Persistent antigen at vaccination sites induces tumor-specific CD8⁺ T cell sequestration, dysfunction and deletion.

To understand why cancer vaccine-induced T cells often do not eradicate tumors, we studied immune responses in mice vaccinated with gp100 melanoma peptide in incomplete Freund's adjuvant (peptide/IFA), which is commonly used in clinical cancer vaccine trials. Peptide/IFA vaccination primed tumor-specific CD8(+) T cells, which accumulated not in tumors but rather at the persisting, antigen-rich vaccination site. Once there, primed T cells became dysfunctional and underwent antigen-driven, interferon-γ (IFN-γ)- and Fas ligand (FasL)-mediated apoptosis, resulting in hyporesponsiveness to subsequent vaccination. Provision of CD40-specific antibody, Toll-like receptor 7 (TLR7) agonist and interleukin-2 (IL-2) reduced T cell apoptosis but did not prevent vaccination-site sequestration. A nonpersisting vaccine formulation shifted T cell localization toward tumors, inducing superior antitumor activity while reducing systemic T cell dysfunction and promoting memory formation. These data show that persisting vaccine depots can induce specific T cell sequestration, dysfunction and deletion at vaccination sites; short-lived formulations may overcome these limitations and result in greater therapeutic efficacy of peptide-based cancer vaccines.

IFN-alpha enhances peptide vaccine-induced CD8+ T cell numbers, effector function, and antitumor activity.

Type I IFNs, including IFN-alpha, enhance Ag presentation and promote the expansion, survival, and effector function of CD8(+) CTL during viral infection. Because these are ideal characteristics for a vaccine adjuvant, we examined the efficacy and mechanism of exogenous IFN-alpha as an adjuvant for antimelanoma peptide vaccination. We studied the expansion of pmel-1 transgenic CD8(+) T cells specific for the gp100 melanocyte differentiation Ag after vaccination of mice with gp100(25-33) peptide in IFA. IFN-alpha synergized with peptide vaccination in a dose-dependent manner by boosting relative and absolute numbers of gp100-specific T cells that suppressed B16 melanoma growth. IFN-alpha dramatically increased the accumulation of gp100-specific, IFN-gamma-secreting, CD8(+) T cells in the tumor through reduced apoptosis and enhanced proliferation of Ag-specific CD8(+) T cells. IFN-alpha treatment also greatly increased the long-term maintenance of pmel-1 CD8(+) T cells with an effector memory phenotype, a process that required expression of IFN-alpha receptor on the T cells and IL-15 in the host. These results demonstrate the efficacy of IFN-alpha as an adjuvant for peptide vaccination, give insight into its mechanism of action, and provide a rationale for clinical trials in which vaccination is combined with standard-of-care IFN-alpha therapy for melanoma.