functional role of these lymphocyte subsets, which may constitute an underestimated mechanism affecting graft outcome in solid organ transplantation.

Human CD80/IL2 lentivirus-transduced acute myeloid leukaemia (AML) cells promote natural killer (NK) cell activation and cytolytic activity: implications for a phase I clinical study

Immunotherapeutic strategies may promote T and/or natural killer (NK) cell cytotoxicity. NK cells have the potential to exert a powerful anti-leukaemia effect, as demonstrated by studies of allogeneic transplantation. We have previously shown that CD80/interleukin 2 (IL2) lentivirus (LV)-transduced AML cells stimulate in-vitro T cell activation. The present study demonstrated that allogeneic and autologous culture of peripheral blood mononuclear cells with CD80/IL2-expressing AML cells also promoted NK cell cytotoxicity. Expression of the activation receptors NKp30, NKp44, CD244, CD25, CD69 and HLA-DR significantly increased following allogeneic culture and a consistent increased expression of NKp30, NKp44, NKp46, NKG2D, NKG2C and CD69, and up-regulation of the cytolytic marker CD107a was detected following autologous culture with LV-CD80/IL2 AML cells. Furthermore, increased NK cell lysis of K562 and primary AML blasts was detected. The lytic activity increased by twofold against K562 (from 46.6% to 90.4%) and allogeneic AML cells (from 11.8% to 20.1%) following in-vitro stimulation by CD80/IL2-expressing AML cells. More importantly for potential therapeutic applications, lysis of primary AML cells by autologous NK cells increased by more than 40-fold (from 0.4% to 22.5%). These studies demonstrated that vaccination of patients with CD80/IL2-transduced AML cells could provide a powerful strategy for T/NK cell-mediated stimulation of anti-leukaemic immunological responses.

Natural killer cells in allogeneic transplantation: effect on engraftment, graft- versus-tumor, and graft-versus-host responses

Natural killer (NK) cells are effectors of the innate immune system and recognize cells transformed by viruses or neoplasia. Their response to "missing self" signals was described 3 decades ago, but the recent discovery of a panoply of activating receptors has made it clear that NK cell reactivity arises from a combination of inhibitory and activating signals. Successful clinical exploitation of NK cell reactivity was demonstrated in allogeneic transplantation for acute myelogenous leukemia from HLA-haploidentical donors when matched donors were not available. Multiple clinical studies have since attempted to use NK reactivity in the setting of both HLA-matched and -mismatched transplantation, with varying results. This review summarizes the heterogeneous clinical results and explains them based on a succinct description of NK cell biology.

Negative effect of KIR alloreactivity in recipients of umbilical cord blood transplant depends on transplantation conditioning intensity

We examined the clinical impact of killer-immunoglobulin receptor-ligand (KIR-L) mismatch in 257 recipients of single (n = 91) or double (n = 166) unit umbilical cord blood (UCB) grafts after myeloablative (n = 155) or reduced intensity (n = 102) conditioning regimens. Analyses of double unit grafts considered the KIR-L match status of the dominant engrafting unit. After myeloablative conditioning, KIR-L mismatch had no effect on grade III-IV acute graft-versus-host disease (GVHD), transplantation-related mortality (TRM), relapse, and survival. In contrast, after reduced intensity conditioning, KIR-L mismatch between the engrafted unit and the recipient resulted in significantly higher rates of grade III-IV acute GVHD (42% [CI, 27-59] vs 13% [CI, 5-21], P < .01) and TRM (27% [CI, 12%-42%] vs 12% [CI, 5%-19%], P = .03) with inferior survival (32% [CI, 15%-59%] vs 52% [CI, 47%-67%], P = .03). Multivariate analysis identified KIR-L mismatch as the only predictive factor associated with the development of grade III-IV acute GVHD (RR, 1.8 [CI, 1.1-2.9]; P = .02) and demonstrated a significant association between KIR-L mismatch and increased risk of death (RR, 1.8; 95% CI, 1.0-3.1; P = .05). Our results do not support the selection of UCB units based on KIR-L status and suggest that KIR-L mismatching should be avoided in reduced intensity UCB transplantation.

