Dual roles of autologous CD8+ T cells in hematopoietic progenitor cell mobilization and engraftment

BACKGROUND Poor marrow cellularity alone cannot explain poor hematopoietic progenitor cell (HPC) mobilization. This study assessed the role of CD8+ T cells in HPC cell mobilization and engraftment. STUDY DESIGN AND METHODS Mobilization and engraftment were assessed in 192 autologous HPC donors. CD34+, CD4+, and CD8+ T-cell contents in apheresis products were evaluated. Using a chemotaxis assay, we assessed the effect of purified autologous CD8+ T cells from low and high mobilizers on HPC migration from high to low stromal cell-derived factor (SDF-1α) concentration gradients. We also assessed CD8+ T-cell content association with days to neutrophil engraftment. RESULTS The median number of CD34+ cells/kg was 4.7 × 10⁶. Patients were categorized according to their total CD34+ cell collection quartile distribution into low, moderate, and high mobilizers. We found that HPC products from low mobilizers contained more CD8+ T cells than HPC products from moderate and high mobilizers. Chemotaxis assays showed depletion of CD8+ T cells enhances HPC mobilization independent of SDF-1α concentration. Neutrophil engraftment analysis showed that the higher the CD8+ T-cell content per unit CD34+ cell, the faster the rate of engraftment. CONCLUSION Our findings suggest CD8+ T cells inhibit HPC mobilization and facilitate homing and engraftment.