Role of KIRs and KIR ligands in hematopoietic transplantation

Metabolic instruction of the graft-versus-leukemia immunity

Allogeneic hematopoietic cell transplantation (allo-HCT) is frequently performed to cure hematological malignancies, such as acute myeloid leukemia (AML), through the graft-versus-leukemia (GVL) effect. In this immunological process, donor immune cells eliminate residual cancer cells in the patient and exert tumor control through immunosurveillance. However, GVL failure and subsequent leukemia relapse are frequent and associated with a dismal prognosis. A better understanding of the mechanisms underlying AML immune evasion is essential for developing novel therapeutic strategies to boost the GVL effect. Cellular metabolism has emerged as an essential regulator of survival and cell fate for both cancer and immune cells. Leukemia and T cells utilize specific metabolic programs, including the orchestrated use of glucose, amino acids, and fatty acids, to support their growth and function. Besides regulating cell-intrinsic processes, metabolism shapes the extracellular environment and plays an important role in cell-cell communication. This review focuses on recent advances in the understanding of how metabolism might affect the anti-leukemia immune response. First, we provide a general overview of the mechanisms of immune escape after allo-HCT and an introduction to leukemia and T cell metabolism. Further, we discuss how leukemia and myeloid cell metabolism contribute to an altered microenvironment that impairs T cell function. Next, we review the literature linking metabolic processes in AML cells with their inhibitory checkpoint ligand expression. Finally, we focus on recent findings concerning the role of systemic metabolism in sustained GVL efficacy. While the majority of evidence in the field still stems from basic and preclinical studies, we discuss translational findings and propose further avenues for bridging the gap between bench and bedside.

NK cell defects: implication in acute myeloid leukemia

Acute Myeloid Leukemia (AML) is a complex disease with rapid progression and poor/unsatisfactory outcomes. In the past few years, the focus has been on developing newer therapies for AML; however, relapse remains a significant problem. Natural Killer cells have strong anti-tumor potential against AML. This NK-mediated cytotoxicity is often restricted by cellular defects caused by disease-associated mechanisms, which can lead to disease progression. A stark feature of AML is the low/no expression of the cognate HLA ligands for the activating KIR receptors, due to which these tumor cells evade NK-mediated lysis. Recently, different Natural Killer cell therapies have been implicated in treating AML, such as the adoptive NK cell transfer, Chimeric antigen receptor-modified NK (CAR-NK) cell therapy, antibodies, cytokine, and drug treatment. However, the data available is scarce, and the outcomes vary between different transplant settings and different types of leukemia. Moreover, remission achieved by some of these therapies is only for a short time. In this mini-review, we will discuss the role of NK cell defects in AML progression, particularly the expression of different cell surface markers, the available NK cell therapies, and the results from various preclinical and clinical trials.

The Influence of KIR Gene Polymorphisms and KIR-ligand Binding on Outcomes in Hematologic Malignancies following Haploidentical Stem Cell Transplantation: A Comprehensive Review

Natural killer (NK) cell behavior and function are controlled by a balance between negative or positive signals generated by an extensive array of activating and inhibiting receptors, including killer cell immunoglobulin-like receptor (KIR) proteins, main components of the innate immune system that contribute to initial responses against viral infected-transformed cells through generation of the release of cytokines and cytotoxicity. What is certain is that KIRs are genetically polymorphic and the extent of KIRs diversity within the individuals may have the potential outcomes for hematopoietic stem cell transplantation (HSCT). In this regard, recent studies suggest that KIR is as imperative as its ligand (HLA) in stem cell transplantation for malignant diseases. However, unlike HLA epitope mismatches, which are well-known causes of NK alloreactivity, a complete understanding of KIR genes' role in HSCT remains unclear. Because of genetic variability in KIR gene content, allelic polymorphism, and cell-surface expression among individuals, an appropriate selection of donors based on HLA and KIR profiles is crucial to improve outcomes of stem cell transplantation. In addition, the impact of the KIR/HLA interaction on HSCT outcomes needs to be investigated more comprehensively. The present work aimed to review the NK cell regeneration, KIR gene polymorphisms, and KIRligand binding on outcomes in hematologic malignancies following haploidentical stem cell transplantation. Comprehensive data gathered from the literature can provide new insight into the significance of KIR matching status in transplantations.

Protective and causative killer Ig-like receptor (KIR) and metalloproteinase genetic patterns associated with Herpes simplex virus 1 (HSV-1) encephalitis occurrence

BACKGROUND

The cerebral innate immune system has a critical role in control processes of viral replication in the brain after primary infactivo and immunologic disregulation and inflammation has been reported as a primary determinant of pathogenesis and prognosis of subsequent HSV-1 related encephalitis (HSE). Interaction linking LTR3-activated DCs is also represented by the killer Ig-like receptor (KIR) + pathways on NK cells. Only a few studies analyzed the role of of MMP-9 activity regulating genetic polymorphism on clinical outcome of viral infections. Susceptibility to symptomatic encephalitis depends on SNC viral invasion and BBB disruption. We hypothesize that certain KIR genes and MMP allele may help to characterize a risk profile of developing an acute encephalitis due to HSV 1.

AIM OF THE STUDY

Analyze the frequency of KIR genes and the C(-1562)T MMP-9 allels in subjects with HSV-1 encephalitis and to analyze their interaction with regard of the risk of occurrence of a symptomatic encephalitis.

MATERIALS AND METHODS

Between November 2014 and January 2019, all consecutive patients with symptomatic acute encephalitis were recruited from three wards (Internal Medicine, Neurology, and Infectious Diseases) of "P. Giaccone" University Hospital, Palermo.

RESULTS

Patients with acute viral encephalitis in comparison to controls showed a higher frequency AA KIR haplotype, HLA-C2 and of HLA-A-Bw4 alleles. With regard of HLA allele frequency patients with acute viral encephalitis In comparison to controls also showed a higher frequency of HLA-C2 and of HLA-A-Bw4 alleles. With regard of MMP-9 alleles, subjects with acute viral encephalitis were more likely to have the TT genotype. The multiple logistic regression analysis considering variables predictive of the occurrence of acute viral encephalitis showed the detrimental effect of AA KIR, HLAC1, HLA-A-BW4 and HLA-B-BW4T and of TT aplotype of MMP-9 genotype.

CONCLUSIONS

Our study shows that in immunocompetent adult subjects there is an association between some KIR genes, MMP-9 alleles and HLA-ligand alleles and susceptibility to develop a symptomatic acute viral encephalitis. Definition of the genetic and immunological background of acute viral encephalitis can play a key role to determine personalized medicine.

