Healthy Donor NK Cells Research Articles

Blockade of the TIGIT-CD155/CD112 axis enhances functionality of NK-92 but not cytokine-induced memory-like NK cells toward CD155-expressing acute myeloid leukemia

TIGIT is an alternative checkpoint receptor (CR) whose inhibition promotes Graft-versus-Leukemia effects of NK cells. Given the significant immune-permissiveness of NK cells circulating in acute myeloid leukemia (AML) patients, we asked whether adoptive transfer of activated NK cells would benefit from additional TIGIT-blockade. Hence, we characterized cytokine-induced memory-like (CIML)-NK cells and NK cell lines for the expression of inhibitory CRs. In addition, we analyzed the transcription of CR ligands in AML patients (CCLE and Beat AML 2.0 cohort) in silico and evaluated the efficacy of CR blockade using in vitro cytotoxicity assays, CD69, CD107a and IFN-γ expression. Alternative but not classical CRs were abundantly expressed on healthy donor NK cells and even further upregulated on CIML-NK cells. In line with our finding that CD155, one important TIGIT-ligand, is reliably expressed on AMLs, we show improved killing of CD155+-AML blasts by NK-92 but interestingly not CIML-NK cells in the presence of TIGIT-blockade. Additionally, our in silico data (n = 671) show that poor prognosis AML patients rather displayed a CD86low CD112/CD155high phenotype, whereas patients with a better outcome rather exhibited a CD86high CD112/CD155low phenotype. Collectively, our data evidence that the complex CR ligand expression profile on AML blasts may be one explanation for the intrinsic NK cell exhaustion observed in AML patients which might be overcome with adoptive NK-92 transfer in combination with TIGIT-blockade.

Redirecting NK cells to the lymph nodes to augment their lymphoma-targeting capacity

CAR-NK cells can induce remission in lymphoma patients. We speculate that the full potential of adoptive NK cell immunotherapy against lymphoma is restricted by their poor lymph node (LN) homing capacity. Here, we have utilized a clinically approved transfection method with the aim of redirecting NK cells to LNs. Electroporation of ex vivo expanded NK cells with mRNAs coding for CCR7, CXCR5, and CD62L resulted in increased in vitro migration towards chemokines and mouse LN-derived supernatant. Following infusion into SCID/Beige mice, modified NK cells showed enhanced LN homing. Importantly, lymphoma patient-derived NK cells were equally well expanded and engineered as healthy donor NK cells, highlighting their translational potential. Additionally, the introduction of high-affinity CD16, together with the homing molecules, also augmented their ADCC capacity against autologous lymphoma cells. Hence, genetic engineering can be utilized to enhance NK cell LN homing. The homing concept may synergize with CAR- or monoclonal/bi-/tri-specific antibody-based approaches.

Immunoglobulins and serum proteins impair anti-tumor NK cell effector functions in malignant ascites.

Malignant ascites indicates ovarian cancer progression and predicts poor clinical outcome. Various ascites components induce an immunosuppressive crosstalk between tumor and immune cells, which is poorly understood. In our previous study, imbalanced electrolytes, particularly high sodium content in malignant ascites, have been identified as a main immunosuppressive mechanism that impaired NK and T-cell activity. In the present study, we explored the role of high concentrations of ascites proteins and immunoglobulins on antitumoral NK effector functions. To this end, a coculture system consisting of healthy donor NK cells and ovarian cancer cells was used. The anti-EGFR antibody Cetuximab was added to induce antibody-dependent cellular cytotoxicity (ADCC). NK activity was assessed in the presence of different patient ascites samples and immunoglobulins that were isolated from ascites. Overall high protein concentration in ascites impaired NK cell degranulation, conjugation to tumor cells, and intracellular calcium signaling. Immunoglobulins isolated from ascites samples competitively interfered with NK ADCC and inhibited the conjugation to target cells. Furthermore, downregulation of regulatory surface markers CD16 and DNAM-1 on NK cells was prevented by ascites-derived immunoglobulins during NK cell activation. Our data show that high protein concentrations in biological fluids are able to suppress antitumoral activity of NK cells independent from the mechanism mediated by imbalanced electrolytes. The competitive interference between immunoglobulins of ascites and specific therapeutic antibodies could diminish the efficacy of antibody-based therapies and should be considered in antibody-based immunotherapies.

Elevated levels of cell-free NKG2D-ligands modulate NKG2D surface expression and compromise NK cell function in severe COVID-19 disease.

