Induction Of Antibody-dependent Cellular Cytotoxicity Research Articles

Phase I–II study of OBI-888, a humanized monoclonal IgG1 antibody against the tumor-associated carbohydrate antigen Globo H, in patients with advanced solid tumors

PurposeOBI-888 is a humanized, monoclonal IgG1 antibody specific to the tumor-associated carbohydrate antigen Globo H. We conducted a phase I-II study of OBI-888 in patients with advanced cancer.MethodsPatients were treated with OBI-888 5, 10, or 20 mg/kg IV weekly in Part A (“3 + 3” design) and 20 mg/kg IV weekly in Part B (Simon’s 2-stage design) (1 cycle = 28 days).ResultsOverall, 54 patients were treated (Part A, n = 14; Part B, n = 40). OBI-888 was safe and well tolerated across the doses studied, with a low incidence of OBI-888-related treatment emergent adverse events. The maximum tolerated dose of OBI-888 was not reached. No dose-limiting toxicities were noted up to the 20 mg/kg dose level (recommended phase 2 dose). Stable disease (SD) was noted in 28.6% and 20% of Parts A and B, respectively, including three patients with SD for 6+, 7+, and 9 months. Antibody-dependent cellular cytotoxicity (ADCC) was induced after each OBI-888 treatment (average increase, 3.8-fold and 4.7-fold in Parts A and B, respectively), suggesting that ADCC induction is a potential mechanism of action of OBI-888.ConclusionsOBI-888 was well tolerated. Prolonged SD was noted in three patients. ADCC was induced after each OBI-888 treatment.

CD16, CD57 and DNAM-1 Positive NK Cells Predict MRD Negativity in Newly Diagnosed Multiple Myeloma Patients Treated with Daratumumab, Bortezomib, Thalidomide and Dexamethasone

Introduction: Daratumumab-based quadruplets are the current standard of care for newly diagnosed transplant-eligible multiple myeloma (MM) patients, because of improved depth of response and survival, compared with triplet regimens without daratumumab. Since one of the primary mechanisms of action of daratumumab is the induction of antibody-dependent cellular cytotoxicity (ADCC) via the Fc-gamma receptor CD16 on natural killer (NK) cells, it is crucial to understand the role of NK cells in combination therapy. We therefore set out to comprehensively profile NK cells by flow cytometry in newly diagnosed MM (NDMM) patients treated with either daratumumab, bortezomib, thalidomide, and dexamethasone (D-VTD) or VTD. Methods: A subset of NDMM patients (n = 152) who were treated in the Cassiopeia trial (EudraCT: 2014-004781-15) was included in this immunomonitoring analysis. In this trial, patients were first randomized to receive either four induction cycles and two consolidation cycles of D-VTD or VTD in conjunction with autologous stem cell transplantation (ASCT). In the second part of this trial, patients who achieved partial response or better at day 100 post-ASCT were randomized to either receive daratumumab maintenance or observation for the duration of two years. Bone marrow (BM) and peripheral blood (PB) samples were collected at study entry (baseline), and for PB at additional time points: cycle 1 day 28, cycle 4 day 28, day 100 (post-ASCT) and week 52 (maintenance). All baseline BM and PB samples and a selection of longitudinal PB samples were profiled by flow cytometry, with a focus on NK cell phenotype (CD56, CD16, CD57, DNAM-1, TIGIT, KLRG1, PD1, TIM3, NKG2A, NKG2C, NKG2D). To identify NK cell profiles associated with minimal residual disease (MRD) negativity, baseline PB and BM data were compared between MM patients based on MRD status after consolidation. Additionally, longitudinal data of PB samples collected during treatment were assessed to understand the impact of D-VTD and VTD on NK cell profiles. Results: In this cohort, 49 patients out of 77 (64%) randomized to the D-VTD arm achieved MRD negativity post-consolidation, while this was the case in 28 out of 75 patients (37%) in the VTD arm (fisher exact-test, p = 0.008). Patients with a higher proportion of BM-residing NK cells expressing the ADCC receptor CD16 (median 86 vs 72%, p = 0.007), the activating receptor DNAM-1 (median 94 vs 89%, p = 0.029), or the maturation marker CD57 (median 58 vs 48 %, p = 0.049) at baseline were more likely to achieve MRD-negativity post-consolidation in the D-VTD arm (Figure 1). Notably, this association was not present in the VTD arm. Although not significant, we found a similar trend for CD16 in PB in the D-VTD arm. During D-VTD treatment, we observed an increase in the proportion of CD56 bright and NKG2A + in PB NK-cells, and a corresponding decline in cells expressing CD16, CD57 and DNAM-1 (linear mixed effect model (LME) p <0.001). During VTD treatment we also observed a decrease in CD16 + NK-cells and an increase in CD56 bright and NKG2A + NK-cells (LME p <0.05), although these changes were more pronounced in the D-VTD arm. In patients who were assigned D-VTD at the first randomization and were subsequently randomized to the observation arm, we observed a restoration of the proportion of CD16 +, CD57 +, and CD56 bright NK cells to baseline values at week 52 after ASCT (Figure 2). As expected, the daratumumab associated NK cell changes persisted in the group that was randomized to the daratumumab maintenance arm. Conclusion: This study highlights the importance of NK cell immunophenotypic profiles in bone marrow as predictive markers for MRD negativity in NDMM patients treated with D-VTD in in conjunction with ASCT. Additionally, our findings illustrate that NK cell changes associated with daratumumab return to baseline levels after treatment cessation, indicating the potential for sequential NK cell-based therapies. In conclusion, this study not only provides valuable insights into the role of NK cells in the treatment of NDMM patients with D-VTD and ASCT, but also indicates that further research to optimize NK cell function in the context of combination therapies is warranted.

