Natural Killer Cell Alloreactivity Predicted By Killer Cell Immunoglobulin-Like Receptor Ligand Mismatch Does Not Impact Engraftment in Umbilical Cord Blood and Haploidentical Stem Cell Transplantation.

Natural killer cell alloreactivity is determined by killer cell immunoglobulin-like receptor (KIR) ligands in donor and recipient pairs. A small, single institution study suggested that the risk of primary graft failure after cord blood hematopoietic cell transplantation (CBT) can be predicted by host-versus-graft (HvG)-directed natural killer cell alloreactivity. In the haploidentical transplantation (Haplo HCT) cohort, graft failures were observed only in graft-versus-host (GvH) KIR ligand mismatched pairs. A subsequent study was designed to explore the association between HvG and GvH KIR ligand mismatching and engraftment in both CBT and Haplo HCT using the large, multicenter transplant population of the Center for International Blood and Transplant Research database. Nine hundred single CBT (sCBT), 954 double CBT (dCBT), and 671 Haplo HCT performed between 2008 and 2017 for acute leukemias and myelodysplastic syndrome were examined. Several models of KIR-L interactions were analyzed by multiple regression analyses for their association with engraftment, overall survival (OS), and transplant-related mortality (TRM). In sCBT, although HvG or bidirectional KIR ligand mismatch (KIR-L-MM) was initially associated with higher TRM in the first 6 months after transplantation, this effect was nullified after 6 months such that long-term survival was not different compared to GvH KIR-L-MM or KIR-L matched (KIR-L-M) pairs. There was no significant difference in neutrophil and platelet engraftment. In dCBT, no significant differences were seen in engraftment, OS and TRM. In the Haplo cohort there was faster platelet recovery in the GvH KIR-L-MM/KIR-L-M pairs versus HvG KIR-L-MM or bidirectional mismatch (HR 1.23, P= .0116). There was no significant association with OS, TRM, or neutrophil engraftment. In this large registry study, KIR-L mismatching did not significantly impact engraftment, TRM, or survival in CBT and Haplo HCT, although an association with platelet engraftment in Haplo HCT was demonstrated.

Killer Cell Immunoglobulin-Like Receptor Haplotype B Modulates Susceptibility to EBV-Associated Classic Hodgkin Lymphoma.

Tumor cells of classic Hodgkin lymphoma (cHL) are derived from antigen presenting B cells that are infected by Epstein Barr virus (EBV) in ~30% of patients. Polymorphic Killer cell immunoglobulin-like receptors (KIRs) expressed on NK cells interact with human leukocyte antigen (HLA) class I and play a key role in immune surveillance against virally infected cells and tumor cells. We investigated the effect of KIR types on cHL susceptibility overall (n=211) and in EBV-stratified subgroups using the Dutch GoNL cohort as controls (n=498). The frequency of the KIR haplotype B subgroup was significantly different between EBV+ and EBV- cHL patients (62% vs. 77%, p=0.04) and this difference was more pronounced in nodular sclerosis (NS) cHL (49% vs. 79%, p=0.0003). The frequency of KIR haplotype B subgroup was significantly lower in EBV+ NS cHL compared to controls (49% vs. 67%, p=0.01). Analyses of known KIR - HLA interaction pairs revealed lower carrier frequencies of KIR2DS2 - HLA-C1 (29% vs. 46%, p=0.03) and KIR2DL2 - HLA-C1 (29% vs. 45%, p=0.04) in EBV+ NS cHL patients compared to controls. Carriers of the KIR haplotype B subgroup are less likely to develop EBV+ NS cHL, probably because of a more efficient control over EBV-infected B cells.

Functional Competence of NK Cells via the KIR/MHC Class I Interaction Correlates with DNAM-1 Expression.

