Cytotoxic activity of natural killer cells lacking killer-inhibitory receptors for self-HLA class I molecules against autologous hematopoietic stem cells in healthy individuals

Cancer treatment and the KIR-HLA system: an overview

Accumulating evidence indicates that the success of cancer therapy depends not only on a combination of adequate procedures (surgery, chemotherapy and radiotherapy) that aim to eliminate all tumor cells, but also on the functional state of the host immune system. HLA and KIR molecules, in particular, are critical to the interactions between tumor cells and both innate and adaptive immune cells such as NK cells and T cells. Different KIR-HLA gene combinations as well as different HLA expression levels on tumor cells associate with variable tumor prognosis and response to treatment. On the other hand, different therapies have different effects on HLA molecules and immune cell functions regulated by these molecules. Here, we provide an overview of the KIR-HLA system, a description of its alterations with clinical relevance in diverse tumor types, and an analysis of the consequences that conventional cancer therapies may have on it. We also discuss how this knowledge can be exploited to identify potential immunological biomarkers that can help to select patients for tailored therapy.

Modulation of T-bet and Eomes during Maturation of Peripheral Blood NK Cells Does Not Depend on Licensing/Educating KIR

Peripheral natural killer (NK) cells upregulate T-bet and downregulate Eomes, the key transcription factors regulating NK cell maturation and function during the last maturation steps toward terminally differentiated effector cells. During this process, NK cells acquire killer immunoglobulin-like receptors (KIR) and effector functions, such as cytotoxicity and target cell-induced cytokine production. Inhibitory KIR are pivotal in the control of effector functions, but whether they also modulate T-bet/Eomes expression is unknown. We have measured T-bet/Eomes levels, KIR expression, and effector functions of maturing CD94^negCD56^dimNK cells using CD57 as surface marker for maturation. Our cohort consisted of 23 healthy blood donors (HBD) homozygous for the KIR A haplotype that contains only inhibitory KIR2DL1 (ligand HLA-C2), KIR2DL3 (ligand HLA-C1), and KIR3DL1 (ligand HLA-Bw4). We confirm that during maturation of NK cells, the number of KIR increases, levels of T-bet/Eomes are modulated, and that cells acquire effector functions, such as cytotoxicity (CD107) and target cell-induced cytokine production (TNF-α). Because maturation was associated with the increase of the number of KIR as well as with the modulation of T-bet/Eomes, the number of KIR correlated with the extent of T-bet/Eomes modulation. However, whether the KIR were triggered by their cognate HLA ligands or not had no impact on T-bet and Eomes expression, indicating that modulation of T-box transcription factors during NK cell maturation does not depend on signals conveyed by KIR. We discuss the relevance of this finding in the context of models of NK cell maturation while cautioning that results obtained in a perhaps quite heterogeneous cohort of HBD are not necessarily conclusive.

Use of NK cell activity in cure by transplant

Analogous to T cells, Natural Killer (NK) cells may facilitate engraftment, combat infection, and control cancer in bone marrow or haematopoietic stem cell transplantation (HSCT); however, NK cells do not cause graft-versus-host disease. Killer immunoglobulin-like receptors (KIRs) regulate NK cell function, and recent data suggest that KIR is as important as its ligand (human leucocyte antigen; HLA) in HSCT for both malignant and non-malignant conditions. Because there is substantial variability in KIR gene content, allelic polymorphism, and cell-surface expression among people, careful selection of donors based on HLA and KIR is essential to optimize HSCT outcomes. Furthermore, NK cells may be used for adoptive immunotherapy after HSCT in place of conventional donor lymphocyte infusion, as part of pre-transplant cytoreductive therapy, or as an independent therapeutic agent in high-risk leukaemia in place of sibling donor HSCT.