NNV024, a Humanized Anti-CD37 Antibody with Enhanced ADCC and Extended Plasma Half-Life for the Treatment of B-Cell Malignancies

Background: There is a significant unmet clinical need for new therapeutic approaches for patients with B-cell non-Hodgkin lymphomas (B-NHL) who relapse or are refractory to anti-CD20 therapies. Moreover, certain B-cell malignancies do not express CD20. High expression of the CD37 antigen on malignant B-cells associated with limited or no expression on other hematopoietic cells makes CD37 a highly attractive alternative target for B-cell depleting therapies. We have therefore developed a humanized anti-CD37 monoclonal antibody (NNV024) engineered to exhibit a strong antibody-dependent cellular cytotoxicity (ADCC). Methods: Generation of NNV024 was performed by combining in silico CDR-grafting and structure-based back mutation. Candidates were then selected for their affinity to CD37 expressing cell line, Ramos. In silico immunogenicity prediction tools were integrated in the selection process to support the generation of a candidate with low immunogenicity potential (NNV023). Last, to increase ADCC, the selected candidate was afucosylated at the N-linked bi-antennary glycan at N297 of the Fc region (NNV024). The NNV024 was characterized in vitro and in vivo. Binding to human Fc gamma receptors (FcγRs), neonatal Fc receptor (FcRn), and complement component 1q (C1q) was confirmed by ELISA and SPR. ADCC and antibody-dependent cellular phagocytosis (ADCP) induction were measured using cell-based reporter assays with eleven cell lines derived from B-NHL subtypes such as Burkitt's lymphoma, diffuse large B-Cell lymphoma (DLBCL), and mantel cell lymphoma (MCL). All cell lines express both CD20 and CD37 on their cell surface. In addition, B cell chronic lymphocytic leukaemia (B-CLL) cells isolated from patient samples were used to test induction of ADCC, ADCP and complement-dependent cytotoxicity (CDC) in vitro. NNV024 plasma pharmacokinetics were assessed in Tg32 transgenic mice expressing human FcRn, which is considered a key regulator of IgG plasma half-life. A therapy study comparing NNV024 (n=10) and obinutuzumab (n=10) was performed using a disseminated tumor (Daudi) model in CB17-SCID mice (107 cells/mouse, i.v.). The anti-CD20 Abs rituximab and obinutuzumab as well as the anti-CD37 Ab, Duohexabody-CD37, were used for benchmarking. Results: As expected, the glyco-engineering increased affinity of NNV024 to FcγRIIIa (KD before afucosylation: 460.8 ng/mL; KD after: 104.1 ng/mL). Binding of Abs to FcγRIIIa activates immunological effector cells such as Natural Killer cells, macrophages, monocytes, and eosinophils. NNV024 demonstrated ADCC superior to that observed with obinutuzumab, rituximab, and Duohexabody-CD37. NNV024 exhibited a 2-fold prolonged plasma half-life in mice (8.9±0.8 days) compared to obinutuzumab (4.4±1.3 days) and Duohexabody-CD37 (4.1±1.2 days). Mice survival was enhanced up to ~ 40% when treated with NNV024 (10 µg/mouse - 70.5 days; 50 µg/mouse - 84 days) compared to obinutuzumab at a dose of 10 µg (70.5 days vs. 53 days) or 50 µg (84 days vs. 62 days). Conclusion: These encouraging preclinical results support further development of NNV024 as a potential therapeutic mAb candidate for the treatment of B-cell malignancies and B-cell driven autoimmune disorders.

CD47-SIRPα Controls ADCC Killing of Primary T Cells by PMN Through a Combination of Trogocytosis and NADPH Oxidase Activation

Immunotherapies targeting the “don’t eat me” myeloid checkpoint constituted by CD47 SIRPα interaction have promising clinical potential but are limited by toxicities associated with the destruction of non-tumor cells. These dose-limiting toxicities demonstrate the need to highlight the mechanisms of anti–CD47-SIRPα therapy effects on non-tumor CD47-bearing cells. Given the increased incidence of lymphopenia in patients receiving anti-CD47 antibodies and the strong ADCC (antibody-dependent cellular cytotoxicity) effector function of polymorphonuclear cells (PMNs), we investigated the behavior of primary PMNs cocultured with primary T cells in the presence of anti-CD47 mAbs. PMNs killed T cells in a CD47-mAb–dependent manner and at a remarkably potent PMN to T cell ratio of 1:1. The observed cytotoxicity was produced by a novel combination of both trogocytosis and a strong respiratory burst induced by classical ADCC and CD47-SIRPα checkpoint blockade. The complex effect of the CD47 blocking mAb could be recapitulated by combining its individual mechanistic elements: ADCC, SIRPα blockade, and ROS induction. Although previous studies had concluded that disruption of SIRPα signaling in PMNs was limited to trogocytosis-specific cytotoxicity, our results suggest that SIRPα also tightly controls activation of NADPH oxidase, a function demonstrated during differentiation of immature PMNs but not so far in mature PMNs. Together, our results highlight the need to integrate PMNs in the development of molecules targeting the CD47-SIRPα immune checkpoint and to design agents able to enhance myeloid cell function while limiting adverse effects on healthy cells able to participate in the anti-tumor immune response.

Characterization of humoral and cell-mediated immunity induced by mRNA vaccines expressing influenza hemagglutinin stem and nucleoprotein in mice and nonhuman primates

In response to immune pressure, influenza viruses evolve, producing drifted variants capable of escaping immune recognition. One strategy for inducing a broad-spectrum immune response capable of recognizing multiple antigenically diverse strains is to target conserved proteins or protein domains. To that end, we assessed the efficacy and immunogenicity of mRNA vaccines encoding either the conserved stem domain of a group 1 hemagglutinin (HA), a group 2 nucleoprotein (NP), or a combination of the two antigens in mice, as well as evaluated immunogenicity in naïve and influenza seropositive nonhuman primates (NHPs). HA stem-immunized animals developed a robust anti-stem antibody binding titer, and serum antibodies recognized antigenically distinct group 1 HA proteins. These antibodies showed little to no neutralizing activity in vitro but were active in an assay measuring induction of antibody-dependent cellular cytotoxicity. HA-directed cell-mediated immunity was weak following HA stem mRNA vaccination; however, robust CD4 and CD8 T cell responses were detected in both mice and NHPs after immunization with mRNA vaccines encoding NP. Both HA stem and NP mRNA vaccines partially protected mice from morbidity following lethal influenza virus challenge, and superior efficacy against two different H1N1 strains was observed when the antigens were combined. In vivo T cell depletion suggested that anti-NP cell-mediated immunity contributed to protection in the mouse model. Taken together, these data show that mRNA vaccines encoding conserved influenza antigens, like HA stem and NP in combination, induce broadly reactive humoral responses as well as cell-mediated immunity in mice and NHPs, providing protection against homologous and heterologous influenza infection in mice.

Natural Killer Cell-Mediated Antibody-Dependent Cellular Cytotoxicity Against SARS-CoV-2 After Natural Infection Is More Potent Than After Vaccination.