Neural progenitors derived from human embryonic stem cells are targeted by allogeneic T and natural killer cells

Neural progenitor cells (NPC) of foetal origin or derived from human embryonic stem cells (HESC) have the potential to differentiate into mature neurons after transplantation into the central nervous system, opening the possibility of cell therapy for neurodegenerative disorders. In most cases, the transplanted NPC are genetically unrelated to the recipient, leading to potential rejection of the transplanted cells. Very few data provide reliable information as to the potential immune response of allogeneic neural progenitors derived from HESC. In this study, we analyzed in vitro the allogeneic immune response of T lymphocytes and natural killer (NK) cells to NPC derived from HESC or of foetal origin. We demonstrate that NPC induce T-cell stimulation and a strong NK cytotoxic response. NK-cell activity is unrelated to MHC-I expression but driven by the activating NKG2D receptor. Cyclosporine and dexamethasone previously used in clinical studies with foetal NPC did not only fail to prevent NK alloreactivity but strongly inhibited the terminal maturation from NPC into mature neurons. We conclude that allogenic transplantation of NPC in the central nervous system will most likely require an immunosuppressive regimen targeting allogenic T and NK cells, whereas possible interference with the differentiation of NPC needs to be carefully evaluated.

Haploidentical stem cell transplantation after a reduced-intensity conditioning regimen for the treatment of advanced hematologic malignancies: posttransplantation CD8-depleted donor lymphocyte infusions contribute to improve T-cell recovery

Haploidentical hematopoietic stem cell transplantation provides an option for patients with advanced hematologic malignancies lacking a compatible donor. In this prospective phase 1/2 trial, we evaluated the role of reduced-intensity conditioning (RIC) followed by early add-backs of CD8-depleted donor lymphocyte infusions (DLIs). The RIC regimen consisted of thiotepa, fludarabine, cyclophosphamide, and 2 Gy total body irradiation. Twenty-eight patients with advanced lymphoproliferative diseases (n = 24) or acute myeloid leukemia (n = 4) were enrolled. Ex vivo and in vivo T-cell depletion was carried out by CD34(+) cell selection and alemtuzumab treatment. The 2-year cumulative incidence of nonrelapse mortality was 26% and the 2-year overall survival (OS) was 44%, with a better outcome for patients with chemosensitive disease (OS, 75%). Overall, 54 CD8-depleted DLIs were administered to 23 patients (82%) at 3 different dose levels without loss of engraftment or acute toxicities. Overall, 6 of 23 patients (26%) developed grade II-IV graft-versus-host disease, mainly at dose level 2. In conclusion, our RIC regimen allowed a stable engraftment with a rather low nonrelapse mortality in poor-risk patients; OS is encouraging with some long-term remissions in lymphoid malignancies. CD8-depleted DLIs are feasible and promote the immune reconstitution.

Bortezomib treatment and regulatory T-cell depletion enhance the antitumor effects of adoptively infused NK cells

Ligation of inhibitory receptors renders natural killer (NK) cells inactive against autologous tumors. Recently, the proteasome inhibitor bortezomib was shown to sensitize tumors to autologous NK-cell cytotoxicity in vitro. Here, we show bortezomib augments the antitumor effects of syngeneic NK-cell infusions in tumor-bearing animals; this effect is further enhanced in regulatory T cell (Treg cell)-depleted hosts. In vitro, bortezomib-treated tumors had higher tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and perforin/granzyme-mediated caspase-8 activity, which enhanced their susceptibility to NK-cell lysis. Bioluminescence imaging of mice with established tumors showed treatment with bortezomib and syngeneic NK cells reduced tumor growth and prolonged survival compared with controls receiving bortezomib or NK cells alone. In contrast, tumor progression was not delayed when animals received bortezomib and perforin-deficient NK cells, showing drug-induced augmentation in NK-cell cytotoxicity was mediated through perforin/granzyme. Furthermore, tumor growth was slower in bortezomib-treated recipients when host Treg cells were eradicated with anti-CD25 antibody before infusing NK cells compared with mice without Treg-cell ablation (tumor doubling time, 16.7 vs 4.9 days, respectively; P = .02). These findings suggest that depletion of Treg cells followed by bortezomib-induced tumor sensitization to autologous NK cells could be used as a novel strategy to treat cancer.