Non-Genetically Improving the Natural Cytotoxicity of Natural Killer (NK) Cells

The innate lymphocyte lineage natural killer (NK) is now the target of multiple clinical applications, although none has received an agreement from any regulatory agency yet. Transplant of naïve NK cells has not proven efficient enough in the vast majority of clinical trials. Hence, new protocols wish to improve their medical use by producing them from stem cells and/or modifying them by genetic engineering. These techniques have given interesting results but these improvements often hide that natural killers are mainly that: natural. We discuss here different ways to take advantage of NK physiology to improve their clinical activity without the need of additional modifications except for in vitro activation and expansion and allograft in patients. Some of these tactics include combination with monoclonal antibodies (mAb), drugs that change metabolism and engraftment of specific NK subsets with particular activity. Finally, we propose to use specific NK cell subsets found in certain patients that show increase activity against a specific disease, including the use of NK cells derived from patients.

The Graft-Versus-Leukemia Effect in AML

Allogeneic hematopoietic stem cell transplantation (allo-SCT) is the most established and commonly used cellular immunotherapy in cancer care. It is the most potent anti-leukemic therapy in patients with acute myeloid leukemia (AML) and is routinely used with curative intent in patients with intermediate and poor risk disease. Donor T cells, and possibly other immune cells, eliminate residual leukemia cells after prior (radio)chemotherapy. This immune-mediated response is known as graft-versus-leukemia (GvL). Donor alloimmune responses can also be directed against healthy tissues, which is known as graft-versus-host disease (GvHD). GvHD and GvL often co-occur and, therefore, a major barrier to exploiting the full immunotherapeutic benefit of donor immune cells against patient leukemia is the immunosuppression required to treat GvHD. However, curative responses to allo-SCT and GvHD do not always occur together, suggesting that these two immune responses could be de-coupled in some patients. To make further progress in successfully promoting GvL without GvHD, we must transform our limited understanding of the cellular and molecular basis of GvL and GvHD. Specifically, in most patients we do not understand the antigenic basis of immune responses in GvL and GvHD. Identification of antigens important for GvL but not GvHD, and vice versa, could impact on donor selection, allow us to track GvL immune responses and begin to specifically harness and strengthen anti-leukemic immune responses against patient AML cells, whilst minimizing the toxicity of GvHD.

Natural killer cell-based immunotherapy with CTLA4Ig-primed donor lymphocytes following haploidentical transplantation

NK cell-based immunotherapy is one of the more exciting propositions in the field of cellular therapy for hematological malignancies. Current protocols are largely based on expanded and activated NK cells which are used both with and without allogeneic transplantation. Based on our recent findings, we discuss the concept of CTLA4Ig-primed donor lymphocyte infusions following haploidentical transplantation as an effective tool to garner NK cell-mediated antitumor effect with abrogation of T cell-mediated alloreactivity. This approach might widen the possibility of immunotherapy following haploidentical transplantation without increase in graft-versus-host disease. Further studies would be needed to establish the veracity of this concept with better understanding of the antitumor effect via this pathway. Future studies would decide if CTLA4Ig might be used to augment NK-cell activation in vitro as well.

Modification of NK cell subset repartition and functions in granulocyte colony-stimulating factor-mobilized leukapheresis after expansion with IL-15

The ability of natural killer (NK) cells to kill tumor cells without antigen recognition makes them appealing as an adoptive immunotherapy. However, NK cells are not routinely used in the context of leukemic relapse after hematopoietic stem cell transplantation. Patients who experience relapse can be treated with donor lymphocyte infusions (DLI) based on small-cell fractions frozen at the time of transplantation. Since peripheral blood stem cells (PBSCs) are increasingly used as a stem cell source and as a source of cells for DLI, we aimed to evaluate the impact of G-SCF mobilization on NK cell phenotype, subset repartition, and functionality. Immunomagnetically isolated NK cells from healthy donor blood, donor PBSCs, and patient PBSCs were expanded for 14 days with IL-15. The expansion capacity, phenotype, and functions (cytokine secretion and cytotoxicity) of NK cell subsets based on CD56 and CD16 expression were then evaluated. Mobilized sources showed a significant decrease of CD56^brightCD16⁺ NK cells (28 versus 74%), whereas a significant increase (64 versus 15%) of CD56^brightCD16^- NK cells was observed in comparison with peripheral blood. Patient-mobilized NK cells showed a significantly decreased cytotoxicity, and antibody-dependent cell cytototoxicity (ADCC) was also observed to a lesser extent in NK cells from healthy donor PBSC. G-CSF-mobilized NK cell TNF-α and IFN-γ secretion was impaired at day 0 compared to healthy donors but was progressively restored after culture. In conclusion, expansion of NK cells from G-CSF-mobilized sources may progressively improve their functionality.

Patients Lacking a KIR-Ligand of HLA Group C1 or C2 Have a Better Outcome after Umbilical Cord Blood Transplantation

Donor natural killer (NK) cells can destroy residual leukemic cells after allogeneic hematopoietic stem cell transplantation. This effect is based on the interaction of killer-cell immunoglobulin-like receptors (KIR) of donor NK cells with ligands of the major histocompatibility complex found on the surface of the target cells. HLA-C1 subtypes provide the ligand for KIR2DL2 and KIR2DL3 and the HLA-C2 subtypes for KIR2DL1. We have studied the probability of relapse (PR) after single-unit unrelated cord blood transplantation (UCBT) in relation to the potential graft-vs.-leukemia effect mediated by NK cells present in the umbilical cord blood (UCB) by analyzing KIR-ligand and HLA-C typing of the receptor. Data from 33 consecutive patients given a single unit UCBT were included. We have considered two groups of patients based on the absence or the presence of one of the C-ligands for inhibitory KIR and the incompatibility HLA-C1/2 between UCB and patients. Group 1 (n = 21): the patient lacks a C-ligand for inhibitory KIR present in UCB NK cells, i.e., patients homozygous C1/C1 or C2/C2. Group 2 (n = 12): patients heterozygous C1/C2 in which KIR-mediated graft-vs.-leukemia effect is not expected (presence of both C ligands for inhibitory KIR in the receptor). With a median follow-up post-UCBT of 93 months, patients with absence of a C-ligand for inhibitory KIRs (Group 1) showed a lower actuarial PR than patients with both C-ligands (group 2): 21 ± 10 vs. 68 ± 18% at 2 year and 36 ± 13 vs. 84 ± 14% at 5 years (p = 0.025), respectively. In patients with acute lymphoblastic leukemia, the 2-year PR was 36 ± 21% for group 1 and 66 ± 26% for 2 (p = 0.038). Furthermore, group 1 had a lower incidence of grades II–IV acute graft-vs.-host disease (p = 0.04). In the setting of UCBT, the absence of a C-ligand (C1 or C2) of inhibitory KIR in the patient is associated with lower PR, which is probably due to the graft-vs.-host leukemia effect caused by UCB NK cells that lack a ligand for the inhibitory KIR 2DL1/2DL2/2DL3.

