Donor-derived Natural Killer Cells Research Articles

Natural Killer Cells Are Active Against Myeloma, Leukemia or Lymphoma Cells with Loss of Tumor Suppressor Genes

The therapeutic targeting of tumor cells with loss of function (LOF) for tumor suppressor genes (TSGs) is challenging across cancers, including hematologic neoplasias, because pharmacological mechanisms to restore the function(s) of such genes are not readily feasible, in contrast to e.g., inhibition of oncogenic drivers. We reasoned, however, that, although LOF for TSGs leads to de-repressed growth of neoplastic hematopoietic cells, it may not necessarily protect them from immune attack. We thus explored the hypothesis that CRISPR-based loss of function of TSGs in cells from multiple myeloma (MM), leukemias or lymphoma may still be associated with substantial response to immune effector cells such as NK cells, which have the advantage to kill tumor cells across HLA barriers. We have conducted CRISPR-based studies in 7 cell lines that represent different hematologic malignancies and different levels of sensitivity to natural killer (NK) cells, namely the B-cell lymphoma (SUDHL4), precursor B cell acute lymphoblastic leukemia (NALM6), multiple myeloma (MM1.S, LP1, KMS11), chronic myeloid leukemia (K562), and acute myeloid leukemia (MOLM14). In these genome-scale or focused CRISPR screens for LOF (CRISPR-based gene editing) or gain of function (GOF, CRISPR activation), the blood cancer lines were exposed to allogeneic donor-derived NK cells (vs. control cultures without NK cells). We evaluated the performance of genes known to represent recurrent TSGs based on genomic data of patient samples or cell lines; as well as candidate TSGs, based on results from genome-scale CRISPR gene editing screens (e.g., CERES or CHRONOS scores >0.4 in multiple DepMap releases and TPM>1 [RNA-seq]) in the same cell lines as the NK cell resistance screens. These analyses sought to identify any TSGs whose LOF may potentially alter the response of blood cancer cells to NK cells. We also evaluated genes identified as top recurrent TSGs in patient samples from MM and other hematologic neoplasias (e.g., based on prior genomic studies). On aggregate, we evaluated a collection of known and recurrent TSGs (e.g., PTEN, TP53, RB1, CDKN2C, CDKN1B, TENT5C/FAM46C) as well as other, previously underappreciated candidate genes with TSG properties in hematologic neoplasias (e.g., HIF1A, DEPDC5). Perturbation of none of these genes was identified to meet criteria for association with significant resistance to allogeneic donor-derived NK cells (e.g., log2FC>1.0, at least 3-4 sgRNAs with enrichment upon CRISPR KO or depletion with CRISPR activation, p-value <0.05, enrichment rank <100, based on rank aggregation algorithm) in any of the MM, leukemia or lymphoma cell lines examined in LOF or GOF CRISPR screens for NK cell resistance. In fact, for a limited set of cases (e.g., PTEN in KMS11 cells), KO of a TSG was associated with sensitization to NK cell treatment. To probe the mechanistic basis for this lack of effect of TSG loss, we examined the molecular sequelae of CRISPR-based KO for one of these recurrent TSGs, PTEN, by performing scRNAseq using the CROP-seq platform. Pools of MM1.S and LP1 cells expressing sgRNAs targeting select hits from our CRISPR screens and also PTEN were co-cultured with NK cells for 24 h or left untreated, followed by scRNA-seq and sgRNA detection, differential gene-expression analysis. We observed in these studies that the transcriptional changes induced in MM cells by KO of PTEN included limited, if any, changes in the expression of key genes involved in regulation of NK cell responses of tumor cells, e.g., ligands for activating or inhibitor receptors in NK cells, death receptors (e.g., TRAIL, Fas) or their downstream effectors/regulators or other molecules identified from our aforementioned genome-scale and focused CRISPR LOF and GOF studies. Notably, our in-house results from studies of NK exposure of cell lines from hematologic neoplasias are concordant with results for these TSGs in CRISPR screens of non-hematological cancer cells treated with cytotoxic T-cells (e.g., 4T1 or RENCA cells; GSE149933). Overall, our observations indicate that MM, leukemia or lymphoma cells that become deficient for diverse TSGs based on CRISPR-based gene editing are equally responsive to NK cells as their TSG-proficient counterparts. NK cell-based therapies may thus be a promising approach to target TSG-deficient hematologic malignancies for which specific pharmacological therapies are not currently available.

CTLA-4 Blockade Results in the Enrichment of Proliferative CD56 dimCD16 + NK Cells Following Infusion of Haploidentical Donor Memory-like Natural Killer Cells Plus IL-15 Superagonist in a Phase 1 Trial

Introduction Regulatory T cells (Tregs) blunt anti-tumor responses of major immune effector cells including CD8 T cells and natural killer (NK) cells. Tregs constitutively express CTLA-4 and thus the use of ipilimumab, a CTLA-4 blocker can potentially overcome the Treg-mediated immune suppression. We (and others) have shown that a brief activation of conventional NK cells with the cytokine combination IL-12, IL-15, and IL-18 generates cytokine-induced memory-like (CIML) NK cells which exhibit enhanced anti-tumor responses, have a longer half-life (up to 90 vs ~12 days of conventional NK cells), and show promising activity in several early phase clinical trials. N-803 is an IL-15 super-agonist with a long half-life that preferentially activates and expands NK and CD8+ T cells without affecting Tregs, making it an ideal cytokine for combining with adoptive immunotherapy. In the current study, we hypothesized the use of ipilimumab (IPI) will abrogate Treg-mediated inhibition and thus allow enhanced proliferation, activation, and anti-tumor responses of the adoptively transferred CIML NK cells.To address this, we conducted a phase 1 trial of HLA-haploidentical CIML NK cells in combination with IPI and N-803 in patients with advanced head and neck cancer (HNC). Using flow cytometry and CITE-Seq on the banked peripheral blood samples, we performed an in-depth characterization of NK cells expanded following IPI pre-exposure and compared it to those who did not receive IPI. Methods We enrolled 10 patients with refractory HNC regardless of human papillomavirus (HPV) status who had prior platinum and immunotherapy (NCT04290546). All patients received lymphodepletion with fludarabine (25 mg/m 2 x 5 days) and cyclophosphamide (60 mg/kg x 2 days) during days -6 to -2 prior to haploidentical CIML NK cell infusion on day 0 (5-10 x 10 6 cells/kg=dose level 0) followed by N-803 (15 mcg/kg subcutaneously) starting on day +1 every 21-days for 4-doses. In cohort 2, patients received IPI (3 mg/kg) on day -7, no ipilimumab was given to the first 6 patients treated on the lead-in safety cohort 1. Flow cytometry using a custom NK cell panel was performed on samples collected on days +7, +14, +21, +28, +42, and +60 after CIML NK cell infusion. FlowSOM clustering was performed on NK cell markers. UMAP clustering was applied to CITE sequencing data acquired from samples collected on day +7 and day +28, and well-defined markers genes for each cluster were used to identify cell populations. NK cell function (cytotoxicity, IFNg, and CD107a) was assessed using flow-cytometry based assays. Results The median age of the patients was 58, 90% were men and 80% had oropharyngeal primaries. Mild CRS (grade 2 or lower) was observed in 60% of patients. No neurotoxicity or graft-versus-host disease was observed. Maximal expansion of NK cells occurred on day +7 following CIML NK cell infusion in 9/10 of patients. The single patient without NK cell expansion was found to have a donor-specific anti-HLA antibody. Day +7 NK cells exhibited upregulation of IFNg expression following cytokine restimulation as compared to resting NK cells. Tumor regression was observed in 50% of treated patients at day +30 based on RECIST v1.1 criteria. Patients who had tumor regression had an expansion of CD56 dimCD16 + NK cell clusters by day +14. IPI treated patients were noted to have a relative enrichment of CD16 + NK cell metaclusters at day +14 compared to no IPI patients (Figure 1A). At the time of maximal NK cell expansion, CITEseq defined NK cell clusters were dominant in both IPI and no IPI patients, but the proliferative gene sets were enriched in the IPI treated patient (Figure 1B). IPI exposure had no effect on the distribution of regulatory T cells or CD8 + T cell populations at day +28 compared to the no IPI patients. Conclusions The use of donor-derived CIML NK cells is safe and associated with tumor regression in patients with advanced HNC. The use of IPI was associated with the preferential expansion of CD16 + NK cell clusters that had enrichment of proliferative gene sets. Tumor regression was associated with CD56 dimCD16 + NK cell expansion. Further work is required to elucidate the mechanism by which IPI exposure is associated with the expansion of specific subsets of CIML NK cells.

