Tolerance-associated circulating T-cells in immunologically tolerant liver transplant recipients

A.A. Duizendstra, R.J. de Knegt, M.G.H. Betjes, M.P. Peppelenbosch, J. Kwekkeboom, N.H.R. Litjens

Wednesday 13 march 2019

14:10 - 14:12h at Koningin Máximazaal

Categories: Basaal, Parallelsessie

Parallel session: Parallelsessie III - Basaal I

Background: Treatment with immunosuppressive drugs (IS) in liver transplant (LTx) recipients is accompanied by side effects. Some recipients have been withdrawn from IS late after LTx and are immunologically tolerant (TOL) towards their graft. If these TOL LTx recipients are recognized earlier after LTx and withdrawn from IS, side effects may be reversed or avoided. Studies have used circulating T-cells to identify TOL LTx recipients, e.g. Vδ1/Vδ2 γδT-cell ratios and FoxP3+CD25+ T-cells characterizing regulatory T-cells (Tregs). However, the biomarker potential of these markers is limited. Moreover, cytomegalovirus (CMV) influences circulating T-cells. In this study, by matching the study groups for CMV, we characterized circulating T-cells.

Methods: TOL LTx recipients (n=11) withdrawn from IS for on average 4.2 years, and a control group on regular IS regimen (CTRL; n=12) matched for time after LTx (on average 15.2 years), primary disease, age, gender and CMV serostatus were included. In addition, healthy controls (HC; n=12) matched for age, gender and CMV serostatus were included. Circulating T-cells were characterized by flow cytometry. Activated Tregs (aTregs), resting Tregs (rTregs) and activated T-helper (aTh) were characterized by FoxP3 and CD45RA expression. Stimulatory molecule ICOS and inhibitory molecule CTLA4 were assessed.

Results: Vδ1 and Vδ2 γδT-cells and Vδ1/Vδ2 ratios did not differ between TOL and CTRL. In TOL FoxP3+CD25+ T-cells were significantly higher compared to CTRL (p=0.02) and HC (p=0.03). However, aTregs and rTregs did not differ between groups, whereas aTh was significantly higher in TOL compared to HC (p=0.02) and a higher trend was present compared to CTRL (p=0.07). ICOS expression on CD4 T-cells was significantly higher in TOL compared to CTRL (p=0.04) and HC (p=0.02). FoxP3+CTLA4+ T-cells were significantly higher in TOL compared to CTRL (p=0.01), but TOL did not differ with HC.

Conclusions: The Vδ1/Vδ2 γδT-cell ratio could not discriminate TOL from CTRL, most probably because of the matched CMV serostatus. This shows that the Vδ1/Vδ2 γδT-cell ratio is not influenced by the state of tolerance. Furthermore, our data indicates that FoxP3+CD25+ T-cells discriminate TOL from CTRL, but the higher number of FoxP3+CD25+ T-cells in TOL LTx recipients could possibly reflect a higher number of aTh and not Tregs. Higher expression of CTLA4 in the FoxP3+ T-cell compartment and expression of ICOS could indicate a more enhanced inhibitory immune response in TOL compared to CTRL.