The invention features methods for inhibiting enhancement of expression of a FoxP3 gene in a cell, methods for inhibiting induction of differentiation of a cell into a regulatory T cell, methods for reducing immunosuppression, methods for stimulating tumor immunity, and methods for treating a patient with a tumor. The methods of the invention involve suppressing function of an FSTL1 protein in the cell. In the methods of the invention, function of an FSTL1 protein in the cell may be suppressed using an anti-FSTL1 antibody.
