Subset-specific Retention of Donor Myeloid Cells After Major Histocompatibility Complex-matched and Mismatched Liver Transplantation

BACKGROUND. During solid organ transplantation, donor leukocytes, including myeloid cells, are transferred within the organ to the recipient. Both tolerogenic and alloreactive roles have been attributed to donor myeloid cells; however, their subset-specific retention posttransplantation has not been investigated in detail. METHODS. Major histocompatibility complex (MHC)–matched and mismatched liver transplants were performed in mice, and the fate of donor and recipient myeloid cells was assessed. RESULTS. Following MHC-matched transplantation, a proportion of donor myeloid cells was retained in the graft, whereas others egressed and persisted in the blood, spleen, and bone marrow but not the lymph nodes. In contrast, after MHC-mismatched transplantation, all donor myeloid cells, except Kupffer cells, were depleted. This depletion was caused by recipient T and B cells because all donor myeloid subsets were retained in MHC-mismatched grafts when recipients lacked T and B cells. Recipient myeloid cells rapidly infiltrated MHC-matched and, to a greater extent, MHC-mismatched liver grafts. MHC-mismatched grafts underwent a transient rejection episode on day 7, coinciding with a transition in macrophages to a regulatory phenotype, after which rejection resolved. CONCLUSIONS. Phenotypic and kinetic differences in the myeloid cell responses between MHC-matched and mismatched grafts were identified. A detailed understanding of the dynamics of immune responses to transplantation is critical to improving graft outcomes.