Killing Of Targets Research Articles

Preclinical Development of Inducible MyD88/CD40 (iMC)-Enhanced Chimeric Antigen Receptor Natural Killer (GoCAR-NK) Cells to Target BCMA+ Tumors

Background: Natural Killer (NK) cells possess potent innate anti-tumor cytotoxicity that can be augmented and focused by engineering with chimeric antigen receptors (CARs). Because NK cells do not express T cell receptors that can direct alloreactivity, they have potential as an off-the-shelf (OTS) cell therapy for the treatment of cancer. We recently demonstrated that a drug-inducible co-activation molecule (inducible MyD88/CD40; iMC) synergizes with transgenic IL-15 to boost CAR-NK cell proliferation, survival and anti-tumor cytotoxic effects (Blood Adv.4:1950 [2020]). Here, we describe the pre-clinical development of an OTS iMC/IL-15-enhanced CAR-NK cell platform targeting B cell maturation antigen (BCMA) for the treatment of multiple myeloma. Methods: NK cells were isolated from peripheral blood mononuclear cells by CD56+ selection, activated with IL-15 and microparticles conjugated with IL-21 and 4-1BB ligand. Activated NK cells were transduced with retrovirus encoding an optimized iMC and IL-15-expressing BCMA CAR construct (iMC-BCMA.z-IL15) where iMC signaling could be activated by exposure to rimiducid (Rim), a small molecule dimerizing ligand. Anti-tumor cytotoxicity and cytokine production was assessed using co-culture assays with control or modified CAR-NK cells against BCMA-expressing myeloma cells (NCIH929, RPMI8226, MM1S, U266 and NALM-6-BCMA). Additional experiments were performed with BCMA-edited cell lines (CRISPR/Cas9) to evaluate the innate cytotoxic potential of GoCAR-NK cells. In vivo anti-tumor efficacy and NK cell expansion was measured using immunodeficient NSG mice engrafted with 1.5 x 106 NCIH929-GFPffluc, MM1S-GFPffluc or THP1-GFPffluc cells followed by i.v. treatment with up to 1 x 107 BCMA GoCAR-NK cells. Tumor and NK cells were tracked via bioluminescence imaging. Results: Following IL-15 and IL-21/4-1BBL microparticle stimulation, NK cells were efficiently transduced (40-70%) and exhibited rapid ex vivo expansion (200-fold in 13 days). iMC-BCMA.CAR-IL15-modified NK cells exhibited potent cytotoxicity against BCMA+target cells compared with mock-transduced NK cells (MM1S, 58±4% versus 17±2%; Nalm-6-BCMA, 61±2% versus 19±6%) after 24 hours. Long-term (7 day) co-culture assays revealed the effect of iMC/IL-15 enhancement on NK cell potency, proliferation and cytokine production where iMC-BCMA.z-IL15-modified NK cells stimulated with Rim showed a >70% increase in tumor-specific killing compared to cells without iMC activation. Further, rimiducid-induced activation led to NK cell persistence and proliferation, 8.1±4.0-fold expansion compared to the start of the coculture. In comparison, there was an 80% reduction mock transduced NK cells or GoCAR-NK cells in cocultures without rimiducid. Induced-MC signaling also drove production of cytokines such as TNF-α, IFN-g (6.6X stimulation with 1 nM Rim relative to no drug), GMCSF, IP-10, and IL-13. In addition, activation of the iMC co-activation protein in combination with IL-15 secretion prevented NK cell exhaustion and led to retained functional activity of the modified GoCAR-NK cells for over 4-weeks in culture. In contrast, unmodified NK cells or modified GoCAR-NK cells without Rim exposure became functionally deficient. Of interest, a comparison of NK and T cells modified with the iMC/IL-15 BCMA CAR construct indicated that CAR-NK cells display more rapid target killing, which is further augmented by iMC-mediated cell signaling in the presence of Rim. Furthermore, GoCAR-NK cells were capable of lysis of BCMA-null target cells due to their innate anti-tumor activity. In vivo efficacy studies showed that neither iMC activation nor IL-15 secretion alone were sufficient to support CAR-NK cell engraftment in NSG mice but, in combination, they resulted in CAR-NK cell expansion and persistence. iMC/IL-15-enhanced BCMA GoCAR-NK cells proliferation was associated with improved control of tumor outgrowth in mice challenged with BCMA+ myeloma cells. Summary: These results indicate that the synergistic activity of iMC signaling combined with transgenic IL-15 production can enhance BCMA-specific CAR-NK cytotoxicity, cytokine production, long-term proliferation and persistence and may improve overall anti-tumor efficacy of a potential OTS cell therapy for the treatment of myeloma. Disclosures Wang: Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Duong:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Guerrero:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Mahendravada:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Sharp:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Brandt:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Gagliardi:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Foster:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company. Bayle:Bellicum Pharmaceuticals: Current Employment, Current equity holder in publicly-traded company.

A Feasibility and Safety Study of a Novel CD19-Directed Synthetic T-Cell Receptor and Antigen Receptor (STAR) T-Cell Therapy for Refractory and Relapsed (R/R) B Cell Acute Lymphoblastic Leukemia (B-ALL)

