Tissue Engineering Cells for Allogeneic Trasnplantation

Abstract

The immune response is a major barrier to the successful transplantation of organs and tissues required in the treatment of many human diseases. Although the field of tissue engineering was created to address the shortage of human organs and tissues, the immune response remains a substantial challenge, impeding the development of allogeneic biological substitutes to repair, replace and regenerate tissues. Specifically, the T cell mediated immune response initiated through the recognition of cell surface Major histocompatibility complex Class I (MHCI) molecules is the primary cause of acute allograft rejection. In nature, viruses have evolved many mechanisms to exploit weaknesses of the T cell response to evade detection. Viral mechanisms to modulate the MHCI molecule can be effectively applied to allogeneic cells in a tissue-engineered construct to evade detection by CD8+ Cytotoxic T Lympocytes (CTLs) and Natural Killer (NK) cells of the immune system. We demonstrate the successful application of a retroviral vector to over-express the Kaposi's sarcoma-associated herpesvirus (KSHV) immunomodulatory protein, MIR2, in human monocyte-like leukemia cells to differentially downregulate cell surface MHCI, ICAM-1 and B7-2 molecules. We also developed a novel flow cytometry-based cytotoxicity assay to demonstrate that this differential downregulation of immunoactive molecules has the functional effect of significantly reducing CTL-mediated cytotoxicity, without altering NK-mediated cytotoxicity. We believe that this approach provides a potential solution to circumvent the acute immune rejection of allografts in vivo, and can also lead to the development of "universal" donor cells for tissue engineering applications that will not require anti-rejection drugs.