title: The critical role of mouse CD4+ cells in the rejection of highly disparate xenogeneic pig thymus grafts.
abstract: Long-term survival of fetal pig thymus (FP THY) grafts and efficient repopulation of mouse CD4+ T cells is achieved in thymectomized (ATX) B6 mice that receive T and NK cell depletion by injection of a cocktail of mAbs (GK1.5, 2.43, 30-H12, and PK136) and fetal pig thymus/liver (FP THY/LIV) grafts. The requirement for each mAb in this conditioning regimen in order to avoid the rejection of FP THY grafts has not yet been defined. In our present studies, CD4 cell-depleted ATX B6 mice and euthymic MHC class II-deficient (IIKO) mice were employed to investigate the role of mouse CD4+ cells in the rejection of FP THY grafts in vivo. After grafting FP THY/LIV to CD4+ cell-depleted ATX B6 mice, efficient repopulation of mouse CD4+ T cells was observed in the periphery. However, only two of four mice had remaining FP THY grafts by 17 weeks post-implantation, and these were of poor quality, whereas four of four T and NK cell-depleted ATX B6 mice had well-developed FP THY grafts. Furthermore, three of four FP THY/LIV-grafted, CD4+ cell-depleted ATX B6 mice rejected donor MHC-matched pig skin grafts. In contrast, three of three FP THY/LIV grafted, T and NK cell-depleted, ATX B6 mice accepted donor MHC-matched pig skin grafts, suggesting that optimal tolerance to xenogeneic pig antigens was not achieved in mice conditioned only with anti-CD4 mAb. ATX B6 mice treated with only anti-CD8 mAb rejected FP THY completely by 6 weeks post-grafting, a time when CD4+ cell-depleted ATX B6 mice had well-vascularized FP THY grafts. In addition, when euthymic IIKO mice were pre-treated with the standard conditioning regimen that includes four different mAbs, FP THY grafts survived and supported the repopulation of mouse CD4+ T cells in the periphery, while high levels of mouse CD8+ T cells developed in host thymi. These studies suggest that mouse CD4+ T cells play a critical role in the acute rejection of xenogeneic FP THY grafts. Without help from CD4+ cells, mouse CD8+ cells, NK, NK/T, and TCR(gamma/delta)+ T cells do not mediate acute rejection of FP THY grafts. Furthermore, our results suggest that other cell subsets besides CD4+ T cells play a role in the delayed rejection of highly disparate xenogeneic FP THY grafts.
authors.affiliation: Bone Marrow Transplantation Section, Transplantation Biology Research Center, Massachusetts General Hospital/Harvard Medical School, Boston 02129, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhao
authors.forename: K
authors.initials: K
authors.lastname: Swenson
authors.forename: T
authors.initials: T
authors.lastname: Wekerle
authors.forename: J I
authors.initials: JI
authors.lastname: Rodriguez-Barbosa
authors.forename: J S
authors.initials: JS
authors.lastname: Arn
authors.forename: M
authors.initials: M
authors.lastname: Sykes
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D006084:Graft Rejection / Q000276:immunology*; D006085:Graft Survival / Q000276:immunology; D016031:Liver Transplantation / Q000276:immunology; D008212:Lymphocyte Depletion; D051379:Mice; D008810:Mice, Inbred C57BL; D016038:Skin Transplantation / Q000276:immunology; D013552:Swine; D013934:Thymectomy; D013950:Thymus Gland / Q000637:transplantation*; D013997:Time Factors; D014183:Transplantation, Heterologous / Q000276:immunology*