MHC Class II Sharing Appears to Promote Intestinal Allograft Tolerance Through Linked Suppression in a Large Animal...

Area of Science:

• Immunology
• Transplantation Science
• Regulatory T cell biology

Background:

• The role of major histocompatibility complex (MHC) class I and class II matching in achieving transplantation tolerance is not fully understood.
• Intestinal transplantation (ITx) presents unique challenges due to the complex immune environment of the gut.

Purpose of the Study:

• To investigate the impact of selective MHC mismatches on transplantation tolerance induction in a swine model of ITx.
• To elucidate the mechanisms underlying tolerance development in relation to MHC compatibility.

Main Methods:

• Orthotopic ITx was performed in swine with varying degrees of MHC matching: haplotype-matched, partially matched (class II overlap), and fully mismatched.
• Immunosuppression was administered and gradually weaned off post-transplantation.
• In vitro assays, including a novel mucosal mixed lymphocyte reaction, were used to analyze immune responses.

Main Results:

• Fully mismatched grafts did not achieve tolerance.
• Partially matched grafts developed "split tolerance," characterized by local graft acceptance mediated by donor regulatory T cells (Tregs).
• Haplotype-matched animals showed peripheral Tregs, donor-specific hyporesponsiveness, and durable mixed chimerism, linked to shared class II alleles.

Conclusions:

• Sharing of major histocompatibility complex class II alleles, even partially, can promote regulatory T cell-mediated tolerance in intestinal transplantation.
• The mechanism involves linked suppression dependent on coexpressed alleles on antigen-presenting cells.
• These findings have significant implications for improving clinical tolerance induction in human intestinal transplantation through pre-transplant tissue typing.