Clinical-grade natural killer cells expanded from donor peripheral blood and anti-leukemia effect against myeloid leukemia.

e19018 Background: Natural killer (NK) cells play a crucial role in immune surveillance and tumor clearance. It has been reported that allogeneic NK cell therapy has good safety and curative effect in patients with refractory and relapsed acute myeloid leukemia (AML). However, the clinical application of adoptive NK infusion is limited due to the lower number of human NK cells. We established a feeder-free NK cell expansion system from peripheral blood (PB) and explore the anti-leukemia potential in preclinical and clinical studies. Methods: The killing capacity of ex vivo-expanded NK cells were detected by Flow cytometry. The in vivo expansion, survival and anti-leukemia activity of the expanded NK cells were detected in K562-bearing NSG mice. Six AML patients with hematological/extra medullary relapsed (n = 3) or persistent positive minimal residual disease (n = 3) after consolidation and maintenance therapy were enrolled in Peking University Institute of Hematology from 2021 to 2022. The patients were treated with high-dose cyclophosphamide and fludarabine, then combined with adoptive infusion of donor-derived expanded NK cells. The chimerism, the number and function of NK cells were analyzed, and the safety and clinical efficacy were evaluated. Results: The ex vivo-expanded NK cells exhibit highly anti-leukemia activity. NK cells proliferate in mice and the CD56+ cells to reach the peak time in each organ is 3-7 days and drop to the level before infusion after 14 days. NK cell infusion significantly improve the survival of leukemia mice, and the anti-leukemia effect is NK cell dose-dependent. In the clinical trial, six patients received a total of 7 cases of NK cell infusion, including 3 cases in low-dose group and 4 cases in middle-dose group, among which 1 patient received 2 dose (1 low-dose and 1 middle-dose). In the low-dose group, 1 patient got response (1/3), with the minimal residual disease turned negative. In the middle-dose group, 3 patients responded (3/4), of which 1 patient had the fusion gene CBFB /ABL decreased from 0.99% to 0.13%, 1 case of extramedullary recurrence of AML turned negative, and NK cells could be detected in cerebrospinal fluid, 1 case of hematological recurrence got hematological remission after treatment. The survival time of NK cells in vivo was 7d-30d, with longer time in middle dose group than those in low dose group. The proportion and number of NK cells in responding cases were significantly higher than those in non-responsive group. Conclusions: Clinical grade expanded NK cells has strong anti-leukemia activity in patients with relapse or minimal residual positive AML patients. NK cells can survive for 2 weeks and can enter the central nervous system without obvious adverse reactions. The response rate in middle-dose group is higher than that in low-dose group. However, the efficacy of NK cells still needs to be further confirmed in a large sample size. Clinical trial information: NCT04221971 .

Abstract 2902: Off-the-Shelf CAR-NK cells engineered to express calibrated release IL-15 exhibit enhanced persistence and anti-tumor activities

Abstract Chimeric antigen receptor (CAR) natural killer (NK) cell therapy is an attractive immunotherapy strategy due to potential for increased anti-tumor activity and favorable safety. Allogeneic donor derived NK cells have shown promising clinical outcomes in both hematological and solid tumor malignancies but have a short lifespan in the absence of cytokine support. Interleukin (IL)-15 is a pleiotropic cytokine that promotes the survival, proliferation, and cytotoxicity of NK cells. In this study, we engineered human peripheral blood-derived NK cells to co-express a CAR and calibrated release (cr) IL-15 and studied how crIL-15 affected CAR-NK cell functions. Senti Bio has designed the calibrated release technology to simultaneously produce membrane bound and secreted cytokines, such as IL-15 and IL-12, to provide autocrine and paracrine activity. We further validated crIL-15 activity in vitro and demonstrated enhanced NK cell persistence, tumor killing and autocrine activity in CAR NK cells as well as paracrine stimulation of neighboring T cells and NK cells via pSTAT5 activation. Additionally, we examined in vivo persistence and biodistribution of NK cells engineered with crIL-15 and a nanoluc reporter. crIL-15 NK cells were intravenously (i.v.) injected into NSG mice. These NK cells were detected in the lung, femur, spleen, liver and stomach 1 day post injection by bioluminescence imaging and polymerase chain reaction (PCR) and lasted up to 20 days in the lung. In addition, crIL-15 increased CAR-NK cells persistence in a dose-dependent manner compared to unengineered NK cells. Injection of higher CAR-NK cell numbers (15× 106 vs 7.5× 106 CAR+ cells per mouse) or multiple NK dosages (1 vs 3 doses) both contributed to prolonged persistence. Finally, we studied how crIL-15 affected CAR-NK cell anti-tumor function in acute myeloid leukemia (AML) xenograft models. MV4-11-Fluc AML tumor cells were co-injected with engineered NK cells expressing a FLT3 and/or CD33 bivalent activating CAR, a EMCN inhibitory CAR and crIL-15 into NSG-Tg (Hu-IL15) mice via i.v. injection. Our data showed that these CAR-NK cells significantly reduced MV4-11 tumor burden and prolonged mouse survival compared to unengineered NK cells. The improved anti-tumor functions correlated with IL-15 levels produced by the CAR-NK cells. In conclusion, our results demonstrated that crIL-15 can improve persistence and anti-tumor activity of CAR-NK cells. Citation Format: Chen-Ting Lee, Michelle Hung, Andrew Banicki, Wenqi Song, Niran Almudhfar, Deepika Kaveri, Priscilla Wong, Lawrence Naitmazi, Marcela Guzman, Alice Lam, Gozde Yucel, Timothy Lu, Alba G. Junca, Brian Garrison, Philip Lee. Off-the-Shelf CAR-NK cells engineered to express calibrated release IL-15 exhibit enhanced persistence and anti-tumor activities [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2902.

