In vitro migration of potential hemopoietic precursors from the murine fetus.

An in vitro migration system demonstrated the presence in murine fetal tissues of cells that migrate to thymus, spleen or lymph node. Preincubation of these cells with facteur thymique sérique, a factor derived from the thymus, produced changes in the migration patterns, suggesting a maturation sequence in fetal hemopoietic precursor-cell migration capacity, with migration to the thymus as the initial potential homing target, followed in order by a potential to migrate to the spleen, than to lymph-node tissue.