We compared the ability of SARS-CoV2 Spike-specific antibodies to induce natural killer (NK) cell-mediated antibody dependent cellular cytotoxicity (ADCC) in patients with natural infection and vaccinated persons. Analyzing plasma samples from 39 COVID-19 patients and 11 vaccinated individuals, significant induction of ADCC could be observed over a period of more than three months in both vaccinated and recovered individuals. Although plasma antibody concentrations were lower in recovered patients, we found antibodies elicited by natural infection induced a significantly stronger ADCC response compared to those induced by vaccination, which may affect protection conferred by vaccination.

Role of Fcγ receptors in HER2-targeted breast cancer therapy.

Several therapeutic monoclonal antibodies (mAbs), including those targeting epidermal growth factor receptor, human epidermal growth factor receptor 2 (HER2), and CD20, mediate fragment crystallizable gamma receptor (FcγR)–dependent activities as part of their mechanism of action. These activities include induction of antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP), which are innate immune mechanisms of cancer cell elimination. FcγRs are distinguished by their affinity for the Fc fragment, cell distribution, and type of immune response they induce. Activating FcγRIIIa (CD16A) on natural killer cells plays a crucial role in mediating ADCC, and activating FcγRIIa (CD32A) and FcγRIIIa on macrophages are important for mediating ADCP. Polymorphisms in FcγRIIIa and FcγRIIa generate variants that bind to the Fc portion of antibodies with different affinities. This results in differential FcγR-mediated activities associated with differential therapeutic outcomes across multiple clinical settings, from early stage to metastatic disease, in patients with HER2+ breast cancer treated with the anti-HER2 mAb trastuzumab. Trastuzumab has, nonetheless, revolutionized HER2+ breast cancer treatment, and several HER2-directed mAbs have been developed using Fc glyco-engineering or Fc protein-engineering to enhance FcγR-mediated functions. An example of an approved anti-HER2 Fc-engineered chimeric mAb is margetuximab, which targets the same epitope as trastuzumab, but features five amino acid substitutions in the IgG 1 Fc domain that were deliberately introduced to increase binding to activating FcγRIIIa and decrease binding to inhibitory FcγRIIb (CD32B). Margetuximab enhances Fc-dependent ADCC in vitro more potently than the combination of pertuzumab (another approved mAb directed against an alternate HER2 epitope) and trastuzumab. Margetuximab administration also enhances HER2-specific B cell and T cell–mediated responses ex vivo in samples from patients treated with prior lines of HER2 antibody-based therapies. Stemming from these observations, a worthwhile future goal in the treatment of HER2+ breast cancer is to promote combinatorial approaches that better eradicate HER2+ cancer cells via enhanced immunological mechanisms.

Efficient Targeting of CD38 in Mature T-Cell Neoplasms with Daratumumab and Allogeneic NK Cells

Introduction: Mature T-cell neoplasms (MTCN) are a heterogeneous and aggressive group of lymphoid neoplasms with very limited options for precision immunotherapy. Targeted immunotherapy with antibodies directed against surface markers on tumor cells has emerged as an effective treatment for B-cell neoplasms, but the development of immunotherapy strategies for MTCN has been much slower. CD38 is expressed at low levels in a subset of normal resting T-cells. Data on the frequency and level of CD38 expression is MTCN are lacking. Our goal was to study the expression and stability of CD38 on a spectrum of neoplastic T-cell populations and assess the potential anti-tumor effect of anti-CD38 monoclonal antibodies in combination with allogeneic natural killer (NK) cells in MTCN.Methods and results: We searched the Thomas Jefferson University Hospital (TJUH) pathology records for all cases of MTCN for which immune-phenotypical characterization of the neoplastic T-cell population by multi-color flow cytometry (FC) was available. CD38 expression was evaluated in cases where an abnormal T-cell population (defined as loss of one on more pan T-cell markers and/or a skewed CD4 to CD8 ratio). A total of 103 unique patients with MTCN were identified. Of these, 51 had at least one biopsy whereby tumor cells had an abnormal immunophenotype which could then be assessed for CD38 expression. CD38 was expressed to some extent in all but 2 cases with expression levels on peripheral T-cell lymphoma-not other specified (PTCL-NOS)(% Mean±SEM = 80.84±10.26, N=11), angioimmunoblastic T-cell lymphoma (AITL) (% Mean±SEM = 80.56±7.34, N=6), nodal PTCL with T follicular-helper (T FH) phenotype (% Mean±SEM = 55.00±12.72, N=7), anaplastic large cell lymphoma (ALCL) (% Mean±SEM = 77.38±10.75, N=3), large granular lymphocytic leukemia (LGLL) (% Mean±SEM = 80.27±7.49, N=4), T-cell prolymphocytic leukemia (T-PLL) (% Mean±SEM = 88.26±4.20, N=7), cutaneous T-cell lymphoma (CTCL) (% Mean±SEM = 49.52±14.77, N=7), adult T‐cell leukemia/lymphoma (ATLL) (% Mean±SEM = 76.68±10.45, N=3), hepatosplenic T-cell lymphoma/monomorphic epitheliotropic intestinal T-cell lymphoma (HSTCL/MEITL) (% Mean±SEM = 75.00±11.37, N=3). The medians and ranges of the MFI of CD38 on CD38+ tumor cells were the following: PTCL-NOS 29.46 (3.1-115.62), AITL 13.64 (2.67-29.41), other PTCL-T FH 5.87 (0-48.67), ALCL 11.13 (3.6-11.28), LGL (13.52 (9.72-18.25), T-PLL 6.49 (3.09-18), CTCL 8.36 (0-116.75), ATLL 27.17 (3.54-60.5), HSTCL/MEITL 15.96 (6.96-167.85). We also measured surface expression of CD38 on the patient-derived MTCN cell lines HuT-78, HuT-102, Jurkat, H9, HH, and MOTN1, all of which expressed CD38, to determine which of these cell lines could be used for in vitro experiments. We next evaluated if the CD38 molecule is an effective target for antibody-mediated therapy in MTCN, by testing the ability of daratumumab (dara) to enhance antibody-dependent cellular cytotoxicity (ADCC) elicited by NK cells. For this, we purified normal NK-cells from TJUH Blood Bank leukoreduction filters and cultured with recombinant IL-15 for 48 hours prior to all experiment. T-cell lines and primary MTCN cells were treated with increasing concentrations (0.1 µg/mL - 2 µg/mL) of dara or isotype control. NK-cells were added at Effector:Target ratio of 5:1 and incubated for 4 hours at 37⁰ Celsius. Cytotoxicity was measured by LDH release assay. Dara induced significant cell lysis starting at doses as low as 0.1μg/mL in both T-cell lines and primary MTCN cells, reaching maximum cytotoxicity at 0.5-2μg/mL (mean±SEM cytotoxicity in isotype vs dara treated cells= 50.0±5.05% vs 97.5±2.5%, N=4, p-value=0.0002). The degree of ADCC induction also correlated with interferon-gamma (IFN-g) release by NK cells in vitro for both T-cell lines and primary MTCN cells.Conclusions: The majority of MTCN analyzed (N=49, 96%) showed any degree of CD38 expression by FC with a wide variation of intensity, including within the same subtype. Allogeneic NK cells efficiently elicited dara-mediated ADCC of tumor cells from all MTCN subtypes and produced abundant IFN-g. These data highlight the potential of targeting CD38 in MTCN with anti-CD38 antibodies and allogeneic NK cells. The strong CD38 expression observed in most tumor cells from ultra-rare and very aggressive subtypes of MTCL opens the door to much needed new treatment strategies. DisclosuresBrammer: Celgene: Research Funding; Kymera Therapeutics: Consultancy; Seattle Genetics: Speakers Bureau. Chakravarti: Kiadis Pharma: Patents & Royalties. Porcu: Viracta: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Innate Pharma: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BeiGene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Incyte: Research Funding; Daiichi: Honoraria, Research Funding; Kiowa: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Spectrum: Consultancy; DrenBio: Consultancy.