Introduction Chimeric antigen receptor (CAR) T -cell therapy has demonstrated high response rates among patients with B cell malignancies yet remission durability and safety could be improved. We have developed a novel double-chain chimeric receptor Synthetic T Cell Receptor and Antigen Receptor (STAR) consisting of 2 protein modules each containing an antibody light or heavy chain variable region, the T Cell Receptor (TCR) a or b chain constant region fused to the OX-40 co-stimulatory domain, with the 2 modules linked by a self-cleaving Furin-p2A sequence that allows the modules to be proteolytically separated and reconstituted (Fig. 1A). Here, we report pre-clinical and first-in-human phase I trial results of CD19 STAR-T cell therapy for CD19+ R/R B-ALL. Methods Peripheral blood (PB) mononuclear cells were obtained from healthy donors and patients for the pre-clinical and clinical studies, respectively. T-cells were transduced with the STAR lentiviral vector. A leukemia xenograft mouse model was used to assess the STAR T-cell antitumor function. For the clinical trial, from Dec. 2019 to Jun. 2020, 18 CD19+ R/R B-ALL patients (M/F 10:8) with a median age of 22.5 years (range: 6-68) were enrolled (NCT03953599). Patients received a conditioning regimen of IV fludarabine (25mg/m2/d) and cyclophosphamide (250mg/m2/d) for 3 days followed by a single STAR T-cell infusion. Once patients achieved complete remission (CR), they were given the option to proceed to consolidation allogeneic hematopoietic stem cell transplantation (allo-HSCT) or not. Results In preclinical studies, we found CD19 STAR T-cells to be superior to conventional CAR (BBz CAR) measured by the following parameters: 1) faster/stronger T-cell activation within 3 hours (76.67±2.621% vs 46.4±9.318%; p=0.0253); 2) higher cytokine production (4100.92±174.4 pg/ml vs 2556.78±563.39 pg/ml; p<0.05, Fig.1B) ;3) superior target killing ability (effector: target [E: T] ratio=1:1, 50.39±1.74% vs 60.85±1.52%, p<0.05. E:T ratio>1:1, p<0.01, Fig.1B); 4) robust elimination of B-ALL in a xenograft mouse model, where a lower E:T ratio was sufficient to eliminate an equal number of tumor cells (E:T ratio =1:1, STAR vs. BBz-CAR, p<0.01, Fig.1C). In the phase I trial, the median observation time was 69 (20-180) days. The median pre-treatment bone marrow (BM) blast level was 7.0% (0.1%-86.6%). All 18 patients received a single infusion of STAR T-cells at a median dose of 1×106/kg (5×105/kg-2.5×106/kg): low dose (5×105/kg) (n=3), medium dose (1×106/kg) (n=8) and high-dose (2-2.5×106/kg) (n=7). Three early enrollees subsequently received a second consolidation infusion of STAR T-cells at 1×106/kg (n=2) and 2×106/kg (n=1). The median STAR T-cell production time was 9 (7-13) days with a transduction efficacy of 57.4% (41.0%-78.2%). Two weeks post STAR T-cell infusion, 18/18 (100%) patients achieved CR with a negative minimal residual disease (MRD) status. After a median of 57 (43-66) days following STAR T-cell therapy, 8/18 patients made a choice to pursue consolidation allo-HSCT and all have remained in CR after a median follow-up of 110 (75-180) days. Of the 10 patients who did not undergo allo-HSCT, 1 relapsed on day 58 and died from relapse on day 63. This patient had a pre-CAR T-cell BM blast level of 86.6% with central nervous system leukemia. Another patient became MRD-positive with 0.09% blasts on day 30 per flow cytometry (FCM). The other 8 patients have remained in CR. Despite the achievement of a high CR rate, cytokine release syndrome (CRS) occurred only in 10/18 (55.6%) patients with 8 Grade I, and 2 Grade II CRS. Two patients developed Grade III neurotoxicity. After STAR T-cell infusion, CD19 STAR T-cells in PB were followed by qPCR and FCM. We saw high in vivo proliferation and persistence regardless of the infusion dose. The median peak level was reached on day 8.5 (day 4-10) with 4.9×104 (0.104-175×104) copy number/ug PB genomic DNA detectable at 6 months. Conclusion This study demonstrates the superiority of STAR T-cells compared to conventional CAR T-cells in terms of signaling capacity, cytokine production capability and anti-tumor potency in an animal model. The Phase I first-in-human study demonstrated technical feasibility, clinical safety and efficacy of STAR-T in treating CD19+ R/R B-ALL. A high CR could be achieved on day 14 with low toxicity. Longer-term observation of these patients and studies of larger patient cohorts are warranted. Disclosures No relevant conflicts of interest to declare.

Potential of Sea-CD70 for the Treatment of Myeloid Leukemia

CD70 (CD27L) is a member of the tumor necrosis factor superfamily transiently expressed on activated adaptive and innate immune cells. Engagement of CD70 to the co-stimulatory receptor CD27, which is present on adaptive immune cells, promotes antigen-specific T cell responses. Both CD70 and CD27 have been reported to be aberrantly expressed on AML and MDS blasts, but are absent on normal hematopoietic progenitor cells, making them appealing therapeutic targets. CD70-CD27 interactions, working through auto- and/or paracrine signaling, can induce a stem-like signature and stimulate the proliferation of leukemic blasts. In addition, the CD70-CD27 interaction drives inflammatory cytokine production from both CD27 and CD70 pathways, resulting in cytokine production from leukemic blasts and the myeloid cells. Inflammatory signaling is a critical component of the crosstalk between hematopoietic stem and progenitor cells and their microenvironment during infection or hematopoietic stress. However, chronic inflammation can suppress normal hematopoietic stem cell function and eventually lead to bone marrow failure. Similarly, preleukemic and leukemic cell' interactions with the bone marrow microenvironment can induce secretion of pro-inflammatory factors, which in turn, could suppress normal blood cell formation. Therefore, blockade of the CD70-CD27 inflammatory signal pathway could help restore normal hematopoiesis, limit immune evasion, and increase the immune directed responses in MDS and AML. SEA-CD70 is a humanized, nonfucosylated monoclonal antibody targeting CD70. SEA-CD70 retains the ability to block CD27 mediated signaling and binds significantly better than the fucosylated parent to the FcγRIIIa receptor. SEA-CD70 mediates potent target killing through Fc-dependent antibody effector functions, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). SEA-CD70 can also disrupt CD70-CD27 signaling and could block cellular proliferation and survival of blast cells in vitro. SEA-CD70 may also inhibit the inflammatory signals originating from the interaction between the tumor microenvironment and leukemic blasts. In vivo, SEA-CD70 delayed tumor growth and increased survival in subcutaneous AML xenograft mouse tumor models both as a single agent and when combined with standard of care (SOC) agents. Overall, our data highlight the therapeutic potential of SEA-CD70 for the treatment of AML and MDS patients. Disclosures Diolaiti: Seattle Genetics:Current Employment, Current equity holder in publicly-traded company.Haass:Seattle Genetics:Current Employment, Current equity holder in publicly-traded company.Ulrich:Seattle Genetics:Current Employment, Current equity holder in publicly-traded company.Chen:Seattlke Genetics:Current Employment, Current equity holder in publicly-traded company.Ho:Seattle Genetics:Current Employment, Current equity holder in publicly-traded company.Gardai:Seattle genetics:Current Employment, Current equity holder in publicly-traded company.

