Effective adoptive immunotherapy of triple-negative breast cancer by folate receptor-alpha redirected CAR T cells is influenced by surface antigen expression level.

BACKGROUND: The poor prognosis and the limited efficacy of targeted therapy in patients with triple-negative breast cancer (TNBC) have raised the need for alternative therapies. Recent studies have demonstrated that folate receptor-alpha (FRα) may represent an ideal tumor-associated marker for immunotherapy for TNBC. METHODS: The aim of the present study was to apply a chimeric antigen receptor (CAR) approach for the targeting of FRα expressed on TNBC cells and evaluate the antitumor activity of CAR-engineered T cells in vitro and in vivo. RESULTS: We found that human T cells expressing a FRα-specific CAR were potent and specific killers of TNBC cells that express moderate levels of FRα in vitro and significantly inhibited tumor outgrowth following infusion into immunodeficient mice bearing an MDA-MB-231 tumor xenograft. However, the antitumor activity of the FRα CAR T cells was modest when compared to the same CAR T cells applied in an ovarian tumor xenograft model where FRα expression is more abundant. Notably, FRα CAR T cells induced superior tumor regression in vivo against MDA-MB-231 that was engineered for overexpression of FRα. CONCLUSIONS: Taken together, our results show that FRα CAR T cells can mediate antitumor activity against established TNBC tumor, particularly when FRα is expressed at higher levels. These results have significant implications for the pre-selection of patients with high antigen expression levels when utilizing CAR-based adoptive T cell therapies of cancer in future clinical trials.

Folate receptor α expression and significance in endometrioid endometrium carcinoma and endometrial hyperplasia.

Endometrioid-type endometrial carcinoma (EEC) developing on the ground of endometrial hyperplasia (EH) is amongst the most commonly observed type of cancer in the world. Folate receptor α (FRα) is a vitamin molecule that has a role in cell proliferation. The fact that FRα, which is known to be needed extremely by the cells of malignancies that proliferate rapidly, is present in limited amounts in normal tissues while it is overexpressed in malignant cells of the same tissues makes folate a candidate for target molecular therapy. In our study, FRα expression in 214 cases, with 95 diagnosed within EEC and 119 with EH, was studied immunohistochemically. FRα expression in EEC was found significantly high compared to EH and normal endometrium (P<0.01). Similarly, FRα expression in EH cases with complex atypia were significantly high compared to other hyperplasia subgroups (P<0.01). The findings of our results make us think that FRα overexpression may play a role in the EEC carcinogenesis and carcinoma progression from EH. Furthermore, we suggest that it can be helpful in the treatment of EEC and/or transition from hyperplasia stage to EEC as a molecular therapy targeting receptors labeled with antibody-based props containing FRα. Finally, we suggest that FRα may be used, based on the expression intensity, as a supplemental option to determine the patients that shall be directed to radical therapy amongst patients with complex atypical EH.