Tolerization of Anti–Galα1-3Gal Natural Antibody–forming B Cells by Induction of Mixed Chimerism

Abstract

Xenotransplantation could overcome the severe shortage of allogeneic organs, a major factor limiting organ transplantation. Unfortunately, transplantation of organs from pigs, the most suitable potential donor species, results in hyperacute rejection in primate recipients, due to the presence of anti–Galα1-3Gal (Gal) natural antibodies (NAbs) in their sera. We evaluated the ability to tolerize anti-Gal NAb–producing B cells in α1,3-galactosyltransferase knockout (GalT KO) mice using bone marrow transplantation (BMT) from GalT+/+ wild-type (WT) mice. Lasting mixed chimerism was achieved in KO mice by cotransplantation of GalT KO and WT marrow after lethal irradiation. The levels of anti-Gal NAb in sera of mixed chimeras were reduced markedly 2 wk after BMT, and became undetectable at later time points. Immunization with Gal+/+ xenogeneic cells failed to stimulate anti-Gal antibody production in mixed chimeras, whereas the production of non–Gal-specific antixenoantigen antibodies was stimulated. An absence of anti-Gal–producing B cells was demonstrated by enzyme-linked immunospot assays in mixed KO+WT→ KO chimeras. Thus, mixed chimerism efficiently induces anti-Gal–specific B cell tolerance in addition to T cell tolerance, providing a single approach to overcoming both the humoral and the cellular immune barriers to discordant xenotransplantation.

Induction of molecular chimerism by gene therapy prevents antibody-mediated heart transplant rejection

“…Inducing molecular chimerism results in the same stable and specific tolerance to αGal established following induction of mixed cellular chimerism. 11,26 We suggest that similar approaches could be used to prevent rejection of ABO incompatible allotransplants and autoimmune diseases.…”

“…11 Indeed, it has been known for many years that a state of mixed (donor and host) hematopoietic chimerism, induced by bone marrow transplantation, can lead to permanent tolerance of T and B cells across allogeneic and concordant xenogeneic species barriers. [12][13][14][15][16][17] However, because bone marrow transplantation across discordant xenogeneic barriers has not yet been successful for a variety of reasons, this approach is not clinically applicable as a means of inducing tolerance to αGal.…”

Efficacy and Limitations of Cyclophosphamide‐induced Tolerance against αGal Antigen

“…For analysis of anti-aGal nAb, rabbit red blood cells (RRBC) were used as described previously [17]. To analyze anti-aGal Abs after the immunization with 1 Â 10 9 RRBC, SC from SCID mice were used [6]. Sera were taken from GalT -/-recipients at each time points.…”

“…B-cell tolerance against xenogenic antigens including nAb has been induced in rats treated with cyclosporine plus Leflunomide [3] or CVF [4]. On the other hand, the Sykes' group have demonstrated the efficacy of mixed chimeric approach in the induction of B-cell as well as T-cell tolerance by using major histocompatibility complex (MHC)-disparate wild-type (GalT þ/þ ) and GalT -/-mice [5,6].…”

Long-Term Survival of Hamster Hearts in Presensitized Rats

“…We (34) and others (41) have shown that hamster RBC express xenoantigens recognized by rat anti-hamster IgM and IgG Abs at a level quantitatively and qualitatively comparable with that expressed on hamster PBMC. The advantage of using RBC as target cells is the decrease in nonspecific binding by Abs via cell surface Ig and Fc receptors (34,42). Fig.…”