This invention provides methods of treating, reducing the incidence of, and inducing immune responses to a WT1-expressing cancer, by administering a combination of at least one WT1 peptide, or cytotoxic T cells (CTLs) against a WT1-expressing cancer, and at least one checkpoint inhibitor. The at least one WT1 peptide can be administered to the subject by administering one or more agents to the subject resulting in delivery of one or more WT1 peptides and induction of an immune response against the WT1-expressing cancer. Examples of these WT1 delivery agents include: (i) an isolated WT1 peptide, (ii) a nucleic acid encoding the at least one WT1 peptide, and (iii) an immune cell comprising or presenting the at least one WT1 peptide or nucleic acid encoding the at least one WT1 peptide.