Large Scale Ex Vivo Expansion of Γδ T Cells Using Artificial Antigen Presenting Cells for the Treatment of Acute Myeloid Leukemia

Patients with relapsed or refractory acute myeloid leukemia (AML) are at increased risk of mortality. Higher γδ T cell count in a bone marrow or peripheral blood of patients with leukemia is associated with better survival. However, γδ T cells are rare in the blood and functionally impaired or exhausted in patients with malignancies. Promising results are reported on the treatment of various malignancies with in vivo expansion of autologous γδ T cells using zoledronic acid (zol) and IL-2. Here we demonstrated that zol and IL-2, in combination with a novel genetically engineered K562 CD3/CD137L/CD28/IL15RA quadruplet artificial antigen presenting cell (aAPC), efficiently expand allogeneic donor-derived γδ T cells using a GMP-compliant protocol sufficient to achieve cell doses for future clinical use. We achieved a 633-fold expansion of γδ T cells after day 10 of co-culture with aAPC, the majority of which exhibited central (47%) and effector (43%) memory phenotypes. Additionally, >90% of the expanded γδ T cells expressed NKG2D, while they have low cell surface expression of PD1 and LAG2 inhibitory checkpoint receptors. In vitro real-time cytotoxicity analysis showed that expanded, previously cryopreserved, γδ T cells were effective in killing target cells. Our results demonstrate that large scale ex vivo expansion of donor-derived γδ T cells can be achieved with the use of CD3/CD137L/CD28/IL15RA quadruplet aAPC and zol/IL-2 for clinical application as promising antineoplastic immunotherapy. Figure 1 Disclosures Lancet: Abbvie: Consultancy; Agios Pharmaceuticals: Consultancy, Honoraria; Astellas Pharma: Consultancy; Celgene: Consultancy, Research Funding; Daiichi Sankyo: Consultancy; ElevateBio Management: Consultancy; Jazz Pharmaceuticals: Consultancy; Pfizer: Consultancy. Sallman:Celgene, Jazz Pharma: Research Funding; Agios, Bristol Myers Squibb, Celyad Oncology, Incyte, Intellia Therapeutics, Kite Pharma, Novartis, Syndax: Consultancy. Bejanyan:Kiadis Pharma: Membership on an entity's Board of Directors or advisory committees.

IL-15 superagonist N-803 improves IFN\u03b3 production and killing of leukemia and ovarian cancer cells by CD34+\u2009progenitor-derived NK cells

Allogeneic natural killer (NK) cell transfer is a potential immunotherapy to eliminate and control cancer. A promising source are CD34 + hematopoietic progenitor cells (HPCs), since large numbers of cytotoxic NK cells can be generated. Effective boosting of NK cell function can be achieved by interleukin (IL)-15. However, its in vivo half-life is short and potent trans-presentation by IL-15 receptor α (IL-15Rα) is absent. Therefore, ImmunityBio developed IL-15 superagonist N-803, which combines IL-15 with an activating mutation, an IL-15Rα sushi domain for trans-presentation, and IgG1-Fc for increased half-life. Here, we investigated whether and how N-803 improves HPC-NK cell functionality in leukemia and ovarian cancer (OC) models in vitro and in vivo in OC-bearing immunodeficient mice. We used flow cytometry-based assays, enzyme-linked immunosorbent assay, microscopy-based serial killing assays, and bioluminescence imaging, for in vitro and in vivo experiments. N-803 increased HPC-NK cell proliferation and interferon (IFN)γ production. On leukemia cells, co-culture with HPC-NK cells and N-803 increased ICAM-1 expression. Furthermore, N-803 improved HPC-NK cell-mediated (serial) leukemia killing. Treating OC spheroids with HPC-NK cells and N-803 increased IFNγ-induced CXCL10 secretion, and target killing after prolonged exposure. In immunodeficient mice bearing human OC, N-803 supported HPC-NK cell persistence in combination with total human immunoglobulins to prevent Fc-mediated HPC-NK cell depletion. Moreover, this combination treatment decreased tumor growth. In conclusion, N-803 is a promising IL-15-based compound that boosts HPC-NK cell expansion and functionality in vitro and in vivo. Adding N-803 to HPC-NK cell therapy could improve cancer immunotherapy.

Development of novel benzimidazole-derived neddylation inhibitors for suppressing tumor growth invitro and invivo.

Ubiquitin-like protein neddylation is overactivated in various human cancers and correlates with disease progression, and targeting this pathway represents a valuable therapeutic strategy. Our previous work disclosed an antihypertensive agent, candesartan cilexetic (CDC), serves as a novel neddylation inhibitor for suppressing tumor growth by targeting Nedd8-activating enzyme (NAE). In this study, 42 benzimidazole derivatives were designed and synthesized based on lead compound CDC to improve the neddylation inhibition and anticancer efficacy. Optimal benzimidazole-derived 35 displayed superior neddylation inhibition in enzyme assay compared to CDC (IC50=5.51μM vs 16.43μM), along with promising target inhibitory activity and killing selectivity in cancer cell. The results of cellular mechanism research combined with tumor growth suppression in human lung cancer cell A549 invivo, accompanied with docking model, revealed that 35 has the potential to be developed as a promising neddylation inhibitor for anticancer therapy.