The interaction of inhibitory receptors with self-MHC class I (MHC-I) molecules is responsible for NK cell education. The intensity of DNAM-1 expression correlates with NK cell education. However, whether DNAM-1 expression directly influences the functional competence of NK cells via the KIR/MHC-I interaction remains unclear. Based on allogeneic haploidentical hematopoietic stem cell transplantation, we investigated the intensity of DNAM-1 expression on reconstituted NK cells via the interaction of KIR with both donor HLA and recipient HLA at days 30, 90, and 180 after hematopoietic stem cell transplantation. The reconstituted NK cells educated by donor and recipient HLA molecules showed the highest DNAM-1 expression, whereas DNAM-1 expression on educated NK cells with only recipient HLA molecules was higher than that on educated NK cells with only donor HLA molecules, indicating that NK cells with donor or recipient HLA molecules regulate DNAM-1 expression and thereby affect NK cell education. Additionally, the effects of recipient cells on NK cell education were greater than those of donor cells. However, only when the DNAM-1, NKP30, and NKG2D receptors were blocked simultaneously was the function of educated and uneducated NK cells similar. Therefore, activating receptors may collaborate with DNAM-1 to induce educated NK cell hyperresponsiveness. Our data, based on in vitro and in vivo studies, demonstrate that the functional competence of NK cells via the KIR/MHC-I interaction correlates with DNAM-1 expression in human NK cells.

KIR3DL3-HHLA2 is a human immunosuppressive pathway and a therapeutic target.

The B7 family ligand HERV-H LTR-associating protein 2 (HHLA2) is an attractive target for cancer immunotherapy because of its coinhibitory function, overexpression in human cancers, and association with poor prognoses. However, the knowledge of the HHLA2 pathway is incomplete. HHLA2 has an established positive receptor transmembrane and immunoglobulin (Ig) domain containing 2 (TMIGD2) but a poorly characterized negative receptor human killer cell Ig-like receptor, three Ig domains, and long cytoplasmic tail (KIR3DL3). Here, KIR3DL3 and TMIGD2 simultaneously bound to different sites of HHLA2. KIR3DL3 was mainly expressed on CD56dim NK and terminally differentiated effector memory CD8+ T (CD8+ TEMRA) cells. KIR3DL3+ CD8+ TEMRA acquired an NK-like phenotype and function. HHLA2 engagement recruited KIR3DL3 to the immunological synapse and coinhibited CD8+ T and NK cell function and killing, inducing immune-evasive HHLA2+ tumors. KIR3DL3 recruited SHP-1 and SHP-2 to attenuate Vav1, ERK1/2, AKT, and NF-κB signaling. HHLA2+ tumors from human kidney, lung, gallbladder, and stomach were infiltrated by KIR3DL3+ immune cells. KIR3DL3 blockade inhibited tumor growth in multiple humanized mouse models. Thus, our findings elucidated the molecular and cellular basis for the inhibitory function of KIR3DL3, demonstrating that the KIR3DL3-HHLA2 pathway is a potential immunotherapeutic target for cancer.

Peptide: MHC-based DNA vaccination strategy to activate natural killer cells by targeting killer cell immunoglobulin-like receptors.

BACKGROUND: Natural killer (NK) cells are increasingly being recognized as agents for cancer immunotherapy. The killer cell immunoglobulin-like receptors (KIRs) are expressed by NK cells and are immunogenetic determinants of the outcome of cancer. In particular, KIR2DS2 is associated with protective responses to several cancers and also direct recognition of cancer targets in vitro. Due to the high homology between activating and inhibitory KIR genes to date, it has been challenging to target individual KIR for therapeutic benefit. METHODS: A novel KIR2DS2-targeting therapeutic peptide:MHC DNA vaccine was designed and used to immunize mice transgenic for KIR genes (KIR-Tg). NK cells were isolated from the livers and spleens of vaccinated mice and then analyzed for activation by flow cytometry, RNA profiling and cytotoxicity assays. In vivo assays of NK cell function using a syngeneic cancer model (B16 melanoma) and an adoptive transfer model for human hepatocellular carcinoma (Huh7) were performed. RESULTS: Injecting KIR-Tg mice with the vaccine construct activated NK cells in both liver and spleens of mice, with preferential activation of KIR2DS2-positive NK cells. KIR-specific activation was most marked on the CD11b+CD27+ mature subset of NK cells. RNA profiling indicated that the DNA vaccine upregulated genes associated with cellular metabolism and downregulated genes related to histone H3 methylation, which are associated with immune cell maturation and NK cell function. Vaccination led to canonical and cross-reactive peptide:MHC-specific NK cell responses. In vivo, DNA vaccination led to enhanced antitumor responses against B16F10 melanoma cells and also enhanced responses against a tumor model expressing the KIR2DS2 ligand HLA-C*0102. CONCLUSION: We show the feasibility of a peptide-based KIR-targeting vaccine strategy to activate NK cells and hence generate functional antitumor responses. This approach does not require detailed knowledge of the tumor peptidomes nor HLA matching with the patient. It therefore offers a novel opportunity for targeting NK cells for cancer immunotherapy.

