Abstract 3242: CT-0508 is an anti-HER2 chimeric antigen receptor (CAR) macrophage with targeted anti-tumor activity that promotes a pro-inflammatory solid tumor microenvironment
Authors: Klichinsky Michael , Gabrusiewicz Konrad , Anderson Nicholas , Schmierer Maggie , Best Andrew , Zeeman Martha , Chhum Sotheavy , Ohtani Yumi , Shestova Olga , Lu Xueqing , Petty Nicholas , Shan Xinhe , Shen Feng , Gill Saar 
Published: September 2020

Abstract
Despite recent advances in T cell immunotherapy for the treatment of human cancer, metastatic solid tumors remain an intractable challenge. Macrophages are often the most abundant immune cell in the tumor microenvironment (TME) where, as immunosuppressive tumor associated macrophages (TAMs), they participate in disease progression. Currently, most macrophage based immunotherapeutic approaches are focused on the depletion, repolarization, or phagocytic disinhibition of TAMs. We have developed a new paradigm based on the adoptive transfer of genetically engineered CAR macrophages (CAR-M) for the treatment of human cancer. CAR-M can be efficiently produced using the chimeric adenoviral vector Ad5f35. We have previously shown that the primary mechanism of action of CAR-M is antigen dependent phagocytosis, and that a single dose of primary human anti-HER2 CAR-M leads to significantly improved overall survival in multiple solid tumor xenograft models. Given that Ad5f35-transduced anti-HER2 CAR-M (CT-0508) adopt a unique pro-inflammatory M1-like phenotype, we hypothesized that CT-0508 may have the capacity to reprogram the TME toward an activated state. Functional evaluation and transcriptome-wide characterization revealed that CT-0508 maintain a pro-inflammatory phenotype despite challenge with immunosuppressive environments in vitro. By engrafting immunodeficient mice with human hematopoietic cells and human cancer cells we established a novel xenografted human TME model. We demonstrate with single cell resolution that CT-0508 maintain their M1 phenotype within the human TME. Additionally, CT-0508 augmented the human TME by inducing a pro-inflammatory signature in surrounding immune cells, characterized by induction of MHC-II and TNFα. To further investigate the potential of CT-0508 for TME activation, we modeled the interaction of CT-0508 with primary human M2 macrophages, dendritic cells, and T cells in vitro. CT-0508 repolarized bystander M2 macrophages toward a pro-inflammatory phenotype, induced activation and maturation markers on immature dendritic cells, and recruited resting as well as activated T cells in chemotaxis assays. CT-0508 demonstrated enhanced antigen presentation when compared to control human macrophages and cross-presented tumor derived intracellular antigens to CD8 T cells after tumor phagocytosis. Our results show that in addition to direct anti-tumor activity, the anti-HER2 CAR macrophage cell product CT-0508 is capable of promoting a pro-inflammatory tumor microenvironment and has the potential to induce epitope spreading via T cell recruitment and antigen presentation.
Citation Format: Michael Klichinsky, Konrad Gabrusiewicz, Nicholas Anderson, Maggie Schmierer, Andrew Best, Martha Zeeman, Sotheavy Chhum, Yumi Ohtani, Olga Shestova, Xueqing Lu, Nicholas Petty, Xinhe Shan, Feng Shen, Saar Gill. CT-0508 is an anti-HER2 chimeric antigen receptor (CAR) macrophage with targeted anti-tumor activity that promotes a pro-inflammatory solid tumor microenvironment [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 3242.