DIFFERENTIATION OF HUMAN BONE MARROW CELLS INTO T LYMPHOCYTES BY IN VITRO INCUBATION WITH THYMIC EXTRACTS

SUMMARY Extracts ofhumanorcalf thymus influence differentiation ofhumanbonemarrow cells invitro. Incubation ofaputative stemcell fraction ofhumanmarrowwith extracts ofthymus foraperiod of2hrledtotheappearance oflymphocytes with surface antigens recognized byahighly specific anti-T-cell antiserum. Toalesser degree, development oflymphocytes having thecapacity toformrosettes with sheep erythrocytes wasobserved. Treatment oftheso-called stemcell fraction withthymic extracts didnotyield cells responsive tomitogenic influences ofphytohaemagglutinin orallogeneic cells. Thismodelshould permit further analyses of immunodeficiency diseases andprovide auseful technique forpurification and analysis ofthymus extracts active withhumanhaematopoietic cells.