Increase in numbers of 6-thioguanine-resistant human lymphocytes in short-term culture.

Lymphocytes from healthy young adults and from adolescent patients with cancer were examined for their ability to incorporate [3H]thymidine in short-term culture in the presence of phytohemagglutinin and 6-thioguanine (6-TG). The numbers of labeled nuclei after 72 h in culture were compared to numbers of labeled nuclei after 30 h in culture. The numbers of labeled nuclei in the presence of 6-TG increased 6-65-fold between 30 and 72 h. The increases in number could be accounted for by 3-6 cycles of cell division. The data suggest that 6-TG-resistant peripheral blood lymphocytes are capable of reproduction in short-term culture, but factors other than reproduction may also contribute to increases in numbers of 6-TG-resistant cells.