The surface dominant antigen MUC1 is required for colorectal cancer stem cell vaccine to exert anti-tumor efficacy

Colorectal cancer (CRC), initiated and maintained by colorectal cancer stem cells (CCSCs), ranks the third most common cancers and has drawn wide attentions worldwide. Therefore, targeting clearance of CCSCs has become an important strategy of CRC immunotherapy. Mucin1 (MUC1) is a tumor-associated cell surface antigen of CRC, but its role in CCSC vaccine remains unclear. In the study, we demonstrated that MUC1 may be a dominant antigen to exert antitumor immunity in CCSC vaccine. First, CCSCs were enriched from CT26 cell line via a serum-free sphere formation approach, and were identified by detecting expression of CD133, ALDH, and ALCAM. Then, the isolated CCSCs were frozen for 30 min and thawed for 30 min to prepare the cell lysate. The specific anti-MUC1 antibody was added to the cell lysate to neutralize the dominant antigen MUC1. Finally, mice were subcutaneously immunized with the cell lysate, followed by a challenge with CT26 cells at one week after final vaccination. Attractively, CCSC vaccine significantly activated the NK cells, T cells, and B cells, resulting in inhibiting the tumor growth via a target killing of CCSCs as evidenced by a decrease of CD133+cells in tumor compared to CCSC vaccine with specific anti-MUC1 antibody. In addition, CCSC vaccine reduced expression of inflammatory factors in vaccinated mice. As expected, neutralizing antibody against MUC1 significantly impaired the antitumor efficacy of CCSC vaccine. Overall, CCSC vaccine could serve as a potent vaccine for CRC immunotherapy. The surface dominant antigen MUC1 may play a key role in regulating immunogenicity of CCSCs.

Potent Cytolytic Activity and Specific IL15 Delivery in a Second-Generation Trispecific Killer Engager.

Natural killer (NK) cells are potent immune modulators that can quickly lyse tumor cells and elicit inflammatory responses. These characteristics make them ideal candidates for immunotherapy. However, unlike T cells, NK cells do not possess clonotypic receptors capable of specific antigen recognition and cannot expand via activating receptor signals alone. To enable NK cells with these capabilities, we created and have previously described a tri-specific killer engager (TriKE) platform capable of inducing antigen specificity and cytokine-mediated NK-cell expansion. TriKE molecules have three arms: (i) a single-chain variable fragment (scFv) against the activating receptor CD16 on NK cells to trigger NK-cell activation, (ii) an scFv against a tumor-associated antigen (CD33 here) to induce specific tumor target recognition, and (iii) an IL15 moiety to trigger NK-cell expansion and priming. Here, we demonstrate that by modifying the anti-CD16 scFv with a humanized single-domain antibody against CD16, we improved TriKE functionality. A CD33-targeting second-generation TriKE induced stronger and more specific NK-cell proliferation without T-cell stimulation, enhanced in vitro NK-cell activation and killing of CD33-expressing targets, and improved tumor control in preclinical mouse models. Given these improved functional characteristics, we propose rapid translation of second-generation TriKEs into the clinic.

Antimicrobial Synergism Toward Pseudomonas aeruginosa by Gallium(III) and Inorganic Nitrite.

The ubiquitous involvement of key iron-containing metalloenzymes in metabolism is reflected in the dependence of virtually all bacteria on iron for growth and, thereby, potentially provides multiple biomolecular targets for antimicrobial killing. We hypothesized that nitrosative stress, which induces damage to iron metalloproteins, would sensitize bacteria to the ferric iron mimic gallium(III) (Ga3+), potentially providing a novel therapeutic combination. Using both laboratory and clinical isolates of Pseudomonas aeruginosa, we herein demonstrate that Ga3+ and sodium nitrite synergistically inhibit bacterial growth under both aerobic and anaerobic conditions. Nitric oxide also potentiated the antimicrobial effect of Ga3+. Because many chronic pulmonary infections are found as biofilms and biofilms have very high antibiotic tolerance, we then tested the combination against biofilms grown on plastic surfaces, as well as the apical surface of airway epithelial cells. Ga3+ and sodium nitrite had synergistic antimicrobial activity against both biofilms grown on plastic and on airway epithelial cell. Both Ga3+ and various NO donors are (independently) in clinical development as potential antimicrobials, however, we now propose the combination to have some particular advantages, while anticipating it should ultimately prove similarly safe for translation to treatment of human disease.

Abstract 2824: In vitro tumor killing assays for predicting cellular therapeutic efficacy

Abstract Cellular immunotherapy is emerging as a fifth pillar of cancer treatment. Clinical efficacy has been proven for a variety of cancers; however, its true potential has yet to be unlocked. Development of reliable and mechanistically appropriate in vitro screening assays that recapitulate in vivo immune-tumor interactions have been outpaced by in vivo living cell therapy efficacy models. Here we describe a range of in vitro primary human assays to model tumor killing by immune cells. This platform addresses multiple anti-tumor immune effector pathways and has been validated with standard of care therapeutics. Fluorescently labelled target cells (PDX-cell lines, tumor cell lines or human primary/iPSC derived cells) screened for relevant antigen expression were cultured in monolayer or spheroid forms and co-cultured with the cellular therapeutic. On target killing by effectors is driven by binding of the TCR or CAR to its cognate antigen (MHC/peptide or protein, respectively) with readouts of cell killing utilising live cell imaging (IncuCyte) and flow cytometry based approaches to measure target cell growth and apoptosis. Additional analysis of soluble mediators can determine the extent of effector cell activation. To discriminate between ‘on' and ‘off' target killing by cellular therapeutics, primary/iPSC-derived normal cell types representative of different tissue types were screened for expression of an HLA subtype capable of binding exogenously applied tumor-associated antigen (TAA) prior to co-culture. Under these conditions in the case of a TCR based cellular therapeutic, efficacy can be screened for, or in the absence of the putative TAA expression, the extent of off-target killing determined. Enhancement of tumor targeting and killing by immune cells is an attractive therapeutic modality partly due to the clinical success of checkpoint inhibitors which can enhance the activation and effector function of endogenous T/NK cells or cellular therapeutics. The presented data highlight the importance of assays which can recapitulate tumor-immune interactions and include immune effector pathways known to potentiate anti-tumor immune responses. These assays represent valuable screening tools capable of informing cellular therapeutic target selection and refinement before moving to more complex in vivo models. Citation Format: Robert Nunan, Michelle Yap, Enrique Garcia-Alvarez, Marie Carkill, Anna Pascoe, Louise Brackenbury, Jezrom Self-Fordham, S. Rhiannon Jenkinson. In vitro tumor killing assays for predicting cellular therapeutic efficacy [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 2824.