The infusion of ex vivo, interleukin-15 and -21-activated donor NK cells after haploidentical HCT in high-risk AML and MDS patients-a randomized trial.

Clinical effect of donor-derived natural killer cell infusion (DNKI) after HLA-haploidentical hematopoietic cell transplantation (HCT) was evaluated in high-risk myeloid malignancy in phase 2, randomized trial. Seventy-six evaluable patients (aged 21-70 years) were randomized to receive DNKI (N = 40) or not (N = 36) after haploidentical HCT. For the HCT conditioning, busulfan, fludarabine, and anti-thymocyte globulin were administered. DNKI was given twice 13 and 20 days after HCT. Four patients in the DNKI group failed to receive DNKI. In the remaining 36 patients, median DNKI doses were 1.0 × 108/kg and 1.4 × 108/kg on days 13 and 20, respectively. Intention-to-treat analysis showed a lower disease progression for the DNKI group (30-month cumulative incidence, 35% vs 61%, P = 0.040; subdistribution hazard ratio, 0.50). Furthermore, at 3 months after HCT, the DNKI patients showed a 1.8- and 2.6-fold higher median absolute blood count of NK and T cells, respectively. scRNA-sequencing analysis in seven study patients showed that there was a marked increase in memory-like NK cells in DNKI patients which, in turn, expanded the CD8+ effector-memory T cells. In high-risk myeloid malignancy, DNKI after haploidentical HCT reduced disease progression. This enhanced graft-vs-leukemia effect may be related to the DNKI-induced, post-HCT expansion of NK and T cells. Clinical trial number: NCT02477787.

Higher-Dose Donor Derived Ex Vivo Expanded Natural Killer Cell Infusion Prior to Haploidentical Stem Cell Transplantation on Acute Myeloid Leukemia: Efficacy and Safety

Adoptive immunotherapy with donor-derived natural killer (NK) cell was deemed as a promising therapeutic in hematological malignancies with anti-cancer, anti-graft-versus-host disease (GvHD), and anti-viral potential. However, the clinical usage was limited by lacking evidence on optimal dosage and timing. Here, we conducted a retrospective cohort study of compassionate use of higher dose (1x10^9/kg) NK cell infusion prior to haploidentical stem cell transplantation on acute myeloid leukemia. NK cells were obtained by 50ml donor peripheral blood through purifying, and ex vivo expanding with interleukin (IL)-2 and IL-15. Twelve patients enrolled in this cohort receiving an average dose of 1 x 109/kg (0.8 - 1.8 x 109/kg) NK cell infusion 12 hours prior to day 0. All patients achieved hematologic reconstitution. I° acute GVHD (aGVHD) appeared in three patients (25%). No chronic GVHD (cGVHD) occurred. With a median follow-up of 12.5 months (range 9-62 months), eight patients are still alive and in disease free survival status. Minimal residual disease (MRD) in alive patient was sustaining negative on day +60, +180 +360 and +720. Three patients relapsed six months posttransplant and one patient died from late bone marrow failure. Our small cohort study implied that infusion of high doses ex vivo expanded donor-derived NK cell infusion prior to haploidentical stem cell transplantation was safe and could potentially have a role to decrease relapse of patients with high-risk AML.

CD82 Is Sufficient to Uniquely Identify Pluripotent Stem Cell-Derived Hemogenic Endothelium with the Hematopoietic Lineage Potency to Give Rise to Bona Fide Lymphocytes

Chimeric antigen receptor (CAR)-T and natural killer (NK) cells represent compelling opportunities for the treatment of hematological malignancies and solid tumors. However, autologous and donor-derived allogeneic CAR-T and NK cell therapies are limited based on the quantity and quality of the starting engineered cells. We previously described our off-the-shelf induced pluripotent stem cell (iPSC)-derived CAR-T (CAR-iT) and CAR-NK (CAR-iNK) cell platforms that eliminate some of the hurdles associated with patient-derived cells by creating a homogenous cell product that is derived from a renewable bank of iPSC master cell lines. A major challenge in the manufacturing of iPSC derived immune cells is the derivation of hemogenic endothelium (HE), which is the rare and transient direct precursor of hematopoietic cells, making its in vitro specification from iPSCs inefficient and challenging. Furthermore, there is not a reliable marker or set of markers for the identification of HE in culture. HE identification has traditionally relied on detection of the transcription factor RUNX1 and the establishment of reporter cell lines, neither of which are suitable for the manufacture of HE cells destined to become therapeutic immune cells. We have established a cytokine driven protocol for the differentiation of iPSCs that improves the efficiency of the derivation of RUNX1+ HE cells. To identify candidate HE surface markers, we compared iPSC-derived cells containing a high percentage of HE, based on RUNX1 expression, to control differentiated cells containing a low percentage of HE, via a cell surface antibody array. Through the array we identified several surface markers that were expressed by a higher percentage of CD34+ endothelial cells compared to control CD34+ cells. Several of the candidates identified, including CD44, CD61, CD226 and CD143 have been previously identified by other groups as candidate HE markers, thereby validating our screening method. We identified CD82 as a novel candidate HE marker, with expression uniquely restricted to the CD34+ endothelial population and positively correlating with RUNX1 expression (Fig. 1A). Furthermore, we demonstrated via limiting dilution assays that HE is enriched in the CD34+CD43-CD82+ population (HE frequency, 1/38) compared to the CD34+CD43-CD82- population(HE frequency, 1/736) (Fig. 1B). Even more strikingly, isolation of cells based on CD82 alone was sufficient to enrich for HE cells (HE frequency, 1/44) and outcompeted CD34 enrichment alone, suggestive of its unique ability to identify the HE population (Fig. 1B). To determine if CD82+ HE cells could give rise to lymphocytes we carried them forward into T cell differentiation and showed thatthey efficiently gave rise to CAR-iT cells (i.e. >95% CD7+ T lymphocytes). The identification of CD82 for the enrichment of iPSC derived HE is a critical step to the development of definitive hematopoiesis with ability to give rise to all lineages of the hematopoietic compartment and facilitates the scaled and consistent manufacture of high-quality T and NK cells for off-the-shelf therapeutic applications. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Haploidentical Hematopoietic Stem Cell Transplant Plus Add-Back NK Cells in Pediatric High-Risk ALL

