CAR T cell therapy for breast cancer: harnessing the tumor milieu to drive T cell activation

• Published in: Journal for immunotherapy of cancer 2018-05, Vol.6 (1), p.34-34, Article 34
• Main Authors: Bajgain, Pradip, Tawinwung, Supannikar, D'Elia, Lindsey, Sukumaran, Sujita, Watanabe, Norihiro, Hoyos, Valentina, Lulla, Premal, Brenner, Malcolm K, Leen, Ann M, Vera, Juan F
• Format: Article
• Language: English
• Subjects: Antibodies; Antigens; Breast cancer; Cancer; Cancer treatment; Carbon dioxide; Chimeric antigen receptor; Cytokines; Flow cytometry; Genetic engineering; Genetically modified organisms; Health aspects; Immunotherapy; Inverted cytokine receptor; Laboratories; Lymphocytes; Metastasis; Mucins; Prognosis; T cell receptors; T cell therapy; T cells; Tumor antigens
• ISSN: 2051-1426; 2051-1426
• DOI: 10.1186/s40425-018-0347-5

The adoptive transfer of T cells redirected to tumor via chimeric antigen receptors (CARs) has produced clinical benefits for the treatment of hematologic diseases. To extend this approach to breast cancer, we generated CAR T cells directed against mucin1 (MUC1), an aberrantly glycosylated neoantigen that is overexpressed by malignant cells and whose expression has been correlated with poor prognosis. Furthermore, to protect our tumor-targeted cells from the elevated levels of immune-inhibitory cytokines present in the tumor milieu, we co-expressed an inverted cytokine receptor linking the IL4 receptor exodomain with the IL7 receptor endodomain (4/7ICR) in order to transform the suppressive IL4 signal into one that would enhance the anti-tumor effects of our CAR T cells at the tumor site. First (1G - CD3ζ) and second generation (2G - 41BB.CD3ζ) MUC1-specific CARs were constructed using the HMFG2 scFv. Following retroviral transduction transgenic expression of the CAR±ICR was assessed by flow cytometry. In vitro CAR/ICR T cell function was measured by assessing cell proliferation and short- and long-term cytotoxic activity using MUC1+ MDA MB 468 cells as targets. In vivo anti-tumor activity was assessed using IL4-producing MDA MB 468 tumor-bearing mice using calipers to assess tumor volume and bioluminescence imaging to track T cells. In the IL4-rich tumor milieu, 1G CAR.MUC1 T cells failed to expand or kill MUC1+ tumors and while co-expression of the 4/7ICR promoted T cell expansion, in the absence of co-stimulatory signals the outgrowing cells exhibited an exhausted phenotype characterized by PD-1 and TIM3 upregulation and failed to control tumor growth. However, by co-expressing 2G CAR.MUC1 (signal 1 - activation + signal 2 - co-stimulation) and 4/7ICR (signal 3 - cytokine), transgenic T cells selectively expanded at the tumor site and produced potent and durable tumor control in vitro and in vivo. Our findings demonstrate the feasibility of targeting breast cancer using transgenic T cells equipped to thrive in the suppressive tumor milieu and highlight the importance of providing transgenic T cells with signals that recapitulate physiologic TCR signaling - [activation (signal 1), co-stimulation (signal 2) and cytokine support (signal 3)] - to promote in vivo persistence and memory formation.