The present invention provides for peptide conjugates of precursors derived from WT1 antigen protein for use in cancer immunotherapy that can be subjected to trimming by the peptidase ERAP1. The particular conjugates of the invention are depicted in formula (1) in which Xa and Ya are each a single bond, cancer antigen peptide A is a peptide consisting of any amino acid sequence selected from the following amino acid sequences: RMFPNAPYL (SEQ ID NO: 2), ALLPAVPSL (SEQ ID NO: 5), SLGEQQYSV (SEQ ID NO: 6) and RVPGVAPTL (SEQ ID NO: 7), an amino group of an N-terminal amino acid of the cancer antigen peptide A binds to Ya in the formula (1), and the hydroxyl group in the formula (1) represents the hydroxyl group of the carboxy-terminus of cancer antigen peptide A, R1 is a cancer antigen peptide C, the cancer antigen peptide C has a sequence different from that of the cancer antigen peptide A, which is a peptide consisting of any amino acid sequence selected from the following amino acid sequences: CMTWNQMNL (SEQ ID NO: 3) and CYTWNQMNL (SEQ ID NO: 4), and the thiol group of the cysteine residue of the cancer antigen peptide C is bonded to the sulfur atom in the formula (1), or a pharmaceutically acceptable salts thereof.
