Tumour models for screening immunomodulators: suppression of tumour growth by delayed hypersensitivity reactions

The suppression of tumour growth at the site of delayed type hypersensitivity (DTH) reactions has been examined with a range of three transplanted rat mammary carcinomas of spontaneous origin. Growth of subcutaneous challenge inocula was suppressed by addition of BCG organisms, but only in rats pre-sensitized to BCG. Purified protein derivative (PPD) was equally effective, but again only in BCG pre-immunized rats. The tumour suppressive response could be adoptively transferred to untreated rats with BCG-immune lymph node cells. Liposomally encapsulated PPD suppressed pulmonary tumour growth in BCG immune rats. These findings indicate the feasibility of therapeutic suppression of tumour growth by agents eliciting DTH reactions, if these can be selectively targeted to tumour sites.