Scientific Report 2007

Molecular and Experimental Medicine

Division of Blood Cell and Vascular Biology

Functional Genomics, Angiogenesis, and Gene Therapy in Transplantation and Retroviral Risks in Xenotransplantation

D.R. Salomon, S.M. Kurian, S. Cherqui, M. Auerbach, K. Marcucci, Y. Grigorev, J. Yang, D. Campbell, C. Marsh, S. Head,* J.R. Yates,** A. Nakorchevskiy,** P.Y. Kwok,*** J. Warrington,**** S. Horvath,***** J. Papp,***** C.A. Wilson^†

* DNA Microarray Core, Scripps Research
** Department of Cell Biology, Scripps Research
*** University of California, San Francisco, California
**** Affymetrix, Santa Clara, California
***** University of California, Los Angeles, California
^† Food and Drug Administration, Bethesda, Maryland

Successful transplantation requires the orchestration of complex mechanisms set in motion by surgical implantation of cells or organs into a patient. Regulation of the immune response with immunosuppressive drugs has received the most attention. But equally important is the unique cell biology of the transplanted tissue that evolves under stress after transplantation and ultimately determines the function of the transplant.

We use functional genomics to understand the expression and function of genes and proteins after transplantation. How do immunosuppressive drugs work at this fundamental level? What is the difference between a successful and an unsuccessful transplant? Another challenge is to develop an unlimited supply of healthy tissues for transplantation, for example, pancreatic islets to cure diabetes. Progenitor cells, including stem cells from adults, could be used to enhance angiogenesis, the formation of new blood vessels. Revascularization of cell transplants is a critical step in successful engraftment and function. We are showing how revascularization can be enhanced by gene therapy.

Animals could be used as donors, called xenotransplantation, although the potential risks for infectious disease inherent in using animal donors must be better understood so that this method can be used safely. In studies on xenotransplantation, we have focused on the risk associated with porcine endogenous retrovirus (PERV) in pig tissues.

Functional Genomics in Organ Transplantation

We are using high-density gene chip arrays, tandem mass spectrometry proteomics, and complex trait genetics based on single nucleotide polymorphisms to establish profiles to diagnose acute and chronic transplant rejection. These studies include patients with both kidney and liver transplants. A major objective is to identify new pathways that drive the immune response and cell biology of organ transplants that might be used as the next generation of targets for therapy. For example, with all current drug therapies, the target is the patient's immune response; none target the transplant itself, even though the function of the transplant is the ultimate determinant of success or failure.

We would like to test the hypothesis that gene expression profiles can be used to create a metric or simple diagnostic test for adequate immunosuppression. Physicians could then adjust a patient's drugs on the basis of an objective measure. Our long-term goal is to identify genes, proteins, and genetic polymorphisms that determine the outcome of a transplant to create a systems biology–based understanding of immunity at the molecular level.

Angiogenesis and Gene Therapy

A major unmet medical need is a treatment for ischemic vascular diseases of the peripheral vasculature and the heart. We are using retroviral gene therapy to deliver novel proangiogenic molecules to endothelial progenitors that significantly enhance revascularization of transplanted islet cells. We have also created models for ischemia in the leg and in the heart and are testing the effect of transplanting a novel population of human stem cells from adults. In another project, we are using gene therapy and stem cells from adults to treat a congenital form of kidney failure.

Xenotransplantation and Risk for Infectious Disease

Although xenotransplantation is a logical strategy to address current shortages of human donor organs, a critical concern is the potential of moving infections from the animals to humans. We established a new mouse model for pig islet xenotransplantation, showed that multiple tissues become infected with PERV, identified the human receptors for this retrovirus, identified functional defects in nonhuman primate cells for viral infection, and continued to refine our understanding of the viral biology and potential risks in a new model of mice transgenic for the human receptor for PERV. The results of our studies in the transgenic mice have provided the first evidence of a productive PERV infection in any animal (Fig. 1). We are now using this model to study the immune response and develop a vaccine. Our objective is to develop a vaccine to eliminate the risk of PERV and thus safely advance clinical islet xenotransplantation.

Fig. 1. Infection of the liver with PERV. Mice transgenic for the human receptor for PERV were exposed to PERV produced by pig cells, including via transplantation of pig islets. The micrograph shows widespread infection of hepatocytes. Infected cells are green, cell membranes are red, and nuclei are blue.

Publications

Cherqui, S., Kingdon, K.M.,Thorpe, C., Kurian, S.M., Salomon, D.R. Lentiviral gene delivery of vMIP-II to transplanted endothelial cells and endothelial progenitors is proangiogenic in vivo. Mol. Ther. 15:1264, 2007.

de Jonge, J., Kurian, S., Shaked, A., Salomon, D.R., Olthoff, K.M. Molecular networks of hepatic regeneration and metabolism in human living and deceased donor liver transplants. Hepatology, in press.

Flechner, S.M., Godfarb, D., Solez, K., Modlin, C.S., Mastroianni, B., Savas, K., Babineau, D., Kurian, S.M., Salomon, D.R., Novick, A.C., Cook, D.J. Kidney transplantation with sirolimus and mycophenolate mofetil-based immunosuppression: 5-year results of a randomized prospective trial compared to calcineurin inhibitor drugs. Transplantation 83:883, 2007.

Hermida-Prieto, M., Doménech, N., Moscoso, I., Diaz, T., Ishii, J., Salomon, D.R., Mañez, R. Lack of cross-species transmission of porcine endogenous retrovirus (PERV) to transplant recipients and abattoir workers in contact with pigs. Transplantation 84:548, 2007.

Niculescu, A.B., Lulow, L.L., Ogden, C.A., Le-Niculescu, H., Salomon, D.R., Schork, N.J., Caligiuri, M.P., Lohr, J.B. PhenoChipping of psychotic disorders: a novel approach for deconstructing and quantitating psychiatric phenotypes. Am. J. Med. Genet. B Neuropsychiatr. Genet. 141:653, 2006.

Solez, K., Colvin, R.B., Racusen, L.C., Sis, B., Halloran, P.F., Birk, P.E., Campbell, P.M., Cascalho, M., Collins, A.B., Demetris, A.J., Drachenberg, C.B., Gibson, I.W., Grimm, P.C., Haas, M., Lerut, E., Liapis, H., Mannon, R.B., Marcus, P.B., Mengel, M., Mihatsch, M.J., Nankivell, B.J., Nickeleit, V., Papadimitriou, J.C., Platt, J.L., Randhawa, P., Roberts, I., Salinas-Madriga, L., Salomon, D.R., Seron, D., Sheaff, M., Weening, J.J. Banff '05 Meeting Report: differential diagnosis of chronic allograft injury and elimination of chronic allograft nephropathy ('CAN'). Am. J. Transplant. 7:518, 2007.