A role for T lymphocytes in tumor inhibition and enhancement caused by systemic administration of Corynebacterium parvum

In contrast to the consensus of previous reports in other tumor systems, these studies show that the anti-tumor action of systemically administered C. parvum against the fibrosarcoma (FSa) used in this study is highly dependent on T lymphocytes (T cells). This dependency was demonstrated following both intravenous (i.v.) and subcutaneous (s.c.) injection of FSa cells but was most evident in the latter case. In intact mice injected s.c. with ≥ 5 x 10³ viable FSa cells, C. parvum (i.v., day + 3) did not affect the number of tumors that became palpable. However, some 15 days later 20 to 50% of these tumors completely regressed. Surprisingly, when inocula of less than 5 x 10³ FSa cells were injected C. parvum enhanced number of tumors that grew conpared to untreated mice. Furthermore, few tumors that grew from small inocula in C. parvum-treated mice regressed. Corynebacterium parvum-induced regression of established tumors (large tumor inoculum) was found to be dependent upon an intact T cell system. This contrasts with observations in other tumor systems where most of the anti-tumor action of systemic C. parvum was found to be T cell independent. There was an indication that the C. parvum-induced enhancement of tumor incidence (small tumor inoculum) was also T cell dependent although more work will be required to establish this point. The degree of splenomegaly induced by C. parvum and the anti-C. parvum serum agglutinin levels were also shown to be partly T cell dependent. While there is no doubt that systemically administered C. parvum can exert anti-tumor activity by a pathway which is not T cell dependent, the present report suggests that systemic C. parvum may bring its effect about by more than one mechanism. Indeed with certain tumors stimulation of T cell dependent responses may be essential for the induction of complete tumor regression.