DENDRITIC CELLS RETROVIRALLY TRANSDUCED WITH A MODEL ANTIGEN GENE ARETHERAPEUTICALLY EFFECTIVE AGAINST ESTABLISHED PULMONARY METASTASES

Dendritic cells (DCs) are bone marrow-derived leukocytes that function as potent antigen presenting cells capable of initiating T cell-depen dent responses from quiescent lymphocytes. DC pulsed with tumor-associ ated antigen (TAA) peptide or protein have recently been demonstrated to elicit antigen-specific protective antitumor immunity in a number o f murine models. Transduction of DCs with TAA genes may allow stable, prolonged antigen expression as well as the potential for presentation of multiple, or unidentified, epitopes in association with major hist ocompatibility complex class I and/or class II molecules. To evaluate the potential efficacy of retrovirally transduced DCs, bone marrow cel ls harvested from BALB/c mice were transduced with either a model anti gen gene encoding beta-galactosidase (beta-gal) or a control gene enco ding rat HER-2/neu (Neu) by coculture with irradiated ecotropic retrov iral producer lines. Bone marrow cells were differentiated into DC in vitro using granulocyte/macrophage colony-stimulating factor and inter leukin-4. After 7 d in culture, cells were 45-78% double positive for DC phenotypic cell surface markers by FACS(C) analysis, and DC transdu ced with beta-gal were 41-72% positive for beta-gal expression by X-ga l staining. In addition, coculture of beta-gal transduced DC with a be ta-gal-specific T cell line (CTLx) resulted in the production of large amounts of interferon-gamma, demonstrating that transduced DCs could process and present endogenously expressed beta-gal. DC transduced wit h beta-gal and control rat HER-2/neu were then used to treat 3-d lung metastases in mice bearing an experimental murine tumor CT26.CL25, exp ressing the model antigen, beta-gal. Treatment with beta-gal-transduce d DC significantly reduced the number of pulmonary metastatic nodules compared with treatment with Hank's balanced salt solution or DCs tran sduced with rat HER-2/neu. In addition, immunization with beta-gal-tra nsduced DCs resulted in the generation of antigen-specific cytotoxic T lymphocytes (CTLs), which were significantly more reactive against re levant tumor targets than CTLs generated from mice immunized with DCs pulsed with the L-d-restricted beta-gal peptide. The results observed in this rapidly lethal tumor model suggest that DCs transduced with TA A may be a useful treatment modality in tumor immunotherapy.