Transgenic Pigs Expressing Human Cd59 and Decay-Accelerating Factor Produce an Intrinsic Barrier to Complement-Mediated Damage1

Thymus transplantation is a promising strategy to induce xenotolerance, but may also induce an autoimmune syndrome (AIS). The pathogenesis of this AIS was explored using nude rats as recipients. Thymus grafts consisted of fetal hamster thymic tissue with or without mixing with fetal rat tissue such as thymus, thyroid, salivary gland, and heart. All hamster thymus recipients died of AIS within 2–3 mo. In most recipients of xenothymus mixed with rat tissues such as thymus, thyroid, and salivary gland, but not heart, AIS was prevented, indicating an insufficient presence of rat epithelial cell Ags within the xenothymus. AIS could be transferred to control nude rats by whole splenocytes or by splenocyte subpopulations such as CD3+, CD3−, and B lymphocytes, but not by non-T, non-B cells from AIS animals. This transfer could be suppressed by cotransferring either CD4+ or CD8+ lymphocytes from euthymic rats, but not by splenocytes from recipients of syngeneic or xenogeneic thymus mixed with rat tissue, indicating a defective generation of regulatory lymphocytes. As for CD4+ regulatory cells this defect was probably qualitative, because the percentages of CD4+CD25+ or CD4+CD45RClow populations were normal after xenothymus transplantation. As for the CD8+ regulatory cells, the defect was quantitative, as CD8+ cell levels always remained low. The latter was related to the nonvascularized nature of thymus grafts. In conclusion, AIS after xenothymus transplantation in nude rats is due to a combination of insufficient intrathymic presence of host-type epithelial cell Ags and a defective generation of regulatory T lymphocytes.

Section: Pathogenesis Of Autoimmunity After Xenogeneic Thymus Transplmentioning

confidence: 99%

Pathogenesis of Autoimmunity After Xenogeneic Thymus Transplantation

Yan

Devos

et al. 2003

“…By forming pores in the cell membrane, C5b-9 causes cell death in part through unregulated Ca 2ϩ influx (21,22). However, OLG, like other nucleated cells, survive limited complement attack through protection by complement-inhibitory proteins and by elimination of membranes carrying C5b-9 complexes (23)(24)(25)(26)(27)(28). We recently demonstrated that sublytic doses of C5b-9 inhibit the caspase-3-dependent OLG apoptosis induced in vitro by serum deprivation or TNF-␣ (29).…”

Section: O Ligodendrocytes (Olg)mentioning

confidence: 99%

C5b-9 Terminal Complement Complex Protects Oligodendrocytes from Death by Regulating Bad Through Phosphatidylinositol 3-Kinase/Akt Pathway

Soane¹,

Cho²,

Niculescu

et al. 2001

103

Apoptosis of oligodendrocytes is induced by serum growth factor deprivation. We showed that oligodendrocytes and progenitor cells respond to serum withdrawal by a rapid decline of Bcl-2 mRNA expression and caspase-3-dependent apoptotic death. Sublytic assembly of membrane-inserted terminal complement complexes consisting of C5b, C6, C7, C8, and C9 proteins (C5b-9) inhibits caspase-3 activation and apoptotic death of oligodendrocytes. In this study, we examined an involvement of the mitochondria in oligodendrocyte apoptosis and the role of C5b-9 on this process. Decreased phosphatidylinositol 3-kinase and Akt activities occurred in association with cytochrome c release and caspase-9 activation when cells were placed in defined medium. C5b-9 inhibited the mitochondrial pathway of apoptosis in oligodendrocytes, as shown by decreased cytochrome c release and inhibition of caspase-9 activation. Phosphatidylinositol 3-phosphate kinase and Akt activities were also induced by C5b-9, and the phosphatidylinositol 3-phosphate kinase inhibitor LY294002 reversed the protective effect of C5b-9. Phosphatidylinositol 3-phosphate kinase activity was also responsible for the phosphorylation of Bad at Ser112 and Ser136. This phosphorylation resulted in dissociation of Bad from the Bad/Bcl-xL complex in a Giα-dependent manner. The mitochondrial pathway of oligodendrocyte apoptosis is, therefore, inhibited by C5b-9 through post-translational regulation of Bad. This mechanism may be involved in the promotion of oligodendrocyte survival in inflammatory demyelinating disorders affecting the CNS.

“…Many porcine cell types and all vascularized organs transplanted into primate models are rejected by both humoral and cellular mechanisms (5,6). Major advances have been made in abrogating the humoral component that leads to hyperacute rejection, mainly through complement inhibition (7)(8)(9)(10). However, even in the presence of complement inhibitors and systemic immunosuppression, xenografts are rejected due to delayed xenograft rejection (DXR) 4 (3,6,(11)(12)(13)(14).…”

mentioning

confidence: 99%

Human NK Cell-Mediated Cytotoxicity Triggered by CD86 and Galα1,3-Gal Is Inhibited in Genetically Modified Porcine Cells

Costa

Barber

Fodor

2002

Delayed xenograft rejection is a major hurdle that needs to be addressed to prolong graft survival in pig-to-primate xenotransplantation. NK cell activation has been implicated in delayed xenograft rejection. Both Ab-dependent and independent mechanisms are responsible for the high susceptibility of porcine cells to human NK cell-mediated cytotoxicity. Previous reports demonstrated a role of Galα1,3-Gal Ag in triggering the Ab-independent responses. We hypothesize that expression of CD80 and/or CD86 on porcine cells may also play a role in NK cell activation as human NK cells express a variant of CD28. Our initial analysis showed that porcine endothelial cells and fibroblasts express CD86, but not CD80. Genetic engineering of these cells to express hCD152-hCD59, a chimeric molecule designed to block CD86 in cis, was accompanied by a reduction in susceptibility to human NK cell-mediated cytotoxicity. The use of a specific anti-porcine CD86-blocking Ab and the NK92 and YTS cell lines further confirmed the involvement of CD86 in triggering NK cell-mediated lysis of porcine cells. Maximal protection was achieved when hCD152-hCD59 was expressed in H transferase-transgenic cells, which show reduced Galα1,3-Gal expression. In this work, we describe two mechanisms of human NK cell-mediated rejection of porcine cells and demonstrate that genetically modified cells resist Ab-independent NK cell-mediated cytotoxicity.