Rapid, flow cytometric assay for NK alloreactivity reveals exceptions to rules governing alloreactivity

KIR specificity and avidity of standard and unusual C1, C2, Bw4, Bw6 and A3/11 amino acid motifs at entire HLA:KIR interface between NK and target cells, the functional and evolutionary classification of HLA class I molecules

Natural killer (NK) cells make vital contributions to the immune system and the reproductive system. Notably, NK cells of donor origin can recognize and kill residual leukaemic cells and cure malignant patients in hematopoietic stem cell (HSC) transplant setting. NK cell function is regulated by KIRs that recognize cognate HLA class I molecules on target cells, depending on their amino acid residues. In review, we addressed the question of binding capacity and avidity of HLA class I molecules to different killer cell immunoglobulin-like receptors (KIRs) depending on all interacting amino acid residues both on HLA and KIR side. We searched PubMed database and analysed available HLA:KIR crystallographic data for amino acid residues in HLA molecules, those physically involved in binding KIRs (termed here the "entire KIR interface"). Within entire KIR interface, we selected five functional sequence motifs (14-19, 66-76, 77-84, 88-92 and 142-151) and classified them according to the conservation of their amino acid sequences among 8,942 HLA class I molecules. Although some conserved amino acid motifs were shared by different groups of KIR ligands, the HLA motif combinations were exclusive for the ligand groups. In 135 common HLA class I molecules with known HLA:KIR recognition, we found 54 combinations of five motifs in each of the KIR-binding interfaces (C1, C2, Bw4, A3/11) and conserved non-KIR-binding interfaces. Based on the entire KIR interface, this analysis allowed to classify 8,942 HLA class I molecules into KIR specificity groups. This functional and evolutionary classification of entire KIR interfaces provides a tool for unambiguously predicting HLA:KIR interactions for common and those HLA molecules that have not yet been functionally tested. Considering the entire KIR interface in HLA class I molecules, functional interactions of HLA and KIR can be predicted in immune responses, reproduction and allotransplantation. Further functional studies are needed on the HLA:KIR interaction variations caused by the repertoires of peptides presented by HLA molecules and KIR polymorphisms at allelic level.

The More, The Better: "Do the Right Thing" For Natural Killer Immunotherapy in Acute Myeloid Leukemia

Natural killer (NK) cells are circulating CD3⁻ lymphocytes, which express CD56 or CD16 and an array of inhibitory receptors, called killer-immunoglobulin-like receptors (KIRs). Alloreactive KIR-ligand mismatched NK cells crucially mediate the innate immune response and have a well-recognized antitumor activity. Adoptive immunotherapy with alloreactive NK cells determined promising clinical results in terms of response in acute myeloid leukemia (AML) patients and several data demonstrated that response can be influenced by the composition of NK graft. Several data show that there is a correlation between NK alloreactivity and clinical outcome: in a cohort of AML patients who received NK infusion with active disease, more alloreactive NK cell clones were found in the donor repertoire of responders than in non-responders. These findings demonstrate that the frequency of alloreactive NK cell clones influence clinical response in AML patients undergoing NK cell immunotherapy. In this work, we will review the most recent preclinical and clinical data about the impact of alloreactive NK cells features other than frequency of alloreactive clones and cytokine network status on their anti-leukemic activity. A better knowledge of these aspects is critical to maximize the effects of this therapy in AML patients.

Novel strategies of adoptive immunotherapy: How natural killer cells may change the treatment of elderly patients with acute myeloblastic leukemia

Although many attempts have been made to identify novel molecular-targeted therapies for patients with acute myeloid leukemia, their translation into the clinic have had limited impact. In particular, the question of effective and curative treatments for elderly patients, who are not eligible for stem cell transplantation, remains an unmet medical need. To answer this question, a wide range of immunologic therapeutic strategies, mostly T cell based, have been proposed and investigated. At present, however, the clinical results have been largely unsatisfactory. Natural killer cells have recently been used as a means of adoptive immunotherapy with promising clinical results. On the basis of recent clinical reports and moving from the basic immunobiology of natural killer cells, here we discuss some open issues in the clinical translation of natural killer-based adoptive immunotherapy for the management of elderly patients with acute myeloid leukemia.