Graft-versus-Leukemia Effect Following Hematopoietic Stem Cell Transplantation for Leukemia

The success of hematopoietic stem cell transplantation (HSCT) lies with the ability of the engrafting immune system to remove residual leukemia cells via a graft-versus-leukemia effect (GvL), caused either spontaneously post-HSCT or via donor lymphocyte infusion. GvL effects can also be initiated by allogenic mismatched natural killer cells, antigen-specific T cells, and activated dendritic cells of leukemic origin. The history and further application of this GvL effect and the main mechanisms will be discussed and reviewed in this chapter.

Identifying NK Alloreactive Donors for Haploidentical Hematopoietic Stem Cell Transplantation

NK cell alloreactivity mediated by donor NK cells is a fundamental therapeutic tool in HLA haplotype mismatched hematopoietic transplantation in adult acute myeloid leukemia and pediatric acute lymphoblastic leukemias. NK cell is mediated by donor NK cells recovering very early after transplant. The self donor KIR ligands educates the donor NK repertoire and arms functional NK cells which express inhibitory killer cell immunoglobulin-like receptor(s) (KIRs) for self-class I ligand(s), They sense missing expression of donor KIR ligand(s) in the recipient and mediate alloreactivity. Donor-versus-recipient NK cell alloreactivity is evaluated by KIR genotyping and phenotyping and functional assay.

Specific removal of alloreactive T-cells to prevent GvHD in hemopoietic stem cell transplantation: rationale, strategies and perspectives

Hemopoietic stem cell transplantation (HSCT) is a standard procedure for treatment of malignant and non-malignant hematological diseases. HSCT donors include HLA-identical siblings, matched or mismatched unrelated donors and haploidentical related donors. Graft-versus-host disease (GvHD), mediated by donor alloreactive T-cells in the graft, can be triggered by minor histocompatibility antigens in HLA-identical pairs, by alleles at loci not considered for MUD-matching or by the mismatched haplotype in haplo-HSCT. Therefore, removal of donor T-cells, that contain the alloreactive precursors, is required, but T-cell depletion associates with opportunistic infections and with reduced graft-versus-leukemia effect. Selective T-cell depletion strategies have been introduced, like removal of αβ T-lymphocytes and of naive T-cells, two subsets including the alloreactive precursors, but the ultimate goal is specific removal of alloreactive T-cells. Here we review the different approaches to deplete alloreactive T-cells only and discuss pros and cons, specificity, efficiency and efficacy. Combinations of different methods and innovative approaches are also proposed for depleting specific alloreactive T-cells with high efficiency.

The role of the killer cell immunoglobulin-like receptor (KIR) "missing self" model in unrelated donor HSCT: a meta-analysis

Some studies have found that donor-recipient killer cell immunoglobulin g-like receptor (KIRs) ligand compatibility or incompatibility influences the prognosis of hematopoietic stem cell transplantation between unrelated individuals, although the conclusions of these studies are controversial. We performed a meta-analysis concerning unrelated donor transplantation with donor-recipient KIRs compatible or incompatible. A higher 5-year overall survival rate (odds ratio [OR] = 1.93, 95% confidence interval [CI] = 1.03 to 3.61, P = .04) was found in KIR-mismatched transplantations; however, no difference was observed in the incidence of grade 2 to 4 acute graft-vs-host disease (OR = 0.94, 95% CI = 0.71 to 1.24, P = .64), 5-year relapse rate (OR = 1.05, CI = 0.75 to 1.47, P = .77), or transplantation/treatment-related mortality (OR = 0.61, CI = 0.15 to 2.51, P = .50). Our meta-analysis confirmed that incompatibility in KIR ligands favors 5-year overall survival rate but has no effect on the incidence of grade 2 to 4 acute graft-vs-host disease, relapse, or transplantation/treatment-related mortality.

Imputation of KIR Types from SNP Variation Data

Large population studies of immune system genes are essential for characterizing their role in diseases, including autoimmune conditions. Of key interest are a group of genes encoding the killer cell immunoglobulin-like receptors (KIRs), which have known and hypothesized roles in autoimmune diseases, resistance to viruses, reproductive conditions, and cancer. These genes are highly polymorphic, which makes typing expensive and time consuming. Consequently, despite their importance, KIRs have been little studied in large cohorts. Statistical imputation methods developed for other complex loci (e.g., human leukocyte antigen [HLA]) on the basis of SNP data provide an inexpensive high-throughput alternative to direct laboratory typing of these loci and have enabled important findings and insights for many diseases. We present KIR^∗IMP, a method for imputation of KIR copy number. We show that KIR^∗IMP is highly accurate and thus allows the study of KIRs in large cohorts and enables detailed investigation of the role of KIRs in human disease.

Identification of Anti-tumor Cells Carrying Natural Killer (NK) Cell Antigens in Patients With Hematological Cancers

Natural killer (NK) cells, a cytotoxic lymphocyte lineage, are able to kill tumor cells in vitro and in mouse models. However, whether these cells display an anti-tumor activity in cancer patients has not been demonstrated. Here we have addressed this issue in patients with several hematological cancers. We found a population of highly activated CD56^dimCD16⁺ NK cells that have recently degranulated, evidence of killing activity, and it is absent in healthy donors. A high percentage of these cells expressed natural killer cell p46-related protein (NKp46), natural-killer group 2, member D (NKG2D) and killer inhibitory receptors (KIRs) and a low percentage expressed NKG2A and CD94. They are also characterized by a high metabolic activity and active proliferation. Notably, we found that activated NK cells from hematological cancer patients have non-NK tumor cell antigens on their surface, evidence of trogocytosis during tumor cell killing. Finally, we found that these activated NK cells are distinguished by their CD45RA⁺RO⁺ phenotype, as opposed to non-activated cells in patients or in healthy donors displaying a CD45RA⁺RO⁻ phenotype similar to naïve T cells. In summary, we show that CD45RA⁺RO⁺ cells, which resemble a unique NK population, have recognized tumor cells and degranulate in patients with hematological neoplasias.

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Expression of both CD45 isoforms RA and RO identifies anti-leukemia NK cells.

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Anti-leukemia NK cells proliferate, degranulate and perform trogocytosis in vivo.

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The presence of CD45RARO population identifies hematological cancer patients.

NK cells are thought to have an intrinsic anti-tumor activity. However, the presence of anti-leukemia NK cells in patients is unknown. We present a relatively simple protocol to identify and characterize them. This is based on differential protein expression and on the fact that they gain tumor cell proteins by the process of trogocytosis. These phenotypic differences should be taken into account in analysis to identify different NK cell subpopulations. Hence, NK cells are actively recognizing tumor cells in leukemia patients; but this seems to be insufficient to eradicate disease. Future efforts should enhance the antitumor activity of this population.

