Augmenting dendritic cells through pathways that synergize with a HER-2/neu targeted whole-cell tumor vaccine

Tumor vaccine strategies must overcome pre-existing immune tolerance to the antigen, as vaccine alone is rarely effective. HER-2/neu transgenic mice over-express HER-2 in a mammary tissue-specific manner that leads to the development of tumors and offers the opportunity to study mechanisms tolerance. Immunization of parental FVB/N mice induces high avidity CD8 + T cell responses, while neu-N mice are tolerant to vaccination and develop a low avidity CDS+ repertoire. Depletion of CD4' T cells prior to vaccination in both mice completely abrogates tumor-free survival. Studies were conducted to evaluate the HER-2 epitopes against which CD4+ T cell responses are directed. Overlapping peptides were screened using CD4+ T cells isolated from immunized FVB/N mice. Attempts to identify positive peptides were complicated by inconsistent results, indicating a plasticity of peptide binding to the I-Aq complex and suggest that successful CD4+ T cell responses are against many neu epitopes.;Tolerance can be partially broken by immune modulating agents which can disrupt tolerance mechanisms long enough for high-avidity CD8+ T cell populations to develop. Cyclophosphamide and paclitaxel work best when combined with vaccine rather than when each is given with vaccine alone. Paclitaxel treatment does not deplete CD4+ foxp3+ Tregs. We found that while paclitaxel, can act as a ligand for the TLR-4 receptor it does not mature DC's in the same manner as LPS. High concentrations of paclitaxel were unable to match the degree of maturation stimulated by LPS at the late stage of development. Paclitaxel did enhance DC maturation when added to culture media early in development. Paclitaxel-treated DCs were better able to activate naive CD8+ T cells presumably through enhanced cross-priming. Treatment before vaccination results in a greater percentage of mature DCs in vaccine-draining lymph nodes, which are better able to mature naive CD8+ T cells ex vivo.;In conclusion, the addition of the TLR-4 ligand paclitaxel enhances the function of DCs, resulting in a significantly potent response against neu expressing tumors in neu-N mice. These data provide new evidence for the use of TLR-4 agonists like paclitaxel as adjuvants for enhancing the clinical activity of DC-based vaccines for the treatment of cancer. These findings also provide the scientific rationale for combining Treg depleting agents with TLR-4 agonists in combination with DC-based vaccines to optimize cancer targeted immunotherapies.