Daratumumab Mitigates B-Cell Receptor Signaling and Enhances Antitumor Activity of Ibrutinib in Chronic Lymphocytic Leukemia (CLL) Cells

Introduction: B-cell receptor (BCR) signaling is a central driver of proliferation in chronic lymphocytic (CLL) cells. BCR engagement leads to recruitment of several intracellular kinases such Lyn, Syk and BTK, that activate ERK, NFkB and induce CLL cell proliferation. While this pathway is effectively targeted with the BTK inhibitor, ibrutinib, various combination treatment strategies that result in greater tumor cell killing are under investigation. On B-cells, the BCR interacts with the CD19 and CD38 cell surface antigens; where the later amplifies intracellular pro-survival signal transmission through the BCR. CD38 is a multifunctional protein, which possess both enzymatic and receptor functions. As such, we hypothesized that concurrent targeting of CD38 and BTK would lead to enhanced mitigation of BCR signaling as well as direct cell death than use of either agent alone.Materials: CD19+ cells were isolated from CLL patients (n=30, collected under an IRB-approved protocol) by magnetic bead sorting. JVM13 (CD38+) and MEC1 (CD38-) cell lines were also used. CD38 expression was measured by flow cytometry with quantification of MFI and surface antibody binding (sAbc). Drug-induced antibody-dependent cellular cytotoxicity (ADCC) in target Calcein AM labeled CLL cells was assessed by co-culturing them with healthy donor PBMCs as effectors (effector: target [E:T] ratio, 50:1) and complement dependent cytotoxicity (CDC) was measured using complement-containing serum from a healthy donor. Antibody dependent cellular phagocytosis (ADCP) was measured by co-culturing calcein AM labeled CLL cells with healthy human macrophages at a 2:1 ratio. Apoptosis by annexin-V/PI dual staining along with mitochondrial outer membrane potential (MOMP) using MitoProbeTMDilC1(5) were assessed by flow cytometric analysis. Immunoblotting was performed using antibodies against Lyn, Syk, BTK, PLCγ2, ERK1/2, AKT, Ikβα, NFAT2 and their phosphorylated isoforms along with GAPDH followed by densitometry analysis.Results: Using a cutoff of 30% (gated CD38 expressing cells), we observed 26.6% (n=8) of CLL pts. to be CD38+ and 73.3% of pts. to be CD38- (n=22). As some pts. deemed CD38- had high CD38 MFI or sAbc, we applied an interquartile range (IQR with 95% confidence interval) for CD38 MFI; re-classifying pts. as CD38lo (56.75 - 199) vs. CD38hi (199 - 355). Using this system, specific-lysis of CLL cells from Dara-mediated ADCC was 23.74±2.55% vs. 14.17±1.27, CDC: 15.93±1.68% vs. 12.29±0.88, ADCP: 8.630.96% vs. 9.50±0.97% and apoptosis: 32.42±3.42 vs. 23.65±1.82 in CD38hi vs. CD38lo pts., respectively. Apoptosis was accompanied by a significant shift in MOMP [21.65±7.90% (CD38hi) vs. 32.52±7.42% (CD38lo), p<0.05]. In CLL cells treated with the combination of Ibr + Dara (ID), ADCC increased to 54.21±4.09% vs. 37.66±2.16; CDC: 34.35±2.47% vs. 28.88±1.51%, ADCP 25.56±2.30% vs. 16.69±1.97%, apoptosis: 61.63±3.14% vs 62.06±3.41% and MOMP: 66.22±3.68% vs 71.13±3.31%: in CD38hi vs. CD38lo pts., respectively. Next we examined the effect of Dara +/- Ibr on BCR signaling in CD38hi and CD38lo CLL cells. In CD38hi cells, single agent Dara significantly decreased phosphorylation Lyn, Syk, BTK and PLCγ2 as well as ERK1/2, AKT, Ikβα and NFAT; the ID combination decreasing these further (except Ikβα and NFAT2) (p<0.01). In CD38lo cells, Dara significantly downregulated phosphorylation of Lyn and PLCγ2, however, insignificant changes were noted in all other proteins. In ID combination treated CD38lo cells, Lyn, Syk, BTK, PLCγ2 and AKT were further decreased.Conclusions: Herein, we provide first evidence on the ability of Dara to modulate BCR signaling and associated proteins in primary CLL cells and that this can be further augmented with Ibr. Dara-induced protein changes were more prominent in CD38hi cells; accompanied by higher % apoptosis vs. that observed in CD38lo cells, yet the ID combination significantly enhanced mitochondrial-mediated apoptosis in both CD38hi and CD38lo cells. This indicates that the combination can potentially overcome lower induction of apoptosis and ADCC in CD38lo cells treated with single agent Dara or Ibr. Studies on how Dara and the ID combination induce direct programmed cell death (independent of modulating BCR signaling) are underway. Overall, our investigations provide rationale for clinical testing of Ibr combined with Dara in CLL. DisclosuresParikh:Pharmacyclics: Research Funding; Pharmacyclics: Honoraria; AstraZeneca: Honoraria. Ding:Merck: Research Funding. Sher:LAM Therapeutics, Inc: Research Funding. Malavasi:Jaansen Pharmaceuticals: Research Funding. Ailawadhi:Novartis: Consultancy, Honoraria; Pharmacyclics: Research Funding; Amgen: Consultancy, Honoraria; Takeda: Consultancy, Honoraria.