A high proportion of bone marrow T cells with regulatory phenotype (CD4+CD25hiFoxP3+) in Ewing sarcoma patients is associated with metastatic disease

Immunosuppressive CD4+CD25(hi)FoxP3+ T cells (T(reg) cells) have been found at increased densities within the tumor microenvironment in many malignancies and interfere with protective antitumor immune responses. Osseous Ewing sarcomas (ESs) are thought to derive from a bone marrow (BM) mesenchymal cell of origin, and microscopic marrow involvement defines a subpopulation of patients at a high risk of relapse. We hypothesized that BM-resident T cells may contribute to a permissive milieu for immune escape of ESs. Using 6-color-flow cytometry, we investigated the pattern of immune cell subset distribution including NK cells, gammadelta T cells, central and effector memory CD8+ and CD4+ T cells as well as T cells with regulatory phenotype (T(reg) cells) in BM obtained at diagnosis from 45 primary or relapsed ES patients treated within standardized protocols. Although patients at relapse had an inverted CD4:CD8 T-cell ratio, neither CD8+ effector/memory T-cell subsets nor T(reg) cells significantly differed from patients at diagnosis. No significant associations of innate and effector/memory T-cell subpopulations with known risk factors were found, including age, gender, tumor site, primary metastases and histological tumor response. By contrast, T(reg) cells were found at significantly higher frequencies in patients with primary metastatic disease compared with localized ESs (5.0 vs. 3.3%, p = 0.01). Thus, increased BM T(reg) cells in patients with metastasized ES may reflect an immune escape mechanism that contributes to the development of metastatic disease. Immunotherapeutic strategies will have to adequately consider the regulatory milieu within areas of Ewing tumor-immune interactions.

Autologous antitumor activity by NK cells expanded from myeloma patients using GMP-compliant components

Multiple myeloma (MM) is an incurable plasma cell malignancy with poor outcome. The most promising therapeutic options currently available are combinations of transplantation, targeted pharmacotherapy, and immunotherapy. Cell-based immunotherapy after hematopoietic stem-cell transplantation has been attempted, but with limited efficacy. Natural killer (NK) cells are interesting candidates for new means of immunotherapy; however, their potential clinical use in MM has not been extensively studied. Here, we explored the possibility of expanding NK cells from the peripheral blood of 7 newly diagnosed, untreated MM patients, using good manufacturing practice (GMP)-compliant components. After 20 days of culture, the number of NK cells from these patients had expanded on average 1600-fold. Moreover, expanded NK cells showed significant cytotoxicity against primary autologous MM cells, yet retained their tolerance against nonmalignant cells. Based on these findings, we propose that autologous NK cells expanded ex vivo deserve further attention as a possible new treatment modality for MM.

HLA and KIR polymorphisms affect NK-cell anti-tumor activity

Killer cell immunoglobulin-like receptors (KIRs) and their cognate human leukocyte antigen (HLA) ligands are key to the maintenance of natural killer (NK) cell tolerance. The gene complexes encoding both KIRs and HLA ligands are extremely polymorphic. Because the extent of NK cell inhibition varies with the allelic forms expressed, NK cell tolerance can be broken more easily in some individuals than in others. This explains why particular combinations of KIR and HLA genes are associated with an increased risk of autoimmune diseases or with more efficient antiviral responses. Breaking of NK cell tolerance might be prerequisite to kill leukemic blasts. At present, there are ample indications that NK cells can eradicate acute myeloid leukemia blasts in patients with a favorable combination of HLA and KIR genes. Selecting these individuals for clinical trials should give insight into the feasibility of anti-tumor therapy mediated through NK cells.

