Induction of tolerance toward rat cardiac allografts by treatment with allochimeric class I MHC antigen and FTY720

Background. The combination of FTY 720, a novel immunosuppressant, and allochimeric class I MHC proteins bearing donor-type amino acid (aa) epitope substitutions for host-type sequences induces tolerance of Wistar Furth (WF; RT1.A(u)) heart allografts in ACI (RT1.A(a)) recipients. Methods. Allochimeric alpha(1) (1)(h)58-80-RT1.A(a) proteins were produced by substituting the allogeneic nucleotide sequence encoding 10 aa residues unique to the alpha(1) helical (alpha(1h)) region of RT1.A(1) Lewis (Asp(58), Arg(62), Glu(63), Gln(65), Lys(66), Gly(69), Asn(70), Asn(73), Ser(77), and Asn(80)) for native RT1.A(a) residues. The RT1.A(u) and the RT1.A(1) haplotypes share four of these aa (Arg(62), Glu(63), Gln(65), and Gly(69)). A baculovirus/Spodoptera frugiperda insect cell system was used to express the alpha(1h)(1)58-80-RT1.A(a) proteins. Results. The addition of a 3-day oral gavage of 0.05 mg/kg/day FTY720 to a single portal vein injection of 10 mu g alpha(1h)(1)58-80-RT1.A(a) protein induced permanent acceptance of WF heart allografts in 16 of 26 ACI recipients (> 100 days); the alpha(1h)(1)58-80-RT1.A(a) protein alone only modestly prolonged WF heart survival (13.8+/-0.8 days). The same tolerogenic protocol did not prolong the survival of third-party Brown Norway (RT1.A(n)) heart allografts (14.3+/-2.5 days) compared with FTY720 alone (14.0+/-2.3 days; NS), Tolerant ACI recipients bearing primary WF heart allografts for more than 100 days accepted second WF hearts, but promptly rejected third-party Brown Norway heart grafts (9.3+/-1.5 days). The tolerant state was transferred to irradiated ACI rats (400 rad) with either purified T cells (4-10x10(7)) or serum (1-2 ml) from tolerant hosts, and was not broken by daily intraperitoneal injections of interleukin a (1000 U/day; 7 days). Conclusions, The combination of allochimeric protein with FTY720 induces transplantation tolerance, a state that may be associated with the appearance of donor-specific regulatory factors.