Combined IL-15 and IL-12 drives the generation of CD34+-derived natural killer cells with superior maturation and alloreactivity potential following adoptive transfer

Adoptive transfer of allogeneic natural killer (NK) cells represents a promising treatment approach against cancer, including acute myeloid leukemia (AML). Previously, we reported a cytokine-based culture method for the generation of NK cell products with high cell number and purity. In this system, CD34⁺ hematopoietic progenitor cells (HPC) were expanded and differentiated into NK cells under stroma-free conditions in the presence of IL-15 and IL-2. We show that combining IL-15 with IL-12 drives the generation of more mature and highly functional NK cells. In particular, replacement of IL-2 by IL-12 enhanced the cytolytic activity and IFNγ production of HPC-NK cells toward cultured and primary AML cells in vitro, and improved antileukemic responses in NOD/SCID-IL2Rγnull (NSG) mice bearing human AML cells. Phenotypically, IL-12 increased the frequency of HPC-NK cells expressing NKG2A and killer immunoglobulin-like receptor (KIR), which were more responsive to target cell stimulation. In addition, NK15/12 cell products demonstrated superior maturation potential, resulting in >70% positivity for CD16 and/or KIR within 2 weeks after infusion into NSG mice. We predict that higher functionality and faster in vivo maturation will favor HPC-NK cell alloreactivity toward malignant cells in patients, making this cytokine combination an attractive strategy to generate clinical HPC-NK cell products for cancer adoptive immunotherapy.

Current and future immunotherapeutic approaches to multiple myeloma therapy

SUMMARY 

Multiple myeloma (MM) is a hematologic malignancy associated with heterogeneous treatment and survival outcomes due in part to the ability of MM to evade and suppress the immune system. Research has focused on finding ways to modulate and enhance immunity while targeting the bone marrow microenvironment. Contemporary therapies include immunomodulatory drugs, proteasome inhibitors and autologous and allogeneic stem cell transplant and have improved outcomes for patients with MM. Future therapies, including monoclonal antibodies, chimeric antigen receptor cells and MM vaccines, show promise to further improved outcomes, particularly when used in combination with existing therapies. This review covers the mechanism of action of currently available and future therapies and explores ways in which treatment may be more specifically directed in the future.

Donor Haplotype B of NK KIR Receptor Reduces the Relapse Risk in HLA-Identical Sibling Hematopoietic Stem Cell Transplantation of AML Patients

Successful allogeneic hematopoietic stem cell transplantation (HSCT) depends not only on good HLA match but also on T-cell mediated graft-versus-leukemia (GvL) effect. Natural killer (NK) cells are able to kill malignant cells by receiving activation signal from the killer-cell immunoglobulin-like receptors (KIR) recognizing HLA molecules on a cancer cell. It has been recently reported that the risk of relapse in allogeneic hematopoietic stem cell transplantation (HSCT) is reduced in acute myeloid leukemia (AML) patients whose donors have several activating KIR genes or KIR B-motifs in unrelated donor setting, obviously due to enhanced GvL effect by NK cells. We studied the effect on relapse rate of donor KIR haplotypes in the HLA-identical adult sibling HSCT, done in a single center, in Helsinki University Central Hospital, Helsinki, Finland. Altogether, 134 patients with 6 different diagnoses were identified. Their donors were KIR genotyped using the Luminex and the SSP techniques. The clinical endpoint, that is, occurrence of relapse, was compared with the presence or absence of single KIR genes. Also, time from transplantation to relapse was analyzed. The patients with AML whose donors have KIR2DL2 or KIR2DS2 had statistically significantly longer relapse-free survival (P = 0.015). Our data support previous reports that donors with KIR B-haplotype defining genes have a lower occurrence of relapse in HSCT of AML patients. Determination of donor KIR haplotypes could be a useful addition for a risk assessment of HSCT especially in AML patients.

Indirectly Recognized HLA-C Mismatches and Their Potential Role in Transplant Outcome

HLA-C mismatches are clearly associated to alloreactivity after hematopoietic stem-cell transplantation; in a number of large cohorts, HLA-C mismatches are correlated to an increased risk of acute graft-versus-host disease (GVHD) or even impaired survival. While for HLA-A and -B, both antigenic as well as allelic mismatches are associated with an increased risk of acute GVHD, such an increased risk is only observed for antigenic HLA-C mismatches and not for allelic mismatches. These observations raise the question what sets HLA-C apart from HLA-A and -B. The difference may well be related to the reduced levels of cell-surface expression of HLA-C as compared to HLA-A and -B, possibly due to, among other factors, a limited peptide-binding capacity. This limited peptide-binding capacity may retain HLA-C in the ER and enhance degradation of the HLA-C protein. Once degraded, HLA-C-derived peptides can be presented to the immune system via other HLA alleles and are thus available for indirect recognition. Indeed, such HLA-C-derived peptides have previously been eluted from other HLA alleles. We have recently developed an approach to predict indirect recognition of HLA molecules, by establishing the numbers of predicted indirectly recognizable HLA epitopes (PIRCHES). The number of PIRCHES presented on HLA class I and II (PIRCHE-I and -II, respectively), are highly correlated to clinical measures of alloreactivity, such as acute GVHD. In the present “Hypothesis & Theory,” we reviewed the current knowledge on HLA-C mismatches and alloreactivity. Moreover, we speculate about the role of direct and indirect recognition of HLA-C and the consequences for donor selection in HLA-C mismatched stem-cell transplantation.

All-trans retinoic acid (ATRA) induces miR-23a expression, decreases CTSC expression and granzyme B activity leading to impaired NK cell cytotoxicity

NK cell is an innate immune system lymphocyte lineage with natural cytotoxicity. Its optimal use in the clinic requires in vitro expansion and activation. Cytokines and encounter with target cells activate NK cells and induce proliferation, and this could depend on the presence of other immune cells. Here we activated PBMCs during 5 days with IL-2, with IL-2 plus the tumor cell line K562 and with the lymphoblastoid cell line R69 and perform integrated analyses of microRNA and mRNA expression profiles of purified NK cells. The samples cluster depending on the stimuli and not on the donor, indicating that the pattern of NK cell stimulation is acutely well conserved between individuals. Regulation of mRNA expression is tighter than that of miRNA expression. All stimuli induce a common preserved genetic remodeling. In addition, encounter with target cells mainly activates pathways related to metabolism. Different target cells induce different NK cell remodeling which affects cytokine response and cytotoxicity, supporting the notion that encounter with different target cells significantly changing the activation pattern. We validate our analysis by showing that activation down regulates miR-23a, which is a negative regulator of cathepsin C (CTSC) mRNA, a gene up regulated by all stimuli. The peptidase CTSC activates the granzymes, the main effector proteases involved in NK cell cytotoxicity. All-trans retinoic acid (ATRA), which induces miR-23a expression, decreases CTSC expression and granzyme B activity leading to impaired NK cell cytotoxicity in an in vivo mouse model.