Inhibitory KIR-HLA receptor-ligand mismatch in autologous haematopoietic stem cell transplantation for solid tumour and lymphoma

Genes that encode killer Ig-like receptors (KIRs) and their HLA class I ligands segregate independently; thus, some individuals may express an inhibitory KIR gene but not its cognate ligand. We hypothesised that these patients with KIR-HLA receptor-ligand mismatch have a low risk of relapse after an autologous haematopoietic stem cell transplantation (HCT). Sixteen consecutive patients with lymphoma or solid tumour were enrolled onto a prospective study. They received high-dose busulphan and melphalan followed by autologous CD133(+) HCT. We found that 8 of the 16 patients experienced disease progression after autologous HCT, including 5 of the 6 patients (83%) with no inhibitory KIR-HLA mismatch and 3 of the 6 patients (50%) with 1 mismatched pair; none of the 4 (0%) patients with 2 mismatched pairs experienced disease progression. Survival analyses showed that inhibitory KIR-HLA mismatch was the only significant prognostic factor (P=0.01). The potential applicability of the receptor-ligand mismatch model to autologous HCTs and to patients with lymphoma or solid tumour is clinically significant because of the prevalence of the HCT procedure.

Investigation of KIR gene frequencies in type 1 diabetes mellitus

The frequency of killer immunoglobulinlike receptors (KIR) genes was examined in type 1 diabetes mellitus patients and controls from Finland. The KIR gene 2DS5 was significantly decreased in patients versus controls, but this was no longer significant after correction for the number of comparisons made.

Beyond HLA: the significance of genomic variation for allogeneic hematopoietic stem cell transplantation

The last 2 years have seen much excitement in the field of genetics with the identification of a formerly unappreciated level of “structural variation” within the normal human genome. Genetic structural variants include deletions, duplications, and inversions in addition to the recently discovered, copy number variants. Single nucleotide polymorphisms are the most extensively evaluated variant within the genome to date. Combining our knowledge from these studies with our rapidly accumulating understanding of structural variants, it is apparent that the extent of genetic dissimilarity between any 2 individuals is considerable and much greater than that which was previously recognized. Clearly, this more diverse view of the genome has significant implications for allogeneic hematopoietic stem cell transplantation, not least in the generation of transplant antigens but also in terms of individual susceptibility to transplant-related toxicities. With advances in DNA sequencing technology we now have the capacity to perform genome-wide analysis in a high throughput fashion, permitting a detailed genetic analysis of patient and donor prior to transplantation. Understanding the significance of this additional genetic information and applying it in a clinically meaningful way will be one of the challenges faced by transplant clinicians in the future.

The relevance of natural killer cell human leucocyte antigen epitopes and killer cell immunoglobulin-like receptors in bone marrow transplantation

The discovery that killer cell immunoglobulin-like receptors (KIR) interact with genetically polymorphic epitopes on class I human leucocyte antigen (HLA) molecules and that the KIR receptor repertoire itself is genetically variable has led to investigation of the relevance of the KIR system to stem cell transplantation. A number of retrospective studies of transplant outcome have now demonstrated either beneficial or deleterious effects of mismatching for class I natural killer (NK) epitopes. A smaller number of studies have shown effects of the donor and/or patient KIR repertoire on outcome, irrespective of the patient and donor HLA type. The most parsimonious interpretation of the data, which are often conflicting, is that the effect of NK epitope matching is very much dependent on transplant protocols, with the extent of donor T-cell depletion possibly being the most important variable. A clearer picture of the role of matching for NK epitopes and the KIR-receptor repertoire of the donor is needed.

Natural killer cell receptors: regulating innate immune responses to hematologic malignancy

Critical to innate immunity, the natural killer (NK) cell performs its function of immunosurveillance through its recognition of altered or missing self on damaged, infected, or transformed malignant cells. NK cell receptors responsible for detection of human leukocyte antigen (HLA) class I and class I-like proteins on potential target cells transmit inhibitory and activating signals that integrate to determine NK cell function. Advances in the fields of NK cell receptor biology and immunogenetics have enhanced our understanding of NK cell target recognition and may now guide studies to determine NK cell effects in the clinical setting. Analysis of NK cell receptor-ligand relationships, such as the inhibitory killer immunoglobulin-like receptors (KIRs) and their HLA class I ligands, has revealed the potential for NK cell-mediated benefit in allogeneic hematopoietic stem cell transplantation for hematologic malignancies.

