The numerical development of lymphoid cells during human embryogenesis.

We have studied the cellular growth rates in the fetal thymus, spleen, and bone marrow of 12 human fetuses ranging in gestational age from 7 to 20 weeks. In all instances growth rates were linear when plotted logarithmically. However, the spleen had a biphasic growth curve. These data are useful in predicting the cellular yields which can be obtained from human fetal lymphoid organs which are to be used for transplantation in immune deficiency diseases and other clinical conditions.