Genetic profile of KIR and HLA in southern Chinese Han population

KIR and their HLA ligands are encoded by two of the most diverse gene families in the human genome. The function of KIR on the NK cell is highly dependent on the normal expression of class I HLA on the target cell. Previous population studies in southern Chinese have been focused on the KIR framework genes and genotypes but little is known about the compound profiles of KIR/HLA. The present study examined 503 unrelated individuals from southern Chinese Han population for the polymorphism of KIR and class I HLA genes. All 16 KIR genes were detected in the study population and the four framework genes KIR3DL2, 3DL3, 3DP1, and 2DL4 were present in all individuals. Thirty unique KIR gene profiles were found reflecting a rather limited number of KIR haplotypes in this population. KIRAA1 was the most common profile observed in 54.7% of the samples. Among the AA1 individuals, 15.6% were homozygous for the deleted KIR2DS4. Haplotype A (74.8%) was more common than haplotype B (25.2%). HLA-C1 was a much more common ligand for 2D KIRs than C2. Bw4-80I, Bw4-80T, and the Bw4-bearing HLA-A alleles were detected at similar frequencies. The matched KIR+HLA pairs 2DL2/3+C1 (98.1%), 3DL1+Bw4 (73.3%), 3DL2+A3/11 (60.0%) were the most common ones whereas 3DS1+Bw4-80I was the least common (9.4%). A total of 193 unique compound profiles of KIR-HLA were identified in 480 informative individuals, 130 of the profiles being detected only once. The study provided a comprehensive analysis of the KIR/HLA profiles in southern Chinese in regards of the presence/absence of KIR genes, HLA ligands, matched KIR+HLA pairs, and KIR/HLA compound profiles. The results could help to better understand the role played by KIR/HLA interaction in associated diseases and clinical transplantation in southern Chinese.

Increased numbers of NK cells, NKT-like cells, and NK inhibitory receptors in peripheral blood of patients with chronic obstructive pulmonary disease

T cells and B cells participate in the pathogenesis of COPD. Currently, NK cells and NKT cells have gained increasing attention. In the present study, 19 COPD patients and 12 healthy nonsmokers (HNS) were recruited, and their pulmonary function was assessed. The frequencies of CD3⁺ T, CD4⁺ T, CD8⁺ T, B, NK, and NKT-like cells were determined using flow cytometry. The frequencies of spontaneous and inducible IFN-γ⁺ or CD107a⁺ NK and NKT-like cells as well as activating or inhibitory receptors were also detected. The potential association of lymphocyte subsets with disease severity was further analyzed. Significantly decreased numbers of CD3⁺ and CD4⁺ T cells, and the CD4⁺/CD8⁺ ratio, but increased numbers of CD3⁻CD56⁺ NK and CD3⁺CD56⁺ NKT-like cells were observed in COPD patients compared to HNS. The frequencies of inducible IFN-γ-secreting NK and NKT-like cells were less in COPD patients. The frequencies of CD158a and CD158b on NK cells and CD158b on NKT-like cells were greater. The frequency of CD158b⁺ NK cells was negatively correlated with FEV₁% prediction and FEV₁/FVC. Our data indicate that COPD patients have immune dysfunction, and higher frequencies of inhibitory NK cells and NKT-like cells may participate in the pathogenesis of COPD.

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.

New approaches to graft engineering for haploidentical bone marrow transplantation

Haploidentical transplantation opens the possibility to offer this treatment to a large number of patients with an otherwise incurable disease, such as some hematologic or oncologic malignancies, inborn or acquired bone marrow failure syndromes, hemoglobinopathies, immunodeficiencies, or other genetic diseases. Initial attempts at haploidentical transplantation using unmanipulated bone marrow were associated with a high transplant-related mortality. However, recent insights into the biology of haploidentical transplantation, the availability of effective in vivo large-scale graft-manipulation technology, and improved supportive care strategies have led to and are still leading to significantly better outcomes compared to previous decades. Methods for the in vitro depletion of T lymphocytes from mobilized peripheral blood stem cells (PBSC) to prevent graft-versus-host disease (GvHD) have facilitated the wider use and acceptance of haploidentical transplantation in children and adult patients. Besides in vitro T-cell depletion techniques, other methods, such as the isolation of alloreactive natural killer (NK) cells, virus-specific T lymphocytes, and other effector or regulatory cells are nowadays available to rapidly rebuild the immune system after haploidentical transplantation for the prevention of severe infections or relapses of the underlying diseases.

KIR2DS2 and KIR2DS4 promoter hypomethylation patterns in patients undergoing hematopoietic cell transplantation (HCT)

The killer cell Ig-like receptor (KIR)-MHC class I pathway is an integral part of natural killer cell immunity, and its role in host protection from both cancer and infection is important. In addition, we have shown elevated KIR2DS2 and 2DS4 expression in PBMCs of patients undergoing hematopoietic cell transplantation (HCT) [1]. Since all inhibitory KIR promoters are known to be heavily methylated, the question asked here is how and when KIR2DS2 and 2DS4 promoters had changed their methylation profile in association with HCT. Genomic DNA, extracted from 20 KIR2DS2/4+ donor and recipient cells, was treated with sodium bisulfate that will modify the unmethylated cytosine into uracil. Sequencing chromatographs were examined for C/T double peak indicative of base conversion. A CpG island in KIR2DS2 promoter spans from -160 to +26 with six cytosine sites. In contrast, the KIR2DS4 promoter CpG island contains three cytosine sites. The noted increase of unmethylated sites was associated with increased KIR expression as measured by mRNA-cDNA Q-PCR. In addition, the frequency of unmethylated sites in the CpG island was increased after HCT. The mechanism through which hypomethylation occurs after HCT is not known but it suggests a linkage to NK clonal expansion during the process of NK education in response to transplant therapy or viral infection.

In vivo imaging of therapy-induced anti-cancer immune responses in humans

Immunotherapy aims to re-engage and revitalize the immune system in the fight against cancer. Research over the past decades has shown that the relationship between the immune system and human cancer is complex, highly dynamic, and variable between individuals. Considering the complexity, enormous effort and costs involved in optimizing immunotherapeutic approaches, clinically applicable tools to monitor therapy-induced immune responses in vivo are most warranted. However, the development of such tools is complicated by the fact that a developing immune response encompasses several body compartments, e.g., peripheral tissues, lymph nodes, lymphatic and vascular systems, as well as the tumor site itself. Moreover, the cells that comprise the immune system are not static but constantly circulate through the vascular and lymphatic system. Molecular imaging is considered the favorite candidate to fulfill this task. The progress in imaging technologies and modalities has provided a versatile toolbox to address these issues. This review focuses on the detection of therapy-induced anticancer immune responses in vivo and provides a comprehensive overview of clinically available imaging techniques as well as perspectives on future developments. In the discussion, we will focus on issues that specifically relate to imaging of the immune system and we will discuss the strengths and limitations of the current clinical imaging techniques. The last section provides future directions that we envision to be crucial for further development.