Breaking tolerance to self, circulating natural killer cells expressing inhibitory KIR for non-self HLA exhibit effector function after T cell-depleted allogeneic hematopoietic cell transplantation

Alloreactive natural killer (NK) cells are an important influence on hematopoietic stem cell transplantation (HSCT) outcome. In HLA-mismatched HSCT, alloreactivity occurs when licensed donor NK cells expressing inhibitory killer Ig-like receptors (KIR) for donor MHC class I ligands recognize the lack of the class I ligands in the mismatched recipient ("missing self"). Studies in HLA-matched HSCT, however, have also demonstrated improved outcome in patients lacking class I ligands for donor inhibitory KIR ("missing ligand"), indicating that classically nonlicensed donor NK cells expressing KIR for non-self MHC class I ligands may exhibit functional competence in HSCT. We examined NK function in 16 recipients of T cell-depleted allografts from HLA-identical or KIR-ligand matched donors after myeloablative therapy. After HSCT, nonlicensed NK cells expressing inhibitory KIR for non-self class I exhibit robust intracellular IFN-gamma and cytotoxic response to target cells lacking cognate ligand, gradually becoming tolerized to self by day 100. These findings could not be correlated with cytokine environment or phenotypic markers of NK development, nor could they be attributed to non-KIR receptors such as CD94/NKG2A. These findings confirm that NK alloreactivity can occur in HLA-matched HSCT, where tolerance to self is either acquired by the stem cell-derived NK cell after exiting the bone marrow or where tolerance to self can be temporarily overcome.

KIR-ligand incompatibility in the graft-versus-host direction improves outcomes after umbilical cord blood transplantation for acute leukemia

Donor killer cell immunoglobulin-like receptor (KIR)-ligand incompatibility is associated with decreased relapse incidence (RI) and improved leukemia-free survival (LFS) after haploidentical and HLA-mismatched unrelated hematopoietic stem cell transplantation. We assessed outcomes of 218 patients with acute myeloid leukemia (AML n=94) or acute lymphoblastic leukemia (n=124) in complete remission (CR) who had received a single-unit unrelated cord blood transplant (UCBT) from a KIR-ligand-compatible or -incompatible donor. Grafts were HLA-A, -B or -DRB1 matched (n=21) or mismatched (n=197). Patients and donors were categorized according to their degree of KIR-ligand compatibility in the graft-versus-host direction by determining whether or not they expressed HLA-C group 1 or 2, HLA-Bw4 or HLA-A3/-A11. Both HLA-C/-B KIR-ligand- and HLA-A-A3/-A11 KIR-ligand-incompatible UCBT showed a trend to improved LFS (P=0.09 and P=0.13, respectively). Sixty-nine donor–patient pairs were HLA-A, -B or -C KIR-ligand incompatible and 149 compatible. KIR-ligand-incompatible UCBT showed improved LFS (hazards ratio=2.05, P=0.0016) and overall survival (OS) (hazards ratio=2.0, P=0.004) and decreased RI (hazards ratio=0.53, P=0.05). These results were more evident for AML transplant recipients (2-year LFS and RI with or without KIR-ligand incompatibility 73 versus 38% (P=0.012), and 5 versus 36% (P=0.005), respectively). UCBT for acute leukemia in CR from KIR-ligand-incompatible donors is associated with decreased RI and improved LFS and OS.

Natural killer cell receptor repertoire and their ligands, and the risk of CMV infection after kidney transplantation

Cytomegalovirus (CMV) infection is the most common viral complication after solid organ transplantation (SOT). Whilst current immunosuppression is known to impair antiviral-specific T-cell immunity in SOT, a potential role for natural killer (NK) cells not affected by immunosuppressive therapy remains to be determined. To address this, we compared the genotype of the NK immunoglobulin-like receptor (KIR) genes and their HLA cognate ligands to the rate of CMV infection in 196 kidney transplant recipients. We have shown that the absence of the HLA-C ligand for inhibitory KIR and the presence of activating KIR genes in the recipients were both associated with a lower rate of CMV infection after transplantation. In a cohort of 17 recipients with acute CMV infection, NK cells were phenotyped over a period of time after diagnosis by their expression profile of C-type lectin receptors and capacity to secrete IFN-gamma. The increased expression of the activating C-type lectin receptors NKG2C and NKG2D was paralleled by the decreased IFN-gamma secretion during the early phase of CMV infection. In conclusion, our findings suggest that KIR/HLA genotype and expression of NKG2C and NKG2D might play a significant role in regulating NK cell function and anti-CMV immunity after kidney transplantation.

