Eliminating mesothelioma by AAV-vectored, PD1-based vaccination in the tumor microenvironment.

The potency of cancer vaccines is often compromised by a variety of immunoinhibitory mechanisms, including stimulation of the programmed cell death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) immune checkpoint pathway. Here, to overcome inhibition, we determined the potential of recombinant adeno-associated virus (rAAV)-vectored, PD1-based vaccination in the tumor microenvironment (TME) to activate antigen-specific T cell responses in the immune-competent murine mesothelioma model. We found that our rAAV-soluble PD1 (sPD1)-TWIST1 vaccine elicited and maintained TWIST1-specific cytotoxic T lymphocyte (CTL) responses and the PD-1 blocker systemically against lethal mesothelioma challenge after intramuscular injection, which was more effective than rAAV-TWIST1 or rAAV-sPD1 alone. More importantly, intratumoral injection of rAAV-sPD1-TWIST1 significantly enhanced immune surveillance by inducing TWIST1-specific CTL responses against vaccine-encoded TWIST1 and bystander gp70-AH1 epitopes, increasing CTL infiltration into the TME and decreasing tumor-associated immunosuppression, leading to complete elimination of established mesothelioma in 5 of 8 tumor-bearing mice. In addition, direct oncosuppression synergized with recruitment of T cells after localized rAAV-sPD1-TWIST1 treatment in a humanized mouse model to inhibit growth of REN human mesothelioma. Our results warrant clinical development of the rAAV-sPD1-TWIST1 vaccine to enhance immunotherapy against a wide range of TWIST1-expressing tumors.