• Safa Tahmasebi, Reza Elahi, and Abdolreza Esmaeilzadeh.
• Department of Immunology, Health Faculty, Tehran University of Medical Sciences, Tehran, Iran.
• Stem Cell Rev Rep. 2019 Oct 1; 15 (5): 619-636.

AbstractAdoptive cell therapy using CAR T cells has emerged as a novel treatment strategy with promising results against B cell malignancies; however, CAR T cells have not shown much success against solid malignancies. There are several obstacles which diminish the efficacy of CAR T cells, but the immunosuppressive tumor microenvironment (TME) of the tumor stands out as the most important factor. TME includes Tumor-Associated Stroma, Immunosuppressive cells and cytokines, tumor hypoxia and metabolism, and Immune Inhibitory Checkpoints which affect the CAR T cell efficacy and activity in solid tumors. A precise understanding of the TME could pave the way to engineer novel modifications of CAR T cells which can overcome the immunosuppressive TME. In this review, we will describe different sections of the TME and introduce novel approaches to improve the CAR T cells potential against solid tumors based on recent clinical and preclinical data. Also, we will provide new suggestions on how to modify CARs to augment of CAR T cells efficacy. Since there are also some challenges beyond the TME that are important for CAR function, we will also discuss and provide data about the improvement of CAR T cells trafficking and delivery to the tumor site and how to solve the problem of tumor antigen heterogeneity.

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