*Purpose: Liver transplantation (LTx) has been associated with the phenomenon of “cross-dressing” of recipient dendritic cells (DCs) by donor exosome-derived MHC antigens, and acquisition of PD-L1 expression by the same graft infiltrating leukocytes (GIL). Although GIL were not yet available for analysis, we were able to obtain peripheral blood leukocytes (PBL) from individuals 2-3 yrs after live donor liver transplantation (LD-LTx) for DC analysis.We hypothesized that a small number of circulating recipient DC would show acquired donor HLA molecules, and that this DC subset would have a selective increase in PD-L1 expression.

*Methods: We obtained PBL from 2 recipients of live donor liver transplants and performed conventional and imaging flow cytometry to study the presence of donor HLA cross-dressed DCs and compare immunophenotypes with non cross-dressed DCs.

*Results: We found in 2 LD-LTx that cells expressing donor-type (HLA-A2, or-B44) HLA class I antigens were present in a subset of circulating mDC (4.89-13.7%) and pDC (6.16-17.9%). Although relatively few in frequency, the “cross-dressed” (XD) DC had 2-4-fold greater PD-L1 expression than the non-XD cells. This effect was more pronounced in the recipient of a living related donor LTx as compared to the patient receiving a liver from a living unrelated donor.

*Conclusions: The findings of increased PD-L1 expression by “XD” circulating DC of LD-LTx patients support the previous observation in a rat liver transplant model that GIL-DCs of host origin selectively increase their expression of this tolerance-associated “co-inhibitory” molecule.

« Back to 2020 American Transplant Congress