Conference Proceedings: RNA-transfected CD40-activated B cells as a vaccine strategy in canine malignancies

Introduction:Cell-based vaccine strategies using dendritic cells as cellular adjuvant have entered phase III trials in humans and have been found to be safe, feasible, and potentially efficacious. Canine patients are generally smaller than adult human patients, which makes production of canine dendritic cell (DC) vaccines problematic, given patient size and the small number of available DC precursors. Here we describe feasibility studies of a novel cell-based vaccine strategy which uses CD40-activated B-cells (CD40-B) loaded with RNA. This strategy is based on our observations that RNA-transfected human CD40-B can drive anti-tumor T cell responses. One advantage of using CD40-B cells is the ability to expand this cell population ex vivo, allowing for the numbers of cells required for therapeutic vaccines. Methods:Twenty milliliters of blood were drawn from 6 normal dogs and 5 canine lymphoma patients. Peripheral blood mononuclear cells were separated by Ficoll centrifugation. Culture conditions for B cell activation were optimized using CD40-ligand, canine IL-4, and Toll-like receptor stimulus with CpGoligodinucleotides (ODN). Cyclosporine was added to eliminate peripheral T lymphocytes. Proliferation and activation of CD40-B cells were demonstrated by CFSE dilution of B cells quantified by flow cytometry. Gene transfer was achieved by mRNA electroporation. Results:Marked in vitro stimulation and proliferation of canine peripheral B cells were achieved with soluble trimeric CD40L, canine IL-4, and ODN. CD40-B cells showed dramatic upregulation of MHC class II molecules and CD21 (B-cell activation marker). After two weeks in culture, cells were negative for CD3 and CD4. Canine CD40-B cells were efficiently transfected with mRNA, with >60% of CD40-B expressing green fluorescent protein after GFP mRNA electroporation. Conclusion:RNA-transfected CD40-B cells can be efficiently generated from normal and tumor-bearing dogs. These results provide rationale to test tumor RNA-transfected CD40-B as a novel therapeutic approach to treating canine malignancies. Clinical trials in canine lymphoma have been proposed.