Generation of cytotoxic T lymphocytes specific for the prostate and breast tissue antigen TARP

Expansion of cytotoxic T lymphocytes (CTL) directed against peptide epitopes from antigens that are specifically expressed by normal and neoplastic prostate epithelial cells has during the last years emerged as an interesting therapeutic approach to treat advanced prostate cancer. TCRgamma alternate reading frame protein (TARP) is a protein that in males is specifically expressed by normal prostate epithelial cells and prostate cancer cells. We have evaluated TARP for human leukocyte antigen (HLA)-A*0201-restricted peptides capable of triggering TARP-specific CTL.

Dendritic cells (DC) were pulsed either with synthetic peptides derived from the natural amino acid sequence of TARP or with cognate peptides having enhanced affinity for HLA-A*0201 due to an N-terminal anchor residue substitution. The peptide-pulsed DC were used to stimulate autologous T cells ex vivo.

We were able to generate T cells against TARP(27-35) and TARP(4-13) and their mutated counterparts TARP(V28L)(27-35) and TARP(P5L)(4-13). The use of affinity-enhanced peptides resulted in the generation of T cells recognizing target cells displaying either wild-type or mutated peptide. We further show that TARP-specific T cells can be tetramer-sorted and subsequently expanded to large numbers by general T cell stimulation, with retained specificity and activity. Sorted and expanded T cells, obtained by stimulation with TARP(P5L)(4-13), exert moderate lysis of the TARP-expressing prostate cancer cell line, LNCaP, and breast cancer cell line, MCF-7, indicating that the TARP(4-13) epitope may be endogenously processed and presented by TARP-positive, HLA-A*0201-positive cells.

Our findings suggest that synthetic TARP peptides, such as TARP(P5L)(4-13), may play a role in prostate and breast cancer immunotherapy.