TWIST1, a basic helix-loop-helix transcription factor, is overexpressed in a variety of tumors such as melanoma, breast, colon cancer and mesothelioma, and associated with tumorigenesis and metastasis. We have previously shown that full-length TWIST1 vaccine elicited cytotoxic T lymphocytes (CTLs) that recognized TWIST1-expressing tumors and conferred protection against tumor challenge in the form of DNA vaccine and adeno-associated viral vector system, highlighting TWIST1 as a promising target for cancer immunotherapy. In this study, we sought to apply optimization approach on the TWIST1-based vaccine platform in order to enhance T cell immunity and reduce potential toxicity.

We developed a novel soluble PD-1 (sPD1)-based DNA vaccine encoding a truncated version of TWIST1 (sPD1-TruncT1) that includes a conserved region found in both human and mouse proteins. The immunogenicity and antitumor efficacy of the TruncT1 vaccine were evaluated and compared in parallel to full-length TWIST1 vaccine in two murine models of TWIST1-expressing tumors.

By doing epitope mapping, we identified immunodominant T cell epitopes within the TWIST1 antigen, showing that majority of T cells recognized a C-terminal conserved region. sPD1-based DNA vaccine encoding epitopes of this conserved region, via in vivo electroporation (EP), elicited more robust TWIST1-specific T cell responses compared to full-length TWIST1 vaccine. Furthermore, these TWIST1-specific T cells were polyfunctional because they produced multiple effector cytokines when encountering TWIST1-expressing tumors. In addition, immunotherapy with the sPD1-TruncT1 vaccine showed a notable enhancement in antitumor efficacy in both preventive and therapeutic scenarios.

With the widespread expression of TWIST1 in different cancer types, truncated TWIST1 vaccination has high potential for cancer immunotherapy and warrants investigation in human clinical trials to evaluate its applications as a vaccine for patients with WT1-expressing cancers.