NIV Congres

Background Mesenchymal stromal cells (MSCs), a prominent nonhematopoietic cell type with immunomodulatory and regenerative properties. There is evidence to support that MSCs require priming stimuli with inflammatory cytokines to be able to elicit their immunomodulatory function. However, so far no evidence for this MSCs priming has been shown in vivo. Since profound inflammatory changes are observed in liver grafts from non-heart beating (NHB) and heart beating (HB) donors, the aim of this study was to quantify differences in mobilization of MSCs and their immune suppressive capacity between NHB and HB donors.

Methods During liver transplantation, graft preservation solutions (perfusates) of nine HB and seven NHB donor livers were collected. Mononuclear cells (MNCs) from perfusates were stained with a cocktail of antibodies specific for human CD45, CD146, CD73, and CD44 to quantify percentage MSCs using multi-colour flow cytometry. Liver MSCs obtained from the adherent MNC fraction underwent expansion. Following expansion, MSCs were stimulated with 10 ng/mL of human IFN-g and 10 ng/mL of human TNF-a and examined for expression of T-cell suppressive receptor, PD-L1. MSCs obtained from healthy bone marrow (BM) were used as positive controls.

Results No difference in the growth potential of liver perfusate-derived MSCs from NHB versus HB donors was observed. However, mobilization of CD45-CD146+CD44+ cells was more pronounced in perfusate from HB (mean 0.62% ± 0.5 SD) versus NHB (0.16% ± 0.25) donors. Moreover, baseline PD-L1 expression in ex vivo expanded MSCs from HB donors (24% ± 20.5) was elevated when compared to NHB donors (4.7% ± 8.6, n=5). PD-L1 in BM-MSCs isolated from healthy subjects was 3.6% ± 3.2 (n=5). Following stimulation with IFN-g/TNF-a, PD-L1 expression was upregulated on 95% ± 6.4, 96.6% ± 1.5 and 96.3% ± 4 of MSCs from HB, NHB and BM, respectively. 

Discussion MSCs mobilized from liver grafts may contribute to systemic immunomodulation of alloresponses after liver transplantation. Tissue injury associated with the donor type plays an important role in mobilization of MSCs. Moreover, MSCs from HB donors had elevated level of PD-L1 expression compared to MSCs from NHB donors, suggesting in vivo priming of the immune regulatory capacity. The effect of upregulation of PD-L1 on liver perfusate-derived MSCs in modulating T cell-mediated immune responses is currently being investigated.