The use of pigs as organ donors for human transplantation represents a solution to the escalating shortage of organs that are available for patients with end-stage diseases. Wild type pig organs are hyperacutely rejected, however, by pre-existing natural antibodies directed at the 1-D-galactosyl-(1->3)-1-D-galactoside (gal 11,3gal) carbohydrate, which is expressed on pig, cells and absent in humans. Organs derived from gal knockout pigs have been bred as potential donors, but recent studies from several laboratories have shown that although these organs do not undergo hyperacute rejection, they are still rejected within six months. Acute humoral rejection (AHXR) and thrombosis contribute to the demise of these grafts. Anti-non-gal xenoantibodies have been shown to be induced in non-human primates transplanted with gal knockout donor organs, but the specificity, origin and structure of these antibodies has not been determined. Currently available immunosuppressive drugs are ineffective in preventing AHXR. Additional research is needed to determine why acute humoral xenograft rejection occurs, and to define a means to prevent it.
Our specific aims propose a detailed and systematic study on the origin and binding specificity of xenoantibodies that still reject genetically-manipulated xenografts in non-human primates transplanted with genetically-modified organs. This work would provide information that is lacking but necessary for the design of a successful approach to preventing xenograft rejection. The experimental samples that we plan to examine in our study have been bred on a gal knockout background and have additional transgenes such as CD39 to prevent thrombosis. We will further determine whether an anti-idiotypic antibody that identifies B cells producing xenoantibodies will prevent AHXR in vivo. This grant proposal will extend our work in the previous grant period in which we defined the structure of immunoglobulin genes encoding xenoantibodies to wild type pig organs in non-human primates and have identified an anti-idiotypic antibody with the ability to define B cells producing xenoantibodes.

Public Health Relevance

The use of specifically bred pigs as organ donors for human transplantation (xenotransplantation) could provide organs for the many patients who may otherwise die waiting. These organs function for three to six months before the grafts are rejected by antibodies. This study will identify the genes that encode these antibodies and will test novel ways to prevent this antibody response.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Transplantation, Tolerance, and Tumor Immunology (TTT)
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Nabavi, Nasrin N
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Loma Linda University
Anatomy/Cell Biology
Schools of Medicine
Loma Linda
United States
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Stewart, John M; Tarantal, Alice F; Hawthorne, Wayne J et al. (2015) Clonidine inhibits anti-non-Gal IgM xenoantibody elicited in multiple pig-to-primate models. Xenotransplantation 22:413-26
Chen, Yan; Stewart, John M; Gunthart, Mirja et al. (2014) Xenoantibody response to porcine islet cell transplantation using GTKO, CD55, CD59, and fucosyltransferase multiple transgenic donors. Xenotransplantation 21:244-53
Stewart, John M; Tarantal, Alice F; Chen, Yan et al. (2014) Anti-non-Gal-specific combination treatment with an anti-idiotypic Ab and an inhibitory small molecule mitigates the xenoantibody response. Xenotransplantation 21:254-66
Stewart, John M; Tarantal, Alice F; Hawthorne, Wayne J et al. (2014) Rhesus monkeys and baboons develop clotting factor VIII inhibitors in response to porcine endothelial cells or islets. Xenotransplantation 21:341-52
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Fischer-Lougheed, Jacqueline; Gregory, Clare; White, Zena et al. (2008) Identification of an anti-idiotypic antibody that defines a B-cell subset(s) producing xenoantibodies in primates. Immunology 123:390-7
Kiernan, K; Harnden, I; Gunthart, M et al. (2008) The anti-non-gal xenoantibody response to xenoantigens on gal knockout pig cells is encoded by a restricted number of germline progenitors. Am J Transplant 8:1829-39
Kearns-Jonker, Mary; Barteneva, Natasha; Mencel, Robert et al. (2007) Use of molecular modeling and site-directed mutagenesis to define the structural basis for the immune response to carbohydrate xenoantigens. BMC Immunol 8:3
Zahorsky-Reeves, Joanne L; Kearns-Jonker, Mary K; Lam, Tuan T et al. (2007) The xenoantibody response and immunoglobulin gene expression profile of cynomolgus monkeys transplanted with hDAF-transgenic porcine hearts. Xenotransplantation 14:135-44
Fischer-Lougheed, J Y; Tarantal, A F; Shulkin, I et al. (2007) Gene therapy to inhibit xenoantibody production using lentiviral vectors in non-human primates. Gene Ther 14:49-57

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