Ex vivo induction of viral antigen-specific CD8+ T cell responses using mRNA-electroporated CD40-activated B cells

Cell-based immunotherapy, in which antigen-loaded antigen-presenting cells (APC) are used to elicit T cell responses, has become part of the search for alternative cancer and infectious disease treatments. Here, we report on the feasibility of using mRNA-electroporated CD40-activated B cells (CD40-B cells) as alternative APC for the ex vivo induction of antigen-specific CD8(+) T cell responses. The potential of CD40-B cells as APC is reflected in their phenotypic analysis, showing a polyclonal, strongly activated B cell population with high expression of MHC and co-stimulatory molecules. Flow cytometric analysis of EGFP expression 24 h after EGFP mRNA-electroporation showed that CD40-B cells can be RNA transfected with high gene transfer efficiency. No difference in transfection efficiency or postelectroporation viability was observed between CD40-B cells and monocyte-derived dendritic cells (DC). Our first series of experiments show clearly that peptide-pulsed CD40-B cells are able to (re)activate both CD8+ and CD4(+) T cells against influenza and cytomegalovirus (CMV) antigens. To demonstrate the ability of viral antigen mRNA-electroporated CD40-B cells to induce virus-specific CD8+ T cell responses, these antigen-loaded cells were co-cultured in vitro with autologous peripheral blood mononuclear cells (PBMC) for 7 days followed by analysis of T cell antigen-specificity. These experiments show that CD40-B cells electroporated with influenza M1 mRNA or with CMV pp65 mRNA are able to activate antigen-specific interferon (IFN)-gamma-producing CD8(+) T cells. These findings demonstrate that mRNA-electroporated CD40-B cells can be used as alternative APC for the induction of antigen-specific (memory) CD8(+) T cell responses, which might overcome some of the drawbacks inherent to DC immunotherapy protocols.