Killer-cell immunoglobulin-like receptors reactivity and outcome of stem cell transplant

PURPOSE OF REVIEW

This review focuses on advances in the field of natural killer (NK) cell alloreactivity as a form of immunotherapy in the setting of allogeneic haematopoietic transplantation.

RECENT FINDINGS

Recent research has focused on mechanisms underlying the acquisition of function by NK cells after haematopoietic transplantation, on the therapeutic impact of NK-cell alloreactivity in various forms of transplantation and in adoptive immunotherapy. Finally, studies have highlighted the role of NK-cell responses in viral infections after transplantation.

SUMMARY

Donor-versus-recipient NK-cell alloreactivity is established as a key therapeutic element in human leukocyte antigen haplotype-mismatched haematopoietic transplants in adult acute myeloid leukaemia (AML) and paediatric acute lymphoblastic leukaemia (ALL). NK-cell allotherapy for leukaemia is deployed through stem cell transplantation (and ensuing NK-cell reconstitution) across killer-cell immunoglobulin-like receptor ligand mismatches. Donor-derived NK cells were also reported to respond to cytomegalovirus by acquiring features that are reminiscent of the specificity and memory of adaptive (T-cell) immune responses. As NK cells are the earliest immune cells to recover after transplant, this observation suggests they may contribute to controlling viral reactivation early after transplant.

Protein Kinase C-θ (PKC-θ) in Natural Killer Cell Function and Anti-Tumor Immunity

The protein kinase C-θ (PKCθ), which is essential for T cell function and survival, is also required for efficient anti-tumor immune surveillance. Natural killer (NK) cells, which express PKCθ, play a prominent role in this process, mainly by elimination of tumor cells with reduced or absent major histocompatibility complex class-I (MHC-I) expression. This justifies the increased interest of the use of activated NK cells in anti-tumor immunotherapy in the clinic. The in vivo development of MHC-I-deficient tumors is much favored in PKCθ^−/− mice compared with wild-type mice. Recent data offer some clues on the mechanism that could explain the important role of PKCθ in NK cell-mediated anti-tumor immune surveillance: some studies show that PKCθ is implicated in signal transduction and anti-tumoral activity of NK cells elicited by interleukin (IL)-12 or IL-15, while others show that it is implicated in NK cell functional activation mediated by certain killer-activating receptors. Alternatively, the possibility that PKCθ is involved in NK cell degranulation is discussed, since recent data indicate that it is implicated in microtubule-organizing center polarization to the immune synapse in CD4⁺ T cells. The implication of PKC isoforms in degranulation has been more extensively studied in cytotoxic T lymphocyte, and these studies will be also summarized.

Increasing the clinical efficacy of NK and antibody-mediated cancer immunotherapy: potential predictors of successful clinical outcome based on observations in high-risk neuroblastoma

Disease recurrence is frequent in high-risk neuroblastoma (NBL) patients even after multi-modality aggressive treatment [a combination of chemotherapy, surgical resection, local radiation therapy, autologous stem cell transplantation, and cis-retinoic acid (CRA)]. Recent clinical studies have explored the use of monoclonal antibodies (mAbs) that bind to disialoganglioside (GD₂), highly expressed in NBL, as a means to enable immune effector cells to destroy NBL cells via antibody-dependent cell-mediated cytotoxicity (ADCC). Preclinical data indicate that ADCC can be more effective when appropriate effector cells are activated by cytokines. Clinical studies have pursued this by administering anti-GD₂ mAb in combination with ADCC-enhancing cytokines (IL2 and GM-CSF), a regimen that has demonstrated improved cancer-free survival. More recently, early clinical studies have used a fusion protein that consists of the anti-GD₂ mAb directly linked to IL2, and anti-tumor responses were seen in the Phase II setting. Analyses of genes that code for receptors that influence ADCC activity and natural killer (NK) cell function [Fc receptor (FcR), killer immunoglublin-like receptor (KIR), and KIR-ligand (KIR-L)] suggest patients with anti-tumor activity are more likely to have certain genotype profiles. Further analyses will need to be conducted to determine whether these genotypes can be used as predictive markers for favorable therapeutic outcome. In this review, we discuss factors that affect response to mAb-based tumor therapies such as hu14.18-IL2. Many of our observations have been made in the context of NBL; however, we will also include some observations made with mAbs targeting other tumor types that are consistent with results in NBL. Therefore, we hypothesize that the NBL observations discussed here may also be relevant to mAb therapy for other cancers, in which ADCC is known to play a role.

The role of natural killer cells in immunity against multiple myeloma

Multiple myeloma (MM) is an essentially incurable malignancy associated with profound immune dysregulation. Despite the advent of novel therapies and improvements in survival over the last 10 years, death from progressive disease and infection remains a common outcome. Natural killer (NK) cells are CD56(+)CD3(-) large granular lymphocytes that constitute a key cellular subset of the innate immune system. For over 30 years, the relationship between NK cells and MM has been described in the clinical setting and characterized in the laboratory. Data suggest that NK cells may play a role in the immune response to MM; however, this effect is lost due to immunoevasive strategies utilized by MM. Nevertheless, progress in the understanding of the mechanisms perpetuating this effect have led to new opportunities to recover or augment NK cell function therapeutically in MM. In fact, the novel agents thalidomide, lenalidomide and bortezomib all confer anti-MM effects, in part, through enhancement of NK cell function. Currently, the development of therapies designed specifically to increase NK cell cytotoxicity against MM is under way. The present review summarizes the current understanding of the NK cell versus MM effect and characterizes therapeutic interventions that exert anti-MM efficacy via NK cell function against the disease.

An overview of methods required to evaluate donor NK cell alloreactivity for haploidentical haemopoietic stem cell transplantation

Donor-vs.-recipient NK cell alloreactivity has been established as a key therapeutic element in HLA haplotypemismatched hematopoietic transplants in acute myeloid leukemia. NK cell allotherapy for leukemia is deployed through stem cell transplantation and ensuing NK cell reconstitution across KIR ligand mismatches. It is effected by functional NK cells which express inhibitory killer cell immunoglobulin-like receptor(s) (KIRs) for self-class I ligand(s), sense missing expression of donor KIR ligand(s) in the recipient, and mediate alloreactions. Donor-vs.-recipient NK cell alloreactivity is evaluated by integrating genetic, phenotypic, and functional features.

