Kinetics of B, CD4 T, and CD8 T Cells Infused into Humans: Estimates of Intravascular:Extravascular Ratios and Total Body Counts

Little is known about the rate of T and B cell traffic from blood to extravascular compartments or about the steady-state distribution of T and B cells between intravascular and extravascular compartments in humans. We quantitated circulating T and B cell subsets before and during the first 24 h after the infusion of an allogeneic or syngeneic peripheral blood stem cell graft (containing ∼1010 lymphocytes) into 10 patients conditioned with chemotherapy and/or total body irradiation. For all lymphocyte subsets measured, <15% of the infused cells were present in the blood at the end of the 0.5-h infusion and <3% of the infused cells were present in the blood 1 h later. Thereafter, CD4 T cell counts plateaued at ∼1% and CD8 T cell counts at ≤0.4% of the infused cells, whereas B cell counts declined slowly (1.5% of the infused B cells were present in the blood at 2 h and 0.3% at 24 h postinfusion). We conclude that the rate of lymphocyte traffic from blood to extravascular spaces can be extraordinary (∼1010 lymphocytes can leave blood within 0.5 h) and that at steady state the blood contains ∼1% total body CD4 T cells, ≤0.4% total body CD8 T cells, and ∼1.4% total body B cells. By inference, an average-size person may carry a total of ∼4.1 × 1011 CD4 T cells, ≥4.5 × 1011 CD8 T cells, and ∼1.0 × 1011 B cells.