Comparison of the Sensitivity of Normal Hematopoietic and Transplanted Lymphoma Colony-Forming Cells to Tritiated Thymidine2

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Abstract
Dose-survival curves were obtained for normal hematopoietic and transplanted lymphoma colony-forming cells of mice to high specific activity tritiated thymidine administered by repeated intraperitoneal injections for 24 hours. While the curve for normal cells decreased to a plateau value of about 20 percent of normal value at the maximum dose studied (6 mc/mouse), the curve for lymphoma cells decreased to a value less than 0.1 percent at this dose. An experiment in which the responses of normal and lymphoma colony-forming cells were measured in the same host showed that this difference was not due to differences between normal and lymphoma-bearing hosts. Furthermore, the survival time of mice bearing transplanted lymphoma was significantly increased (from 6.5 to 13 days) if they were given injections of 6 mc of tritiated thymidine over a period of 24 hours. The results indicate that most normal cells do not pass through deoxyribonucleic acid synthesis in 24 hours, but that most lymphoma cells do and consequently may incorporate tritiated thymidine and be killed during this period. The difference between the cycle of normal hematopoietic colony-forming cells and malignant colony-forming cells may explain the action of chemotherapeutic agents that kill cells passing through cycle.