It is now clear that coronavirus disease 19 (COVID-19) severity is associated with a dysregulated immune response, but the relative contributions of different immune cells is still not fully understood. SARS CoV-2 infection triggers marked changes in NK cell populations, but there are contradictory reports as to whether these effector lymphocytes play a protective or pathogenic role in immunity to SARS-CoV-2. To address this question we have analysed differences in the phenotype and function of NK cells in SARS-CoV-2 infected individuals who developed either very mild, or life-threatening COVID-19 disease. Although NK cells from patients with severe disease appeared more activated and the frequency of adaptive NK cells was increased, they were less potent mediators of ADCC than NK cells from patients with mild disease. Further analysis of peripheral blood NK cells in these patients revealed that a population of NK cells that had lost expression of the activating receptor NKG2D were a feature of patients with severe disease and this correlated with elevated levels of cell free NKG2D ligands, especially ULBP2 and ULBP3 in the plasma of critically ill patients. In vitro, culture in NKG2DL containing patient sera reduced the ADCC function of healthy donor NK cells and this could be blocked by NKG2DL-specific antibodies. These observations of reduced NK function in severe disease are consistent with the hypothesis that defects in immune surveillance by NK cells permit higher levels of viral replication, rather than that aberrant NK cell function contributes to immune system dysregulation and immunopathogenicity.

PD-L1/PD-1 blockage enhanced the cytotoxicity of natural killer cell on the non-small cell lung cancer (NSCLC) by granzyme B secretion

ObjectiveTo explore the role of PD-L1/PD-1 blockage in the cytotoxicity of natural killer cell in NSCLC.MethodsTwo NSCLC cell lines, Calu-1 and H460, were tested for susceptibility to the cytolytic activity of freshly isolated healthy donor NK cells by a non-radioactive cellular cytotoxicity assay kit. Western blot analysis, FACS, ELISA and antibody blockage experiments were conducted to determine the mechanisms. NK cells isolated from NSCLC patients were also collected for functional assays.ResultsCalu-1 and H460 cells were lysed by NK cells in a dose-dependent manner. H460 cells showed less susceptibility to NK cell-mediated lysis than Calu-1 cells at all ratios. The expression of PD-L1 on H460 cells was higher than that on Calu-1 cells, as determined by FACS and western blot analysis. The specific lysis of H460 cells by NK cells was enhanced when the PD-L1/PD-1 interaction was blocked by anti-PD-L1 antibody. This finding was also demonstrated in NK cells isolated from NSCLC patients.ConclusionsThe present study revealed that PD-L1/PD-1 blockage enhanced the cytotoxicity of natural killer cells in NSCLC via granzyme B secretion. This study will greatly facilitate the precise treatment of lung cancer through determination of PD-L1 expression in tumors.

1044. Identification and Characterization of an Unconventional NK Subset in COVID-19

Abstract Background Coronavirus Disease 2019 (COVID-19) caused by the SARS-CoV-2 virus is associated with dysregulation in the innate immune response including NK cells. NK cells are integral in the innate immune response against viral infections. Canonical NK cells are classified as CD56dim CD16+ and CD56bright CD16-. An unconventional subset of CD56dim CD16- NK cells has previously been identified in COVID-19 that is not present in other viral infections. Here we characterize phenotypic changes in the NK cells of patients with severe COVID-19 as work towards determining the functional status of this unconventional subset. Methods Peripheral blood mononuclear cells (PBMCs) and plasma were isolated from healthy donors (n=5) and patients with severe COVID-19 on Extra Corporeal Membrane Oxygenation (ECMO) (n=15). Primary NK cells were stimulated in vitro with plasma from patients with severe COVID-19 or healthy donors. Flow cytometry was used to phenotype the NK cells. A separate cohort of PBMC samples (n=7) from patients requiring hospitalization for COVID-19 underwent Cellular Indexing of Transcriptomes and Epitopes by Sequencing (CITE-Seq) analysis. Results The CD56bright CD16- NK subset was expanded in PBMCs from patients with severe COVID-19 as compared to healthy controls. CITE-Seq demonstrated that NK cells without surface CD16 clustered separately based on transcriptional profiling and did express FCGR3A at the translational level. Stimulation with COVID-19 plasma recapitulated the loss of CD16 from primary human NK cells and led to increased activity of Caspase 3/7. Figure 1.NK cells shift from the CD56dim CD16+ subset to the CD56dim CD16-subset in patients with severe COVID-19. a) Representative gating of NK cell subsets by Flow Cytometry in healthy and COVID-19 patient peripheral blood mononuclear cells (PBMCs). b) Percentage of total NK cells belonging to a particular cell subset compared between healthy donor samples (n=4) and COVID-19 patient samples (n=8). Data points represent an individual patient sample. Error bars represent the standard deviation of the mean. Differences between groups was analyzed using a two tailed t-test. *: p< 0.05, ns: not significant Figure 2.NK cells shift from the CD56dim CD16+ subset to the CD56dim CD16-subset after stimulation with COVID-19 plasma in vitro a) Representative gating of NK cell subsets by Flow Cytometry analysis in healthy donor NK cells stimulated by healthy plasma and COVID-19 patient plasma. b)Relative change in percentage of total NK cells belonging to a particular cell subset compared between healthy donor plasma (n=6)and COVID-19 patient plasma (n=15) stimulation conditions. Error bars represent the standard deviation of the mean and the difference between groups was analyzed using a two-tailed T-test. **: p< 0.01, ***: p< 0.001, ns: not significant. Conclusion We demonstrate and characterize a nonclassical population of CD56dim CD16- NK cells that are present in patients with severe COVID-19 and replicate this phenotype in vitro. Reproduction of this in vivo phenotype in an in vitro system will allow for additional studies on the functional state of NK cell subsets in COVID-19. The presence of this NK cell population may reflect a dysregulated innate immune response and immunopathogenesis of COVID-19. Disclosures All Authors: No reported disclosures.

