CHARACTERIZATION OF CD7-CELLS AFTER EPSTEIN-BARR-VIRUS TRANSFORMATION(CD19+ LYMPHOID)

The early stages of lymphoid differentiation preceding T and B lineage commitment remain poorly defined. We hypothesized that early lymphoid precursor cells are possibly common progenitors and would express a v ery early T cell-associated Ag (CD7) and a very early B cell-associate d Ag (CD19) simultaneously. We therefore transformed CD7+CD19+ fetal b one marrow lymphoid cells using EBV. Extensive characterization of the resulting cell lines indicated that two cell lines corresponded to pr e-B and early B cells co-expressing CD7. The third cell line resembled a thymocyte, which co-expressed a number of B cell-associated Ag incl uding CD19 and the stem cell Ag CD34. The two predominantly B lineage cell lines have their Ig genes rearranged, whereas the predominantly T lineage cell line has TCR and Ig H chain genes rearranged. Cross-line age Ag were not expressed any more after culturing for a prolonged per iod of time, i.e., B lineage cells became CD7 negative and the thymocy te lineage became negative for the B cell-associated Ag. However, in a ll three cell lines TCR and/or Ig gene rearrangements remained unchang ed. These observations support the existence of a common lymphoid prec ursor co-expressing CD7 and CD19 that gives rise to either T or B cell s.