Abstract 6153: MyD88-mediated chimeric antigen receptor macrophage suppresses brain metastasis by target-specific phagocytosis and bystander effect through TNF-α
Authors: Wu Shih-Ying , Wu Kerui , Tyagi Abhishek , Xing Fei , Zhao Dan , Deshpande Ravindra Pramod , Liu Yin Liu , Watabe Kounosuke 
Published: June 2022

Abstract
Treating patients with brain metastasis of lung cancer poses significant challenges because a surgical approach is limited due to the sensitive nature of the brain and also because most chemotherapeutic drugs are ineffective owing to the blood-brain barrier (BBB). Although chimeric antigen receptor (CAR)-T cell and immune checkpoint inhibitors have been used in clinical trials for patients with recurrent brain tumors, the efficacy of these treatments has been limited due to severe side effects and poor penetrance of these reagents through BBB. Published data as well as the results of our own study indicate that macrophage is the major component of infiltrated immune cells in the brain metastatic lesions, suggesting that engineering to reprogram macrophages is a viable therapeutic strategy for patients with brain metastasis. Given the unique ability of macrophages to cross BBB and exert their phagocytic function to tumor cells, we genetically engineered macrophage that expressed tumor-specific antibody (scFv) to Mesothelin (MSLN) and activated the anti-tumor immune signaling molecule, MyD88. We hypothesize that MyD-88-driven chimeric antigen receptor macrophage (MyD-CARMA) suppresses brain metastasis of lung cancer by phagocytosis and increasing anti-tumor immune response. To investigate the effect of MyD-CARMA on brain metastasis in vivo, mice were intracranially transplanted with lung cancer brain metastasis cell (H2030BrM) which expresses a high level of MSLN followed by administration of MyD-CARMA every 2 weeks for 40 days. This CARMA indeed penetrated BBB and drastically decreased brain metastasis growth in our humanized mouse model. The MyD-CARMA showed antigen-specific phagocytosis activity against MSLN+ tumor cells. We then utilized NCI-H522 cell which lacks MSLN expression and overexpressed MSLN in this cell line followed by co-culturing with CARMA. We found that CARMA suppressed tumor growth of only MSLN+ but not MSLN- cells. However, when CARMA was co-cultured with both MSLN+ and MSLN- cells, CARMA exhibited a bystander killing effect even on MSLN- cells. When TNF-α was knocked out in CARMA by CRISPR/Cas9, CARMA lost the ability to show the bystander effect on MSLN- cells, suggesting that CARMA exhibited the bystander killing effect via up-regulation of TNF-α upon engagement with MSLN+ cells. Importantly, CARMA showed much less liver and neuron toxicities compared to CAR-T. In conclusion, our results showed that these unique features of MyD-CARMA represent significant advantage over other immune therapies, and therefore, MyD-CARMA may serve as a promising therapeutic tool for the treatment of brain metastasis.
Citation Format: Shih-Ying Wu, Kerui Wu, Abhishek Tyagi, Fei Xing, Dan Zhao, Ravindra Pramod Deshpande, Yin Liu Liu, Kounosuke Watabe. MyD88-mediated chimeric antigen receptor macrophage suppresses brain metastasis by target-specific phagocytosis and bystander effect through TNF-α [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 6153.