Introduction: Natural killer (NK) lymphocytes are cells of innate immunity that protect against tumor and infections. NK cells recognize self and non-self HLA class I ligands, are regulated by a balance between activator and inhibitory signals through surface receptors, and can interact with HLA class I molecules on target cells. Killer-cell Immunoglobulin-like Receptors (KIRs) are inhibitory molecules expressed on NK cells and belong to the immunoglobulin superfamily. KIRs function to "educate" NK cells in effective defense against unhealthy self/non-self cells and tolerance against healthy self cells. NKs are thought to play a key role in preventing early relapse of hematologic malignancies, virus infection and graft versus host disease (GvHD) after haploidentical hematopoietic stem cell transplantation (haplo-HSCT).In B-/T-cell alpha/beta depleted haplo-HSCT, donor-versus-recipient allo-reactive NK cells can exert an efficient graft versus leukemia (GvL) effect, mediated by inhibitory KIRs where the HLA ligand is missing on recipient cells. Donor NK cells after haplo-HSCT are "immature" and not effective as the mature NKs. These immature NK cells are CD56bright, are derived from CD34+ stem cells, and mature to a CD56dim phenotype. The mature CD56dim NK cells are characterized by acquisition of KIRs, CD16 and CD57 in mature stages, which have functional significance in targeting and medicating their cytolytic activity. Based on these considerations, we performed haplo-HSCT with donor NK cell add-back to provide mature, functional immunological surveillance against tumor (MRD) and virus reactivation, which can frequently occur in manipulated haplo-HSCT for pediatric acute lymphoblastic leukemia (ALL). Methods: We evaluated the alloreactive effect of donor-derived NK cells in three pediatric high-risk ALL who underwent B-/T-cell alpha/beta depleted haplo-HSCT followed by donor NK infusion. Patients' characteristics are summarized in the Table. All 3 patients were male; median age was 13 months. Patients 1 and 2 had infant ALL, and patient 3 had refractory-relapsed (r/r) ALL. All patients received a median of 3 lines chemotherapy. Patient 1 received a prior allo-HSCT. Patients 1 and 2 received chemo-based conditioning regimens consisting of thyotepa, and fludarabine; In addition, patient1received treosulfan, and patient 2 received busulfan. Treosulfan was given to patient 1, due to less toxicity profile given prior allo-HSCT. Patient 3 received Total Body Irradiation (TBI), thyotepa, and fludarabine. All patients received rituximab and letermovirfor EBV and CMV prophylaxis, respectively, for all patients. Mother was Donor for all patients. Median CD34+, CD19+, CD3+-alpha/beta cell dose was 8.8, 0.05, 0.41 x 106/kg, respectively. NK cell allo-reactivity was tested by evaluating KIR genotyping and KIR/KIR-ligand mismatch in graft-versus-host direction. All three patients present KIR/KIR-ligand mismatch. Results: Engraftment was day +13, +14 and +19 for ANC, and +14, +18 and +17 for PLT (for both >20K and >50K), for patients 1, 2 and 3, respectively. NK cell number were monitored on day +7, +14, +21 and +28 (data pending). Patients received NK cell infusion on day 30 +/- 2 days. No infusion reactions were observed. MedianNK infused were 256x106/kg. None of the patients developed CMV, EBV or ADV reactivation. Patient 2 developed Grade 2 acute GvHD (skin) treated with steroids. No Grade GvHD 3-4 was observed. Median follow up was 58 days. All patients had full donor chimerism at day 30 ±2. All patients are currently in hematological CR; patient 1 converted to positive MRD at nine months from transplant. Conclusion: Alloreactive NK cell add-back infusion after B-/T-cell alpha/beta depleted haplo-HSCT could represent an effective option to improve transplant outcome and prevent virus reactivation. These NK cells may improve efficacy by enhancing GvL and could contribute to maintain the "disease control" through immunologic surveillance in high-risk ALL. Indeed, NK killing, which is higher in mature NK cells, depends on acquisition of sequential phenotypic maturation. Thus, infusion of mature donor NK cells may help to maintain control of MRD and virus reactivation through immunologic surveillance. Although our preliminary observations seem to be promising, this hypothesis should be confirmed in clinical trial of a larger number of patients. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Expansion, persistence, and efficacy of donor memory-like NK cells infused for posttransplant relapse.

BackgroundResponses to conventional donor lymphocyte infusion for postallogeneic hematopoietic cell transplantation (HCT) relapse are typically poor. Natural killer (NK) cell–based therapy is a promising modality to treat post-HCT relapse.MethodsWe initiated this ongoing phase I trial of adoptively transferred cytokine-induced memory-like (CIML) NK cells in patients with myeloid malignancies who relapsed after haploidentical HCT. All patients received a donor-derived NK cell dose of 5 to 10 million cells/kg after lymphodepleting chemotherapy, followed by systemic IL-2 for 7 doses. High-resolution profiling with mass cytometry and single-cell RNA sequencing characterized the expanding and persistent NK cell subpopulations in a longitudinal manner after infusion.ResultsIn the first 6 enrolled patients on the trial, infusion of CIML NK cells led to a rapid 10- to 50-fold in vivo expansion that was sustained over months. The infusion was well tolerated, with fever and pancytopenia as the most common adverse events. Expansion of NK cells was distinct from IL-2 effects on endogenous post-HCT NK cells, and not dependent on CMV viremia. Immunophenotypic and transcriptional profiling revealed a dynamic evolution of the activated CIML NK cell phenotype, superimposed on the natural variation in donor NK cell repertoires.ConclusionGiven their rapid expansion and long-term persistence in an immune-compatible environment, CIML NK cells serve as a promising platform for the treatment of posttransplant relapse of myeloid disease. Further characterization of their unique in vivo biology and interaction with both T cells and tumor targets will lead to improvements in cell-based immunotherapies.Trial RegistrationClinicalTrials.gov NCT04024761.FundingDunkin’ Donuts, NIH/National Cancer Institute, and the Leukemia and Lymphoma Society.

Evaluation of allogeneic and autologous membrane-bound IL-21–expanded NK cells for chronic lymphocytic leukemia therapy

AbstractSuccesses with anti-CD20 antibodies in chronic lymphocytic leukemia (CLL) and enhanced activity of Fc-engineered vs unmodified antibody therapy suggest a potentially impactful role for natural killer (NK) cells and other innate immune cells in controlling this disease. Stimulated NK cells have shown promise as a cellular therapy, but their application has been constrained by limited expansion capacity and low cytotoxic activity against CLL cells. Here, we demonstrate that both healthy donor-derived and CLL patient-derived NK cells expand rapidly when stimulated with feeder cells expressing membrane-bound interleukin-21 (mbIL-21) and have potent cytotoxic activity against allogeneic or autologous CLL cells. Combination with anti-CD20 antibodies significantly enhances NK recognition and killing of CLL targets. As any CLL immune therapy would likely be given in combination, we assess commonly used treatments and demonstrate that ibrutinib has mixed suppressive and protective effects on expanded NK cells, whereas expanded NKs are highly resistant to venetoclax. We demonstrate efficacy in vivo in 2 xenograft mouse models of human CLL that support building upon a regimen of venetoclax and obinutuzumab with mbIL-21–expanded NK cells. Collectively, these data support development of mbIL-21–expanded NKs combined with the CD20 antibody obinutuzumab and venetoclax in the treatment of CLL.

