Modulation of Graft Arteriosclerosis in a Rat Carotid Transplantation Model

Potent inhibition of OKT3-induced T cell proliferation and suppression of CD147 cell surface expression in HeLa cells by scFv-M6-1B9

CD147, a multifunctional type I transmembrane glycoprotein, has been implicated in various physiological and pathological processes. It is involved in signal transduction pathways and also plays a crucial role in the invasive and metastatic activity of malignant tumor cells. Diminished expression of this molecule has been shown to be beneficial in suppression of tumor progression. In a previous study, we generated and characterized a recombinant antibody fragment, scFv, which reacted specifically to CD147. In the present study, we further investigated the biological properties, function and the effect of generated scFv on CD147 expression. The in vitro study showed that soluble scFv-M6-1B9 produced from E. coli HB2151 bound to CD147 surface molecule and inhibited OKT3-induced T cell proliferation. Furthermore, soluble lysate of scFv-M6-1B9 from 293A cells, transduced with a scFv-M6-1B9 expressing adenovirus vector, recognized both recombinant and native CD147. These results indicate that scFv-M6-1B9 binds with high efficiency and specificity. Importantly, scFv-M6-1B9 intrabody reduced the expression of CD147 on the cell surface of HeLa cells suggesting that scFv-M6-1B9 is biologically active. In conclusion, our present study demonstrated that scFv-M6-1B9 has a great potential to target both the intracellular and the extracellular CD147. The generated scFv-M6-1B9 may be an effective agent to clarify the cellular function of CD147 and may aid in efforts to develop a novel treatment in various human carcinomas.

In vivo effect of bone marrow-derived mesenchymal stem cells in a rat kidney transplantation model with prolonged cold ischemia

Brain death and prolonged cold ischemia are major contributors to the poorer long-term outcome of transplants from deceased donor kidney transplants, with an even higher impact if expanded criteria donors ('marginal organs') are used. Targeting ischemia-reperfusion injury-related intragraft inflammation is an attractive concept to improve the outcome of those grafts. As mesenchymal stem cells (MSCs) express both immunomodulatory and tissue repair properties, we evaluated their therapeutic efficacy in a rat kidney transplant model of prolonged cold ischemia. The in vitro immunomodulatory capacity of bone marrow-derived rat MSCs was tested in co-cultures with rat lymph node cells. For in vivo studies, Dark Agouti rat kidneys were cold preserved and transplanted into Lewis rats. Syngeneic Lewis MSCs were administered intravenously. Transplants were harvested on day 3, and inflammation was examined by quantitative RT-PCR and histology. Similarly to MSCs from other species, rat MSCs in vitro also showed a dose-dependent immunomodulatory capacity. Most importantly, in vivo administration of MSCs reduced the intragraft gene expression of different pro-inflammatory cytokines, chemokines, and intercellular adhesion molecule-1. In addition, fewer antigen-presenting cells were recruited into the renal allograft. In conclusion, rat MSCs ameliorate inflammation induced by prolonged cold ischemia in kidney transplantation.

Exploitation of herpesvirus immune evasion strategies to modify the immunogenicity of human mesenchymal stem cell transplants

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent cells residing in the connective tissue of many organs and holding great potential for tissue repair. In culture, human MSCs (hMSCs) are capable of extensive proliferation without showing chromosomal aberrations. Large numbers of hMSCs can thus be acquired from small samples of easily obtainable tissues like fat and bone marrow. MSCs can contribute to regeneration indirectly by secretion of cytokines or directly by differentiation into specialized cell types. The latter mechanism requires their long-term acceptance by the recipient. Although MSCs do not elicit immune responses in vitro, animal studies have revealed that allogeneic and xenogeneic MSCs are rejected.

METHODOLOGY/PRINCIPAL FINDINGS

We aim to overcome MSC immune rejection through permanent down-regulation of major histocompatibility complex (MHC) class I proteins on the surface of these MHC class II-negative cells through the use of viral immune evasion proteins. Transduction of hMSCs with a retroviral vector encoding the human cytomegalovirus US11 protein resulted in strong inhibition of MHC class I surface expression. When transplanted into immunocompetent mice, persistence of the US11-expressing and HLA-ABC-negative hMSCs at levels resembling those found in immunodeficient (i.e., NOD/SCID) mice could be attained provided that recipients' natural killer (NK) cells were depleted prior to cell transplantation.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate the potential utility of herpesviral immunoevasins to prevent rejection of xenogeneic MSCs. The observation that down-regulation of MHC class I surface expression renders hMSCs vulnerable to NK cell recognition and cytolysis implies that multiple viral immune evasion proteins are likely required to make hMSCs non-immunogenic and thereby universally transplantable.

Intrabody Expression in Mammalian Cells

The intracellular expression of antibodies or antibody fragments (intrabodies) in different compartments of mammalian cells allows to block or modulate the function of endogenous molecules. Intrabodies can alter protein folding, protein-protein, protein-DNA, protein-RNA interactions and protein modification. They can induce a phenotypic knockout and work as neutralizing agents by direct binding to the target antigen, by diverting its intracellular traffic or by inhibiting its association with binding partners. They have been largely employed as research tools and are emerging as therapeutic molecules for the treatment of human diseases as viral pathologies, cancer and misfolding diseases. The fast growing bio-market of recombinant antibodies provides intrabodies with enhanced binding specificity, stability and solubility, together with lower immunogenicity, for their use in therapy. This chapter describes the crucial aspects required to express intrabodies in different intracellular compartments of mammalian cells, their various modes of action and gives an update on the applications of intrabodies in human diseases.

Immune privilege of endothelial cells differentiated from endothelial progenitor cells

AIMS

The application of autologous endothelial progenitor cells (EPC) is a promising approach in cardiovascular regeneration, but the availability of cells in appropriate numbers is the limiting factor. Allogeneic EPC would be an alternative, and we therefore analysed the immunogenicity of EPC-derived endothelial cells (EC) to evaluate their potential usefulness.

METHODS AND RESULTS

Circulating EPC from rat were differentiated into EC and characterized phenotypically and functionally. Major histocompatibility complex (MHC) expression in response to interferon-gamma was determined compared with rat aortic EC, and in vitro humoral and cellular allogeneic responses were analysed. To determine the in vivo effects, acellular aortic grafts were endothelialized in vitro with EPC-derived EC and transplanted in a complete allogeneic mismatch rat aortic interposition model. EPC-derived EC expressed endothelial-specific markers and low levels of MHC class I (MHC I), but no constitutive MHC class II (MHC II). When stimulated with interferon-gamma, they upregulated MHC I and moderately upregulated MHC II. They were protected against alloantibody/complement-mediated lysis and allospecific cytotoxic T lymphocyte activity. They were less potent in allogeneic stimulation of CD4 T cells than aortic EC. Seeding of EPC-derived EC into acellular grafts led to excellent endothelialization, and allogeneic aortic transplantation induced only mild inflammatory responses without signs of rejection.

CONCLUSION

EPC-derived EC are protected against allospecific cellular immune responses and humoral-mediated attacks in vitro. When transplanted in vivo as a component of vascular grafts, these cells are not rejected, which makes them useful in therapeutic applications, especially vascular reconstruction.