Daratumumab Efficiently Targets NK/T Cell Lymphoma with High CD38 Expression

CD38 expression can be detected on a majority of NK/T cell lymphoma (NKTCL). Based on the clinical data of 94 patients with ENKTL, high CD38 surface expression was an adverse prognostic factor for progression free survival, and these patients had significantly inferior outcomes (Wang, 2015). This corroborates with our own studies showing that relapsed and refractory NKTCL patients almost always exhibit high CD38 expression, thereby proposing that it may be worthwhile to target CD38 as a novel therapeutic option.Daratumumab is a human anti-CD38 monoclonal antibody which has shown significant anti-cancer activity in multiple myeloma. In this study, we investigated the potential cytotoxic effects and mechanisms of actions of Daratumumab in a panel of 10 NKTCL cell lines. Firstly, we identified that cell lines can be stratified into CD38Hi, CD38Mid and CD38Lo as quantified by mRNA expression and CD38 protein surface expression which was qualitatively analysed by FACS and IHC. Daratumumab is able to induce antibody dependent cellular cytotoxicity (ADCC) in a CD38-dependent manner and in a dose-dependent fashion. We also observe a greater induction of antibody dependent cellular phagocytosis (ADCP) activation in correlation with CD38 expression. Furthermore, complement-dependent cytotoxicity (CDC) was significantly triggered by Daratumumab in CD38Hi and CD38Mid cells. However, we found evidence of an additional level of regulation provided by the expression of complement inhibitory proteins(CIPs) CD46, CD55 and CD59 on NKTCL cell lines which can limit and inhibit the induction of CDC regardless of CD38 surface expression levels.All-trans retinoic acid (ATRA) is a vitamin A derivative that binds to retinoic acid receptor alpha leading to the upregulation of CD38 expression. Treatment with ATRA increases CD38 mRNA and surface protein expression in all CD38Hi-Lo NKTCL cell lines. Interestingly CD38Lo cell lines showed the greatest fold increase of CD38 mRNA and surface protein expression. Notably, addition of ATRA to SNK-10, a CD38LoCD55Hi cell line, prior to Daratumumab treatment was able to improve the induction of ADCC but not CDC. This suggests a critical role for CIPS in mediating the induction of CDC in NKTCL.Subsequent investigation for the efficacy of Daratumumab in vivo is currently being performed.We also discovered a synergistic cytotoxic effect in NKTCL CD38Hi cell lines mediated by L-Asparaginase (a component of the current chemotherapeutic regimen in NKTCL) treatment in combination with Daratumumab. Altogether,these results propose a rationale therapeutic option for single or combined Daratumumab treatment in the clinic especially for relapsed and refractory patients. DisclosuresJin:Janssen China R&D: Employment. Yu:Janssen China R&D: Employment. Chen:Janssen China R&D: Employment. Yang:Janssen China R&D: Employment. Chng:Janssen China R&D: Research Funding.

Obinutuzumab in Combination with Chemotherapy Enhances Direct Cell Death in CD20-Positive Obinutuzumab-resistant Non-Hodgkin Lymphoma Cells

Follicular lymphoma commonly recurs and is difficult to cure. Obinutuzumab is a humanized glycoengineered type II anti-CD20 antibody with a mode of action that includes induction of antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and direct cell death. There is no evidence on the effectiveness of retreatment with obinutuzumab in patients with prior obinutuzumab treatment. Using obinutuzumab-induced direct-cell-death-resistant cells, we investigated the efficacy of obinutuzumab retreatment in combination with chemotherapeutic agents used in follicular lymphoma treatment. Human non-Hodgkin lymphoma SU-DHL-4 cells were sustainably exposed to obinutuzumab in vitro, and 17 resistant clones expressing CD20 and showing 100-fold higher IC50 of obinutuzumab than parental cells were established. The growth inhibition effect of obinutuzumab in combination with bendamustine, 4-hydroperoxy-cyclophosphamide, doxorubicin, vincristine, or prednisolone was estimated using an interaction index based on the Bliss independence model. For each clone, there were various combinations of obinutuzumab and chemotherapeutic agents that showed supra-additive effects. Obinutuzumab combined with doxorubicin enhanced caspase-dependent apoptosis and growth inhibition effect. Obinutuzumab combined with prednisolone enhanced DNA fragmentation and G0-G1 arrest. These combinations also had an antitumor effect in mouse xenograft models. Our results indicate that retreatment with obinutuzumab, when it is combined with chemotherapeutic agents, is effective in the CD20-positive obinutuzumab-induced direct-cell-death-resistant cells.

Characterization of antibody-dependent cellular cytotoxicity induced by the plasma from persons living with HIV-1 based on target cells with or without CD4 molecules

Antibody-dependent cellular cytotoxicity (ADCC) is essential for reducing the reservoir of latent virus in persons living with HIV-1 (PLWH). This study evaluated the plasma's ADCC activity from treatment-naïve PLWH based on target cells with or without CD4 molecules. We found that the distribution of plasma activities to mediate ADCC is different between 8E5 cells (CD4-) and NL4-3-infected CEM.NKR.CCR5 cells (CD4+). There was no correlation between the IgG-binding ability and ADCC activity. The binding ability of the 8E5 cells (2.2%) to A32 antibody was significantly lower than that of CEM.NKR.CCR5 cells (69.3%). After incubating the 8E5 cells with CD4-mimetic compound, it did not increase the binding ability with the A32 antibody. After incubation with CD4+ T cells, the binding ability of the 8E5 cells for the A32 antibody increased significantly, which implies that the conformation of the Env protein open and expose the CD4-induced epitopes. The effect of the ADCC in plasma directly applied to 8E5 cells was positively correlated with that of the NL4-3-infected CEM.NKR.CCR5 cells. In conclusion, ADCC induction in plasma was general in the treatment-naïve PLWH. The ADCC activity levels differed when target cells with or without CD4 molecules were evaluated; When designing experiments on ADCC, full consideration should be given to this immune phenomenon.