Cancer immunotherapy comes of age

Cancer immunotherapy comprises a variety of treatment approaches, incorporating the tremendous specificity of the adaptive immune system (T cells and antibodies) as well as the diverse and potent cytotoxic weaponry of both adaptive and innate immunity. Immunotherapy strategies include antitumor monoclonal antibodies, cancer vaccines, adoptive transfer of ex vivo activated T and natural killer cells, and administration of antibodies or recombinant proteins that either costimulate immune cells or block immune inhibitory pathways (so-called immune checkpoints). Although clear clinical efficacy has been demonstrated with antitumor antibodies since the late 1990s, other immunotherapies had not been shown to be effective until recently, when a spate of successes established the broad potential of this therapeutic modality. These successes are based on fundamental scientific advances demonstrating the toleragenic nature of cancer and the pivotal role of the tumor immune microenvironment in suppressing antitumor immunity. New therapies based on a sophisticated knowledge of immune-suppressive cells, soluble factors, and signaling pathways are designed to break tolerance and reactivate antitumor immunity to induce potent, long-lasting responses. Preclinical models indicate the importance of a complex integrated immune response in eliminating established tumors and validate the exploration of combinatorial treatment regimens, which are anticipated to be far more effective than monotherapies. Unlike conventional cancer therapies, most immunotherapies are active and dynamic, capable of inducing immune memory to propagate a successful rebalancing of the equilibrium between tumor and host.

IPH2101, a novel anti-inhibitory KIR antibody, and lenalidomide combine to enhance the natural killer cell versus multiple myeloma effect

Multiple myeloma (MM) patients who receive killer cell Ig-like receptor (KIR) ligand-mismatched, T cell-depleted, allogeneic transplantation may have a reduced risk of relapse compared with patients who receive KIR ligand-matched grafts, suggesting the importance of this signaling axis in the natural killer (NK) cell-versus-MM effect. Expanding on this concept, IPH2101 (1-7F9), an anti-inhibitory KIR mAb, enhances NK-cell function against autologous MM cells by blocking the engagement of inhibitory KIR with cognate ligands, promoting immune complex formation and NK-cell cytotoxicity specifically against MM cell targets but not normal cells. IPH2101 prevents negative regulatory signals by inhibitory KIR, whereas lenalidomide augments NK-cell function and also appears to up-regulate ligands for activating NK-cell receptors on MM cells. Lenalidomide and a murine anti-inhibitory NK-cell receptor Ab mediate in vivo rejection of a lenalidomide-resistant tumor. These mechanistic, preclinical data support the use of a combination of IPH2101 and lenalidomide in a phase 2 trial for MM.

A gene-specific primer extension and liquid bead array system for killer-cell immunoglobulin-like receptor genotyping

A simple and accurate method for killer-cell immunoglobulin-like receptor (KIR) genotyping is developed using KIR gene-specific primer extension (GSPE) followed by bead array hybridization (GSPE method). After amplification of exons 4, 5, and 9, KIR GSPE and bead array hybridization were performed to verify the presence or absence of 16 KIR subfamilies. GSPE method was validated with natural killer/KIR reference panel I consisting of 48 cell types provided by 13th International Histocompatibility Working Group (IHWG) and genomic DNA from 17 peripheral blood cells, 8 cell lines, and 8 buccal cells. The results of reference panel from GSPE method were 100% concordant with the IHWG reference typing information. All genomic DNAs except reference panel were typed for KIR genes with sequence-specific primer methods and showed 100% identical typing results using this novel system. In addition, GSPE method can obtain results in 8 h from DNA with 10 ng genomic DNA in a 96-well-based assay format.

Major histocompatibility complex class-I-interacting natural killer cell receptors of nonhuman primates

Human natural killer (NK) cell receptors are known to be highly polymorphic, to show complex genetics and to be associated with susceptibility to a variety of immunological diseases. Nonhuman primates are used as important models of these diseases, yet the knowledge of nonhuman primate NK cell receptors and ligands is not as advanced as in humans. Recently published data indicated that diversity and polymorphism of NK cell receptors are similar between nonhuman primates and humans. Comparative genomics revealed instructive insights into the evolution and function of primate NK cell receptor genes and contributed to the understanding of how present-day NK cell receptors and their ligands have evolved. Here, I review the current knowledge of nonhuman primate NK cell receptors that interact with major histocompatibility complex class I proteins.

Interactions of NK cell receptor KIR3DL1*004 with chaperones and conformation-specific antibody reveal a functional folded state as well as predominant intracellular retention

Variable interaction between the Bw4 epitope of HLA-B and the polymorphic KIR3DL1/S1 system of inhibitory and activating NK cell receptors diversifies the development, repertoire formation, and response of human NK cells. KIR3DL1*004, a common KIR3DL1 allotype, in combination with Bw4(+) HLA-B, slows progression of HIV infection to AIDS. Analysis in this study of KIR3DL1*004 membrane traffic in NK cells shows this allotype is largely misfolded but stably retained in the endoplasmic reticulum, where it binds to the chaperone calreticulin and does not induce the unfolded protein response. A small fraction of KIR3DL1*004 folds correctly and leaves the endoplasmic reticulum to be expressed on the surface of primary NK and transfected NKL cells, in a form that can be triggered to inhibit NK cell activation and secretion of IFN-γ. Consistent with this small proportion of correctly folded molecules, trace amounts of MHC class I coimmunoprecipitated with KIR3DL1*004. There was no indication of any extensive intracellular interaction between unfolded KIR3DL1*004 and cognate Bw4(+) HLA-B. A similarly limited interaction of Bw4 with KIR3DL1*002, when both were expressed by the same cell, was observed despite the efficient folding of KIR3DL1*002 and its abundance on the NK cell surface. Several positions of polymorphism modulate KIR3DL1 abundance at the cell surface, differences that do not necessarily correlate with the potency of allotype function. In this context, our results suggest the possibility that the effect of Bw4(+) HLA-B and KIR3DL1*004 in slowing progression to AIDS is mediated by interaction of Bw4(+) HLA-B with the small fraction of cell surface KIR3DL1*004.

Linkage disequilibrium organization of the human KIR superlocus: implications for KIR data analyses

An extensive family-based study of linkage disequilibrium (LD) in the killer cell immunoglobulin-like receptors (KIR) cluster was performed. We aimed to describe the LD structure in the KIR gene cluster using a sample of 418 founder haplotypes identified by segregation in a group of 106 families from Northern Ireland. The LD was studied at two levels of polymorphism: the structural level (presence or absence of KIR genes) and the allelic level (between alleles of KIR genes). LD was further assessed using the predictive value of one KIR polymorphism for another one in order to provide an interpretative framework for the LD effect in association studies. In line with previous research, distinct patterns of KIR genetic diversity within the genomic region centromeric to KIR2DL4 (excluding KIR2DL4) and within the telomeric region including KIR2DL4 were found. In a comprehensive PPV/NPV-based LD analysis within the KIR cluster, robust tag markers were found that can be used to identify which genes are concomitantly present or absent and to further identify groups of associated KIR alleles. Several extended KIR haplotypes in the study population were identified (KIR2DS2*POS–KIR2DL2*001–KIR2DL5B*002–KIR2DS3*00103–KIR2DL1*00401; KIR2DL4*011–KIR3DL1/S1*005–KIR2DS4*003–KIR3DL2*003; KIR2DL4*00802–KIR3DL1/S1*004–KIR2DS4*006–KIR3DL2*005; KIR2DL4*00801–KIR3DL1/S1*00101–KIR2DS4*003–KIR3DL2*001; KIR2DL4*00103–KIR3DL1/S1*008–KIR2DS4*003–KIR3DL2*009; KIR2DL4*00102–KIR3DL1/S1*01502/*002–KIR2DS4*00101–KIR3DL2*002; KIR2DL4*00501–KIR3DL1/S1*013–KIR2DL5A*001–KIR2DS5*002–KIR2DS1*002–KIR3DL2*007). The present study provides a rationale for analyzing associations of KIR polymorphisms by taking into account the complex LD structure of the KIR region.