Abstract 2218: High affinity and cleavage resistant CD16 enhances Trastuzumab mediated killing of gastric cancer targets by human placental CD34+-derived natural killer cells

Abstract Introduction: When targeting tumors with monoclonal antibodies, natural killer (NK) cells are key effectors of antibody dependent cellular cytotoxicity (ADCC) following recognition of antibody Fc by CD16. Celularity has developed a novel proprietary technology platform that enables production of an allogeneic, off-the-shelf, placental CD34+-derived NK cell therapy for the treatment of hematologic and solid tumor malignancies. Here we report the genetic modification of CD16 in NK cells for high binding affinity to IgG and resistance to protease cleavage, together with functional evaluation of anti-tumor ADCC activity against epidermal growth factor receptor 2 (HER2) positive gastric cancer cells in combination with Trastuzumab (anti-Her2). Methods: Human placental CD34+ cells were transduced with lentivirus expressing a high binding affinity (158Val) and protease resistant (197Pro) CD16 variant (CD16VP) and cultured for 35 days in the presence of cytokines, including thrombopoietin, SCF, Flt3 ligand, IL-7, IL-15 and IL-2, to generate CD16VP cells. The tumorigenic activity of CD16VP cells against HER2-positive gastric cancer cell lines NCI-N87 and OE19 was assessed in combination with Trastuzumab. ADCC activity was measured by real-time xCELLigence, and cytokine secretion by Luminex. The kinase inhibitors PD98059 (MEK/ERK), SB203580 (p38 MAPK), SP600125 (JNK), and Wortmannin (PI3K) were used to study the molecular mechanisms underlying cytotoxicity of CD16VP cells against gastric cancer. Results and conclusion: High transduction efficiency was achieved in multiple placental CD34+ donors with an average of 64.6 ± 10.3% (n=8) CD16 expression on NK cells compared to 12.1 ± 3.3% (n=8) on non-transduced cells. These cells expanded [7095 ± 2998-fold (n=8)] and differentiated into NK cells with >90% purity (CD56+CD3-). While treatment of PMA/ionomycin for 4 hours resulted in >89% CD16 cleavage on non-transduced cells, <11% cleavage was observed on CD16VP cells, demonstrating shedding resistance. CD16VP cells in the presence of Trastuzumab compared to IgG control, showed enhanced lysis of NCI-N87 and OE19 targets (97 ± 7% and 95 ± 2% vs. 55 ± 19% and 42 ± 14% respectively, p<0.01), secreted higher levels of GM-CSF, IFN-γ, and TNF-α, and demonstrated increased degranulation against OE19. The ADCC mediated cytotoxicity and degranulation were PI3K and JNK pathway-dependent as Wortmannin decreased ADCC by 82.2 ± 17.7% and degranulation by 43.9 ± 1.9%, and SP600125 decreased degranulation by 72.3 ± 1.2%. Our results demonstrate that CD16VP cells have enhanced Trastuzumab-mediated ADCC activity against gastric cancer tumor cell lines with resistance to CD16 cleavage. Development of CD16VP cells provides a combination therapeutic option by harnessing the anti-tumor activities of both targeted biologics and innate cytotoxicity of NK cells. Citation Format: Irene Raitman, Salvatore Rotondo, Tanel Mahlakõiv, Xuan Guo, Andrea DiFiglia, Hemlata Rana, Qian Ye, Srinivas Somanchi, William van der Touw, Lin Kang, Robert Hariri, Xiaokui Zhang. High affinity and cleavage resistant CD16 enhances Trastuzumab mediated killing of gastric cancer targets by human placental CD34+-derived natural killer cells [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 2218.

Abstract 3333: EMT-6 tumor conditioned Breg cells inhibit NK cell proliferation and cytotoxic activity