The strength of inhibitory input during education quantitatively tunes the functional responsiveness of individual natural killer cells

Natural killer (NK) cells express inhibitory receptors for major histocompatibility complex (MHC) class I. If self-MHC is down-regulated or absent, lack of inhibition triggers "missing self" killing. NK cells developing in the absence of MHC class I are hypo-responsive, demonstrating that MHC class I molecules are required for NK-cell education. Here, we show that the number and the type of MHC class I alleles that are present during NK-cell education quantitatively determine the frequency of responding NK cells, the number of effector functions in individual NK cells, and the amount of interferon-gamma production in NK cells of specific Ly49 subsets. A relationship between the extent of inhibitory signals during education and functional responsiveness was corroborated by an enhanced probability of NK cells expressing more than one inhibitory receptor for a single host self-MHC class I allele to degranulate after activation. Our data suggest that the capacity of an individual NK cell to respond to stimulation is quantitatively controlled by the extent of inhibitory signals that are received from MHC class I molecules during NK-cell education.

Reconstitution of the immune system after hematopoietic stem cell transplantation in humans

Hematopoietic stem cell transplantation is associated with a severe immune deficiency. As a result, the patient is at high risk of infections. Innate immunity, including epithelial barriers, monocytes, granulocytes, and NK cells recovers within weeks after transplantation. By contrast, adaptive immunity recovers much slower. B- and T-cell counts normalize during the first months after transplantation, but in particular, T-cell immunity may remain impaired for years. During the last decade, much of the underlying mechanisms have been identified. These insights may provide new therapies to accelerate recovery.

Anti-leukemia activity of alloreactive NK cells in KIR ligand-mismatched haploidentical HSCT for pediatric patients: evaluation of the functional role of activating KIR and redefinition of inhibitory KIR specificity

We analyzed 21 children with leukemia receiving haploidentical hematopoietic stem cell transplantation (haplo-HSCT) from killer immunoglobulin (Ig)-like receptors (KIR) ligand-mismatched donors. We showed that, in most transplantation patients, variable proportions of donor-derived alloreactive natural killer (NK) cells displaying anti-leukemia activity were generated and maintained even late after transplantation. This was assessed through analysis of donor KIR genotype, as well as through phenotypic and functional analyses of NK cells, both at the polyclonal and clonal level. Donor-derived KIR2DL1(+) NK cells isolated from the recipient displayed the expected capability of selectively killing C1/C1 target cells, including patient leukemia blasts. Differently, KIR2DL2/3(+) NK cells displayed poor alloreactivity against leukemia cells carrying human leukocyte antigen (HLA) alleles belonging to C2 group. Unexpectedly, this was due to recognition of C2 by KIR2DL2/3, as revealed by receptor blocking experiments and by binding assays of soluble KIR to HLA-C transfectants. Remarkably, however, C2/C2 leukemia blasts were killed by KIR2DL2/3(+) (or by NKG2A(+)) NK cells that coexpressed KIR2DS1. This could be explained by the ability of KIR2DS1 to directly recognize C2 on leukemia cells. A role of the KIR2DS2 activating receptor in leukemia cell lysis could not be demonstrated. Altogether, these results may have important clinical implications for the selection of optimal donors for haplo-HSCT.

