The sensitivity to methylnitrosourea-induced T-cell leukemogenesis in mice is modified by the injection of hydrocortisone.

T-cell leukemias were induced in adult BDF1 mice by a single i.v. injection of methylnitrosourea (MNU). Leukemogenesis was delayed by a single or repeated injections of hydrocortisone (HC) after MNU and also when HC was given one day before MNU. Enhancement of leukemogenesis was seen in experiments with 10 and 14 days' intervals between HC and MNU. The T-cell subset composition of the thymus after HC treatment was studied at these time intervals, but a specific target cell for the action of MNU, reduced one day after HC and increased in number during the thymic regeneration at 10 and 14 days could not be defined. HC did not prohibit the toxic action of MNU as measured by hemopoietic stem cell numbers in the femur.