Frequency analysis of augmented CTL production associated with Corynebacterium parvum-induced tumour regression

A limiting-dilution frequency assay was employed to estimate the increased production of cytolytic T lymphocytes (CTL) associated with Corynebacterium parvum-induced regression of the P815 mastocytoma growing subcutaneously in semisyngeneic mice. It was found that intratumour C. parvum functioned to augment greatly the underlying concomitant production of CTL that occurs normally in response to a progressively growing untreated immunogenic tumour. The lymph node draining a C. parvum-treated tumour contained about eight times more CTL than the lymph node draining a control tumour. Intratumour C. parvum also caused a large increase in CTL production in the spleen and an increase in the number of CTL that could accumulate in a peritoneal exudate. At the peak of the anti-tumour response, the largest number of CTL was found in the draining lymph node (1.66 X 10(5], followed by the spleen (3.47 X 10(4) and by a 24-hr casein-induced peritoneal exudate (6.01 X 10(3]. Presumably, this greatly augmented production of CTL explains why C. parvum given intralesionally early enough during tumour growth can cause the regression of the weakly immunogenic P815 mastocytoma.