Delineation of the development of T lymphocytes from leukemic null lymphocytes upon induction by conditioned medium

Null lymphocytes, lacking B- and T-lymphocyte markers, were isolated from PBL of patients with acute lymphocytic leukemia. Upon culture in the presence of medium produced from PHA-stimulated allogeneic lymphocytes, induction of these cells to T lymphocytes occurred. Within 18 hr, they acquired the capacity to form SRBC rosettes and bind complement components, IgG or IgM. This differentiation, as supported by cell cycle kinetic analysis, was accompanied by lymphocyte activation, inferable from warm SRBC rosetting. Capping of these rosettes was identified as indicative of early T lymphocytes. During T-lymphocyte development subclasses bearing complement receptors, followed by IgG and finally IgM receptors appeared. The emergence of subclasses, functionally expressed by a gain in MLC responsiveness and stimulatory capacity reflected T-lymphocyte maturation. Simultaneous with the later decrease of the subclasses was a decrease in MLC reactivity. This elucidation of T-lymphocyte development may help in dissection of the lymphoid system.