Two main features of T-cell development: thymus traffic and postthymic maturation.

It appears from the results presented in Table V and discussed in the preceding pages that a precursor population of immunologically competent T cells can be characterized and defined by multiple biological criteria as being probably of postthymic origin and substantially different from either the immunologically competent T lymphocyte or the prethymic stem cells. On the basis of recent data on functional characteristics of of different subsets of T cells, which suggest parallel lines of differentiation (see Chapter 2), it is possibile that the postthymic precursor compartment may also show heterogeneity; however, this cannot be presently asserted from our results.