Obinutuzumab-Retreatment in Combination with Bendamustine Is Effective for Obinutuzumab Resistant Models in Vitro and In Vivo

Background: Follicular lymphoma (FL) commonly recurs and is difficult to cure. Obinutuzumab (OBI) is a humanized type II anti-CD20 antibody. It's mode of action is mainly characterized by the induction of direct cell death and it shows stronger antibody-dependent cellular cytotoxicity (ADCC) than rituximab. While OBI is indicated for previously untreated or relapsed/refractory (r/r) FL, there is no evidence on the efficacy of retreatment with OBI in r/r FL after prior OBI-containing therapy. To demonstrate the effectiveness of OBI-retreatment in a non-clinical study, we established in vitro and in vivo OBI resistant models, consisting of human non-Hodgkin lymphoma (NHL) cells resistant to OBI-induced ADCC and OBI-resistant tumors established from NHL cells under xenotransplantation conditions, and investigated the combination efficacy of OBI and bendamustine (Benda) in these OBI-resistant models. Methods: OBI-induced ADCC resistant clones were established from an RL cell line by inducing ADCC three times with CD16-transfected NK-92 cells. The in vivo resistant model was established from a SU-DHL-4 xenograft model through repeated treatment with OBI and re-inoculation of the regrown tumors. CD20 expression was assessed by flow cytometry or immunohistochemistry (IHC). ADCC activity was evaluated using calcein-AM with CD16-transfected NK-92 cells. To examine antitumor activity, OBI, human immunoglobulin G (HuIgG), Benda, or vehicle were intravenously administered on Day 1, 8 and 15 (OBI and HuIgG) or Day 1 and 2 (Benda and vehicle), and tumor volume was measured. Intratumorally infiltrated NK cells were assessed by IHC of CD335. Cell surface CD107a expression was assessed by flow cytometry. Results: OBI-induced ADCC resistant clones derived from RL (RL-OR-8 and RL-OR-22) showed a reduction in ADCC sensitivity compared with RL. These resistant clones exhibited CD20 expression similar to RL. Pretreatment of the effector NK cells with Benda enhanced ADCC induction of OBI in RL-OR-8 and RL-OR-22. Treatment with OBI (30 mg/kg) in combination with Benda (13.3 mg/kg) also significantly increased antitumor activity compared with each single agent alone on Day 18 (when tumor volume reached euthanasia criteria (*) in control and OBI monotherapy groups) in the RL-OR-22 xenograft model (Table 1). An in vivo OBI resistant model derived from SU-DHL-4 xenografts (SU-DHL-4-OR-18-8) was also established. While SU-DHL-4 xenografted tumors disappeared in 6/6 mice after the third OBI treatment (6 mg/kg), SU-DHL-4-OR-18-8 tumors did not regress in 6/6 mice. CD20 expression in SU-DHL-4-OR-18-8 tumors did not decrease compared with SU-DHL-4 tumors. The ratio of CD335-positive cells to tumor cells after 6 mg/kg of OBI treatment (Day 4) in SU-DHL-4-OR-18-8 was significantly decreased compared with the ratio in SU-DHL-4 (0.31 ± 0.12% vs 0.93 ± 0.23%). The combination efficacy of OBI and Benda was also assessed in an SU-DHL-4-OR-18-8 xenograft model. OBI (6 mg/kg) in combination with Benda (25 mg/kg) significantly increased the antitumor activity compared with each single agent alone on Day 22 (*in control group) and 29 (Table 1). Finally, the expression of CD107a, an NK cell-degranulation marker, was detected to examine the effect of Benda on NK activity in vitro. Pretreating effector NK cells with Benda upregulated CD107a expression on NK cell surfaces after OBI treatment in RL-OR-8 and RL-OR-22. Conclusions: The decreased CD335-positive cell ratio observed in the in vivo SU-DHL-4-OR-18-8 resistant model suggests that the mechanism of resistance to OBI also involves the attenuation of ADCC as in the in vitro OBI-induced ADCC resistant clones. The combination treatment of OBI and Benda was effective in both RL-OR-22 and SU-DHL-4-OR-18-8 xenograft models. It is possible that activation of NK cells by Benda might be involved in this combination mechanism. Although the mechanisms need to be examined in more detail, these results indicate the possible effectiveness of OBI-retreatment after prior OBI-containing therapy. Disclosures Yamashita-Kashima: Nippon Shinyaku Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Current Employment. Kawasaki:Chugai Pharmaceutical Co., Ltd.: Current Employment; Nippon Shinyaku Co., Ltd.: Research Funding. Yorozu:Chugai Pharmaceutical Co., Ltd.: Current Employment; Nippon Shinyaku Co., Ltd.: Research Funding. Yoshiura:Chugai Pharmaceutical Co., Ltd.: Current Employment; Nippon Shinyaku Co., Ltd.: Research Funding. Fujimura:Chugai Pharmaceutical Co., Ltd.: Current Employment; Nippon Shinyaku Co., Ltd.: Research Funding. Kurasawa:Chugai Pharmaceutical Co., Ltd.: Current Employment; Nippon Shinyaku Co., Ltd.: Research Funding. Harada:Chugai Pharmaceutical Co., Ltd.: Current Employment; Nippon Shinyaku Co., Ltd.: Research Funding. Yoshimura:Nippon Shinyaku Co., Ltd.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Current Employment.

The anti-epithelial cell adhesion molecule (EpCAM) monoclonal antibody EpMab-16 exerts antitumor activity in a mouse model of colorectal adenocarcinoma.

The epithelial cell adhesion molecule (EpCAM), which is a calcium-independent homophilic intercellular adhesion factor, contributes to cell signaling, differentiation, proliferation and migration. EpCAM is essential for carcinogenesis in numerous types of human cancer. The purpose of the present study was to establish an anti-EpCAM monoclonal antibody (mAb) for targeting colorectal adenocarcinomas. Thus, an anti-EpCAM mAb, EpMab-16 (IgG2a, κ), was established by immunizing mice with EpCAM-overexpressing CHO-K1 cells, and validated using flow cytometry, western blot, and immunohistochemical analyses. EpMab-16 reacted with endogenous EpCAM specifically in a colorectal adenocarcinoma cell line as determined by flow cytometry and western blot analyses. Immunohistochemical analysis demonstrated that EpMab-16 stained a plasma membrane-like pattern in clinical colorectal adenocarcinoma tissues. The dissociation constant (KD) for EpMab-16 in a Caco-2 colorectal adenocarcinoma cell line determined by flow cytometry was 1.8×10−8 M, suggesting moderate binding affinity of EpMab-16 for EpCAM. Whether the EpMab-16 induced antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) against Caco-2 or antitumor activity was then assessed in a murine xenograft model. In vitro experiments revealed strong ADCC and CDC induction in Caco-2 cells by EpMab-16 treatment. In vivo experiments in a Caco-2 ×enograft model demonstrated that EpMab-16 treatment significantly reduced tumor growth compared with that in mice treated with the control mouse IgG. These results suggested that EpMab-16 may be a promising treatment option for EpCAM-expressing colorectal adenocarcinomas.