276 - A Phase I Clinical Trial Testing the Safety of IL-21-Expanded, Third-Party Donor-Derived Natural Killer Cells for Relapsed/Refractory Acute Myeloid Leukemia and Myelodysplastic Syndrome

276 - A Phase I Clinical Trial Testing the Safety of IL-21-Expanded, Third-Party Donor-Derived Natural Killer Cells for Relapsed/Refractory Acute Myeloid Leukemia and Myelodysplastic Syndrome

Hematopoietic cell transplantation donor-derived memory-like NK cells functionally persist after transfer into patients with leukemia.

Natural killer (NK) cells are innate lymphoid cells that eliminate cancer cells, produce cytokines, and are being investigated as a nascent cellular immunotherapy. Impaired NK cell function, expansion, and persistence remain key challenges for optimal clinical translation. One promising strategy to overcome these challenges is cytokine-induced memory-like (ML) differentiation, whereby NK cells acquire enhanced antitumor function after stimulation with interleukin-12 (IL-12), IL-15, and IL-18. Here, reduced-intensity conditioning (RIC) for HLA-haploidentical hematopoietic cell transplantation (HCT) was augmented with same-donor ML NK cells on day +7 and 3 weeks of N-803 (IL-15 superagonist) to treat patients with relapsed/refractory acute myeloid leukemia (AML) in a clinical trial (NCT02782546). In 15 patients, donor ML NK cells were well tolerated, and 87% of patients achieved a composite complete response at day +28, which corresponded with clearing high-risk mutations, including TP53 variants. NK cells were the major blood lymphocytes for 2 months after HCT with 1104-fold expansion (over 1 to 2 weeks). Phenotypic and transcriptional analyses identified donor ML NK cells as distinct from conventional NK cells and showed that ML NK cells persisted for over 2 months. ML NK cells expressed CD16, CD57, and high granzyme B and perforin, along with a unique transcription factor profile. ML NK cells differentiated in patients had enhanced ex vivo function compared to conventional NK cells from both patients and healthy donors. Overall, same-donor ML NK cell therapy with 3 weeks of N-803 support safely augmented RIC haplo-HCT for AML.

Donor memory-like NK cells persist and induce remissions in pediatric patients with relapsed AML after transplant

AbstractPediatric and young adult (YA) patients with acute myeloid leukemia (AML) who relapse after allogeneic hematopoietic cell transplantation (HCT) have an extremely poor prognosis. Standard salvage chemotherapy and donor lymphocyte infusions (DLIs) have little curative potential. Previous studies showed that natural killer (NK) cells can be stimulated ex vivo with interleukin-12 (IL-12), -15, and -18 to generate memory-like (ML) NK cells with enhanced antileukemia responses. We treated 9 pediatric/YA patients with post-HCT relapsed AML with donor ML NK cells in a phase 1 trial. Patients received fludarabine, cytarabine, and filgrastim followed 2 weeks later by infusion of donor lymphocytes and ML NK cells from the original HCT donor. ML NK cells were successfully generated from haploidentical and matched-related and -unrelated donors. After infusion, donor-derived ML NK cells expanded and maintained an ML multidimensional mass cytometry phenotype for >3 months. Furthermore, ML NK cells exhibited persistent functional responses as evidenced by leukemia-triggered interferon-γ production. After DLI and ML NK cell adoptive transfer, 4 of 8 evaluable patients achieved complete remission at day 28. Two patients maintained a durable remission for >3 months, with 1 patient in remission for >2 years. No significant toxicity was experienced. This study demonstrates that, in a compatible post-HCT immune environment, donor ML NK cells robustly expand and persist with potent antileukemic activity in the absence of exogenous cytokines. ML NK cells in combination with DLI present a novel immunotherapy platform for AML that has relapsed after allogeneic HCT. This trial was registered at https://clinicaltrials.gov as #NCT03068819.

A Phase I Clinical Trial Testing the Safety of IL-21-Expanded, Universally Alloreactive Donor-Derived Natural Killer Cells for Relapsed/Refractory Acute Myeloid Leukemia and Myelodysplastic Syndrome

Background: Natural Killer (NK) cells are cytotoxic lymphocytes that are able to exert an anti-tumor effect in an MHC-I independent manner, but are dysfunctional and reduced in number in patients with leukemia. Several studies have shown therapeutic potential for related donor NK cells expanded and/or activated ex vivo when administered to cancer patients, including patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). However, personalized, donor-derived cell therapies require time for donor identification, manufacturing and product release, resulting in patient attrition. As NK alloreactivity and NKG2C expression play critical roles in mediating anti-tumor effects, we identified ‘ideal’ NK cell donors (in partnership with “Be the Match Biotherapies”) for collection. Human leukocyte antigen (HLA) and Killer immunoglobulin receptor (KIR) genotyping were done to screen and select donors. Following this, a sample was collected from donors to expand NK cells under small-scale conditions. If donor NK cells showed robust expansion, they proceeded with apheresis. To ensure these therapeutic cells would be readily-available, we established a third-party NK cell bank through scalable, affordable mass-production with membrane-bound IL-21 feeder cells (FC21), and cryopreserved large numbers of these NK cells for immediate ‘off-the-shelf’ administration to recipients. Here, we report our initial experience in a Phase I trial of these off-the-shelf (OTS) alloreactive NK cells as immunotherapy for patients with relapsed/refractory AML and MDS.Methods: Patients were treated at Dose level 1, to allow infusion at a dose of 1 x 10e7 NK cells/ kg. Each dose level had two cohorts, stratified by age. Patients were enrolled into Cohort 1 (patients <60 yrs. received Fludarabine (Flu) 30 mg/m2/day & Cytarabine 2 g/m2/day on days -6 to -2) and Cohort 2 (patients ≥ 60 yrs. received Flu 30 mg/m2/day (days -5 to -2) & Decitabine 20 mg/m2/day (days -6 to -2). Patients were evaluated to see if they had any donor-directed antibodies. After chemotherapy, NK cells were infused thrice weekly for 6 doses, to be given over a period of 2 weeks (Clinicaltrials.gov: NCT04220684). Persistence of donor NK cells was determined by flow cytometry using haplotype-discriminating anti-HLA antibodies (Figure 1, 2). NK cells were completely HLA-mismatched between donor and recipients.Results: 6 patients (3/cohort) were treated at the first dose level of 1x10 7 NK cells/kg/dose. All 6 patients had relapsed/refractory AML and had received at least two prior lines of treatment. One patient (005) withdrew from the study prior to infusion of NK cells. 6 patients received the first NK cell dose as an inpatient and were discharged to receive the remaining 5 doses as an outpatient. 5 patients tolerated infusion of all 6 doses of NK cells administered over 2 weeks. One patient (006) developed a Cytokine response (CRS) - like syndrome in the context of streptococcus bacteremia and received only one dose of NK cells. Symptoms suggestive of CRS responded fully with steroids and patient was able to successfully wean off steroids and discharged to the outpatient setting. One patient proceeded to allogeneic hematopoietic cell transplant. No infusion-related reactions, neurotoxicity or graft versus host disease was observed. In vivo persistence/expansion NK cells were superior with FLU/CY lymphodepletion (cohort 1).Conclusions: Cryopreserved, third-party donor-derived NK cells are safe and feasible in relapsed/refractory AML patients, and even at this first dose level, completely HLA-mismatched NK cells can persist and expand to high levels in vivo. [Display omitted] DisclosuresVasu: Kiadis, Inc.: Research Funding; Seattle Genetics: Other: travel support; Boehringer Ingelheim: Other: Travel support; Omeros, Inc.: Membership on an entity's Board of Directors or advisory committees. Walker: Newave: Other: clinical trial support; Geron: Other: clinical trial support; Novartis: Other: clinical trial support. Blachly: INNATE: Consultancy, Honoraria; KITE: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria. de Lima: Incyte: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Miltenyi Biotec: Research Funding. Lee: Kiadis Pharma: Divested equity in a private or publicly-traded company in the past 24 months, Honoraria, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Courier Therapeutics: Current holder of individual stocks in a privately-held company.

