T lymphocytes in chronic lymphocytic leukemia

In cultures of lymphocytes from the peripheral blood of patients with chronic lymphocytic leukemia, the approximate magnitude of the population of lymphocytes characterized by delayed PHA reactivity was estimated. To this end, cells from cultures in an early stage of development were pulse-labeled with 3H-TdR, and their multiplication was expressed by an index of proliferation. On the basis of these data, the proportion of unlabeled blasts in the late stage of cultures was calculated in relation to the late-reacting raction to the mitogen. This fraction comprised 50-100% of blasts in late cultures (6 days). The subpopulation was not detected in only 2 of 17 cases. Its magnitude in the peripheral blood amounted to about 3% of the lymphocytes and nearly one half of the total number of lymphocytes reacting to PHA in patients with CLL. It was concluded that the number of peripheral blood lymphocytes reacting to PHA is not diminished at all in patients with leukocytosis between 11,000 and 17,000/mul. The late-reactive population was relatively resistant to X radiation, dependent on L-asparagine, and insensitive to doses of colchicine which are toxic for leukemic cells. The ability of these lymphocytes to form rosettes spontaneously with sheep red blood cells is preserved in a large measure. Only a small proportion lacked this surface marker. It seems that the population of late-reacting lymphocytes to PHA in the blood of patients with CLL is of thymic origin.