Larger Size of Donor Alloreactive NK Cell Repertoire Correlates with Better Response to NK Cell Immunotherapy in Elderly Acute Myeloid Leukemia Patients

PURPOSE

In acute myeloid leukemia (AML), alloreactive natural killer (NK) cells are crucial mediators of immune responses after haploidentical stem cell transplantation. Allogeneic NK cell infusions have been adoptively transferred with promising clinical results. We aimed at determining whether the composition of NK graft in terms of frequency of alloreactive NK cells influence the clinical response in a group of elderly AML patients undergoing NK immunotherapy.

EXPERIMENTAL DESIGN

Seventeen AML patients, in first complete remission (CR; median age 64 years, range 53-73) received NK cells from haploidentical KIR-ligand-mismatched donors after fludarabine/cyclophosphamide chemotherapy, followed by IL2. To correlate donor NK cell activity with clinical response, donor NK cells were assessed before and after infusion.

RESULTS

Toxicity was moderate, although 1 patient died due to bacterial pneumonia and was censored for clinical follow-up. With a median follow-up of 22.5 months (range, 6-68 months), 9 of 16 evaluable patients (0.56) are alive disease-free, whereas 7 of 16 (0.44) relapsed with a median time to relapse of 9 months (range, 3-51 months). All patients treated with molecular disease achieved molecular CR. A significantly higher number of donor alloreactive NK cell clones was observed in responders over nonresponders. The infusion of higher number of alloreactive NK cells was associated with prolonged disease-free survival (0.81 vs. 0.14, respectively;P= 0.03).

CONCLUSIONS

Infusion of purified NK cells is feasible in elderly AML patients as post-CR consolidation strategy. The clinical efficacy of adoptively transferred haploidentical NK cells may be improved by infusing high numbers of alloreactive NK cells.

Target-induced natural killer cell loss as a measure of NK cell responses

Natural killer (NK) cells are an important effector cell of innate immunity. Their interaction with susceptible target cells triggers NK cell cytotoxicity and the release of cytokines. Immunofluorescence flow cytometry-based assays are now the preferred methods for measuring NK cell responses. For these assays, assessment is made on NK cells (CD3(-)CD56(+) CD16(+)) within the viable lymphocyte gate, defined by the parameters of size (FSC) and granularity (SSC). Accordingly, NK cells that have not dissociated from target cells at the time of measurement, or that have undergone target cell-induced apoptosis, are excluded from the viable lymphocyte gate and therefore from analysis. This unit describes a protocol for assessing NK cell function in response to various target cells (natural killing, antibody-dependent cell cytotoxicity, and NK cell alloreactivity) based on the loss of NK cells from the lymphocyte gate. This target-induced NK loss (TINKL) should provide a sensitive measure of NK cell responses in a clinical laboratory setting.

The detection of NK cell alloreactivity by flow cytometric CD107a assay

Natural killer (NK) cell alloreactivity can be exploited in haploidentical (one haplotype mismatched) haematopoietic stem cell transplantation (HSCT) to prevent leukaemia relapse, rejection, and graft-vs-host disease (GVHD) (Blood 94:333-339; Science 295:2097-2100). If NK cell alloreactivity is to be exploited in HSCT, it is important to be able to reliably select donors who have NK alloreactivity towards the patient. The detection of donor NK alloreactivity towards patient target cells has traditionally been evaluated by NK cell cloning and (51)Cr-release cytotoxicity assay. This approach is complex and time consuming with results taking up to 6 weeks. Here, we detail a novel flow cytometric CD107a-based assay capable of detecting NK cell alloreactivity in 14 days.

Molecular determinant-based typing of KIR alleles and KIR ligands

Killer cell immunoglobulin-like receptors (KIRs) regulate NK cell function. KIRs and their HLA ligands are highly polymorphic in nature with substantial allelic polymorphism. At present, there is a lack of an expedient method for KIR and HLA allele typing with relevant functional information. Here, we developed a single-nucleotide polymorphism (SNP) assay to type various allele groups of KIR2DL1 with distinct functional properties based on polymorphism at position 245. We also established a SNP assay to type different KIR ligands based on polymorphism at position 77 in HLA-C and position 83 in HLA-B and -A. Our SNP assays for KIR and KIR ligand typing are much cheaper and faster than existing high-resolution typing. Importantly, our high-throughput methods provide readouts that are informative in predicting NK cell activity in health, disease, and transplantation.