Characterization of dendritic cell handling of cell-associated membrane and cytoplasmic proteins from live and apoptotic cells

Dendritic cells (DCs) are a heterogeneous population of immune cells that influence a wide variety of immune responses, including immunity to infectious diseases and malignant tumors, and in the generation of tolerance. In their immature state, DCs are highly specialized at capturing and internalizing exogenous antigens. Cell-associated antigens are of special interest because they play a role in both the induction of immunity and tolerance. This study aimed to add to the field of DC biology by further describing how DCs handle cell-associated proteins from both live and apoptotic cells. We hypothesized that the DCs ability to capture, internalize, and process integral membrane proteins would vary based on the target cell's viability and that the DCs ability to capture cell-associated protein would vary based on the protein's intracellular localization. To quantitatively and qualitatively characterize uptake, we created a biologically relevant system using the Epstein Barr virus latent membrane protein 2 and the melanoma protein gp100, each fused to the enhanced green fluorescent protein (EGFP) and expressed at the outer plasma membrane of a tumor cell line, along with a cell line expressing EGFP in the cytoplasm. We found (1) DCs captured integral membrane proteins but not cytoplasmic protein from live cells; (2) DCs captured membrane and cytoplasmic proteins from apoptotic cells more efficiently and at a faster rate than from live cells; (3) during direct physical interactions DCs transiently surveyed live cells capturing small quantities of membrane, but stayed in prolonged contact with apoptotic cells while continuously internalizing membrane fragments; (4) DC internalization of membrane protein from live cells was clathrin-dependent while uptake from apoptotic cells was clathrin- and caveolae-dependent; and (5) internalized membrane protein from both live and apoptotic cells was found in early endosomes, late endosomes, and lysosomes. This work has potential broad public health implications as it is important to understand all aspects of DC biology when developing vaccines for both chronic and acute diseases. We hope that by uncovering the intricacies of DC handling of cell-associated proteins we will gain a better understanding of how to possibly manipulate DCs in order to influence the immune response

High-Level Antigen Expression and Sustained Antigen Presentation in Dendritic Cells Nucleofected with Wild-Type Viral mRNA but Not DNA▿

Dendritic cells (DC) are potent antigen-presenting cells that hold promise as cell-based therapeutic vaccines for infectious diseases and cancer. Ideally, DC would be engineered to express autologous viral or tumor antigens to ensure the presentation of relevant antigens to host T cells in vivo; however, expression of wild-type viral genes in primary cell lines can be problematic. Nucleofection is an effective means of delivering transgenes to primary cell lines, but its use in transfecting DNA or mRNA into DC has not been widely investigated. We show that nucleofection is a superior means of transfecting human and monkey monocyte-derived DC with DNA and mRNA compared to lipofection and conventional electroporation. However, the delivery of DNA and mRNA had significantly different outcomes in transfected DC. DC nucleofected with DNA encoding green fluorescent protein (GFP) had poor antigen expression and viability and were refractory to maturation with CD40 ligand. In contrast, >90% of DC expressed uniform and high levels of GFP from 3 h to 96 h postnucleofection with mRNA while maintaining a normal maturation response to CD40 ligation. Monkey DC nucleofected with wild-type, non-codon-optimized mRNA encoding simian immunodeficiency virus Gag stimulated robust antigen-specific effector T-cell responses at 24 h and 48 h postnucleofection, reflecting sustained antigen presentation in transfected DC, whereas no detectable T-cell response was noted when DC were nucleofected with DNA encoding the same Gag sequence. These data indicate that mRNA nucleofection may be an optimal means of transfecting DC with autologous tumor or viral antigen for DC-based immunotherapy