Novel chimeric CTLA-4 B-cell epitope peptide vaccines demonstrate effective anti-tumor immunity with/without PD1/PDL1 blockade in multiple syngeneic murine models of breast and colorectal cancers.

Cancer immunotherapy with checkpoint inhibitors has resulted in impressive clinical results in several cancer indications. Despite this success, only a fraction of patients shows durable and complete response to blockade by Ipilimumab an anti-CTLA-4 monoclonal antibody. We identified four cytotoxic T Lymphocyte-associated antigen 4 (CTLA-4) peptide sequences from which engineered chimeric B-cell epitope constructs incorporating a "promiscuous" T-cell epitope elicited highly immunogenic anti-CTLA-4 natural polyclonal antibodies by immunization. Combination of CTLA-4 peptide vaccine with other checkpoint inhibitor vaccines PD1-Vaxx or PDL1-Vaxx were investigated in several breast and colon carcinoma BALB/c syngeneic models (CT26, 4T1 and D2F2). CTLA-4 vaccines showed significant tumor suppression and prolonged survival rates as compared to anti-mouse CTLA-4 mAb 9H10. The resulting antipeptide antibodies suppressed tumor proliferation and migration similar to ipilimumab. We focused on one CTLA-4 epitope sequence 130-150 that embodies the "MYPPPY" motif that ipilimumab binds to. Combination of MVF-CTLA-4(130-150) with either PD1-Vaxx or PDL1-Vaxx showed synergistic activity. The 130-150 peptide mimic demonstrated the polyproline type II helix motif showed inhibition of tumor growth and therapeutic efficacy in the syngeneic CT26/BALB/c model. Several CTLA-4 vaccines have been identified which shows synergistic activities with other checkpoint inhibitor vaccines to PD-1 and PDL1.