Donors with group B KIR haplotypes improve relapse-free survival after unrelated hematopoietic cell transplantation for acute myelogenous leukemia

Survival for patients with acute myeloid leukemia (AML) is limited by treatment-related mortality (TRM) and relapse after unrelated donor (URD) hematopoietic cell transplantation (HCT). Natural killer (NK)-cell alloreactivity, determined by donor killer-cell immunoglobulin-like receptors (KIRs) and recipient HLA, correlates with successful HCT for AML. Hypothesizing that donor KIR genotype (A/A: 2 A KIR haplotypes; B/x: at least 1 B haplotype) would affect outcomes, we genotyped donors and recipients from 209 HLA-matched and 239 mismatched T-replete URD transplantations for AML. Three-year overall survival was significantly higher after transplantation from a KIR B/x donor (31% [95% CI: 26-36] vs 20% [95% CI: 13-27]; P = .007). Multivariate analysis demonstrated a 30% improvement in the relative risk of relapse-free survival with B/x donors compared with A/A donors (RR: 0.70 [95% CI: 0.55-0.88]; P = .002). B/x donors were associated with a higher incidence of chronic graft-versus-host disease (GVHD; RR: 1.51 [95% CI: 1.01-2.18]; P = .03), but not of acute GVHD, relapse, or TRM. This analysis demonstrates that unrelated donors with KIR B haplotypes confer significant survival benefit to patients undergoing T-replete HCT for AML. KIR genotyping of prospective donors, in addition to HLA typing, should be performed to identify HLA-matched donors with B KIR haplotypes.

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.

Response and toxicity of donor lymphocyte infusions following T-cell depleted non-myeloablative allogeneic hematopoietic SCT from 3-6/6 HLA matched donors

We report the outcome of early donor lymphocyte infusions (DLIs) after T-cell depleted non-myeloablative transplantation using stem cells from HLA-matched or mismatched donors. Sixty-nine patients with high-risk hematologic malignancies received DLI following fludarabine, CY and alemtuzumab with infusion of stem cells from a matched sibling (52) or partially matched family member donor (17). Patients received the first infusion at a median of 50 days after transplant, and doses ranged from 1 x 10(4) CD3+ cells/kg to 3.27 x 10(8) CD3+ cells/kg, depending on clinical status and the physician's discretion. A median cell dose of 1 x 10(5) CD3+ cells/kg in the mismatched setting and 1 x 10(6) CD3+ cells/kg in the matched sibling setting appears safe with only 1 of 7 (14%) and 4 of 31 patients (13%), respectively, experiencing severe acute GVHD at these doses. Importantly, 38% of patients with persistent disease before DLI attained a remission after infusion. Nine of the 69 patients remain alive and disease-free 32-71 months after the first DLI. In conclusion, low doses of DLI can be safely provided soon after T-cell depleted non-myeloablative therapy and provide a chance of remission. However, long-term survival still remains poor, primarily because of relapse in these patients.

Role of the inhibitory KIR ligand HLA-Bw4 and HLA-C expression levels in the recognition of leukemic cells by Natural Killer cells

Transplantation of acute myeloid leukemia (AML) patients with grafts from related haploidentical donors has been shown to result in a potent graft-versus-leukemia effect. This effect is mediated by NK cells because of the lack of activation of inhibitory killer cell immunoglobulin-like receptors (KIRs) which recognize HLA-Bw4 and HLA-C alleles. However, conflicting results have been reported about the impact of KIR ligand mismatching on the outcome of unrelated HLA-mismatched hematopoietic stem cells transplants (HSCT) to leukemic patients. The interpretation of these conflicting results is hampered by the scant information about the level of expression of HLA class I alleles on leukemic cells, although this variable may affect the activation of inhibitory KIRs. Therefore in the present study, utilizing a large panel of human monoclonal antibodies we have measured the level of expression of HLA-A, -B and -C alleles on 20 B-chronic lymphoid leukemic (B-CLL) cell preparations, on 16 B-acute lymphoid leukemic (B-ALL) cell preparations and on 19 AML cell preparations. Comparison of the level of HLA class I antigen expression on leukemic cells and autologous normal T cells identified selective downregulation of HLA-A and HLA-B alleles on 15 and 14 of the 20 B-CLL, on 2 and 5 of the 16 B-ALL and on 7 and 11 of the 19 AML patients tested, respectively. Most interestingly HLA-C alleles were markedly downregulated on all three types of leukemic cells; the downregulation was most pronounced on AML cells. The potential functional relevance of these abnormalities is suggested by the dose-dependent enhancement of NK cell activation caused by coating the HLA-HLA-Bw4 epitope with monoclonal antibodies on leukemic cells which express NK cell activating ligands. Our results suggest that besides the HLA and KIR genotype, expression levels of KIR ligands on leukemic cells should be included among the criteria used to select the donor-recipient combinations for HSCT.

