Evidence that tilapia islets do not express α-(1,3)gal: Implications for islet xenotransplantation

Background: Cell therapy for diabetes using teleost fish islet tissue has emerged as an intriguing alternative to the use of islet tissue from mammalian pancreases. The islet tissue, called Brockman bodies (BBs), is anatomically distinct from the pancreatic exocrine tissue and can be easily identified and isolated. Islets harvested from Nile tilapia (Oreochromis niloticus), when transplanted into streptozotocin-diabetic nude mice, produce long-term normoglycemia and achieve mammalian-like glucose tolerance profiles. We asked whether tilapia express the α-(1,3)gal epitope, the immunodominant target of human xenogeneic responses. Methods and Results: Immunostaining with the α-(1,3)gal-specific IB4 lectin on tilapia BB, liver, heart, spleen, and head kidney was negative, as was staining with murine anti-α-gal-specific monoclonal antibodies. Absence of α-gal-specific binding of IB4 or murine anti-gal mAbs to dispersed BBs was confirmed by fluorescent-activated cell sorter analysis. Tilapia BB cell membranes failed to reduce binding of anti-α-(1,3)gal-specific mAb in an enzyme-linked immunosorbent assay (ELISA) inhibition assay, while porcine and murine tissue lysates did. Tilapia BB cell lysates were shown to be devoid of α-1,3 galactosyl-transferase activity by ELISA. Transplantation of tilapia BBs into diabetic α-gal knockout (gal KO) mice was not associated with accelerated xenograft rejection when compared with wild type control recipients (mean survival time 6.5 days vs. 7.2 days). Tilapia BBs failed to induce a rise in anti-gal IgG and IgM titers in gal KO mice, while the transplant of wild type mouse islets into gal KO mice caused a significant rise in anti-gal IgG and IgM antibodies. Conclusions: We conclude that tilapia BBs are devoid of α-gal expression, and may offer an alternative to swine as a donor species for islet xenotransplantation.