A comparative study of immunomagnetic methods used for separation of human natural killer cells from peripheral blood

Immunomagnetic sorting of natural killer (NK) cells from the peripheral blood of healthy donors has been evaluated in a comparative study of composition, yield and activation of target cells obtained by positive (Dynabeads, Microbeads) and negative (Microbeads) sorting procedures. Positively sorted target cells were selected by expression of the NK cell marker CD56, whereas NK cells obtained by negative sorting were those remaining after steps to remove all non-NK cell leukocyte populations were accomplished. In positive sorting, both CD56+CD3- NK cells and CD56+CD3+ natural killer T (NKT) cells were included. The NKT cell fraction differed between individuals, but not between the positive sorting methods. Whereas 20-30% of positively sorted target cells were NKT cells, only approximately 3% of negatively sorted cells were CD3+. Contamination with monocytes and B cells was low (1-3%) in all methods studied. Sorting with Microbeads (both positive and negative) gave higher cell yields than those obtained with Dynabeads (14% vs. 5% of total leukocyte numbers). A higher CD56 fluorescence intensity of NK cells and a better discrimination between the CD56bright and CD56dim NK cell subpopulations was obtained after negative sorting. Dynabeads-separated cells had, shortly after separation, a significantly higher expression (approximately 30%) of the early activation marker CD69 than cells either positively or negatively separated by Microbeads (approximately 8%). CD56+ cells positively sorted by Microbeads demonstrated a significantly higher production of TNF-alpha and IFN-gamma after IL-2 stimulation than Dynabeads-sorted cells. However, the cytotoxicity of cells obtained by the two positive sorting procedures did not differ. In conclusion, positive selection of CD56+ cells by Microbeads is better than Dynabeads, as determined from cell yield and procedure-associated cell activation and should be chosen for in vitro studies of NK/NKT cells. However, when pure NK cells and phenotypic subtypes are to be studied, negative sorting seems most appropriate.

Comparison of killer Ig-like receptor genotyping and phenotyping for selection of allogeneic blood stem cell donors

The repertoire of killer Ig-like receptors (KIRs) can be determined at the level of DNA, RNA, or surface protein expression for selection of blood stem cell donors. We compared genotyping and phenotyping of the four inhibitory KIRs that are important in transplantation for leukemia in 73 unrelated persons. In 5 (7%) of the 68 individuals in whom the KIR2DL1 gene was present and in 10 (15%) of the 67 in whom KIR3DL1 was present, the corresponding receptor was not expressed by NK cells, as determined by flow cytometry analysis. In contrast, one or both allelic forms of KIR2DL2/KIR2DL3 were expressed by a high proportion of NK cells in all 73 individuals. However if both KIR2DL2 and KIR2DL3 genes were present, KIR2DL3 was preferentially expressed, as transcripts of KIR2DL2 was not detectable by RT-PCR in 42% of these individuals. In total, repertoire assessment for the four KIRs by genotyping vs phenotyping was not in complete agreement in 18 (25%) of the 73 individuals. Furthermore, among the samples that tested positive for the expression of a certain KIR gene, the levels of transcripts and surface expression varied considerably as measured by both real-time quantitative PCR and flow cytometry analysis. Extension of this comparative analysis to include all 12 KIR family members showed that KIR2DL3 and KIR3DL2 were the only genes whose transcripts were consistently detectable. These results caution the use of genotyping alone for donor selection or leukemia-relapse prognostication because some KIRs may be expressed at a very low level.