Human natural killer cells

Natural killer (NK) cells were discovered more than 30 years ago. NK cells are large granular lymphocytes that belong to the innate immune system because unlike T or B lymphocytes of the adaptive or antigen-specific immune system, NK cells do not rearrange T-cell receptor or immunoglobulin genes from their germline configuration. During the past 2 decades there has been a substantial gain in our understanding of what and how NK-cells "see," lending important insights into their functions and purpose in normal immune surveillance. The most recent discoveries in NK-cell receptor biology have fueled translational research that has led to remarkable results in treating human malignancy.

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.

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.

Blocking NK cell inhibitory self-recognition promotes antibody-dependent cellular cytotoxicity in a model of anti-lymphoma therapy

Human NK cells lyse Ab-coated target cells through the process of Ab-dependent cellular cytotoxicity (ADCC). Improving ADCC responses is desirable because it is thought to be an important antitumor mechanism for some Abs. NK cell inhibitory receptors, such as killer cell Ig-like receptors, engage with MHC class I molecules on self-cells to block NK cell activation. Accordingly, we enhanced ADCC responses by blocking NK cell inhibitory receptors, thus perturbing induction of the self-recognition signal. In a cell line model of anti-lymphoma therapy, the combination of rituximab with an Ab that blocks inhibitory self-recognition yielded increased NK cell-mediated target cell lysis when compared with rituximab alone. To validate this proof-of-concept, we then used a more representative approach in which an individual's fresh primary NK cells encountered autologous, EBV-transformed B cells. In this system, rituximab and a combination of Abs that block NK cell inhibitory receptors yielded improved NK cell-mediated lysis over rituximab alone. The results show, for the first time, that disruption of inhibitory self-recognition can efficiently promote ADCC in a human model, applying an autologous system in which physiologic checkpoints are in place. This method provides an alternative approach to potentiate the therapeutic benefit of antitumor Abs that mediate ADCC.

The number of activating KIR genes inversely correlates with the rate of CMV infection/reactivation in kidney transplant recipients

Viral infection is a common complication after kidney transplantation. The role of natural killer cells (NK cells) in this setting remains unknown. NK cells express activating and inhibitory killer cell immunoglobulin-like receptors (KIR). We analyzed whether activating KIR genes carried by kidney transplant-recipients influence the rate of viral infection during the first year after transplantation. In patients with a KIR A/A genotype (n = 40, KIR2DS4 only activating KIR) the rate of cytomegalovirus (CMV) infection and reactivation was 36%, as compared to 20% in transplant recipients with more than one activating KIR gene (KIR B/X genotype, n = 82, p = 0.04). Adjusting for other risk factors in Cox regression, the relative risk of B versus A genotype patients was 0.34 (95% CI 0.15-0.76, p = 0.009). The degree of protection increased with the number of activating KIR genes. Symptomatic CMV disease was only observed in four individuals, all carrying a KIR A/A genotype. As for viral infections other than CMV, and for bacterial infections, no KIR-linked protective effect could be detected. Also, graft function and the rate-rejection episodes were similar in KIR A/A and KIR B/X genotype individuals. This study supports a role for activating KIR in the control of CMV infection after kidney transplantation.

Separation of graft-vs.-tumor effects from graft-vs.-host disease in allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (HCT) is an increasingly widely used treatment modality in hematological malignancies. Alloreactivity mediated by donor T cells (and, in some settings, by donor natural killer cells) can produce durable immunologic control or eradication of residual malignancy after allogeneic HCT. However, graft-vs.-tumor (GVT) effects are variably effective and are often accompanied by deleterious alloreactivity against normal host tissue, manifesting as graft-vs.-host disease (GVHD). A major focus of current research in HCT is the separation of beneficial GVT effects from GVHD. Here we review a number of approaches currently under investigation to specifically augment GVT effects, including the identification of minor histocompatibility antigens (mHA), adoptive immunotherapy with tumor-specific or mHA-specific cytotoxic T lymphocytes, vaccination of the donor or recipient to stimulate tumor-specific immunity, and adoptive transfer of natural killer cells. In addition, we review strategies being investigated to specifically suppress GVHD while sparing GVT, including the manipulation and infusion of regulatory T cells, the use of novel pharmacologic and biologic agents, and the use of mesenchymal stem cells. Ultimately, advances in separation of GVT from GVHD will further enhance the potential of allogeneic HCT as a curative treatment for hematological malignancies.