Mesenchymal stem cells enhance the impact of KIR receptor-ligand mismatching on acute graft-versus-host disease following allogeneic hematopoietic stem cell transplantation in patients with acute myeloid leukemia but not in those with acute lymphocytic leukemia.

Killer cell immunoglobulin-like receptor (KIR) receptor-ligand mismatch has been shown to be protective for acute and chronic graft-versus-host disease (aGVHD, cGVHD) following allogeneic hematopoietic stem cell transplantation (allo-HSCT) for acute leukemia. Mesenchymal stem cells (MSC) have been considered as one of the most promising prophylaxis for severe GVHD. However, there are no prospective or retrospective studies determining whether they can work synergistically on GVHD. To investigate the potential influence of KIR matching and MSCs, and their synergism on aGVHD and cGVHD after allo-HSCT in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) patients. Data from 104 patients with AML and 50 patients with ALL treated with allo-HSCT in the transplantation unit were retrospectively analyzed. KIR genotyping was performed by the PCR-SSO method. The amplicons were quantified on the Luminex 200 flow analyzer and analyzed using the Quick-Type for Lifecodes software to generate KIR data. Cox proportional hazards models were used in multivariate analyses. KIR receptor-ligand matching was associated with an increased risk of grade II-IV aGVHD compared to KIR receptor-ligand mismatching (p < 0.001) in AML patients, but KIR ligand-mismatching had no significant effect on aGVHD or cGVHD in ALL patients. In contrast, MSCs reduced the incidence of grade II-IV aGVHD in both AML and ALL patients (AML: p = 0.006; ALL: p = 0.008) regardless of KIR mismatching. The combination of KIR receptor-ligand mismatch and MSC transplantation significantly suppressed grade II-IV aGVHD occurrence in AML patients (p = 0.039). In the KIR mismatch group, the incidence of aGVHD was 2.8% in patients receiving MSC compared to 14.6% in those who did not (p = 0.047). KIR receptor-ligand mismatch, MSC transplantation and their combined use significantly reduced the risk of aGVHD after allo-HSCT. These data provide a clinically applicable strategy to reduce aGVHD, thus improving allo-HSCT outcome.

The role of KIR positive NK cells in diseases and its importance in clinical intervention.

Natural killer (NK) cells are essential for the elimination of the transformed and cancerous cells. Killer cell immunoglobulin-like receptors (KIRs) which expressed by T and NK cells, are key regulator of NK cell function. The KIR and their ligands, MHC class I (HLA-A, B and C) molecules, are highly polymorphic and their related genes are located on 19 q13.4 and 6 q21.3 chromosomes, respectively. It is clear that particular interaction between the KIRs and their related ligands can influence on the prevalence, progression and outcome of several diseases, like complications of pregnancy, viral infection, autoimmune diseases, and hematological malignancies. The mechanisms of immune signaling in particular NK cells involvement in causing pathological conditions are not completely understood yet. Therefore, better understanding of the molecular mechanism of KIR-MHC class I interaction could facilitate the treatment strategy of diseases. The present review focused on the main characteristics and functional details of various KIR and their combination with related ligands in diseases and also highlights ongoing efforts to manipulate the key checkpoints in NK cell-based immunotherapy.