NKG2D-mediated cytotoxicity improves after primary surgery for high-grade serous ovarian cancer.

Tumors compromise the patients' immune system to promote their own survival. We have previously reported that HGSC exosomes play a central role, downregulating NKG2D cytotoxicity. Primary surgery's effect on tumor exosomes and NKG2D cytotoxicity in HGSC patients has not been studied before. The overall objective of this study was to explore the effect of surgery on the exosome-induced impairment of NKG2D cytotoxicity in HGSC. Paired pre- and post-operative blood samples were subjected to cell and exosome analyses regarding the NKG2D receptor and ligands, and NKG2D-mediated cytotoxicity. Lymphocytes were phenotyped by immunoflow cytometry. Exosomes, isolated by ultracentrifugation, and characterized by nanoparticle tracking analysis, transmission and immune electron microscopy and western blot were used in functional cytotoxic experiments. HGSC explant culture-derived exosomes, previously studied by us, were used for comparison. HGSC exosomes from patients' sera downregulated NKG2D-mediated cytotoxicity in NK cells of healthy donors. In a subgroup of subjects, NKG2D expression on CTLs and NK cells was upregulated after surgery, correlating to a decrease in the concentration of exosomes in postoperative sera. An overall significantly improved NKG2D-mediated cytotoxic response of the HGSC patients' own NK cells in postoperative compared to preoperative samples was noted. Surgical removal of the primary tumor has a beneficial effect, relieving the exosome-mediated suppression of NKG2D cytotoxicity in HGSC patients, thus boostering their ability to combat cancer.

DR-01, a Non-Fucosylated Anti-CD94 Antibody, Depletes Leukemic Cells in Ex Vivo and In Vivo Models of Large Granular Lymphocyte Leukemia

Large granular lymphocyte leukemia (LGLL) is a rare leukemia more frequently occurring in the elderly population with three major subtypes: T-LGLL, chronic lymphoproliferative disorder of NK cells (CLPD-NK) and aggressive NK cell leukemia (ANKL). Over 50% of patients develop complications including severe neutropenia, thrombocytopenia and anemia, thus predisposing patients to opportunistic infections. In addition, treatments are limited to standard immunosuppressive therapy such as methotrexate, cyclosporine or cyclophosphamide, with complete response rates of only 50% or less for each agent. Thus, novel and effective therapies for LGLL patients are critically needed. Dren Bio is developing DR-01, a non-ligand blocking, non-fucosylated monoclonal antibody targeting CD94. CD94 is a type II transmembrane receptor identified on mature, cytotoxic lymphocytes such as healthy NK and terminally differentiated CD8 T cells. In the context of disease, CD94 is known to be upregulated on LGLL cells. DR-01 functions through depletion of target cells via antibody-mediated cellular cytotoxicity (ADCC) by means of fratricide, a method in which the same cell type induces ADCC on each other. Through characterization of DR-01 using various ELISA and cell-based assays, DR-01 was determined to bind with nanomolar affinity to CD16a (EC50: 0.04µg/mL) and to CD94 on healthy human donor NK cells, cynomolgus monkey NK cells and LGLL cells (EC50: 0.5-1nM). DR-01 induces potent, dose-dependent depletion of CD94+ cells in ex vivo ADCC assays (IC50: 1ng/mL) of peripheral blood mononuclear cells (PBMCs) from healthy and diseased individuals. Furthermore, DR-01 has been shown to be well tolerated in a 4-week dose-range finding and Good Laboratory Practice (GLP) study in cynomolgus monkeys from 5-100mg/kg on a weekly dosing regimen. A 12-color flow cytometry panel was applied to a cohort of patient LGLL PBMCs to profile CD94 expression and other cytotoxic markers associated with the disease, including CD16, CD57 and functional binding partners of CD94 such as NKG2A and NKG2C. CD94 was identified on 97% (37/38) of patient samples screened, ranging from 400 to 725,000 receptors per cell. All patient leukemic cells expressed variable levels of CD16 and CD57. NKG2A and NKG2C were present in over 5% of total leukemic cells in 37% (14/38) and 21% (8/38) of patient samples, respectively. In addition, DR-01 was able to deplete LGL leukemic cells with high potency and in a dose-dependent manner in a functional ADCC assay (IC50:1-10ng/mL). The mechanism of fratricide was demonstrated through degranulation of the leukemic population via expression of CD107a. Cytokine profiling results are pending. To demonstrate in vivo efficacy of DR-01 in a disease model of LGLL, humanized NSG-Tg(hIL-15) mice engrafted with patient LGLL splenocytes were utilized. Optimal splenocyte engraftment (5-20% human CD45+ cells in blood) was achieved within 3 weeks post-inoculation with 10 million PBMCs per pre-sublethally irradiated mouse. The engrafted leukemic population partially preserved the CD94 expression profile from the patient leukemic cells and was successfully depleted (>90%) in blood, bone marrow, spleen and liver 1-week post-treatment with a single dose of DR-01 at 5mg/kg. Overall, DR-01 is a non-fucosylated anti-CD94 antibody with high affinity and potent leukemic cell depleting ability ex vivo and in vivo. The favorable toxicity profile of DR-01 in cynomolgus monkeys precede clinical studies in LGLL patients. Additional profiling and evaluation of DR-01 in LGLL patient samples ex vivo as part of a pre-phase I study is ongoing. A phase I/II trial has been initiated to assess the safety and efficacy of DR-01 in previously treated LGLL patients.

