High Percentage of PD-1+ CD4+ T Cells in a Subset of Tolerant Pediatric Liver Recipients.

Abstract

BACKGROUND: Programmed death-1 (PD-1) is a co-inhibitory receptor up-regulated on activated and functionally exhausted T cells that may limit immune responses to persistent antigenic stimulation. PD-1 inhibits alloimmune responses in skin and cardiac transplant (tx) models, contributing to allograft tolerance. We studied PD-1+ CD4+ T cells at study entry / baseline (BL) and during followup of participants (pts) in ITN029, a multi-center trial of pediatric living donor liver tx recipients undergoing immunosuppression (IS) withdrawal. ITN029 identified 12 tolerant (TOL) pts whose liver tests and biopsies remain stable off IS for 6.5 (5.2-6.9) yrs and 7 non-tolerant (NONTOL) pts. METHODS: Banked PBMCs from ITN029 were stained with directly-labeled antibodies: CD3, CD4, CD8, CD25, CD28, CD2, Ki67, CD45RO, HLA-DR, CD57 and PD-1. Live/Dead Blue was used for viability gating with CD14 and CD19 as dump markers. All individual pt samples were run on the same day on a BD Fortessa and analyzed using FlowJo software. RESULTS: At BL, prior to IS withdrawal, the 12 TOL pts have significantly higher % of PD-1+ CD4+ T cells (Fig) but not CD8+ T cells (data not shown) compared to the 7 NONTOL pts (p=0.021). Among the 12 TOL pts, the % of PD-1+ CD4+ T cell is distinctively higher in 6; the remaining 6 TOL pts are similar to the NONTOL pts. The elevated PD-1+ CD4+ T cell % in the TOL subgroup persists for more than 5 yrs after IS withdrawal (Fig). TOL pts with high vs low PD-1+ CD4+ T cell % had shorter interval between tx and enrollment (7.3±2.18 vs 9.2±2.60 yrs) although small numbers preclude definitive correlation (Fig). CONCLUSIONS: The 12 TOL pts segregate into 2 groups based on BL / pre-withdrawal % of PD1+ CD4+ T cells that persists for more than 5 yrs off IS. CD4+ T cell exhaustion may represent a tolerance mechanism that emerges earlier after liver tx than other mechanisms although larger pt numbers are needed to confirm these preliminary findings.Figure: No Caption available.DISCLOSURES:Turka, L.: Employee, Novartis, Stockholder, Novartis.