T-cell immunity to the folate receptor alpha is prevalent in women with breast or ovarian cancer

Purpose: Studies have demonstrated that the generation of immunity to tumor antigens is associated with improved prognosis for many cancers. A candidate antigen is the folate receptor alpha (FRα), which is overexpressed in breast and ovarian cancers. Our goal in this study was to attain a better understanding of the extent of endogenous FRα immunity. Methods: Using a CD4⁺ T cell epitope prediction algorithm, we predicted promiscuous epitopes of FRα, and tested for immunity in 30 breast (n = 17) or ovarian (n = 13) cancer patients and 18 healthy donors using enzyme-linked immunospot analysis. Results: Fourteen peptides were predicted, seven each from the carboxy- and amino-terminus halves of the protein. More than 70% of patients demonstrated immunity to at least one FRα peptide. Patients responded to an average of 3 ± 0.5 peptides, whereas healthy donors responded to 1 ± 0.4 peptides (P = .004). Five peptides were recognized by more than 25% of patients. Responses to three peptides were higher (P < .05) in patients than in healthy donors, suggesting augmented immunity. Compared with healthy individuals, patients developed higher immunity to the amino-terminus half of the receptor (P = .03). There was no difference between each group in the responses to nonspecific (P = .2) and viral stimuli (P = .5). Lastly, patients demonstrated elevated levels of FRα antibodies consistent with a coordinated immune response. Conclusion: These findings demonstrate that the FRα is a target of the immune system in breast and ovarian cancer patients. Understanding which antigens are targeted by the immune system may be important for prognosis or immune-based therapies.