11P WU-NK-101: An enhanced NK cell therapy optimized for function in the tumor microenvironment (TME)

The efficacy of adoptive cell therapies against solid tumors has been limited by the immune-suppressive TME, which aids immune escape. WU-NK-101, manufactured using the MONETATM platform, is an NK product derived from healthy donor NK cells that addresses challenges of adoptive cell therapy in the setting of an adverse TME.

Method for Identifying Galectin Ligands on Lymphocyte Membrane Glycoproteins.

Glycosylation is one of the most common protein posttranslational modifications. Most human lymphocyte membrane receptors are modified by diverse glycan structures, and functional studies have indicated that a family of glycan-binding proteins, galectins, can significantly modulate lymphocyte development and function by interacting with these glycans. Several galectins have a varying degree of affinity for the N-acetyllactosamine (LacNAc) disaccharide, and some critical lymphocyte receptors can be modified by glycan structures carrying this motif. However, the site-specific glycan composition on primary lymphocyte membrane receptors in healthy individuals is largely limited. The main reason for the limitation is low abundance of available material from a single donor and compositional heterogeneity in glycan structures that can potentially modify a protein. Donor-dependent variability in N-glycan structures on CD16a isolated from primary NK cells of healthy human donors was recently reported. NK cell CD16a is glycosylated at five N-glycosylation sites, and two of the five sites are modified, almost exclusively, by N-glycans with multiple LacNAc repeats which can serve as ligands for endogenous galectins. Thus, the protocol described in this section can be utilized to identify galectin ligands at specific glycosylation sites of endogenous membrane receptor from circulating primary human lymphocytes.

Combinatorial Natural Killer Cell-based Immunotherapy Approaches Selectively Target Chordoma Cancer Stem Cells.

Chordoma is a rare tumor derived from notochord remnants that has a propensity to recur and metastasize despite conventional multimodal treatment. Cancer stem cells (CSC) are implicated in chordoma's resistant and recurrent behavior; thus strategies that target CSCs are of particular interest. Using in vitro cytotoxicity models, we demonstrated that anti-programmed death-ligand 1 (N-601) and anti-epidermal growth factor receptor (cetuximab) antibodies enhanced lysis of chordoma cells by healthy donor and chordoma patient NK cells through antibody-dependent cellular cytotoxicity (ADCC). Treatment of NK cells with an IL-15 superagonist complex (N-803) increased their cytotoxicity against chordoma cells, which was further enhanced by treatment with N-601 and/or cetuximab. PD-L1-targeted chimeric antigen receptor NK cells (PD-L1 t-haNKs) were also effective against chordoma cells. CSCs were preferentially vulnerable to NK cell killing in the presence of N-601 and N-803. Flow cytometric analysis of a chordoma CSC population showed that CSCs expressed significantly more NK activating ligand B7-H6 and PD-L1 than non-CSCs, thus explaining a potential mechanism of selective targeting. These data suggest that chordoma may be effectively targeted by combinatorial NK cell-mediated immunotherapeutic approaches and that the efficacy of these approaches in chordoma and other CSC-driven tumor types should be investigated further in clinical studies.