Allelic polymorphisms of KIRs and antitumor immunity against chronic myeloid leukemia.

The development of BCR-ABL1 tyrosine kinase inhibitors (TKIs) markedly improved the prognosis of patients with chronic myeloid leukemia (CML). Approximately 50% of patients who achieve deep molecular response (DMR) remain in treatment-free remission (TFR) even after discontinuation of TKIs. Although TKIs may achieve clinical "cure" after TKI treatment for specific periods, there are no reliable biomarkers for predicting the response to TKIs and the probability of TFR in CML. An increase in natural killer (NK) cells in the peripheral blood of TKI-treated CML patients is correlated with better outcomes, suggesting that TKIs induce antitumor NK cell immunity against CML cells. Killer immunoglobulin-like receptors (KIRs) are highly polymorphic NK cell receptors that play important roles in the regulation of immune responses. The identification of allelic polymorphisms of KIRs by next-generation sequencing uncovered novel aspects of KIRs. Here we summarize the current knowledge of the genetic and immunological aspects of KIRs and discuss the association between allelic polymorphisms of KIRs and TKI-treated CML.

Asymptomatic SARS-CoV-2 infection: is it all about being refractile to innate immune sensing of viral spare-parts?-Clues from exotic animal reservoirs.

A vast proportion of coronavirus disease 2019 (COVID-19) individuals remain asymptomatic and can shed severe acute respiratory syndrome (SARS-CoV) type 2 virus to transmit the infection, which also explains the exponential increase in the number of COVID-19 cases globally. Furthermore, the rate of recovery from clinical COVID-19 in certain pockets of the globe is surprisingly high. Based on published reports and available literature, here, we speculated a few immunovirological mechanisms as to why a vast majority of individuals remain asymptomatic similar to exotic animal (bats and pangolins) reservoirs that remain refractile to disease development despite carrying a huge load of diverse insidious viral species, and whether such evolutionary advantage would unveil therapeutic strategies against COVID-19 infection in humans. Understanding the unique mechanisms that exotic animal species employ to achieve viral control, as well as inflammatory regulation, appears to hold key clues to the development of therapeutic versatility against COVID-19.

KIR3DL3 Is an Inhibitory Receptor for HHLA2 that Mediates an Alternative Immunoinhibitory Pathway to PD1.

Blockade of the PD1 pathway is a broadly effective cancer therapy, but additional immune-inhibitory pathways contribute to tumor immune evasion. HERV-H LTR-associating 2 (HHLA2; also known as B7H5 and B7H7) is a member of the B7 family of immunoregulatory ligands that mediates costimulatory effects through its interaction with the CD28 family member transmembrane and immunoglobulin domain containing 2 (TMIGD2). However, HHLA2 has also been known to have inhibitory effects on T cells. Here, we report that we have identified killer cell immunoglobulin-like receptor, three immunoglobulin domains and long cytoplasmic tail 3 (KIR3DL3) as an inhibitory receptor for HHLA2 in T cells and natural killer (NK) cells and have generated HHLA2 and KIR3DL3 antibodies that block the immune-inhibitory activity of HHLA2, preserving the costimulatory signal. It is known that HHLA2 is frequently expressed in several tumor types, including clear cell renal cell carcinoma (ccRCC). We found that HHLA2 expression was nonoverlapping with PDL1 expression in ccRCC, suggesting that HHLA2 mediates a mechanism of tumor immune evasion that is independent from PDL1. Blockade of both the PD1 and KIR3DL3 pathways may be a more effective way to reverse tumor immune evasion.See related Spotlight on p. 128.

Umbilical Cord Blood and iPSC-Derived Natural Killer Cells Demonstrate Key Differences in Cytotoxic Activity and KIR Profiles.

