The influence of the thymus on the development of transplanted mammary tumour in mice

The influence of thymectomy and the grafting of additional thymuses on the development of syngeneic mammary tumour has been studied in high cancer C3H/He strains of mice. The effect on the development of the grafted tumour of replacement of the thymus of F1 hybrid mice (C3H/HexC57BL) by thymus derived from donors of the parental streins has also been investigated. In C3H/He mice thymectomized on the 3rd day after birth the development of mammary tumour grafted at the age of 2 months was delayed. One or three additional syngeneic thymuses from 1‐month‐old donors grafted subcutaneously to C3H/He mice stimulated the development of grafted tumours, whereas inhibition of tumour development was observed in mice grafted with five additional thymuses. The replacement of the thymus in F1 hybrid mice (C3H/HexC57BL) at the 5th day after birth by thymus of 5‐day‐old donors of low cancer C57BL strain led to the inhibition of mammary tumour grafted to mice at 2‐3 months of age, while the replacement of the hybrid thymus by that obtained from donors of the high cancer C3H/He strain had no inhibitory effect. The data presented have been interpreted as evidence for genetically determined differences in the functional specificity of the thymus concerning its influence on malignant growth in high and low cancer strain mice. It is suggested that hereditary predisposition to malignant growth is, in particular, related to the functional properties of the thymus in high cancer strains of mice.