The TGF-β/SMAD Signaling Pathway As a Mediator of NK Cell Dysfunction and Immune Evasion in Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) is a spectrum of clonal hematopoietic disorders affecting the myeloid lineage, characterized by ineffective hematopoiesis and dysplastic features. In about a third of patients, MDS transforms to secondary AML, and for this subgroup the overall survival is dismal. Immune responses against MDS have the potential to prevent disease progression; however, immune evasion mechanisms pose a formidable barrier. In fact, NK cells from MDS patients show significant impairment in their effector function but the mechanism underlying this immune dysfunction is not well understood. Although a multiplicity of mechanisms contribute to NK cell immune evasion, two of the most important mechanisms are down-regulation of activating receptors and the production of inhibitory cytokines such as transforming growth factor β1 (TGF-β), a broadly immunosuppressive cytokine that renders NK cells unable to kill tumor cells. We hypothesized that the MDS microenvironment evades NK cell immune surveillance through a mechanism involving TGF-β, and that this immune dysfunction can be reversed by agents that interfere with this inhibitory pathway.Thus, we isolated NK cells from the peripheral blood of MDS patients (n=16) and compared them to the NK cells from healthy donors (n=10). We observed that NK cells from high-risk MDS patients are dysfunctional, produce significantly less cytokines IFNg (p<0.0001) and CD107a (p=0.0029) and display significantly lower cytotoxicity (p=0.04) towards K562 as demonstrated by 51-Cr release assay compared to their healthy counterparts. This was associated with an abnormal phenotype with downregulation of many activating receptors and upregulation of exhaustion/inhibitory molecules such as PD-1 and the TGF-β induced molecules, CD9 and CD103. To show direct involvement of the TGF-β pathway in mediating MDS-induced NK dysfunction , w e examined activation of the TGF-β pathway by measuring phosphorylation of SMAD 2/3and showed that phospho-SMAD 2/3 is constitutively expressed in NK cells from MDS patients but not in healthy donor NK cells (p=0.03). We noted high expression of TGF-β LAP on the surface of myeloid blasts cells from MDS patients (80-90%) but not healthy myeloid cells (p <0.0001). Interestingly, when myeloid blasts were cultured together with NK cells, we detected significantly larger amounts of TGF-β in the supernatant, suggesting that NK-blast cross-talk may modulate TGF-β release by myeloid blasts. To further explore the mechanism of TGF-β-induced NK dysfunction and the contribution of NK-blast cross-talk to this phenomenon, we co-cultured healthy donor NK cells with myeloid blasts either in direct contact or separated using a transwell membrane and measured their cytotoxicity and cytokine release after 72h of co-culture. NK cells cultured in direct contact with myeloid blasts had significantly impaired effector function as evidenced by lower cytokine production (TNFa p<0.0001, IFNg p=0.0003) and CD107a degranulation (p=0.0002), whereas NK cells separated from blasts by a transwell membrane did not show any evidence of dysfunction. These data point to an important role for cell-cell contact in mediating blast-induced NK dysfunction.We next investigated whether targeted inhibition of TGF-β can protect NK cells from TGF-β-mediated dysfunction, using two different approaches. First, we tested the role of a TGFβR1 kinase inhibitor, Galunisertib, currently in clinical trials for MDS. The addition of Galunisertib to cocultures of healthy NK cells and myeloid blasts prevented NK cell dysfunction and blast-induced SMAD2/3 phosphorylation. For the second approach, we tested if TGF-βR2 knockout by CRISPR-CAS9 gene editing can render them resistant to the suppressive effect of TGF-β. When co-cultured with 50ng/ml of recombinant TGF-β or myeloid blasts for 48 hrs, TGF-βR2 KO NK cells retained their ability to mediate a strong effector function. In vivo experiments to assess the in vivo activity of TGF-βR2 KO NK cells in a xenograft model of myeloid leukemia are underway.Together, these data support an important role for the TGF-β/SMAD signaling pathway as a mediator of NK cell dysfunction and hence immune evasion in MDS, and support strategies to target the TGF-β/SMAD signaling axis for next-generation NK cell therapies in MDS. DisclosuresKantarjian:Bristol-Meyers Squibb: Research Funding; Novartis: Research Funding; Pfizer: Research Funding; ARIAD: Research Funding; Delta-Fly Pharma: Research Funding; Amgen: Research Funding.

Overcoming hypoxia-induced functional suppression of NK cells

BackgroundNatural killer (NK) cells are immune cells capable of killing virally infected cells and tumor cells without the need for antigen stimulation. Tumors, however, can create a suppressive microenvironment that...

NK Cell Impairment after Haploidentical Allogeneic Hematopoietic Cell Transplant in Patients Receiving Post-Transplant Cyclophosphamide (PTCy)

