Purpose: Supplementing conventional treatment with gene therapy to induce an immune response might be beneficial to cancer patients. In this study, we evaluated the efficiency of transduction of breast cancer cells with recombinant adeno-associated virus (rAAV) and effects of cytotoxic agents used in chemotherapy. Furthermore, the capacity of tumor cells expressing transgenic CD40 ligand (CD40L) to stimulate dendritic cells was measured.
Methods: Breast cancer cell lines were infected with a rAAV encoding the enhanced green fluorescent protein (EGFP) or murine CD40L and transgene expression was analyzed by flow cytometry. Stimulation of isolated human dendritic cells by CD40L-expressing tumor cells was quantified by measuring secreted interleukin 12.
Results: Infection with an EGFP-encoding rAAV resulted in variable fractions (14-93%, mean 42%) of transgene-expressing cells. Pre-incubation of MM 157, MM 231, and MCF7 cells with epirubicin or carboplatin substantially increased AAV-mediated transgene expression. rAAV/CD40L was used to generate CD40L-transgenic tumor cells, which specifically activated immature dendritic cells, as confirmed by blocking with an antibody binding to CD40L.
Conclusions: The efficiency of rAAV-mediated gene transfer into breast cancer cells is significantly higher than previously reported and can be further enhanced by co-administration of chemotherapeutic agents. We also confirmed that breast cancer cells can activate human dendritic cells after infection with a CD40L-encoding rAAV.