Cancer vaccines can induce robust activation of tumor-specific CD8+ T cells that can destroy tumors.
Understanding the mechanism by which cancer vaccines work is essential in designing next-generation
vaccines with more potent therapeutic activity. We recently reported that short peptides emulsified
in poorly biodegradable, Incomplete Freund’s Adjuvant (IFA) primed CD8+ T cells that did not localize
to the tumor site but accumulated at the persisting, antigen-rich vaccination site. The vaccination site
eventually became a T cell graveyard where T cells responded to chronically released gp100 peptide by
releasing cytokines, including interferon- (IFN-), which in turn upregulated Fas ligand (FasL) on host
cells, causing apoptosis of Fas+ T cells. T cells that escaped apoptosis rapidly became exhausted, memory
formation was poor, and therapeutic impact was minimal. Replacing the non-biodegradable IFA-based
formulation with water-based, short-lived formulation in the presence of immunostimulatory molecules
allowed T cells to traffic to tumors, causing their regression. In this review, we discuss recent advances
in immunotherapeutic approaches that could enhance vaccine-primed immune cells fitness and render
the tumor microenvironment more accessible for immune cell infiltration