Haploidentical hematopoietic cell transplantation (haplo-HCT) with post-transplant cyclophosphamide (PTCy) as graft versus host disease (GVHD) prophylaxis is frequently used for patients who do not have HLA-identical donors. However, the effect of PTCy on immune reconstitution (IR) has not been studied extensively in large prospective cohorts, despite a high incidence of early viral infections. We quantified IR in 60 patients after haplo-HCT with PTCy, mycophenolate mofetil and tacrolimus (TAC) and compared results to 34 patients with 8/8 HLA matched related or unrelated donors (MD) receiving TAC and methotrexate for GVHD prophylaxis. Both groups received reduced intensity conditioning for hematologic malignancies. Samples were prospectively collected at 1, 2, 3, 6, 9, 12, 18, 24 and 30 months after HCT and analyzed using multi-color flow cytometry to characterize distinct lymphocyte populations. Peripheral blood NK cells 1 month after PTCy were characterized using CyTOF and a panel of 35 metal-labeled monoclonal antibodies and compared to age-matched healthy donor NK cells. Recovery of all T cell subsets (CD4Tcon, CD4Treg, CD8) was significantly reduced in the PTCy cohort compared to MD early after HCT (Figure 1A, B, C). Despite delayed CD4Treg recovery, the Treg:Tcon ratio was significantly higher early after HCT in the PTCY cohort due to relatively deeper depression in CD4Tcon (0.18 vs 0.06, p<0.0001 at 1 month, 0.12 vs 0.06, p=0.0004 at 3 months, Figure 1D). Absolute NK cells were lower at 1 month after PTCy (Figure 1E), entirely due to reduced numbers of CD56^dimCD16⁺ NK cells (Figure 1G). Subsequently, CD56^dim NK cells remained significantly lower in the PTCy group until 3 months after HCT. In contrast, recovery of CD56^brightCD16⁻ NK cells was significantly increased in the PTCy cohort at 2, 3 and 6 months after HCT (p<0.01. Figure 1F). The distribution of NK subsets 1 month post-HCT was also significantly different between two cohorts due to a higher frequency of immature NK cells in the PTCY cohort (Figure 1H). CyTOF analysis performed 1 month after haplo-HCT showed that NK cells expressed higher level of activating receptor NKp46, CD95, granzyme-B and inhibitory receptor NKG2A and lower expression of CD57 compared to HD (Figure 2). Functional assays showed that PTCy NK cells displayed reduced degranulation and release of IFNγ after activation compared to HD. These functions were rescued after priming with low dose IL-15 in vitro. In summary, the effect of PTCy on IR was most pronounced at 1 month with significantly delayed recovery of CD3, CD4Tcon, CD4Treg, CD8 and CD56^dim NK cells. After PTCy, NK cells display an immature phenotype and functional impairment that is at least partly corrected by priming with low dose IL-15. Impairment of NK and T cell recovery early after PTCy-based HCT underscores the need to adopt novel strategies to overcome immune defects induced by this platform.

Efficient ADCC killing of meningioma by avelumab and a high-affinity natural killer cell line, haNK.

Meningiomas are the most common adult primary tumor of the central nervous system, but there are no known effective medical therapies for recurrent meningioma, particularly for World Health Organization grade II and III tumors. Meningiomas arise from the meninges, located outside the blood-brain barrier, and therefore may be directly targeted by antibody-mediated immunotherapy. We found that programmed cell death ligand 1 (PD-L1) was highly expressed in multiple human malignant meningioma cell lines and patient tumor samples. PD-L1 was targeted with the anti-PD-L1 antibody avelumab and directed natural killer cells to mediate antibody-dependent cellular cytotoxicity (ADCC) of PD-L1-expressing meningioma tumors both in vitro and in vivo. ADCC of meningioma cells was significantly increased in target cells that upregulated PD-L1 expression and, conversely, abrogated in tumor cells that were depleted of PD-L1. Additionally, the high-affinity natural killer cell line, haNK, outperformed healthy donor NK cells in meningioma ADCC. Together, these data support a clinical trial designed to target PD-L1 with avelumab and haNK cells, potentially offering a novel immunotherapeutic approach for patients with malignant meningioma.

PD‑L1/PD‑1 axis serves an important role in natural killer cell‑induced cytotoxicity in osteosarcoma.

Osteosarcoma is a serious malignancy in pediatric patients, which comprises 2.4% of fatal cancer in children and achieves 20% of all primary bone cancers. In the present study, we employed three human osteosarcoma cell lines MG‑63, HOS and U2OS for susceptibility to cytolytic activity of freshly isolated healthy donor NK cells. Cells were lysed by NK cells in a dose dependent manner. MG‑63 cells exhibited less susceptibility to NK cells than HOS and U2OS cells at all cell ratios. The specific mechanism underlying the effects of NK cells on osteosarcoma cells was determined by antibody blockage experiments. The results revealed that granzymeB was the key factor in the NK cell‑induced cytotoxicity of human osteosarcoma cells. To the best of our knowledge, the present study is the first to investigate the expression of PD‑L1 in MG‑63, HOS and U2OS cells. The relative expression of the PD‑L1 gene and protein in MG‑63 cell was greater than HOS and U2OS cells. The specific lysis of human osteosarcoma cells induced by NK cells was enhanced when PD‑L1/PD‑1 was blocked by the PD‑L1 antibody. The present study proposed that the PD‑L1/PD‑1 axis serves an important role in NK cell‑induced cytotoxicity in osteosarcoma via granzyme B secretion. Our findings may contribute to the development of precise treatments for osteosarcoma based on the expression profile of PD‑L1 in patients with this disease.

