Intragraft Vδ1 γδ T cells with a unique T-cell receptor are closely associated with pediatric semiallogeneic liver transplant tolerance.

Background: T-cell receptor Vδ2 γδ T cells (Vδ2 cells) participate in host defense, whereas Vδ1 γδ T cells (Vδ1 cells) may regulate immune responses. Vδ1 cells appear to play a role in fetomaternal tolerance and our aim was to examine their role in liver transplant tolerance.

Methods: To determine whether Vδ1 cells increase within accepted grafts after semiallogeneic pediatric liver transplantation, the Vδ1/Vδ2 ratio was assessed at the transcriptional level and the complementarity-determining region 3 loop of the δ chain of Vδ1 cells was sequenced in biopsies from immunosuppression-free (n=6) or almost free (n=3) liver transplant recipients, referred to as group tolerance (Gr-Tol; n=9). The results were compared with biopsies from grafts of recipients on maintenance immunosuppression due to concern of rejection (Gr-IS; n=11). Chronically rejected grafts (Gr-CR; n=6) and normal livers (Gr-NL; n=8) were also examined.

Results: The Vδ1/Vδ2 ratio was the highest in Gr-Tol (0.07±0.06) compared with Gr-IS (0.03±0.02; P=0.04), Gr-CR (0.01±0.02; P=0.008), and Gr-NL (0.02±0.04; P=0.01). There was an identical complementarity-determining region 3 sequence (100% homologous) among all recipients in Gr-Tol, which was dominant in six of nine recipients. This sequence was not seen in Gr-IS or Gr-CR, although it was observed in five of six normal livers.

Conclusions: A unique Vδ1-bearing T-cell clone accumulates within accepted human liver grafts. It might be useful as a biomarker of tolerance and the identification of its ligand might aid in the development of a novel strategy for tolerance induction.