CD38brightCD8+ T Cells Associated with the Development of Acute GVHD Are Activated, Proliferating, and Cytotoxic Trafficking Cells.

We have previously reported that a peripheral blood absolute CD38brightCD8+ effector memory T cell (TEM) population expansion of >35 cells/µL predicts the development of acute graft-versus-host disease (GVHD). We hypothesized that these T cells are activated, proliferating, and cytotoxic trafficking cells that are not a response to viral reactivation and may be involved in acute GVHD. We characterized peripheral blood T cell populations at the time of maximum CD38brightCD8+ TEM expansion in patients from our originally reported pediatric allogeneic hematopoietic cell transplantation recipient cohort. Samples were incubated with fluorochrome-conjugated antibodies directed against CD3, CD8, CD38, HLA-DR (T cell activation), Ki-67 (T cell proliferation), granzyme B (marker of cytotoxic T cells), CLA (skin trafficking), CCR5 (visceral trafficking), and CXCR6 (liver trafficking). We also incubated samples with Epstein-Barr virus (EBV) and cytomegalovirus (CMV) peptide pools and measured IFN-γ production by flow cytometry and performed EBV and CMV tetramer staining. Higher median proportions of cell expression of HLA-DR, Ki-67, granzyme B, CLA, CCR5, and CXCR6 were observed for CD38brightCD8+ T cells compared with CD38nonbrightCD8+ T cells in patients with acute GVHD (P < .05) but not in patients without acute GVHD (P not significant). No IFN-γ production was observed after incubation with CMV and EBV peptide pools. EBV-specific tetramer populations of 6.85% and 3.17% were detected in 2 patients with acute GVHD, whereas a CMV-specific tetramer population of 3.77% was detected in 1 patient with acute GVHD. No EBV- or CMV-specific tetramer populations were detected in any patient without acute GVHD. We conclude that CD38brightCD8+ T cells associated with the development of acute GVHD are activated, proliferating, and cytotoxic trafficking cells that do not appear to respond to CMV or EBV reactivation. Further studies are needed to determine whether these cells are directly involved in acute GVHD pathogenesis.