PS1136 THE PI3KD‐SELECTIVE INHIBITOR IDELALISIB INDUCES T AND NK CELL DYSFUNCTION INDEPENDENT OF B‐CELL MALIGNANCY‐ASSOCIATED IMMUNOSUPPRESION

Background:In addition to B‐cell receptor (BCR) signaling, multiple receptor tyrosine kinases (RTKs) and downstream effectors have been reported to be constitutively active in chronic lymphocytic leukemia (CLL) B cells. Activation of these pathways results in resistance to apoptosis and enhanced survival of the leukemic cells. The phosphoinositide 3‐kinase (PI3K) pathway is one of the most commonly activated signaling pathways. Idelalisib, a highly selective inhibitor of the PI3K p110∂ isoform, received FDA approval for the treatment of CLL in patients with relapsed/refractory disease or in CLLs harboring 17p deletions or TP53 mutations. However, the therapeutic success of Idelalisib is hampered by severe opportunistic infections.Aims:We hypothesize that Idelalisib interferes with T‐ and NK‐cell function, thereby contributing to an increased rate of opportunistic infections independent of underlying B‐cell malignancies. We aimed to characterize the modulation of functional properties of lymphoid effector cells by Idelalisib.Methods:All experiments were conducted with different concentrations of Idelalisib (0.05 μM, 0.5 μM, 1 μM) and DMSO as control. The maximum peak concentration (cmax) in patients was mimicked by using 0.5 μM Idelalisib. T‐cell proliferation was evaluated by CFSE dilution. Expression of checkpoint molecules (PD‐ 1, CTLA‐4) on healthy donor (HD) CD4+ and CD8+ T cells and regulatory T cells (Tregs) was assessed by multiparameter flow cytometry (MPFC). Cytometric bead arrays were performed to quantify secreted cytokines after 3 days of stimulation with CD3/CD28 beads. To test the effect of Idelalisib on NK‐cell proliferation, HD NK cells were incubated with IL‐2 in presence of Idelalisib or DMSO for 10 days. NK‐cell cytotoxicity was assessed using Calcein AM+ labeled K562 target cells. Additionally, the cytotoxic capacity of T and NK cells was evaluated by MPFC, utilizing the degranulation marker CD107a and the effector molecules Perforin and Granzyme B.Results:Idelalisib induced a dose‐dependent inhibition of T‐cell proliferation from healthy donors. However, significant effects on the number of CD4+ and CD8+ dividing T cells were only seen at concentrations higher than 5 μM, indicating that T‐cell proliferation is not affected at therapeutic concentrations of the agent. CD4+ T cells, as well as CD8+ T cells, showed reduced expression of CTLA‐4 and PD‐1 after treatment with 0.5 μM Idelalisib upon CD3/CD28 stimulation. Similar effects were detected for the respective Treg subsets. Interestingly, cytokine secretion of T cells was significantly impaired for IL‐10, TNF and IFNγ for all tested Idelalisib concentrations (p = 0.0008; p = 0.03; p = 0.03; n = 11–23). We also found Idelalisib to significantly decrease upregulation of Granzyme B and Perforin in CD8+ and CD4+ T cells (CD8+: p = 0.0002; p = 0.0215; CD4+: p = 0.0002; p = 0.015, n = 12–13) upon CD3/CD28 stimulation.NK cells treated with 0.5 μM Idelalisib showed decreased overall proliferation (p = 0.02; n = 12). NK cell cytotoxicity against K562 target cells was significantly reduced in a concentration dependent manner (0.5 μM, p = 0.0031, n = 12).Summary/Conclusion:Idelalisib impaired the cytotoxicity of T and NK cells at therapeutic concentrations in our in vitro studies. In addition, secretion of pro‐inflammatory and immune‐mediating cytokines like IL‐10,TNF and IFNγ was significantly reduced for T cells by Idelalisib. These observations support the hypothesis that the T‐ and NK‐cell function is directly impaired by Idelalisib, and not by B‐cell malignancy‐inflicted immunosuppression.

Proteome analysis of human CD56neg NK cells reveals a homogeneous phenotype surprisingly similar to CD56dim NK cells.

NK cells lacking CD56 (CD56neg ) were first identified in chronic HIV-1 infection. However, CD56neg NK cells also exist in healthy individuals, albeit in significantly lower numbers. Here, we provide an extensive proteomic characterisation of human CD56neg peripheral blood NK cells of healthy donors and compare them to their CD56dim and CD56bright counterparts. Unbiased large-scale surface receptor profiling clustered CD56neg cells as part of the main NK cell compartment and indicated an overall CD56dim -like phenotype. Total proteome analyses of CD56neg NK cells further confirmed their similarity with CD56dim NK cells, and revealed a complete cytolytic inventory with high levels of perforin and granzyme H and M. In the present study, twelve proteins discriminated CD56neg NK cells from CD56dim NK cells with nine up-regulated and three down-regulated proteins in the CD56neg NK cell population. Those proteins were functionally related to lytic granule composition and transport, interaction with the extracellular matrix, DNA transcription or repair, and proliferation. Corroborating these results, CD56neg NK cells showed modest cytotoxicity, degranulation, and IFN-ɣ secretion as compared to CD56dim NK cells. In conclusion, CD56neg NK cells constitute functionally competent cells sharing many features of bona fide CD56dim NK cells in healthy individuals, but with some distinct characteristics.

