Effect of human serum thymic factor on immature T lymphocytes in acute leukemia and other hematologic malignancies.

In 37 patients with acute leukemia and in 13 patients with other hematologic malignancies, E-rosette formation of peripheral blood mononuclear cells, before and after incubation with human serum thymic factor, was studied. This assay showed that incubation with thymic factor caused a clear-cut increase of E-rosette-forming cells in 8 of the 37 acute leukemia patients. Among the 13 patients with other hematologic malignancies, a similar effect was observed in two with pediatric Hodgkin's disease and in one adult with Waldenström's macroglobulinemia. These results support the contention that a significant percentage of the so-called "null" cells circulating in the blood of the above-mentioned patients were, in fact, immature T cells (T0 lymphocytes) that were shifted to a more mature stage (T1) by thymic factor.