Natural killer (NK) cells derived or isolated from different sources have been gaining in importance for cancer therapies. In this study, we evaluate and compare key characteristics between NK cells derived or isolated from umbilical cord blood, umbilical cord blood hematopoietic stem/progenitor cells, peripheral blood, and induced pluripotent stem cells (iPSCs). Specifically, we find CD56+ NK cells isolated and expanded directly from umbilical cord blood (UCB56) and NK cells derived from CD34+ hematopoietic stem/progenitors in umbilical cord blood (UCB34) differ in their expression of markers associated with differentiation including CD16, CD2, and killer Ig-like receptors (KIRs). UCB56-NK cells also displayed a more potent cytotoxicity compared to UCB34-NK cells. NK cells derived from iPSCs (iPSC-NK cells) were found to have variable KIR expression, with certain iPSC-NK cell populations expressing high levels of KIRs and others not expressing KIRs. Notably, KIR expression on UCB56 and iPSC-NK cells had limited effect on cytotoxic activity when stimulated by tumor target cells that express high levels of cognate HLA class I, suggesting that in vitro differentiation and expansion may override the KIR-HLA class I mediated inhibition when used across HLA barriers. Together our results give a better understanding of the cell surface receptor, transcriptional, and functional differences between NK cells present in umbilical cord blood and hematopoietic progenitor-derived NK cells which may prove important in selecting the most active NK cell populations for treatment of cancer or other therapies.

Resistance of KIR Ligand-Missing Leukocytes to NK Cells In Vivo in Patients with Acquired Aplastic Anemia.

The loss of killer cell Ig-like receptor ligands (KIR-Ls) due to the copy number-neutral loss of heterozygosity of chromosome 6p (6pLOH) in leukocytes of patients with acquired aplastic anemia (AA) may alter the susceptibility of the affected leukocytes to NK cell killing in vivo. We studied 408 AA patients, including 261 who were heterozygous for KIR-Ls, namely C1/C2 or Bw6/Bw4, for the presence of KIR-L-missing [KIR-L(-)] leukocytes. KIR-L(-) leukocytes were found in 14 (5.4%, C1 [n = 4], C2 [n = 3], and Bw4 [n = 7]) of the 261 patients, in whom corresponding KIR(+) licensed NK cells were detected. The incidence of 6pLOH in the 261 patients (18.0%) was comparable to that in 147 patients (13.6%) who were homozygous for KIR-L genes. The percentages of HLA-lacking granulocytes (0.8-50.3%, median 15.2%) in the total granulocytes of the patients with KIR-L(-) cells were significantly lower than those (1.2-99.4%, median 55.4%) in patients without KIR-L(-) cells. KIR2DS1 and KIR3DS1 were only possessed by three of the 14 patients, two of whom had C2/C2 leukocytes after losing C1 alleles. The expression of the KIR3DS1 ligand HLA-F was selectively lost on KIR-L(-) primitive hematopoietic stem cells derived from 6pLOH(+) induced pluripotent stem cells in one of the KIR3DS1(+) patients. These findings suggest that human NK cells are able to suppress the expansion of KIR-L(-) leukocytes but are unable to eliminate them partly due to the lack of activating KIRs on NK cells and the low HLA-F expression level on hematopoietic stem cells in AA patients.

Natural killer cell receptor variants and chronic hepatitis B virus infection in the Vietnamese population.

OBJECTIVES: Genes of host immunity play an important role in disease pathogenesis and are determinants of clinical courses of infections, including hepatitis B virus (HBV). Killer-cell immunoglobulin-like receptor (KIR), expressed on the surface of natural killer cells (NK), regulate NK cell cytotoxicity by interacting with human leukocyte antigen (HLA) class I molecules and are candidates for influencing the course of HBV. This study evaluated whether variations in KIR gene content and HLA-C ligands are associated with HBV and with the development of liver cirrhosis and hepatocellular carcinoma. METHODS: A Vietnamese study cohort (HBV n = 511; controls n = 140) was genotyped using multiplex sequence-specific polymerase chain reaction (PCR-SSP) followed by melting curve analysis. RESULTS: The presence of the functional allelic group of KIR2DS4 was associated with an increased risk of chronic HBV (OR = 1.86, pcorr = 0.02), while KIR2DL2+HLA-C1 (OR = 0.62, pcorr = 0.04) and KIR2DL3+HLA-C1 (OR = 0.48, pcorr = 0.04) were associated with a decreased risk. The pair KIR2DL3+HLA-C1 was associated with liver cirrhosis (OR = 0.40, pcorr = 0.01). The presence of five or more activating KIR variants was associated with hepatocellular carcinoma (OR = 0.53, pcorr = 0.04). CONCLUSIONS: KIR gene content variation and combinations KIR-HLA influence the outcome of HBV infection.