Identification of GAD65 AA 114-122 reactive 'memory-like' NK cells in newly diagnosed Type 1 diabetic patients by HLA-class I pentamers.

Type 1 diabetes is an autoimmune disease, in which pancreatic β cells are destroyed by autoreactive T cells in genetically predisposed individuals. Serum beta cell autoantibody specificities have represented the mainstay for classifying diabetes as autoimmune-mediated and for stratifying risk in first-degree relatives. In recent years, approaches were attempted to solve the difficult issue of detecting rare antigen-specific autoreactive T cells and their significance to etiopathogenesis such as the use of the MHC multimer technology. This tool allowed the specific detection of increased percentages of GAD65 autoreactive T cells by means of HLA A*02:01 GAD65 AA 114–122 pentamers in newly diagnosed diabetics. Here we provide evidence that GAD65 AA 114–122 pentamers can depict a GAD65 AA114-122 peptide expandable population of functionally and phenotypically skewed, preliminary characterized CD3-CD8dullCD56+ ‘memory-like’ NK cells in PBMC of newly diagnosed diabetics. Our data suggest that the NK cell subset could bind the HLA class I GAD65 AA 114–122 pentamer through ILT2 inhibitory receptor. CD107a expression revealed increased degranulation of CD3-CD8dullCD56+ NK cells in GAD65 AA 114–122 and FLU peptide expanded peripheral blood mononuclear cells of diabetics following GAD65 AA 114–122 peptide HLA A*02:01 presentation in respect to the unpulsed condition. CD107a expression was enriched in ILT2 positive NK cells. As opposite to basal conditions where similar percentages of CD3-CD56+ILT2+ cells were detected in diabetics and controls, CD3-CD56+CD107a+ and CD3-CD56+ILT2+CD107a+ cells were significantly increased in T1D PBMC either GAD65 AA 114–122 or FLU peptides stimulated after co-culture with GAD65 AA 114–122 pulsed APCs. As control, healthy donor NK cells showed similar degranulation against both GAD65 AA 114–122 pulsed and unpulsed APCs. The pathogenetic significance of the CD3-CD8dullCD56+ ‘memory-like NK cell subset’ with increased response upon secondary challenge in diabetics remains to be elucidated.

Abstract 2949: TGF-β is a key mediator of NK cell dysfunction in gliolastoma

Abstract Background: NK cells play a crucial role in the antitumor immune response and are involved in controlling tumor formation, progression and metastases. Glioblastoma (GBM) is the most devastating brain tumor, associated with very poor prognosis. While immunotherapy emerged as a promising approach for anti cancer therapy, GBM appears immune resistant. Here, we studied the role of NK cells in targeting glioblastoma and possible mechanisms of NK immune evasion. Methods: NK cells were isolated from freshly resected GBM tissue, matching peripheral blood and the blood of healthy controls. Flow cytometry was used to characterize the cells and their ability to produce cytokines, and chromium release assay was perfumed to assess their cytotoxicity. In vitro assays were performed by co-culturing GBM stem cells (GSCs) with healthy donor NK cells. Results: We found that whereas NK cells were abundant in primary GBM tissue and could efficiently target GBM stem cells (GSCs), GBM infiltrating NK cells (TiNKs) displayed an abnormal phenotype with downregulation of many activating receptors including CD16, NKG2D, DNAM, NKp30, NKp46, 2B4 and NKG2C and upregulation of inhibitory proteins such as PD-1. This inhibitory phenotype was associated with impaired NK cell function when compared with NK cells isolated from the peripheral blood of patients and healthy donors. GSC-NK cell-cell contact resulted in release of TGF-β by GCSs, which in turn led to NK dysfunction through constitutive activating of the p-Smad pathway. TGF-β activation, in turn, is partially mediated by the matrix metalloproteases MMP-2 and MMP-9, secreted by GSCs upon contact with NK cells and enhanced upon TGF-β exposure. We demonstrated that inhibition of the TGF-β axis, in particular by the small molecule inhibitor, galunisertib, can prevent GSC-induced NK cell dysfunction but is unable to inactivate the p-Smad pathway, thus, cannot reverse existing dysfunction. Conclusions: Our results indicate that NK-GBM cross-talk plays an important role in tumor escape and highlight the importance of developing future adoptive transfer therapies with the intent of limiting tumor escape from antitumor immunity. Note: This abstract was not presented at the meeting. Citation Format: Hila Shaim, Abdullah Alsuliman, Konrad Gabrusiewicz, Jun Wei, John Yu, Rafet Basar, May Daher, Lucila Kerbauy, Mayela Mendt, Muharrem Muftuoglu, Li Li, Enli Liu, Nobuhiko Imahashi, Sonny Ang, Young Gi, Pinaki Banerjee, David Marin, Richard Champlin, Elizabeth Shpall, Amy Heimberger, Katayoun Rezvani. TGF-β is a key mediator of NK cell dysfunction in gliolastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2949. doi:10.1158/1538-7445.AM2017-2949