Induction of transplantation tolerance by chimeric donor/recipient class I RT1.A(A) molecules

Donor-specific transplantation tolerance was induced by administration of chimeric antigens in which four donor immunogenic amino acids (a.a.) were substituted onto the host class I MHC protein. We constructed chimeric rat RT1.A^a cDNA molecules by substituting nucleotides in the α₁ helical region that encode 10 Lewis (LEW; RT1.A(l)) a.a., namely Asp₅₈, Arg₆₂, Glu₆₃, Gln₆₅, Lys₆₆, Gly₆₉, Asn₇₀, Asn₇₃, Ser₇₇, and Asn₈₀ ([α(1h)(l))]-RT1.A^a). The chimeric [α(1h)(l)]-RT1.A^a cDNA sequence was verified before transfection into Buffalo (BUF; RT1^b) hepatoma cells. Interestingly, the helical regions of LEW rats (α(1h)(l)) and Wistar Furth (WF; RTI(u)) rats (α(1h)(u)) share four a.a. (Arg₆₂, Glu₆₃, Gln₆₅, and Gly₆₉). Consequently, subcutaneous administration of [α(1h)(l)]-RT1.A^a transfectants (20x10⁶; day -7) immunized BUF rats to reject in rapid fashion either LEW heart allografts (mean survival time [MST] = 4.2±0.4 days vs. 5.6±0.5 days in controls; P<0.001) or WF heart allografts (MST=4.4±0.6 days vs. 6.0±0.0 days in controls; P<0.002). Subcutaneous immunization of ACI (RT1^a) rats with [α₁(l)]-RTl^a transfectants (bearing 10 LEW donor a.a.) accelerated the rejection of LEW hearts (MST=5.0±0.8 days vs. 8.2±0.4 days in controls; P<0.001). In contrast, the same [α₁(l)]-RT1.A^a transfectants (bearing only four WF donor a.a.) injected subcutaneously into ACI rats modestly prolonged the survival of WF hearts to 14.0±10.3 days from 5.4±0.5 days in controls (P<0.001). Furthermore, ACI recipients were rendered tolerant to WF heart allografts by a single injection via the portal vein of soluble [α₁(l)]-RT1.A^a (but not RT1.A^a, RT1.A(u), or [α₂(l)]-RT1.A^a) antigens in conjunction with brief oral gavage treatment with cyclosporine. Thus, selected donor immunogenic a.a. (Arg₆₂, Glu₆₃, Gln₆₅, and Gly₆₉) of class I MHC antigens become tolerogenic when flanked by host sequences.