Abstract Purpose: Breg (B regulatory) cells have been implicated in suppression of anti-tumor response in murine and human solid tumors. Prior studies in our laboratory demonstrated that murine EMT-6 breast carcinoma is rejected in B cell deficient mice (BCDM), but not in wild type (WT) mice, due to an enhanced immune response. Tumor infiltrating B cells (TIL-B), and normal splenic B cells co-cultured with EMT-6 (EMT6-B), express LAP/TGF-β, PD-L1, and suppress CD8+ and NK cell proliferation in vitro. Increased CD8+ and NK cell infiltration into the tumor bed is seen in BCDM. BCDM tumor rejection is abrogated by NK depletion. We studied EMT6-B effects on NK cell phenotype, proliferation and cytokine expression in vitro and in vivo. Experimental design: Normal splenic B cells were co-cultured with mitomycin C treated EMT-6, and Breg phenotype, and effects on NK cell phenotype and proliferation and cytokine function were studied in vitro and in vivo. Results: EMT6-B but not WT splenic B cells inhibited CFSE labeled CD49b+ NK cell proliferation in response to IL-15 in dose dependent fashion. EMT-6-B suppressed expression of CD226 and NKG2D activating receptors on NK cells, and increased expression of PD-1 and PD-L1 respectively. EMT6-B suppressed the induction of IFNγ+/CD49b+ NK cells following PMA/ION stimulation as assayed by intracellular flow cytometry (10%±1.2 to 2%±0.5) and also suppressed IL-2 induced induction of IFNγ+/CD49b+ NK cells (70%±5 to 20%±7.8). EMT-6 and CT26 colon carcinoma conditioned B cells, but not C166 endothelial cell conditioned B cells suppressed NK degranulation (IFNγ+/CD107a+ NK cells). EMT6-B inhibited YAC-1 cell induced NK cell degranulation, and killing of YAC-1 targets, more effectively than naïve B cells (40%±6.2 to 18%±5.1) (P=0.05). NK suppression was inhibited by anti-PD-L1, and anti-TGF-β antibody. EMT6-B expressed increased FasL compared to splenic B cells, and induced NK apoptosis as measured by 7AAD/Annexin-V staining. Blocking antibody to FasL decreased NK apoptosis, and restored NK cell proliferation. Infiltrating NK cells in the EMT6 tumor bed demonstrated increased PD-1 compared to splenic and TDLN NK cells, and higher levels of IFN-γ, CD107a, and Granzyme B in BCDM vs. WT mice. EMT6 expressed high levels of CD155 NK inhibitory ligand compared to C166 endothelial cells. The EMT-6 tumor bed contained higher levels of CD19+CD155+ B cells (22% / tumor bed vs 6% / TDLN, vs 9%/ spleen). BCDM expressed higher levels of CD226+/Ki67+ NK cells in spleen compared to WT splenic NK cells. Antibodies to Fas-L, TGF-beta, and PD-L1 partially restored anti-tumor response in WT mice and decreased tumor growth. Conclusions: EMT-6 TIL-B or normal B cells conditioned by EMT-6 coculture acquire an NK suppressive phenotype which inhibits NK cell activation, proliferation, degranulation and cytotoxic function. Targeting of Breg-NK interactions may improve anti-tumor immune response. Citation Format: Yu Zhang, Muhammad Husnain, Zhifen Luo, Mahmood Al Bayati, Joseph D. Rosenblatt. EMT-6 tumor conditioned Breg cells inhibit NK cell proliferation and cytotoxic activity [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 3333.

Abstract 3426: A synthetic lethality approach to eradicate AML via synergistic activation of pro-apoptotic p53 by MDM2 and BET inhibitors

Abstract Acute Myeloid Leukemia (AML) is a typically-lethal molecularly heterogeneous disease, with few broad-spectrum therapeutic targets. Unusually, over 90% of AML patients retain wild type TP53, encoding pro-apoptotic tumor suppressor p53. However, wild-type p53 functions are frequently suppressed by MDM2, an E3 ubiquitin ligase that targets p53 for proteasomal degradation. MDM2 inhibitors (MDM2i), which activate wild-type p53, show encouraging pre-clinical activity, but limited clinical activity. In an effort to find targets that synergize with p53 activation and minimize toxicity via MDM2i, we performed a cell-based synthetic lethal drug screen and a CRISPR viability screen. By integrating the results of these two screens, we found inhibition of BRD4 activates p53 and its target genes. BRD4 (Bromodomain-containing protein 4) is a member of the bromodomain and extraterminal (BET) family proteins, which has typically been reported to activate genes, such as c-MYC, BCL2 and CDK4/6. However, we unexpectedly reveal that BRD4 acts as a transcriptional repressor of p53 target genes. Our combined therapy of MDM2i and BETi is synergistically lethal to human AML cell lines harboring wild type p53 in vitro, against two mouse models of AML in vivo, and against several primary human patient blasts in vitro. Synergistic cell killing was associated with synergistic activation of p53 target genes, and cell killing and p53 target gene expression. Taken together, our data show BRD4 represses p53-mediated transcription activation and apoptosis in AML. Therefore, targetable wild-type p53 and a transcriptional repressor function of BRD4 together represent a potential broad-spectrum synthetic therapeutic vulnerability for AML. Citation Format: Sha Li, Anne Latif, Ashley Newcombe, Kathryn Gilroy, Neil Robertson, Xue Lei, Darren Finlay, Helen Stewart, Karina Barbosa, Brian Higgins, Tim Chevassut, Xu Huang, Mhairi Copland, Karen Keeshan, Ani Deshpande, Peter Adams. A synthetic lethality approach to eradicate AML via synergistic activation of pro-apoptotic p53 by MDM2 and BET inhibitors [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 3426.

Abstract 3251: Assessment of NK cell-mediated killing and phenotypic analysis using advanced flow cytometry and an optimized multiplexed assay

Abstract In this study, a novel multiplexed assay was developed that simultaneously measures NK cell phenotype and function in relation to tumor target killing. Natural Killer (NK) cells are an essential part of the innate immune system, interface with the adaptive immune system, and play a critical role in tumor immune surveillance and anti-tumor responses. Although chimeric antigen receptor (CAR)-modified T cells have proven to be highly effective as an anti-cancer therapeutic, there are potential problems associated with their use, particularly the risk of inducing graft-versus-host disease (GVHD) resulting in aberrant cytokine release. In contrast to T cells, NK cells are potent cytotoxic effector cells that do not require MHC restriction and have a low risk of inducing GVHD. Recent advances in the development of CAR-modified NK cells have shown great promise for clinical utilization in cancer immunotherapy with capability for both direct tumor killing as well as for use in combination therapy with monoclonal antibodies to boost NK cell antibody-dependent cell-mediated cytotoxicity (ADCC). A critical process in the development of new NK cell-mediated therapeutics is the ability to expediently assay, screen, and analyze data for NK cell activation and tumor killing. To address this need, a novel multiplexed assay was developed that measures tumor target cell killing, target-dependent expression of activation markers (CD69 and CD25), and the quantitation of secreted granzyme B, IFNγ, and TNFα in a single well of a microtiter plate. To validate the assay, a direct NK cell-tumor cell killing model was used. Purified human NK cells were mixed with target cells at different ratios. Tumor cell killing, NK cell activation status, and quantification of secreted proteins were measured at 4 and 24 hours after co-culture. Assay data acquisition was performed on Intellicyt iQue3® platform for advanced flow cytometry. Data analysis and visualization was performed using the integrated ForeCyt® software package. Tumor cell killing along with granzyme B release, was evident by 4 hours following co-culture, and both were increased with the increase in effector to target ratio (E:T). Killing was further enhanced when NK cells were stimulated with IL-2 and IL-15. As expected, an increase in CD69 and CD25 expression was also observed following cytokine stimulation with further increase upon co-culture of NK cells with tumor cell targets, along with increased levels of secreted IFNγ and TNFα. Further validation of the assay using an ADCC model was also performed. These data show that a miniaturized, multiplexed NK cell killing assay, combined with high throughput flow cytometry, is a powerful tool to rapidly screen CAR-NK cell effector functions and other NK cell based therapeutics. Citation Format: Julie Lovchik, Sarita Chauhan, John O'Rourke. Assessment of NK cell-mediated killing and phenotypic analysis using advanced flow cytometry and an optimized multiplexed assay [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 3251.

