Decrease in circulating hematopoietic progenitor cells by trapping in the pulmonary circulation

When stem-cell grafts are infused into the venous circulation and stem/progenitor cells egress from BM, pulmonary capillary beds are the first microcirculation site that they encounter. This provides the potential for circulating progenitor cells to be trapped in the pulmonary circulation.

We compared the number of progenitor cells [CD34(+) cells, colony-forming unit-granulocyte-macrophage (CFU-GM), CD34(+) CD41(+) cells and CFU-megakaryocyte (CFU-meg)] and their expression of cell-adhesion molecules (CAM) in samples taken simultaneously from radial arteries and central veins of 21 patients following PBSC mobilization.

The mean (+/- SD) frequency of progenitor cells in the radial arteries was reduced to 79% +/- 25% for CD34(+) cells, 73% +/- 27% for CFU-GM, 77% +/- 25% for CD34(+) CD41(+) cells and 70% +/- 29% for CFU-meg of the number in the central veins. This suggests that some progenitor cells might be trapped in the lung. No association between progenitor-cell expression of CAM and pulmonary trapping was observed.

Our data demonstrate pulmonary trapping of PBSC during mobilization, suggesting a potential inhibitory effect on PBSC harvest and medullary trafficking following graft infusion. However, the impact associated with pulmonary PBSC trapping may be negligible in the clinical setting if sufficient cells are infused.