Abstract 4053: A mesothelin targeting chimeric antigen receptor macrophage (CAR-M) for solid tumor immunotherapy: pre-clinical development of CT-1119

While adoptive cell therapies have seen significant success in the treatment of hematological malignancies, solid tumors remain challenging for the field. A significant obstacle is the exclusion of T cells from the tumor microenvironment (TME). In contrast, monocytes/macrophages are naturally recruited to the TME. These cells then have the potential to phagocytose tumor cells, activate the TME, and prime a broad anti-tumor adaptive immune response via T cell recruitment and activation. We have previously developed CT-0508, a chimeric antigen receptor macrophage (CAR-M) targeting HER2 which showed efficacy in a variety of pre-clinical models and is currently in a Phase I clinical trial for patients with HER2+ solid tumors. Mesothelin is overexpressed in a variety of solid tumors, including mesothelioma, lung, pancreatic, and ovarian cancers. To leverage tumor biology with myeloid cells, we engineered primary human macrophages using the chimeric adenoviral vector Ad5f35 to express a CAR containing a human scFv against human mesothelin. We used both in vitro cell based assays and in vivo xenograft models to assess the activity of CT-1119. CAR-M engineered with an Ad5f35 vector demonstrated high CAR expression, high viability, upregulated M1 (anti-tumor) macrophage markers, and downregulated M2 (pro-tumor) macrophage markers. CT-1119 specifically phagocytosed multiple mesothelin expressing tumor cell lines in a CAR-dependent and antigen-dependent manner. CT-1119 demonstrated robust in vitro killing of the relevant tumor cell lines A549 and MES-OV expressing mesothelin. CAR engagement also induced the release of pro-inflammatory cytokines such as TNFα following stimulation with mesothelin in both cell-free and cell-based contexts in a dose-dependent manner. In vivo, CT-1119 significantly reduced tumor burden in a murine xenograft model of lung cancer. Similarly, human monocytes targeting mesothelin were successfully generated using the same Ad5f35 vector and demonstrated specific activity against mesothelin positive tumor cells. The presented results demonstrate that CT-1119, an autologous human anti-mesothelin CAR-M, can cause phagocytosis, tumor cell killing, and pro-inflammatory cytokine release in response to stimulation with mesothelin. These results show that CAR-M is a feasible approach for the treatment of mesothelin expressing sold tumors via the potential for induction of a systemic anti-tumor response.

Citation Format: Nicholas R. Anderson, Brinda Shah, Alison Worth, Rashid Gabbasov, Brett Menchel, Kerri Ciccaglione, Daniel Blumenthal, Stefano Pierini, Sabrina Ceeraz DeLong, Sascha Abramson, Thomas Condamine, Michael Klichinsky. A mesothelin targeting chimeric antigen receptor macrophage (CAR-M) for solid tumor immunotherapy: pre-clinical development of CT-1119. [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 4053.

Abstract 582: Pre-clinical development of CAR Monocytes (CAR Mono) for solid tumor immunotherapy

Introduction: Engineered cell therapies have demonstrated significant clinical activity against hematologic malignancies, but responses have been rare in solid tumors. Our previously developed human chimeric antigen receptor macrophage (CAR-M) platform has shown potent anti-tumor activity in pre-clinical solid tumor models1, and the anti-HER2 CAR-M CT-0508 is currently being evaluated in a Phase I trial. The use of myeloid cells as a platform for cell therapy provides the tools to overcome critical solid tumor challenges such as infiltration, immunosuppression within the tumor microenvironment, lymphocyte exclusion, and target antigen heterogeneity. Currently, CAR-M are generated in a week-long ex-vivo process in which peripheral blood monocytes are differentiated into macrophages prior to genetic manipulation. Here, we demonstrate the production feasibility, phenotype, pharmacokinetics, cellular fate, specificity, and anti-tumor activity of human CD14+ CAR monocytes.

Experimental: Using the chimeric adenoviral vector Ad5f35, we engineered primary human CD14+ monocytes to express a CAR (CAR-mono) targeted against HER2. We established a process that allowed for same day manufacturing (from Leukopak to cryopreserved CAR-mono cell product).

Results: CAR-mono showed high CAR expression and viability (>90%), and efficiently differentiated into CAR-expressing macrophages. Adenoviral transduction led to pre-conditioning of CAR-mono, resulting in a strong M1 phenotype upon differentiation into CAR-M. CAR-mono derived macrophages demonstrated potent anti-tumor activity regardless of exposure to GM-CSF or M-CSF, and were protected against M2 switching by immunosuppressive factors. Treating CAR-mono with GM-CSF and IL-4 resulted in their differentiation to monocyte-derived CAR-DCs with an activated phenotype, indicating that these cells retained their myeloid differentiation potential. In vivo, CAR-mono induced anti-tumor activity in various HER2+ solid tumor xenograft models. Following IV administration, CAR-mono demonstrated the ability to traffic to both GM-CSFhigh and GM-CSFlow expressing tumors. Notably, CAR-mono showed long-term CAR expression and persistence (>180 days) in both NSG and NSG-S mouse models, demonstrating lasting persistence irrespective of human cytokine support.

Conclusions: The CAR-mono platform enables an automated, same-day manufacturing process while maintaining the key characteristics of CAR-M therapy. The use of Ad5f35 for human monocyte transduction primes the cells toward M1 macrophage differentiation and produces a cell population phenotypically and functionally similar to our established CAR-M platform. These data provide strong pre-clinical support to advance the CAR-mono platform into clinical testing.1Klichinsky M, et al. Human chimeric antigen receptor macrophages for cancer immunotherapy. Nature Biotechnology. March 2020.

Citation Format: Daniel Blumenthal, Linara Gabitova, Brett Menchel, Patricia Reyes-Uribe, Sabrina Ceeraz DeLong, Sascha Abramson, Michael Klichinsky. Pre-clinical development of CAR Monocytes (CAR Mono) for solid tumor immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 582.