Colorectal cancer stem cell vaccine with high expression of MUC1 serves as a novel prophylactic vaccine for colorectal cancer

Targeted clearance of colorectal cancer stem cells (CCSCs) has become a novel strategy for tumor immunotherapy. Molecule mucin1 (MUC1) is one of targetable cell surface antigens in CCSCs. However, the critical role of MUC1 in anti-tumor effects of CCSC vaccine remains unclear. In the present study, we showed that MUC1 may be required for CCSC vaccine to exert tumor immunity. CD133+CCSCs were isolated from CT26 cell line using a magnetic-activated cell sorting system, and MUC1 shRNA or recombinant plasmid was further used to decrease or increase the expression of MUC1 in CD133+CCSCs. Mice were subcutaneously immunized with the CCSC lysates, MUC1 knockin CCSCs, and MUC1 knockdown CCSCs respectively, followed by a challenge with CT26 cells. We found that CCSC vaccine significantly reduced the tumor growth via a target killing of CCSCs as evidenced by a decrease of CD133+ cells and ALDH+ cells in tumors. Moreover, CCSC vaccine markedly increased the cytotoxicity of NK cells and the splenocytes, and promoted the release of IFN-γ, Perforin, and Granzyme B, and also reduced the TGF-β1 expression. Additionally, CCSC vaccination enhanced the antibody production and decreased the myeloid derived suppressor cells and Treg subsets. More importantly, MUC1 knockdown partly impaired the anti-tumor efficacy of CCSC vaccine, whereas MUC1 overexpression dramatically enhanced the CCSC vaccine immunity. Overall, these results reveal a novel role and molecular mechanisms of MUC1 in CCSC vaccine against colorectal cancer.

Heterogeneous, delayed-onset killing by multiple-hitting T cells: Stochastic simulations to assess methods for analysis of imaging data.

Although quantitative insights into the killing behaviour of Cytotoxic T Lymphocytes (CTLs) are necessary for the rational design of immune-based therapies, CTL killing function remains insufficiently characterised. One established model of CTL killing treats CTL cytotoxicity as a Poisson process, based on the assumption that CTLs serially kill antigen-presenting target cells via delivery of lethal hits, each lethal hit corresponding to a single injection of cytotoxic proteins into the target cell cytoplasm. Contradicting this model, a recent in vitro study of individual CTLs killing targets over a 12-hour period found significantly greater heterogeneity in CTL killing performance than predicted by Poisson-based killing. The observed killing process was dynamic and varied between CTLs, with the best performing CTLs exhibiting a marked increase in killing during the final hours of the experiments, along with a "burst killing" kinetic. Despite a search for potential differences between CTLs, no mechanistic explanation for the heterogeneous killing kinetics was found. Here we have used stochastic simulations to assess whether target cells might require multiple hits from CTLs before undergoing apoptosis, in order to verify whether multiple-hitting could explain the late onset, burst killing dynamics observed in vitro. We found that multiple-hitting from CTLs was entirely consistent with the observed killing kinetics. Moreover, the number of available targets and the spatiotemporal kinetics of CTL:target interactions influenced the realised CTL killing rate. We subsequently used realistic, spatial simulations to assess methods for estimating the hitting rate and the number of hits required for target death, to be applied to microscopy data of individual CTLs killing targets. We found that measuring the cumulative duration of individual contacts that targets have with CTLs would substantially improve accuracy when estimating the killing kinetics of CTLs.

Gamma-Delta CAR-T Cells Show CAR-Directed and Independent Activity Against Leukemia.

Autologous T cells engineered to express a chimeric antigen receptor (CAR) against the CD19 antigen are in the frontline of contemporary hemato-oncology therapies, leading to high remission rates in B-cell malignancies. Although effective, major obstacles involve the complex and costly individualized manufacturing process, and CD19 target antigen loss or modulation leading to resistant and relapse following CAR therapy. A potential solution for these limitations is the use of donor-derived γδT cells as a CAR backbone. γδT cells lack allogenecity and are safely used in haploidentical transplants. Moreover, γδT cells are known to mediate natural anti-tumor responses. Here, we describe a 14-day production process initiated from peripheral-blood mononuclear cells, leading to a median 185-fold expansion of γδ T cells with high purity (>98% CD3+ and >99% γδTCR+). CAR transduction efficacy of γδ T cells was equally high when compared to standard CAR-T cells (60.5 ± 13.2 and 65.3 ± 18.3%, respectively). CD19-directed γδCAR-T cells were effective against CD19+ cell lines in vitro and in vivo, showing cytokine production, direct target killing, and clearance of bone marrow leukemic cells in an NSG model. Multiple injections of γδCAR-T cells and priming of mice with zoledronate lead to enhanced tumor reduction in vivo. Unlike standard CD19 CAR-T cells, γδCAR-T cells were able to target CD19 antigen negative leukemia cells, an effect that was enhanced after priming the cells with zoledronate. In conclusion, γδCAR-T cell production is feasible and leads to highly pure and efficient effector cells. γδCAR-T cell may provide a promising platform in the allogeneic setting, and may target leukemic cells also after antigen loss.