Treatment of cancer with an anti-KIR antibody: a patent evaluation of US9879082 and US2018208652.

Introduction: KIR is an inhibitory receptor expressed by natural killer cells that suppress the immune response against tumor cells. There is a great need to discover and develop new therapies focused on inhibiting the action of KIR and consequently improving the immune response in the various types of cancer. Authors of US9879082 and US2018208652 patents propose a method to eradicate cancer that utilizes anti-KIR antibody.Areas covered: US9879082 and US2018208652 patents describe an anti-KIR antibody, a pharmaceutical composition that contains it, and their application for cancer treatment, particularly, multiple myeloma and acute myeloid leukemia. Anti-KIR antibody is used to a dosage of 0.0003-3 mg antibody/kg patient weight, and is suspended in an isotonic solution consisting of sodium phosphate, sucrose, NaCl, and polysorbate 80.Expert opinion: The results of the clinical trials only support trials regarding the pharmacokinetic, pharmacodynamic, safety, and tolerability. In addition, these results demonstrate that treatment with the anti-KIR antibody can induce an antitumor response in cancer patients.

Decreased iKIR-HLA C Pair Confers Worse Clinical Outcomes for Patients With Myeloid Disease Receiving Antithymocyte Globulin-Based Haploidentical Hematopoietic Stem Cell Transplantation.

Hematopoietic stem cell transplantation (HSCT) is a curative therapy for patients with malignant hematologic diseases. Killer immunoglobin-like receptor (KIR) expressed by NK cells is closely associated with the transplant outcomes, and it has been widely explored and debated for a few decades. Recently published studies have revealed that inhibitory KIRs (iKIRs) are educated by their cognate human lymphocyte antigen (HLA) ligands, and that decreased iKIR-HLA pairs post-transplantation may indicate a reduced NK cell function and impaired control of the primary disease. However, this theory still needs to be validated by additional clinical studies. Here we conducted a retrospective analysis of 246 patients who received haploidentical (haplo)-HSCT at our treatment center between January 2015 and June 2018. Our data suggests that decreased iKIR-HLA C pair post-HSCT correlated with a significantly higher risk of relapse [hazard risk (HR) = 2.95, p = 0.019] and reduced overall survival (OS) (HR = 3.74, p = 0.001) and disease-free survival (DFS) (HR = 4.05, p = 0.0004) in patients with myeloid disease. In conclusion, decreased iKIR-HLA C pair should be avoided during anti-thymocyte globulin (ATG)-based haplo-HSCT, especially for patients with myeloid disease.

Two Occurrences of Leukemia Relapse Due to Mismatched HLA Loss After Haploidentical Stem Cell Transplantation From Different Family Donors With KIR Ligand Mismatch.

Mismatched HLA loss is a cause of leukemia relapse after HLA-haploidentical stem cell transplantation (haplo-SCT). We report a patient with a history of 2 occurrences of leukemia relapse due to mismatched HLA loss after haplo-SCT. He received haplo-SCT from his father but showed leukemia relapse with loss of the maternal HLA haplotype. He then underwent haplo-SCT from his mother, and developed relapse with loss of the paternal HLA haplotype. Both donors had killer cell immunoglobulin-like receptor-ligand mismatch but alloreactive natural killer cells could not prevent relapse. Second haplo-SCT should be conducted carefully for patients with relapse due to mismatched HLA loss.

