Adoptive T Cell Therapy of Viral Infection and Cancer : Ex vivo Expansion of Cytomegalovirus- and Prostate Antigen-specific T Cells

Abstract: The main focus of my thesis has been to develop protocols for generating antigen-specific cytotoxic T lymphocytes (CTLs) and T helper cells (TH) for adoptive transfer to treat cytomegalovirus (CMV) disease and prostate cancer. CMV viremia is a severe complication in immunocompromised stem cell transplanted patients. Prostate cancer is a leading cause of death for men in Western countries. Although different in nature, CMV-infected cells and prostate cancer cells can both be eliminated through specific activation of the adaptive immune system. To generate CMV pp65-specific T cells, I utilized dendritic cells (DCs) modified with an HLA-A'0201/pp65495-503 peptide, a recombinant adenovirus coding for pp65, in vitro transcribed pp65 mRNA and a recombinant pp65 protein. Peptide stimulation yielded large numbers of peptide-specific CD8+ T cells with high lytic activity while adenovirus or mRNA stimulation resulted in the expansion of CTLs against multiple pp65 epitopes. The recombinant protein activated primarily CD4+ TH cells. Stimulation with DCs co-modified with pp65 mRNA and pp65 protein simultaneously generated both pp65-specific CTLs and TH cells. Such T cells would cover all pp65 epitopes while avoiding potential virus related biohazards. The mRNA/protein combinatory approach can be used to stimulate T cells ex vivo from virtually all stem cell donors for adoptive T cell transfer. I have identified two immunogenic HLA-A'0201-restricted peptide epitopes from the prostate tissue antigen TARP. Repeated stimulations with TARP peptide-pulsed DCs yielded up to 20% TARP-directed CD8+ T cells even when starting from undetectable frequencies (<0.01%). The T cells could be sorted to 99% purity and expanded 1000-fold with retained specificity and activity. We also detected TARP-directed CD8+ T cells in the blood of prostate cancer patients. Therefore, TARP seems to have potential as antigen in DC vaccination or adoptive T cell therapy of prostate cancer.