Donor-Derived Ip-10 Initiates Development of Acute Allograft Rejection

An allograft is often considered an immunologically inert playing field on which host leukocytes assemble and wreak havoc. However, we demonstrate that graft-specific physiologic responses to early injury initiate and promulgate destruction of vascularized grafts. Serial analysis of allografts showed that intragraft expression of the three chemokine ligands for the CXC chemo-kine receptor CXCR3 was induced in the order of interferon (IFN)-γ–inducible protein of 10 kD (IP-10, or CXCL10), IFN-inducible T cell α-chemoattractant (I-TAC; CXCL11), and then monokine induced by IFN-γ (Mig, CXCL9). Initial IP-10 production was localized to endothelial cells, and only IP-10 was induced by isografting. Anti–IP-10 monoclonal antibodies prolonged allograft survival, but surprisingly, IP-10–deficient (IP-10^−/−) mice acutely rejected allografts. However, though allografts from IP-10^+/+ mice were rejected by day 7, hearts from IP-10^−/− mice survived long term. Compared with IP-10^+/+ donors, use of IP-10^−/− donors reduced intragraft expression of cytokines, chemokines and their receptors, and associated leukocyte infiltration and graft injury. Hence, tissue-specific generation of a single chemokine in response to initial ischemia/reperfusion can initiate progressive graft infiltration and amplification of multiple effector pathways, and targeting of this proximal chemokine can prevent acute rejection. These data emphasize the pivotal role of donor-derived IP-10 in initiating alloresponses, with implications for tissue engineering to decrease immunogenicity, and demonstrate that chemokine redundancy may not be operative in vivo.