Genetic diversity affects the nanoscale membrane organization and signaling of natural killer cell receptors.

Genetic diversity in human natural killer (NK) cell receptors is linked to resistance and susceptibility to many diseases. Here, we tested the effect of this diversity on the nanoscale organization of killer cell immunoglobulin-like receptors (KIRs). Using superresolution microscopy, we found that inhibitory KIRs encoded by different genes and alleles were organized differently at the surface of primary human NK cells. KIRs that were found at low abundance assembled into smaller clusters than those formed by KIRs that were more highly abundant, and at low abundance, there was a greater proportion of KIRs in clusters. Upon receptor triggering, a structured interface called the immune synapse assembles, which facilitates signal integration and controls NK cell responses. Here, triggering of low-abundance receptors resulted in less phosphorylation of the downstream phosphatase SHP-1 but more phosphorylation of the adaptor protein Crk than did triggering of high-abundance receptors. In cells with greater KIR abundance, SHP-1 dephosphorylated Crk, which potentiated NK cell spreading during activation. Thus, genetic variation modulates both the abundance and nanoscale organization of inhibitory KIRs. That is, as well as the number of receptors at the cell surface varying with genotype, the way in which these receptors are organized in the membrane also varies. Essentially, a change in the average surface abundance of a protein at the cell surface is a coarse descriptor entwined with changes in local nanoscale clustering. Together, our data indicate that genetic diversity in inhibitory KIRs affects membrane-proximal signaling and, unexpectedly, the formation of activating immune synapses.

Missing self triggers NK cell-mediated chronic vascular rejection of solid organ transplants.

Current doctrine is that microvascular inflammation (MVI) triggered by a transplant -recipient antibody response against alloantigens (antibody-mediated rejection) is the main cause of graft failure. Here, we show that histological lesions are not mediated by antibodies in approximately half the participants in a cohort of 129 renal recipients with MVI on graft biopsy. Genetic analysis of these patients shows a higher prevalence of mismatches between donor HLA I and recipient inhibitory killer cell immunoglobulin-like receptors (KIRs). Human in vitro models and transplantation of ß2-microglobulin-deficient hearts into wild-type mice demonstrates that the inability of graft endothelial cells to provide HLA I-mediated inhibitory signals to recipient circulating NK cells triggers their activation, which in turn promotes endothelial damage. Missing self-induced NK cell activation is mTORC1-dependent and the mTOR inhibitor rapamycin can prevent the development of this type of chronic vascular rejection.

Systemic and Intra-Nodal Activation of NK Cells After Rituximab Monotherapy for Follicular Lymphoma.

Monotherapy with the anti-CD20 monoclonal antibody rituximab can induce complete responses (CR) in patients with follicular lymphoma (FL). Resting FcRγIII+ (CD16+) natural killer (NK) cells respond strongly to rituximab-coated target cells in vitro. Yet, the contribution of NK cells in the therapeutic effect in vivo remains unknown. Here, we followed the NK cell repertoire dynamics in the lymph node and systemically during rituximab monotherapy in patients with FL. At baseline, NK cells in the tumor lymph node had a naïve phenotype albeit they were more differentiated than NK cells derived from control tonsils as determined by the frequency of CD56dim NK cells and the expression of killer cell immunoglobulin-like receptors (KIR), CD57 and CD16. Rituximab therapy induced a rapid drop in NK cell numbers coinciding with a relative increase in the frequency of Ki67+ NK cells both in the lymph node and peripheral blood. The Ki67+ NK cells had slightly increased expression of CD16, CD57 and higher levels of granzyme A and perforin. The in vivo activation of NK cells was paralleled by a temporary loss of in vitro functionality, primarily manifested as decreased IFNγ production in response to rituximab-coated targets. However, patients with pre-existing NKG2C+ adaptive NK cell subsets showed less Ki67 upregulation and were refractory to the loss of functionality. These data reveal variable imprints of rituximab monotherapy on the NK cell repertoire, which may depend on pre-existing repertoire diversity.