Introduction: Research on natural antibodies against carbohydrate antigens (alphaGal, NeuGc and Sda), complement, coagulation, inflammation and cell mediated immunity (including innate immunity) has promoted production of suitable genetically modified pigs and development of effective monoclonal antibodies that block T cell-B cell (antigen presenting cell) communication through CD40-154 pathway. Recent advances in genome editing technology improved outcomes in pig to NHP xenotransplantation model.
Currently, clinical trials are planned, but further immunological control is needed to achieve long-term results. As with allogeneic transplantation, understanding and controlling T cell indirect recognition pathway in acquired immunity will be essential for xenotransplantation.  Our attention has been directed towards T cell epitopes (porcine-derived peptides presented by HLA class II).  The purpose of this study was to identify porcine protein-derived peptides that can elicit potent immune response.  
Materials and Methods: In this study, we searched for potential porcine protein-derived peptides presented by HLA-class II on human CD14+ cells after phagocytosis of porcine cells and differentiation into dendritic cells (DCs). Human peripheral blood CD14+ monocytes collected from healthy volunteers were cultured with irradiated porcine aortic endothelial cells (PAECs) for 4 days in IL-4/GM-CSF and 2 days in IL-1β/TGFα. Collected cells were used as DCs. After cell lysis, immunoprecipitation with anti-human HLA-class II DR antibody was conducted. Peptides extracted from the specimens were measured by nanoLC-qTOF/MS/MS (zenoTOF7600, SCIEX).
Results: Human CD14+ monocytes efficiently phagocytosed PAECs and differentiated into DCs that proliferate T cells upon cytokine stimulation. Immunoprecipitation of pig endothelial cell-phagocytosed DCs targeting HLA-DR allowed identification of many heterologous antigen-derived peptides.  Peptides derived from Neuropeptide W, Calcium-activated chloride channel regulator 1, Rho-associated protein kinase 2 and so on were detected as candidates for T cell epitopes.
Discussion: The next research question is to confirm whether candidate peptides actually activate effector memory T cells.  The possibility that results may differ depending on pig species and human HLA class II type needs to be considered. Further experiments are in progress.  If a porcine protein antigen that could be a potent T cell epitope can be identified, a strategy to modify it to the human form by genetic modification is feasible. Control of T cell indirect pathway will lead to suppression of de novo anti-pig antibody production, which may be associated with long-term prognosis.