Making a Killer: Selecting the Optimal Natural Killer Cells for Improved Immunotherapies.

Over the past 20 years natural killer (NK) cell-based immunotherapies have emerged as a safe and effective treatment option for patients with relapsed or refractory leukemia. Unlike T cell-based therapies, NK cells harbor an innate capacity to eliminate malignant cells without prior sensitization and can be adoptively transferred between individuals without the need for extensive HLA matching. A wide variety of therapeutic NK cell sources are currently being investigated clinically, including allogeneic donor-derived NK cells, stem cell-derived NK cells and NK cell lines. However, it is becoming increasingly clear that not all NK cells are endowed with the same antitumor potential. Despite advances in techniques to enhance NK cell cytotoxicity and persistence, the initial identification and utilization of highly functional NK cells remains essential to ensure the future success of adoptive NK cell therapies. Indeed, little consideration has been given to the identification and selection of donors who harbor NK cells with potent antitumor activity. In this regard, there is currently no standard donor selection criteria for adoptive NK cell therapy. Here, we review our current understanding of the factors which govern NK cell functional fate, and propose a paradigm shift away from traditional phenotypic characterization of NK cell subsets towards a functional profile based on molecular and metabolic characteristics. We also discuss previous selection models for NK cell-based immunotherapies and highlight important considerations for the selection of optimal NK cell donors for future adoptive cell therapies.

AFM26 - Targeting B Cell Maturation Antigen (BCMA) for NK Cell-Mediated Immunotherapy of Multiple Myeloma

Significant progress in multiple myeloma (MM) treatment has been made in recent years and achieving sustained minimal residual disease (MRD) negativity now constitutes a major goal of treatment. High dose melphalan combined with autologous stem cell transplantation (ASCT) is currently regarded the standard of care in 1st line treatment of MM in eligible patients, but fails to eradicate MRD in the majority of patients ultimately leading to disease relapse. Consequently, additional therapies are needed to target residual disease to delay or potentially prevent relapse.The cell surface antigen B cell maturation antigen (BCMA, CD269) constitutes a highly attractive target antigen for immunotherapy because of its restricted expression in non-malignant tissue but almost universal expression on MM cells.AFM26 is a BCMA-targeted tetravalent bispecific antibody that selectively engages natural killer (NK) cells to induce myeloma cell lysis. Through its high-affinity bivalent binding to CD16A (FcγRIIIa), AFM26 possesses prolonged cell retention times, and has been shown to be less prone to interference by high levels of circulating IgG than antibody Fc-domains. Thus, AFM26 can be used to “arm” NK cells for effective killing of tumor cells. AFM26 also induces markedly lower levels of pro-inflammatory cytokines in peripheral blood mononuclear cell (PBMC) cultures in the presence of target cells compared to BCMA-directed T cell activating approaches. In contrast to other monoclonal antibodies (mAbs) such as daratumumab and elotuzumab, AFM26 does not confer target-independent NK cell activation or NK cell depletion.NK cells are promising effectors to target MRD. Due to their early reconstitution following ASCT and their ability to rapidly destroy malignant cells through direct cytotoxicity. Redirecting NK cells through AFM26 may therefore offer an effective treatment of MM patients early after ASCT.Employing a wide range of functional assays, we demonstrate here that AFM26 exhibits potent cytotoxic activity against primary myeloma cells using patient (autologous) and donor-derived (allogeneic) NK cells as well as against a panel of high and low BCMA expressing cell lines. In particular, we show that AFM26 induces NK cell cytotoxicity towards cells expressing almost undetectable surface levels of BCMA, suggesting the potential for broad and deep anti-MM activity. In summary, AFM26 is well-differentiated from other mAbs and a promising therapeutic candidate to address the unmet medical need of MRD positivity in MM. DisclosuresGantke:Affimed: Employment. Reusch:Affimed: Employment. Kellner:Affimed: Research Funding. Klausz:Affimed: Research Funding. Haneke:Affimed: Employment. Knackmuss:Affimed: Employment. Müller:Affimed: Employment. Ellwanger:Affimed: Employment. Fucek:Affimed: Employment. Schniegler-Mattox:Affimed: Employment. Koch:Affimed: Employment. Kerber:Affimed: Employment. Peipp:Affimed: Research Funding. Treder:Affimed: Employment.

Cytokine-Induced Memory-Like NK Cells with High Reactivity against Acute Leukemia Blasts and Solid Tumor Cells Suitable for Adoptive Immunotherapy Approaches.

