Class I MHC allochimeric presentation of composite immunogenic and self epitopes induces tolerance to genetically diverse rat strains

Functional topography of rat class I major histocompatibility complex (MHC) molecule was studied. The α₁-helical sequences that are shared by class I RT1.A^l and RT1.A^u were substituted in the RT1.A^a molecule to produce the composite -RT1.A^a MHC class I allochimeric molecule. Dominant immunogenic epitopes that induce accelerated rejection were identified within the hypervariable regions of the α₁ domain of RT1.A^a, RT1.A^l, and RT1.A^u. Peri-transplant portal venous delivery of MHC class I allochimeric proteins, that included composite α₁ helical immunodominant epitopes of RT1.A^u and RT1.A^l, induced donor-specific tolerance to RT1^u (Wistar Furth, WF) and RT1^l Lewis, LEW) disparate cardiac allografts in ACI (RT1^a) hosts. Allochimeric generated tolerance was characterized by absence of T cell deletion or anergy. Donor specific IgM allo-Abs was not detected, while IgG alloresponse was markedly attenuated in sera of tolerant hosts. Further, long-term allografts in allochimeric-conditioned hosts exhibited moderate B cell infiltration when compared to rejecting controls. Analysis of intragraft cytokines revealed selective upregulation of IL-10 and marked inhibition of IL-2, IFN-γ, and IL-4. Our findings indicate the emergence of a peripherally induced tolerant state, afforded by the novel approach of soluble class I allochimeric conditioning that presents donor immunogenic epitopes in the context of recipient class I determinants.