Effect of BCG and C. parvum on in vivo Listeria clearance and tumor growth. Comparative studies in normal and congenitally athymic (nude) mice.

Clinically, it is important to know whether agents used for immunostimulation require the presence of functional thymus-derived (T) cells. Previous studies showed that both BCG and C. parvum induced a macrophage-dependent enhanced in vivo listeria clearance and in vivo inhibition of a fibrosarcoma induced by 20-methylcholanthrene. These two models were re-evaluated in congenitally thymusless (nude or nu/nu) B10LP mice lacking functional T cells. In nu/nu mice, (1) BCG failed to enhance listeria clearance, and when given simultaneously with tumor cells, had no effect on tumor growth; (2) C. parvum enhanced listeria clearance and simultaneous administration of C. parvum and tumor cells exerted an inhibitory effect on tumor growth. The general conclusion was that under the experimental conditions chosen functional T cells are required for an effect of BCG, but not for that of C. parvum. It is not clear whether these observations have any clinical significance.