NCI First International Workshop on The Biology, Prevention and Treatment of Relapse after Allogeneic Hematopoietic Cell Transplantation: report from the committee on prevention of relapse following allogeneic cell transplantation for hematologic malignancies

Prevention of relapse after allogeneic hematopoietic stem cell transplantation is the most likely approach to improve survival of patients treated for hematologic malignancies. Herein we review the limits of currently available transplant therapies and the innovative strategies being developed to overcome resistance to therapy or to fill therapeutic modalities not currently available. These novel strategies include nonimmunologic therapies, such as targeted preparative regimens and posttransplant drug therapy, as well as immunologic interventions, including graft engineering, donor lymphocyte infusions, T cell engineering, vaccination, and dendritic cell-based approaches. Several aspects of the biology of the malignant cells as well as the host have been identified that obviate success of even these newer strategies. To maximize the potential for success, we recommend pursuing research to develop additional targeted therapies to be used in the preparative regimen or as maintenance posttransplant, better characterize the T cell and dendritic cells subsets involved in graft-versus-host disease and the graft-versus-leukemia/tumor effect, identify strategies for timing immunologic or nonimmunologic therapies to eliminate the noncycling cancer stem cell, identify more targets for immunotherapies, develop new vaccines that will not be limited by HLA, and develop methods to identify populations at very high risk for relapse to accelerate clinical development and avoid toxicity in patients not at risk for relapse.

Allogeneic haematopoietic stem cell transplantation: individualized stem cell and immune therapy of cancer

The year 2009 marked the fiftieth anniversary of the first successful allogeneic haematopoietic stem cell transplant (HSCT). The field of HSCT has pioneered some of the most exciting areas of research today. HSCT was the original stem cell therapy, the first cancer immune therapy and the earliest example of individualized cancer therapy. In this Timeline article we review the history of the development of HSCT and major advances made in the past 50 years. We highlight accomplishments made by researchers who continue to strive to improve outcomes for patients and increase the availability of this potentially life-saving therapy for patients with otherwise incurable malignancies.

'Unlicensed' natural killer cells dominate the response to cytomegalovirus infection

Natural killer (NK) cells expressing inhibitory receptors that bind to self-MHC class I are “licensed” or rendered functionally more responsive to stimulation, whereas “unlicensed” NK cells lacking receptors for self-MHC class I are hyporesponsive. Here we show that, contrary to the licensing hypothesis, unlicensed NK cells were the primary mediators of NK cell-mediated control of mouse cytomegalovirus infection in vivo. Depletion of unlicensed, but not licensed, NK cells impaired control of viral titers. Transfer of unlicensed NK cells was more protective than licensed NK cells. SHP-1 signaling limited proliferation of licensed, but not unlicensed NK cells during infection. Thus, “unlicensed” NK cells are critical for protection against viral infection.

The extensive polymorphism of KIR genes

The functions of human natural killer (NK) cells are controlled by diverse families of antigen receptors. Prominent among these are the killer cell immunoglobulin-like receptors (KIR), a family of genes clustered in one of the most variable regions of the human genome. Within this review we discuss the vast polymorphism of the KIR gene complex which rivals that of the human leucocyte antigen (HLA) complex. There are several aspects to this polymorphism. Initially there is presence/absence of individual KIR genes, with four of these genes, termed framework genes, being present in all individuals tested to date, except on those very occasional instances when the gene has been deleted. Within each gene, alleles are present at different frequencies. We provide details of a new website that enables convenient searching for data on KIR gene, allele and genotype frequencies in different populations and show how these frequencies vary in different worldwide populations and the high probability of individuals differing in their KIR repertoire when both gene and allele polymorphism is considered. The KIR genes present in an individual may be classified into A and/or B haplotypes, which respectively have a more inhibitory role or a more activating role on the function of the NK cell. Family studies have been used to ascertain the make-up of these haplotypes, inclusion of allele typing enabling determination of whether one or two copies of a particular gene is present. In addition to genetic diversification the KIR gene complex shows differences at the functional level with different alleles having different protein expression levels and different avidity with their HLA ligand.

Natural-killer cell amplification for adoptive leukemia relapse immunotherapy: comparison of three cytokines, IL-2, IL-15, or IL-7 and impact on NKG2D, KIR2DL1, and KIR2DL2 expression

OBJECTIVE

Natural killer (NK) cells are a lymphocyte subset that, in a hematopoietic stem cell transplantation setting, mediates a graft-vs-leukemia effect without any graft-vs-host disease. We aimed to evaluate an isolation method that can be used with Good Manufacturing Practices-grade reagents and to compare three cytokines for expansion in order to design future clinical protocols based on donor NK-cell infusions to cure relapse after allograft.

MATERIALS AND METHODS

NK cells were enriched using a CD3/CD19 depletion method and expanded for 13 days in the presence of 2, 10, and 50 ng/mL interleukin (IL)-2, IL-15, or IL-7. NK-cell cytotoxicity was evaluated after isolation and culture. Expression of NKG2D, KIR2DL2, and KIR2DL1 was monitored during expansion.

RESULTS

Highly T- and B-cell-depleted NK cells were obtained and enriched 2.6-fold. The optimal cytokine concentration for expansion was 10 ng/mL for IL-2 or 50 ng/mL for IL-15. NK-cell cytotoxicity was significantly improved after an overnight incubation with 10 or 50 ng/mL IL-2 or with 2, 10, or 50 ng/mL IL-15, and after 13 days with 50 ng/mL IL-15. The use of a combination of IL-2 and IL-15 showed no additional benefit and negative results were obtained with IL-7. The three NK cell receptors were significantly upregulated after culture, mainly with IL-2 or IL-15.

CONCLUSION

In our study, 10 ng/mL IL-2 or 50 ng/mL IL-15 were the optimal concentrations for expansion and were equivalent in significantly enhancing cytotoxicity and modifying NK-cell receptor expression patterns.