Tumor antigen - Specific T-cell expansion is greatly facilitated by in vivo priming

Purpose: Adoptive T-cell therapy is a promising strategy for the treatment of patients with established tumors but is often limited to specific cancers where tumor-infiltrating lymphocytes, the source of T cells for ex vivo culture, can be obtained. In this study, we evaluated the feasibility of expanding HER-2/neu - specific T cells derived from peripheral blood ex vivo following in vivo priming with a HER-2/neu peptide vaccine. Experimental Design: Peripheral blood mononuclear cells from cytomegalovirus (CMV)-seronegative and CMV-seropositive donors as well as HER-2/neu - positive cancer patients who had or had not been vaccinated with a HER-2/neu peptide - based vaccine was used as a source of T lymphocytes. Antigen-specific T-cell lines were generated by in vitro stimulation with antigen followed by nonspecific expansion on CD3/CD28 beads. The ability to expand antigen-specific T cells was assessed using IFN-γ and granzyme B enzyme-linked immunosorbent spot. The phenotype of the resultant T-cell lines was evaluated by flow cytometry, including the presence of FOXP3-expressing CD4⁺ T cells. Results: The frequencies of CMV-specific T cells generated from CMV⁺ donors were >11-fold higher than the frequencies from CMV^- donors (P = 0.001), with 22-fold increase of total number of CD3⁺ T cells. The frequencies of HER-2/neu - specific T cells generated from the primed patients were >25-fold higher than the frequencies from unvaccinated patients (P = 0.006), with an average of a 19-fold increase of total number of CD3⁺ T cells. Using peripheral blood as the source of T cells did not result in concurrent expansion of FOXP3⁺CD4⁺ regulatory T cells despite the use of interleukin-2 in in vitro culture. Both CD4⁺ and CD8⁺ HER-2/neu - specific T cells could be expanded. The extent of ex vivo expansion correlated with the magnitude of immunity achieved during immunization (P = 0.008). Conclusion: Tumor-specific T cells can be efficiently expanded from the peripheral blood ex vivo following in vivo priming with a vaccine. This approach provides an effective method to generate tumor-specific polyclonal T cells for therapeutic use that could be applied to cancer patients with any tumor type.