Abstract 3371: Role of the epidermal growth factor receptor expression and internalization in cetuximab-induced antibody-dependent cellular cytotoxicity in head and neck squamous cell carcinoma

Abstract The epidermal growth factor receptor (EGFR)-targeted therapies and immunotherapies are now at the forefront for treatment of head and neck squamous cell carcinoma (HNSCC). However, resistance to cetuximab, an anti-EGFR monoclonal antibody (mAb), is a major clinical problem, limiting the clinical benefit of treatment. Besides inhibition of downstream signalling, cetuximab can also induce antibody-dependent cellular cytotoxicity (ADCC). The aim of this study was to investigate the role of baseline EGFR expression and EGFR internalization following treatment with cetuximab as possible mechanisms that may explain differences in cetuximab-induced ADCC between HNSCC cell lines. Ten HNSCC cell lines, comprising cetuximab sensitive as well as intrinsically and acquired resistant cell lines, differing in HPV-status, were used. ADCC was assessed using the xCELLigence RTCA system, by co-culturing HNSCC cells with natural killer cells from healthy volunteers (E:T; 5:1). Baseline EGFR expression was flow cytometrically determined, following staining with an EGFR PE-conjugated antibody or a PE-conjugated isotype control. Experiments were performed under normoxic and hypoxic (1% O2) conditions. To determine EGFR internalization, cetuximab and the corresponding isotype control were stained with FabFluor-pH reagent prior to incubation with HNSCC cells. Phase-contrast and red fluorescence kinetics were quantified using the IncuCyte Zoom. We demonstrate that cetuximab-induced ADCC was highest in intrinsically cetuximab resistant cell lines compared to the acquired resistant and cetuximab sensitive cell lines. Under hypoxic conditions, a reduced ADCC was observed in the cetuximab sensitive and acquired resistant HNSCC cell lines but not in the intrinsically resistant cell lines. Baseline EGFR was expressed in a cell line-dependent manner and was not correlated with cetuximab sensitivity or HPV-status. Moreover, there was no correlation between baseline EGFR expression and the amount of cetuximab-induced ADCC. Importantly, the intrinsically cetuximab resistant cells demonstrated the highest level of EGFR internalization compared to the acquired resistant and cetuximab sensitive cell lines. Correlation analysis showed that the degree of EGFR internalization positively corelated with cetuximab-induced ADCC. In conclusion, we showed that induction of ADCC is maintained, independent of EGFR expression. Furthermore, internalization of EGFR might play a role in cetuximab resistance and ADCC-induction. Future research further unravelling this mechanism will provide a better understanding of mAb-based anti-EGFR therapies in the future. Citation Format: Hasan Baysal, Ines De Pauw, Hannah Zaryouh, Marc Peeters, Jan Baptist Vermorken, Evelien Smits, Filip Lardon, Julie Jacobs, An Wouters. Role of the epidermal growth factor receptor expression and internalization in cetuximab-induced antibody-dependent cellular cytotoxicity in head and neck squamous cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3371.

Protein-based, but not viral vector alone, HIV vaccine boosting drives an IgG1-biased polyfunctional humoral immune response.

The RV144 HIV-1 vaccine trial results showed moderate reduction in viral infections among vaccinees as well as induction of antibody-dependent cellular cytotoxicity and vaccine-specific IgG and IgG3 responses directed at variable loop regions 1 and 2 of the HIV envelope protein. However, with the recent failure of the HVTN 702 clinical trial, comprehensive profiling of humoral immune responses may provide insight for these disappointing results. One of the changes included in the HVTN 702 study was the addition of a late boost, aimed at augmenting peak immunity and durability. The companion vaccine trial RV305 was designed to permit the evaluation of the immunologic impact of late boosting with either the boosting protein antigen alone, the canarypox viral vector ALVAC alone, or a combination of both. Although previous data showed elevated levels of IgG antibodies in both boosting arms, regardless of ALVAC-HIV vector incorporation, the effect on shaping antibody effector function remains unclear. Thus, here we analyzed the antibody and functional profile induced by RV305 boosting regimens and found that although IgG1 levels increased in both arms that included protein boosting, IgG3 levels were reduced compared with the original RV144 vaccine strategy. Most functional responses increased upon protein boosting, regardless of the viral vector-priming agent incorporation. These data suggest that the addition of a late protein boost alone is sufficient to increase functionally potent vaccine-specific antibodies previously associated with reduced risk of infection with HIV.

Cetuximab-induced natural killer cell cytotoxicity in head and neck squamous cell carcinoma cell lines: investigation of the role of cetuximab sensitivity and HPV status

BackgroundThe epidermal growth factor receptor (EGFR) is overexpressed by 80–90% of squamous cell carcinoma of head and neck (HNSCC). In addition to inhibiting EGFR signal transduction, cetuximab, a monoclonal antibody targeting EGFR can also bind to fragment crystallisable domain of immunoglobulins G1 present on natural killer (NK), causing antibody-dependent cellular cytotoxicity (ADCC). However, presence of cetuximab resistance limits effective clinical management of HNSCC.MethodsIn this study, differences in induction of ADCC were investigated in a panel of ten HNSCC cell lines. Tumour cells were co-cultured with NK cells and monitored using the xCELLigence RTCA.ResultsWhile ADCC was not influenced by HPV status, hypoxia and cetuximab resistance did affect ADCC differentially. Intrinsic cetuximab-resistant cell lines showed an increased ADCC induction, whereas exposure to hypoxia reduced ADCC. Baseline EGFR expression was not correlated with ADCC. In contrast, EGFR internalisation following cetuximab treatment was positively correlated with ADCC.ConclusionThese findings support the possibility that resistance against cetuximab can be overcome by NK cell-based immune reactions. As such, it provides an incentive to combine cetuximab with immunotherapeutic approaches, thereby possibly enhancing the anti-tumoural immune responses and achieving greater clinical effectiveness of EGFR-targeting agents.

177Lu-Lilotomab Satetraxetan Has the Potential to Counteract Resistance to Rituximab in Non-Hodgkin Lymphoma.