Life expectancy and prognostic factors in the classic BCR/ABL-negative myeloproliferative disorders

Among the 'classic' BCR/ABL-negative chronic myeloproliferative disorders, primary myelofibrosis (PMF) is associated with a substantial life-expectancy reduction. In this disease, initial haemoglobin level is the most important prognostic factor, whereas age, constitutional symptoms, low or high leukocyte counts, blood blast cells and cytogenetic abnormalities are also of value. Several prognostic systems have been proposed to identify subgroups of patients with a different risk, which is especially important in younger individuals, who may benefit from therapies with curative potential. Essential thrombocythaemia (ET) affects the patients' quality of life more than the survival, due to the high occurrence of thrombosis, whereas polycythaemia vera (PV) has a substantial morbidity derived from thrombosis but also a certain reduction in life expectancy. Therefore, in the latter disorders, prognostic studies have focused primarily on prediction of the thrombosis, with age and a previous history of thrombosis being the main prognostic factors of such complication. The importance of higher leukocyte counts in thrombosis development has been recently pointed out in ET and PV, where a role for mutated JAK2 allele burden has also been noted. With regard to PMF, the possible association of the mutation with shorter survival and higher acute transformation rate is currently being evaluated.

E2F1 contributes to the transcriptional activation of the KIR3DL1 gene

The KIR3DL1 gene is a member of killer immunoglobulin-like receptors family, which exhibits a variegated expression pattern in NK cells and subsets of CD4(+) and CD8(+) T cells. The E2F family of transcription factors plays a crucial role in the regulation of gene expression. The present study reports a naturally occurring point mutation (TTTGGCGC-->TTCGGCGC) within a putative E2F binding site in the KIR3DL1 promoter in K562 cells. Interestingly, this mutation introduces a new methylation site. This study shows for the first time that E2F1 binds to the KIR3DL1 promoter in vivo. This point mutation and concomitantly altered methylation pattern within the E2F1 binding site abolishes their binding and reduces the promoter activity, while elevated expression of E2F1 correlates with increased promoter activity. Therefore, E2F1 contributes to the transcriptional activation of the KIR3DL1 gene.

The proinflammatory cytokines IL-2, IL-15 and IL-21 modulate the repertoire of mature human natural killer cell receptors

Natural killer (NK) cells play a crucial role in the immune response to micro-organisms and tumours. Recent evidence suggests that NK cells also regulate the adaptive T-cell response and that it might be possible to exploit this ability to eliminate autoreactive T cells in autoimmune disease and alloreactive T cells in transplantation. Mature NK cells consist of a highly diverse population of cells that expresses different receptors to facilitate recognition of diseased cells and possibly pathogens themselves. Ex vivo culture of NK cells with cytokines such as IL-2 and IL-15 is an approach that permits significant expansion of the NK cell subpopulations, which are likely to have potent antitumour, antiviral, or immunomodulatory effects in autoimmunity. Our data indicate that the addition of IL-21 has a synergistic effect by increasing the numbers of NK cells on a large scale. IL-2 and IL-15 may induce the expression of killer cell immunoglobulin-like receptors (KIRs) in KIR-negative populations, the c-lectin receptor NKG2D and the natural cytotoxic receptor NKp44. The addition of IL-21 to IL-15 or IL-2 can modify the pattern of the KIR receptors and inhibit NKp44 expression by reducing the expression of the adaptor DAP-12. IL-21 also preserved the production of interferon-γ and enhanced the cytotoxic properties of NK cells. Our findings indicate that the proinflammatory cytokines IL-2, IL-15 and IL-21 can modify the peripheral repertoire of NK cells. These properties may be used to endow subpopulations of NK cells with specific phenotypes, which may be used in ex vivo cellular immunotherapy strategies.