Simple SummarySeveral strategies have been under investigation on how to enhance anti-tumor responses in patients with poor prognosis. Considering the heterogeneity of antigens expressed by different hematological and solid neoplasia, it is difficult to develop specific immunotherapy approaches. The capacity of Natural Killer (NK) cells to kill tumor cells without specific Ag recognition provides an advantage over T cells and makes them appealing candidate effectors for immunotherapy, even if the effectiveness of their therapeutic use is limited by short-term persistence in vivo. After providing proof of concept regarding the feasibility of inducing NK cells endowed with anti-tumor activity and ability to persist for a protracted period in vivo, considering the relatively short period of in vitro activation, this approach could easily be translated into clinical practice to control tumor growth in high-risk patients.The limited efficacy of Natural Killer (NK) cell-based immunotherapy results in part from the suboptimal expansion and persistence of the infused cells. Recent reports suggest that the generation of NK cells with memory-like properties upon in vitro activation with defined cytokines might be an effective way of ensuring long-lasting NK cell function in vivo. Here, we demonstrate that activation with IL-12, IL-15 and IL-18 followed by a one-week culture with optimal doses of Interleukin (IL-2) and IL-15 generates substantial numbers of memory-like NK cells able to persist for at least three weeks when injected into NOD scid gamma (NSG) mice. This approach induces haploidentical donor-derived memory-like NK cells that are highly lytic against patients’ myeloid or lymphoid leukemia blasts, independent of the presence of alloreactive cell populations in the donor and with negligible reactivity against patients’ non-malignant cells. Memory-like NK cells able to lyse autologous tumor cells can also be generated from patients with solid malignancies. The anti-tumor activity of allogenic and autologous memory-like NK cells is significantly greater than that displayed by NK cells stimulated overnight with IL-2, supporting their potential therapeutic value both in patients affected by high-risk acute leukemia after haploidentical hematopoietic stem cell transplantation and in patients with advanced solid malignancies.

ADAM17-Deficient Pluripotent Stem Cell-Derived Natural Killer Cells Possess Improved Antibody-Dependent Cellular Cytotoxicity and Antitumor Activity

Antibody-dependent cellular cytotoxicity (ADCC) is a key pathway that mediates natural killer (NK) cell cytotoxicity against antibody-opsonized target cells. This process helps mediate the therapeutic efficacy of anti-tumor antibodies. On NK cells, ADCC occurs via engagement of antibody-coated target cells with activating receptor FcγRIIIa, or CD16a, leading to proinflammatory cytokine upregulation, degranulation, and target cell death. Upon cellular activation, the CD16a ectodomain is cleaved from the NK cell surface by A Disintegrin and Metalloprotease-17 (ADAM17). Cleavage of the ectodomain prevents further antibody binding and signaling through CD16a, which dampens NK cell activity. Blocking activation-induced ADAM17-mediated CD16a cleavage has been previously demonstrated to augment ADCC activity and provides a novel strategy to improve efficacy of therapeutic antibodies in combination with adoptive transfer of engineered NK cells. To further define the ability of ADAM17 to regulate NK cell activity, we have generated and characterized ADAM17-deficient (ADAM17-KO) NK cells derived from CRISPR/Cas9-modified human induced pluripotent stem cells (iPSCs). ADAM17-KO iPSCs successfully differentiate into hematopoietic progenitor cells, then to NK cells that uniformly express typical NK cell surface markers including CD56, CD94, NKG2D, NKp44, and NKp46. ADAM17-KO iPSC-NKs are functional and kill K562 erythroleukemia cells comparable to wildtype iPSC-derived NK cells (WT iPSC-NK cells) and healthy donor-derived peripheral blood NK cells (PB-NK cells) in vitro. Surprisingly, upon differentiation, ADAM17-KO iPSC-NK cells express ~20% lower CD16a surface expression compared to WT iPSC-NK cells, but stably retain CD16a expression after enrichment for CD16a+ cells and over 6 weeks of expansion in culture. WT iPSC-NKs and PB-NKs rapidly lose CD16a surface expression upon stimulation with phorbol esters, while ADAM17 KO iPSC-NK cells maintain over 90% CD16a expression after this stimulation. Additionally, a significantly higher proportion of ADAM17-KO iPSCs express TNF-α (71%) and CD62L (L-Selectin) (36%) - two other known ADAM17 substrates, on the cell surface after stimulation with phorbol esters for 4 hours compared to WT iPSC-NK (7% TNF-α+, 2% L-Selectin+) and PB-NK (2% TNF-α+, 1% L-Selectin+). CD16a+ ADAM17-KO iPSC-NK cells mediate increased CD107a (45%) and IFNγ (39%) expression when co-incubated with RAJI B-lymphoma cells in the presence of the anti-CD20 antibody rituximab, compared to CD16a+ WT iPSC-NK (32% CD107a+, 11% IFNγ) and PB-NK (37% CD107a+, 7% IFNγ) cells. Similarly, CD16a+ ADAM17-KO iPSC-NK cells upregulate increased CD107a (29%) and IFNγ (42%) expression when co-incubated with CAL27 squamous cell carcinoma cells in the presence of the anti-EGFR antibody cetuximab, compared to CD16a+ WT iPSC-NK (12% CD107a+, 8% IFNγ) and PB-NK (14% CD107a+, 6% IFNγ). Long-term (24 hour) cytotoxicity assay against RAJI cells in the presence of rituximab demonstrates higher cytotoxicity in CD16a+ ADAM17-KO iPSC-NK cells compared to CD16a+ WT iPSC-NK and CD16a+ PB-NK cells over time (see associated figure). In vivo studies to determine the therapeutic efficacy of ADAM17-KO iPSC-NK cells compared to WT iPSC-NK and PB-NK cells are ongoing. Together, these studies demonstrate ADAM17-KO iPSC-NK cells derived from a renewable source of gene-edited iPSCs possess enhanced ADCC potential, and provide a promising candidate to be used for standardized, off-the-shelf NK cell-based therapies in conjunction with therapeutic antibodies. Figure Disclosures Blum: Fate Therapeutics: Current Employment. Kaufman:Fate Therapeutics: Consultancy.

Inhibition of Wnt/Beta-Catenin Pathway Impairs Natural Killer (NK) Cells Induced Apoptosis of Myeloid Leukemia Cells