Patients with non-Hodgkin lymphoma (NHL) who are treated with rituximab may develop resistant disease, often associated with changes in expression of CD20. The next-generation β-particle–emitting radioimmunoconjugate 177Lu-lilotomab-satetraxetan (Betalutin) was shown to up-regulate CD20 expression in different rituximab-sensitive NHL cell lines and to act synergistically with rituximab in a rituximab-sensitive NHL animal model. We hypothesized that 177Lu-lilotomab-satetraxetan may be used to reverse rituximab resistance in NHL. Methods: The rituximab-resistant Raji2R and the parental Raji cell lines were used. CD20 expression was measured by flow cytometry. Antibody-dependent cellular cytotoxicity (ADCC) was measured by a bioluminescence reporter assay. The efficacies of combined treatments with 177Lu-lilotomab-satetraxetan (150 or 350 MBq/kg) and rituximab (4 × 10 mg/kg) were compared with those of single agents or phosphate-buffered saline in a Raji2R-xenograft model. Cox regression and the Bliss independence model were used to assess synergism. Results: Rituximab binding in Raji2R cells was 36% ± 5% of that in the rituximab-sensitive Raji cells. 177Lu-lilotomab-satetraxetan treatment of Raji2R cells increased the binding to 53% ± 3% of the parental cell line. Rituximab ADCC induction in Raji2R cells was 20% ± 2% of that induced in Raji cells, whereas treatment with 177Lu-lilotomab-satetraxetan increased the ADCC induction to 30% ± 3% of that in Raji cells, representing a 50% increase (P < 0.05). The combination of rituximab with 350 MBq/kg 177Lu-lilotomab-satetraxetan synergistically suppressed Raji2R tumor growth in athymic Foxn1nu mice. Conclusion: 177Lu-lilotomab-satetraxetan has the potential to reverse rituximab resistance; it can increase rituximab binding and ADCC activity in vitro and can synergistically improve antitumor efficacy in vivo.

Fc functional antibody responses to adjuvanted versus unadjuvanted seasonal influenza vaccination in community-dwelling older adults

BackgroundSeasonal influenza vaccination with a standard trivalent influenza vaccine (TIV) induces a modest, and cross-reactive, Fc functional antibody response in older adults. Recent improvements to influenza vaccines include a quadrivalent influenza vaccine (QIV) and a TIV adjuvanted with the squalene-based oil-in-water emulsion MF59. MethodsPre- and post-vaccination serum samples from older adults vaccinated with QIV (n = 27) and adjuvanted TIV (n = 44) were studied using hemagglutination inhibition (HAI) assays and dimeric Fc-gamma receptor IIIa binding ELISAs, as a surrogate of antibody-dependent cellular cytotoxicity (ADCC). ResultsWe found that the unadjuvanted QIV elicited a stronger HAI response against the H1N1 vaccine virus than the adjuvanted TIV. Post-vaccination levels of HA-specific ADCC antibodies were similar for older adults vaccinated with QIV and adjuvanted TIV. The ADCC response to influenza vaccination was largely determined by pre-vaccination or baseline levels of these antibodies, with older adults with low baseline levels of ADCC activity demonstrating greater post-vaccination rises. ConclusionsIn this cohort of community-dwelling older adults, the QIV was at least as good as the adjuvanted TIV in the induction of ADCC and HAI responses. Further studies on how these antibody responses translate to efficacy in preventing influenza infections are warranted.

Abstract 3191: FT516, an off-the-shelf engineered NK cell therapeutic product for universal anti-tumor targeting strategy in combination with monoclonal antibodies

Abstract Monoclonal antibody (mAb) treatment is an effective therapeutic strategy for many cancer types, with significant opportunity to optimize natural killer (NK) cell and mAb interaction to improve antibody-dependent cellular cytotoxicity (ADCC). NK cells are critical mediators of ADCC, where they recognize and kill malignant cells coated with antibody through the Fc receptor CD16. However, NK cell function is often impaired in cancer patients, which limits the induction of ADCC in mAb therapy. To enhance ADCC in combination with commercialized mAb therapies, we have developed FT516; a novel, off-the-shelf NK cell immunotherapeutic engineered to uniformly express a high-affinity, non-cleavable version of CD16 (hnCD16). FT516 is manufactured from a renewable master induced pluripotent stem cell (iPSC) line with the potential to generate hundreds to thousands of doses of allogeneic NK cells uniformly expressing hnCD16 (hnCD16 iNK cells) per manufacturing run. In an in vivo xenograft model of disseminated lymphoma, FT516 reduced tumor burden below the limit of detection at day 28 after transplant when delivered in combination with rituximab, which was significantly more potent than peripheral blood NK cells (p = 0.03). This was attributed to enhanced CD16-mediated activation of FT516, as observed through improved calcium flux and enhanced activation of signaling pathways such as ERK (p = 0.016), LAT (p = 0.0007), and ZAP70 (p = 0.0003), leading to enhanced ADCC and cytokine production. FT516 also maintained tumor cell specificity, with preferential targeting of K562 leukemia cells when presented with a mixture of K562 and normal PBMC targets (p &amp;lt; 0.0001). We also explored strategies to further engineer therapeutic function to enhance FT516 efficacy. Combined expression of hnCD16 with an IL-15/IL-15ra fusion construct enhanced the persistence of iNK cells and allowed survival of up to 8 weeks in vivo without exogenous cytokine (p &amp;lt; 0.0001), with correlation to improved efficacy. In vitro modeling of FT516 with daratumumab demonstrated ADCC against multiple myeloma (MM) targets. However, as reported, daratumumab induced NK cell fratricide through binding of CD38 on NK cells. To rescue daratumumab-mediated fratricide, we specifically deleted CD38 at the iPSC level and demonstrated that fratricide was undetectable in hnCD16 CD38-/- iNK cells (&amp;lt;1% vs. 35% for peripheral blood NK). By avoiding fratricide, hnCD16 CD38-/- iNK cells had improved persistence and efficacy against MM cells in vitro and in a disseminated xenograft model of MM. These data support clinical development of FT516 in combination with rituximab for the treatment of B cell malignancies and demonstrate a targeting platform that enables further modifications to address challenges related to efficacy, safety, and persistence of allogeneic adoptive immunotherapies. Citation Format: Ryan Bjordahl, Huang Zhu, Paul Rogers, Svetlana Gaidarova, Moyar Q. Ge, Robert Blum, Frank Cichocki, Jode Goodridge, Helen Chu, Greg Bonello, Tom Lee, Brian Groff, Ramzey Abujarour, Bruce Walcheck, Jeffrey Miller, Dan Kaufman, Bahram Valamehr. FT516, an off-the-shelf engineered NK cell therapeutic product for universal anti-tumor targeting strategy in combination with monoclonal antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3191.