Studies in a murine B16 melanoma model show that persistent antigen at vaccination sites induces CD8+ T cell sequestration, dysfunction and deletion

To understand why cancer vaccine-induced T cells often fail to eradicate tumors, we studied immune responses in mice vaccinated with gp100 peptide emulsified in incomplete Freund's adjuvant (IFA), commonly used in clinical cancer vaccine trials. After gp100 peptide/IFA vaccination, tumor-specific CD8+ T cells (adoptively transferred from gp100-specific TCR-transgenic pmel-1 mice) accumulated not in tumors but at the persisting, antigen-rich vaccination site. Once there, primed T cells became dysfunctional and underwent antigen-driven, IFN- and FasL-mediated apoptosis, resulting in systemic hyporesponsiveness to subsequent vaccination. Provision of anti-CD40 antibody, TLR7 agonist and interleukin-2 (covax) reduced T cell apoptosis but did not prevent vaccination site sequestration. A non-persisting vaccine formulation shifted T cell localization towards tumors, inducing superior anti-tumor activity. Short-lived formulation also reduced systemic T cell dysfunction and promoted memory formation, as shown by gene expression profiling and other measures. Persisting peptide/IFA vaccine depots, currently used to vaccinate cancer patients, can induce specific T cell sequestration at vaccination sites followed by dysfunction and deletion; short-lived depot formulations may overcome these limitations and result in greater therapeutic efficacy of peptide-based cancer vaccines.

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Hailemichael Y, Dai Z, Jaffarzad N, Ye Y, Medina MA, Huang XF, Dorta-Estremera SM, Greeley NR, Nitti G, Peng W, Liu C, Lou Y, Wang Z, Ma W, Rabinovich B, Sowell RT, Schluns KS, Davis RE, Hwu P, Overwijk WW