Introduction:NK cells play an important role in the immune response to cancer due to their ability to induce T-cell independent apoptosis of neoplastic cells. NK cells recognize tumor cells through the interaction of several distinct cell surface receptors, with the net result of inducing NK cell activation and cytotoxic attack on tumor cells. It is hypothesized that a failure of NK surveillance is a contributing factor in the development of acute myeloid leukemia (AML). The discovery of pathways that regulate AML cell apoptosis in response to NK cells activation may represent a potential therapeutic target. It is known that the Wnt/beta-catenin pathway regulates cellular proliferation, differentiation and resistance to apoptosis in AML cells. However, its contribution to the resistance of AML cells in response to NK cell-induced apoptosis resistance is currently unknown. Objective:The objective of the current study is to determine if inhibition of the Wnt/beta catenin pathway impacts NK cell-induced apoptosis of AML cells. Methods:HL-60 leukemia cells were treated with different concentrations of the Wnt/beta-catenin pathway inhibitor XAV-939 (tankyrase inhibitor) to determine the lowest dose capable of inhibiting the Wnt/beta-catenin pathway without inducing cell apoptosis. Inhibition of the pathway was confirmed by evaluating beta-catenin protein by intracellular flow cytometry and real-time PCR for downstream factors MYC and TCF4. Next, differentiation of HL-60 cells into mature granulocytes was evaluated by analyzing expression of CD11b by flow cytometry after stimulation with dimethyl sulfoxide (DMSO), as another marker of Wnt/Beta-catenin pathway inhibition. After confirming pathway inhibition, HL-60 cells were incubated with healthy donor derived NK cells in a 2:1 ratio for 24 hours in the presence or absence of XAV-939. Apoptosis was evaluated by annexin staining. Expression of NK cell inhibitory proteins were determined by flow cytometry. A panel of 84 genes for hematopoietic transcription factors was evaluated by PCR array (RT2 Profiler PCR Array Gene Expression - Qiagen) in HL-60 cells after exposure to XAV-939 for 2 and 6 hours. Expression of apoptosis related genes in HL-60 cells after exposure to XAV-939 was determined by real-time PCR. Results:The dose of 1mM XAV-939 was selected to evaluate is effect in the HL-60 cell line. Suppression of pathway signaling was confirmed by a decrease in expression of Beta-catenin,MYC,TCF4and blockade of HL-60 differentiation into neutrophils. After coincubation with NK cells, there was a decrease in HL-60 cell death with concomitant exposure to XAV-939 (70% [untreated] vs. 30% [XAV-939]; p&amp;lt;0.05) (figure 1). There was no change in NK cell surface receptors or their putative ligands in HL-60 cells as evaluated by flow cytometry. Analysis of expression of hematopoietic transcription factor in HL-60 cells showed a downregulation of several transcription factors after exposure to XAV-939, includingJUNDandTCF7L2. Since there was a decrease in apoptotic cell death, we next evaluated expression of genes related to apoptotic pathways and could demonstrate a decrease in expression ofFASandTNFR1after exposure to XAV-939 (p&amp;lt;0.05) (figure 2A and 2B). Conclusions:These results suggest that inhibition of the Wnt/beta-catenin pathway decreases apoptosis of myeloid leukemia cells mediated by NK cells, and this effect may be secondary to a decreased expression ofFASandTNFR1in the leukemic cells. Figure Disclosures Santos: Novartis:Other: Speaker fee;Bristol-Myers Squibb:Other: Speaker fee.

A Phase I Clinical Trial Testing the Safety of IL-21-Expanded, Off-the-Shelf, Third-Party Natural Killer Cells for Relapsed/Refractory Acute Myeloid Leukemia and Myelodysplastic Syndrome

Background: Allogeneic transplantation (allo-HCT) is an effective treatment for many patients with Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS). With HCT the long term disease free survival (DFS) rate is approximately 60% for patients transplanted in first remission. After relapse, the rate falls to approximately 40% if the patients are in remission at the time of HCT. However, many patients present with refractory chemo-resistant disease, relapse during or shortly after induction therapy, or develop complicating comorbidities due to prolonged induction. For most such relapse-refractory (R/R) AML patients, allo-HCT is not an option. These patients have a dire prognosis with only 5-10% long term DFS. Natural Killer (NK) cells are cytotoxic lymphocytes that are able to identify tumors and exert an anti-tumor effect in an MHC-I independent manner. However, NK cells from patients with cancer can be dysfunctional and reduced in number. To overcome that, NK cells expanded ex vivo to yield high numbers of cells could provide a cellular therapeutic option for cancer patients, including patients with AML/MDS. The therapeutic potential of ex vivo membrane-bound IL-21 expanded NK cells (FC21-NK) from a haploidentical donor has been established in patients with poor prognosis AML/MDS undergoing a haploidentical HCT. Besides obtaining sufficient cell numbers, having them readily available for patients is another major obstacle for adoptive NK cell immunotherapy. Patients with aggressive disease need prompt intervention yet the manufacture of patient-specific NK cells exceeds three weeks. As NK alloreactivity plays a critical role in mediating anti-tumor effects, we identified KIR and HLA-mismatched 'ideal' donors (selected through "Be The Match Biotherapies"). Using lymphocytes from these donors, we have established a third-party NK cell bank to ensure readily-available immune cell therapies that allows scalable, affordable mass-production of large numbers of NK cells suitable for banking &amp; immediate 'off-the-shelf' administration to a broad population of recipients. This trial is to determine the safety of FC21 expanded Off-the-shelf (OTS), Third-party donor-derived NK cells for relapsed/refractory AML patients. Methods: This phase 1 study follows a 3+3 design to investigate the safety of FC21-expanded, third-party, OTS NK cells for treatment of patients with primary refractory or relapsed AML or myelodysplastic syndrome. Active GvHD is excluding. Patients aged ≥18 or ≤80 years are enrolled into two cohorts: those &amp;lt;60 yrs &amp; able to tolerate intensive chemo &amp; sensitive to Cytarabine will receive Fludarabine 30 mg/m2/day (days -6 to -2) &amp; Cytarabine 2 g/m2/day (days -6 to -2). Patients &amp;gt;60 yrs or &amp;lt;60 yrs &amp; unable/unwilling to tolerate intensive chemo or disease insensitive to Cytarabine will receive Fludarabine 30 mg/m2/day (days -5 to -2) &amp; Decitabine 20 mg/m2/day (days -6 to -2). All patients subsequently receive a total of 6 infusions of NK cells administered thrice weekly for two weeks (between day 0-21). Three NK cell dose-levels: 1x107, 3x107 &amp; 1x108 cells/kg/dose will be explored to determine MTD (maximal tolerated dose). Between 3-18 patients/cohort/dose for MTD determination, plus an additional 10 patients/dose in an expansion phase may be enrolled (maximum 28/cohort = 56 total subjects). Patients will be followed up to day 56 from first NK cell infusion. Primary objectives are to determine the recommended phase 2 dose and overall response rate (CR, CRi &amp; MLFS). Secondary objectives will explore PFS, OS &amp; MRD negativity, cell counts, infectious complications, and patients proceeding to transplant. Enrollment in both cohorts is ongoing. Clinical trial information: NCT04220684. Disclosures Vasu: Kiadis Inc: Other: Kiadis has obtained exclusive licensing requirements from The OHio State University; Janssen: Membership on an entity's Board of Directors or advisory committees; Omeros: Membership on an entity's Board of Directors or advisory committees. Bhatnagar:KaryoPharm Therapuetics: Research Funding; Cell Therapeutics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; KITE: Membership on an entity's Board of Directors or advisory committees. Blachly:AbbVie, AstraZeneca, KITE Pharma: Consultancy. O'Donnell:Kiadis Pharma: Other: Licensing of intellectual property. Lee:Kiadis Pharma Netherlands B.V: Consultancy, Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents &amp; Royalties.