Manifestation and growth of a transplantable osteosarcoma in mice: the effects of thymectomy and thymosin treatment.

Normal and thymectomized CBA mice treated with and without thymosin were injected with 2 x 10(6) viable osteosarcoma cells. The activity and weight of tumors, the cell-mediated and humoral-immune responses against the tumors, and the light microscopic characteristics suggested that thymectomy resulted in a significantly decreased tumor frequency. There were also significant increases in cell-mediated cytotoxic activity in vitro as measured by lysis of 51Cr-labeled tumor cells incubated with spleen cells, and in lymphocytic infiltration around the tumors. While thymosin treatment of thymectomized mice restored these parameters to those of intact animals, thymosin had no demonstrable effects on nonthymectomized animals.