Ability of lymphocytes treated with thymic factor to decrease lung metastasis in tumor-bearing mice

C57BL/6 mice were injected subcutaneously with Lewis-tumor cells and syngeneic spleen lymphocytes. When these lymphocytes had been preincubated with a thymic extract, tumor development was impaired: the tumor weight and volume were significantly decreased and the number and size of lung metastases were strikingly diminished. In addition, the increase in weight of adrenals and spleen, common in tumor-bearing animals, was not observed. Lymphocytes incubated with a thymic factor preparation can therefore enhance the defense against this tumor.