Our studies have showed that CD57⁺ cells are resistant to B7 costimulation blockade (CoB). We hypothesize that CD57⁺ cells are highly sensitive to T cell receptor (TCR) stimulation and undertook this study to explore the phenotypic and functional profile of activated CD57⁺ cells.PBMC from normal subjects (n=12) were assessed by FACS for senescence marker CD57 and the memory subsets of CD57⁺ cells were defined by CCR7/CD45RA classification. Allo-specific memory response was defined as TNF-a/IFN-g producers following stimulation by mature allogeneic dendritic cells (DC). TCR and intracellular mTOR levels in CD57⁺ and CD57- cells were quantified using BD QuanTiBRITE. Purified CD57⁺ and CD57^– cells were stimulated with OKT3 or PMA followed by PhosFlow to detect ZAP70, mTOR, and ERK phosphorylation. MicroRNA (miR) profiles were evaluated by RT-PCR. CD57⁺ cells were largely CCR7^–CD45RA^– effector memory cells (T_EM, CD4⁺ 70.6±16.5%, CD8⁺ 61.4±19.3%). Allo-specific CD8⁺ TNF-a/IFN-g producers (1.56±0.57%) after DC stimulation were mainly CD57⁺ cells (86.4±14.4%). TCR levels on CD4⁺CD57⁺ cells were significantly less (717±166 TCR/cell) than CD4⁺CD57^– cells (947±237 TCR/cell, p=0.016). TCR levels on CD8⁺CD57⁺ cells were similar to CD8⁺CD57^– cells. Significantly higher mTOR levels were present in CD8⁺CD57^– cells (7081±1593 mTOR/cell) compared to CD8⁺CD57⁺ cells (4821±819 mTOR/cell, p=0.001). CD4⁺CD57⁺ and CD4⁺CD57^– cells showed similar mTOR levels. OKT3 induced higher levels of ZAP70 phosphorylation in CD57⁺ cells than CD57^– cells (p<0.05). PMA induced higher phosphorylation for ERK and mTOR in CD57^– than CD57⁺ cells. The miR181 levels were 2 to157 fold higher in CD57⁺ than CD57^– cells (p<0.05). However, the miR17-92 cluster was 3 to 8 fold higher in CD57^– than CD57⁺ cells (p<0.05). The ERK and mTOR phosphorylation in CD57⁺ cells was similar to CD57^– cells after OKT3 stimulation. In summary, allo-specific T cells are largely CD57expressing T_EM cells. This subset is highly sensitive to TCR signaling through the ZAP70 pathway despite lower surface TCR expression. Increased expression of miR-181 in the CD57⁺ subset may increase susceptibility to allo-peptide antigen in the setting of allograft transplantation and underlie their resistance to CoB observed clinically in transplant recipients. Targeting CD57⁺ cell intracellular signaling pathways may provide protection against allo-specific memory responses.

CITATION INFORMATION: Xu H, Brennan T, Li Q, Kirk A. Evaluation of Function and TCR signaling Profile of CD57⁺ T Cells in Allo-Specific Immunity. Am J Transplant. 2017;17 (suppl 3).

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