MHC class I molecules and KIRs in human history, health and survival

MHC class I molecules are ligands for the killer-cell immunoglobulin-like receptors (KIRs), which are expressed by natural killer cells and T cells. The interactions between these molecules contribute to both innate and adaptive immunity. KIRs and MHC class I molecules are encoded by unlinked polymorphic gene families that distinguish all but the most related individuals. Combinations of MHC class I and KIR variants influence resistance to infections, susceptibility to autoimmune diseases and complications of pregnancy, as well as outcome after haematopoietic stem-cell transplantation. Such correlations raise the possibility that interplay between KIR and MHC class I polymorphisms has facilitated human survival in the presence of epidemic infections and has influenced both reproduction and population growth.

Improved outcome in HLA-identical sibling hematopoietic stem-cell transplantation for acute myelogenous leukemia predicted by KIR and HLA genotypes

Inhibitory killer immunoglobulin (Ig)-like receptors (KIRs) recognize HLA-C and -B epitopes on target cells, thereby regulating natural killer (NK) cell activity. In 178 patients receiving T-cell-depleted HLA-identical sibling transplants for acute myelogenous leukemia (AML), chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL), or myelodysplastic syndrome (MDS), analysis of donor KIR genotype with HLA genotype demonstrated that 62.9% of the patients lacked an HLA ligand for donor-inhibitory KIR. Lack of HLA ligand for donor-inhibitory KIR (missing KIR ligand) had no effect on disease-free survival (DFS), overall survival (OS), or relapse in patients receiving transplants for CML and ALL. In patients with AML and MDS, however, there was a significant missing KIR ligand effect on DFS (P = .014; hazard ratio [HR], 0.53; 95% confidence interval [95% CI], 0.28-0.88) and OS (P = .03; HR, 0.53; 95% CI, 0.3-0.93). Incidence of relapse was also lower in patients with AML and MDS who lacked the HLA ligand for donor-inhibitory KIR (P = .04; HR, 0.41; 95% CI, 0.18-0.97). AML and MDS patients lacking 2 HLA ligands for donor-inhibitory KIR had the highest DFS (P = .002) and OS (P = .003). There was no significant contribution of donor-activating KIR to transplantation outcome in these patients. These data indicate that the absence of class I ligand in the recipient for donor-inhibitory KIR can be a prognostic factor for transplantation outcome in HLA-identical sibling transplantation and that the lack of HLA-C or -B ligands for donor-inhibitory KIR can contribute to improved outcomes for patients with AML and MDS.

Inhibitory killer Ig-like receptor genes and human leukocyte antigen class I ligands in haematopoietic stem cell transplantation

Identification of inhibitory killer Ig-like receptor (KIR) genes and their cognate human leukocyte antigen (HLA) class I ligands in donor-recipient pairs for patients undergoing haematopoietic stem cell transplantation (HCT) as treatment for haematopoietic malignancies has recently gained considerable interest. One incentive for these studies is to identify potential donors who are not HLA identical with the recipient but who still could serve as acceptable and potentially preferred donors based on their KIR genotype. It is demonstrated that a majority of individuals have at least one inhibitory KIR gene for which they lack the cognate HLA class I ligand. Therefore, the clinical benefits conferred by 'missing KIR ligand' might not be limited only to HLA mismatched donor-recipient combinations but may be applicable also to HLA identical transplants and even autologous HCT.

Resistant pure red cell aplasia after allogeneic stem cell transplantation with major ABO mismatch treated by escalating dose donor leukocyte infusion

We report a case of pure red cell aplasia (PRCA) following allogeneic stem cell transplantation (SCT) with major ABO mismatch which proved resistant to all standard treatment options such as change in immunosuppressive treatment, high-dose erythropoietin (EPO) or plasma exchange. We therefore proceeded to administer five cycles of Rituximab therapy, without success. Finally, escalating doses of donor-derived leukocyte infusion (DLI) resolved the PRCA of our patient 415 d after bone-marrow transplantation (BMT) and 140 d after the first infusion of donor leukocytes. A review of the literature shows the efficacy of various treatments; the role of DLI and other treatment options are discussed. Furthermore, the underlying pathophysiological mechanisms especially with regard to the role of NK cells in alloreactivity after allogeneic SCT are explained.