Studies on mRNA electroporation of immature and mature dendritic cells: effects on their immunogenic potential

Previous studies have shown that mRNA-electroporated dendritic cells (DCs) are able to process and present tumor-associated antigens, leading to the activation of tumor-specific T cells in vitro and in vivo. However, the optimal maturation state of antigen loading and half-life of the mRNA-translated protein product and its immunogenic epitopes are significant parameters, which needs to be clarified in order to establish an effective electroporation protocol. In addition, despite extensive experimental investigations and their widespread application in research and clinical environments, little is known of the extent to which the immunological properties of DCs are influenced by electrical fields of critical strengths. We found that the mRNA transfection of DCs after maturation with short and low-voltage square-wave electrical pulses resulted in higher level of antigen expression and viability in addition to higher T-cell stimulatory ability compared to transfection of DCs prior to maturation. Mature mRNA-electroporated DCs showed long-lived expression of EGFP and were able to stimulate influenza matrix protein M1 (M1)-specific T cells up to 24 h after electroporation. However, when DCs were subjected to increasing electrical pulses the level of transgene expression was four-fold upregulated, equipping these DCs to be more potent in inducing M1-specific T cells. Also, the application of long electrical pulses induced further upregulation of HLA-DR, CD80, and CD86 expression in mature DCs, but did not promote phenotypic or functional maturation in immature DCs. These findings support the concept of mRNA transfection of DCs after maturation and also highlight the possibility to use long electrical pulses for further improvement of the immune responses by mRNA-transfected DCs.