Control of Viral Infection by Natural Killer Cell Inhibitory Receptors

SUMMARYMajor histocompatibility complex class I (MHC-I)-restricted immune responses are largely attributed to cytotoxic T lymphocytes (CTLs). However, natural killer (NK) cells, as predicted by the missing-self hypothesis, have opposing requirements for MHC-I, suggesting that they may also demonstrate MHC-I-restricted effects. In mice, the Ly49 inhibitory receptors prevent NK cell killing of missing-self targets in effector responses, and they have a proposed second function in licensing or educating NK cells via self-MHC-I in vivo. Here we show MHC-I-restricted control of murine cytomegalovirus (MCMV) infection in vivo that is NK cell dependent. Using mice lacking specific Ly49 receptors, we show that control of MCMV requires inhibitory Ly49 receptors and an inhibitory signaling motif and the capacity for MCMV to downregulate MHC-I. Taken together, these data provide definitive evidence that the inhibitory receptors are required for missing-self rejection and are relevant to MHC-I-restricted NK cell control of a viral infection in vivo.

MUC1 plays an essential role in tumor immunity of colorectal cancer stem cell vaccine

Increasing knowledge of colorectal cancer stem cells (CCSCs) and tumor microenvironment improves our understanding of cellular mechanisms involved in the immunity against colorectal cancer (CRC). Tumor associated antigens were evaluated via RNA-seq and bioinformatics analysis, evoking promising targets for tumor immunotherapy. MUC1 has been demonstrated to participate in the maintenance, tumorigenicity, glycosylation and metastasis of CCSCs, which may provide a new priority for CSC vaccination. In the present study, the vaccination with CCSCs with high expression of MUC1 was evaluated in a murine model for the vaccine’s immunogenicity and protective efficacy against CRC. CD133+ CCSCs were isolated from SW620 cell line using a magnetic-activated cell sorting system, and shMUC1 was further used to knock down the expression of MUC1 in CD133+ CCSCs. Mice were subcutaneously immunized with the cell lysates of CCSCs and shMUC1 CCSCs, followed by a challenge with SW620 cells at ten days after final vaccination. The results indicated CCSC vaccine significantly reduced the tumor growth via a target killing of CCSCs as evidenced by a decrease of CD133+ cells and ALDH+ cells in tumors. Moreover, CCSC vaccine resulted in the elevated NK cytotoxicity, production of perforin, granzyme B, IFN-γ, memory B cells, and anti-MUC1 antibodies. Of note, MUC1 knockdown partly impaired the anti-tumor efficacy of CCSC vaccine. Importantly, the CCSC vaccine has no toxic damage to organs. Overall, CCSC vaccine could serve as a potent and safe vaccine for CRC treatment, and MUC1 might play an essential role in CCSC vaccine.

A phase Ib study of TAK-079, an investigational anti-CD38 monoclonal antibody (mAb) in patients with relapsed/ refractory multiple myeloma (RRMM): Preliminary results.

8539 Background: TAK-079 is a subcutaneously (SC) administered mAb with multiple modes of action for killing target cells. Here we report data from an ongoing dose finding study of TAK-079 monotherapy in patients with RRMM (NCT03439280). Methods: Pt were eligible after ≥ 3 lines of therapy and previous exposure to immunomodulatory drug (IMiD), proteasome inhibitor (PI), alkylating agent, and corticosteroid; prior anti-CD38 therapy allowed. Patients were refractory or intolerant to at least 1 PI and 1 IMiD. TAK-079 given as a SC injection weekly for 8 doses, every other week for 8 doses, then monthly until disease progression (PD) or unacceptable toxicity. SC injection was 2 mL administered in ≤ 1 minute. Results: 34 patients were enrolled across 5 fixed dose cohorts (TAK-079 45-135-300-600-1200 mg SC) as of 09 December 2019. Median age was 65 (50–81) years. At study entry, 65% were refractory to both an IMiD and PI; 82% refractory to last line of therapy, 21% of patients were previously exposed to at least 1 anti-CD38 monoclonal antibody. Median number of prior therapies was 4 (2,12). No ≥ Grade 1 early or late systemic infusion reactions (IRR) reported. Three ( < 1%) injection site reactions described in > 1200 injections administered; 2 mild pruritis and 1 moderate swelling. Drug related adverse events (AEs), any grade, occurring in at least 10% of patients were: fatigue (21%), anemia (18%), neutropenia (18%), leukopenia (15%). Neutropenia was the only drug related grade 3 AEs in 2 or more patients (n = 2); only drug related SAE was 1 Grade 3 diverticulitis. No drug-related grade 4 AEs, AEs leading to study discontinuation, or on-study deaths reported. Recommended phase 2 dose (RP2) is to be 600 mg based on no reported DLTs, no MTD identified, and preliminary efficacy (PFS and response [ORR]). At the RP2 dose, 9 patients received at least 6 cycles of therapy by the data cutoff; their ORR was 33%, median duration of response was not estimable. The clinical benefit rate (minimal response or better) in all 12 patients enrolled at the RP2 dose was 67%. At a median follow-up of 7.5 months, PFS not estimable at the RP2 dose. Conclusions: TAK-079 monotherapy is safe, generally well tolerated, and active in patients with RRMM through tested doses. Clinical activity occurred early and was durable. With no MTD identified, no IRRs, no significant hematologic toxicity, the RP2 dose is 600 mg. PFS, with a median FU of 7.5 months at the data-cut off, is not estimable at the RP2 dose. Updated safety and efficacy data will be presented. Clinical trial information: NCT03439280 .