Background Chimeric antigen receptor (CAR) cell therapy for solid tumors is hampered by the immunosuppressive tumor microenvironment (TME), which can inhibit the function of endogenous and therapeutic immune cells, as well as a paucity of targets. The use of potent immunomodulators to transform the TME, such as interleukin (IL)-12, is limited by the need for regulation to avoid systemic toxicities. Methods To address these challenges, Senti Bio is developing CAR-NK therapies that include Multi-Arming with calibrated release (cr)IL-15 and a Regulator Dial gene circuit to control the expression of crIL-12. Senti's proprietary calibrated release technology enables cytokines to be expressed in both membrane-bound and secreted forms, providing multi-factorial activity via autocrine and paracrine stimulation to increase CAR-NK cell function and activation of endogenous immune cells in the TME. In addition, we have designed a Regulator Dial gene circuit that expresses crIL-12 under the control of grazoprevir (GRZ), an FDA-approved small molecule drug. ResultsWe have tested our Multi-Arming and Regulator Dial gene circuits in combination with a CAR targeting GPC3, a hepatocellular carcinoma (HCC)-relevant target. We observed crIL-15 to promote NK cell persistence and proliferation in an autocrine fashion, while also activating other immune cells in a paracrine manner. In addition, crIL-15 was observed to enhance GPC3 CAR-NK tumor killing in a serial killing assay compared to wild-type secreted IL-15 and showed enhanced antitumor function and increased survival over control groups in vivo.GPC3 CAR-NK cells containing the Regulator Dial gene circuit expressed low crIL-12 levels in the absence of GRZ (<100 pg/1e6 cells/48h), while induction with GRZ led to a 1000-fold increase of crIL-12 expression under the same conditions. The ON and OFF kinetics of crIL-12 induction were determined in vitro. 4 hours of GRZ-treatment was sufficient to induce >600-fold increase in crIL-12 concentrations. By day 3 post-GRZ removal, crIL-12 reverted to basal levels. Lastly, the role of crIL-12 in reversing immunosuppression was validated in a co-culture assay. Specifically, GRZ-induced crIL12 restored CAR-NK cells that were suppressed in the presence of M2 macrophages. Conclusions We have engineered off-the-shelf CAR-NK cell therapies that target GPC3 and express crIL-15. To increase the therapeutic window of the potent immune effector IL-12 in the TME, we have designed a Regulator Dial gene circuit to controllably produce crIL-12. These gene circuits have complementary mechanisms of action to enhance CAR-NK antitumor function and potentially overcome the immunosuppressive TME in solid tumors such as HCC.

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

CD33 and FLT3 are validated targets for myeloid malignancies, including acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). These malignancies have poor prognosis and high clinical unmet need, and current targeted therapies present ample limitations. One challenge is that untargeted leukemic stem cells (LSCs) can contribute to eventual relapse; however, targeting the LSC markers FLT3 and CD33 can contribute to off-tumor toxicities against normal hematopoietic stem cells and progenitor cells (HSCs/HPCs), leading to bone marrow toxicities such as thrombocytopenia, neutropenia, and infectious complications. SENTI-202 is designed to address these challenges and provide a broader therapeutic window. SENTI-202 is a preclinical CAR-NK cell product candidate engineered with an OR and NOT logic gated gene circuit onto allogeneic healthy adult peripheral blood NK cells along with multi-arming via expression of calibrated release IL-15 (crIL-15) to enhance therapeutic activity and tolerability. The OR gate is implemented using a bivalent CAR (aCAR) that binds both CD33 and FLT3 to target both AML blasts and LSCs. Additionally, the NOT gate is implemented using an inhibitory CAR (iCAR) that recognizes the healthy cell protective antigen endomucin (EMCN) and targets endomucin which is designed to prevent CAR-mediated cytotoxicity against healthy cells, such as HSCs and early HPCs, potentially reducing on-target/off-tumor toxicities. Finally, crIL-15 provides NK cell activation and persistence via simultaneous autocrine, juxtracrine, and paracrine activities. Preclinical studies demonstrated the [antitumor] activity and tolerability of SENTI-202. All SENTI-202 components are stably expressed via a single g-retroviral vector. SENTI-202 preclinical pharmacokinetics and secondary pharmacodynamics demonstrated CAR target engagement, function, as well as mechanism of action for all components in different AML models. SENTI-202 CAR-NK cells demonstrated cytotoxic activity when co-cultured with AML target cells and primary patient-derived samples and had increased antitumor capacity compared to non-engineered NK cells. SENTI-202 induced the production of cytotoxic cytokines and increased expression of activation and cytotoxicity markers consistent with CAR-mediated activation of the NK cells. The presence of EMCN iCAR reduced cytotoxicity in an EMCN-dependent manner in target cells and primary HSCs. crIL-15 expression yielded functional pSTAT5 signaling and increased persistence of SENTI-202 in vitro and in vivo. These results demonstrate the antitumor activity and tolerability of SENTI-202 and warrant further clinical development as a novel therapeutic option for patients with CD33+ and/or FLT3+ tumors. Citation Format: Alba Gonzalez, Enping Hong, Gozde Yucel, Elizabeth Leitner, Pearley Chinta, Han Deng, Ian Li, Alice Lam, Abla Bakir, Brandon Lee, Papia Chakraborty, Carmina Blanco, Chen-Ting Lee, Niran Almudhfar, Mengxi Tian, Wenqi Song, Andrew Banicki, Otto Contreras, Martin Gieldin, Brian Garrison, Timothy K. Lu, Kanya Rajangam. Preclinical development of SENTI-202, an off-the-shelf logic gated CAR-NK cell therapy, for the treatment of CD33/FLT3+ hematologic malignancies including AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3195.