Rejection of sarcoma cells at the site of an inflammatory reaction: macrophages are not the only effector cells.

Purified protein derivative (PPD) (a soluble protein from tubercle bacilli), when injected together with sarcoma cells into syngeneic mice that had been immunized previously with Bacillus Calmitte-Guérin (BCG), prevents tumour toxic to sarcoma cells [4]. However, non-adherent mononuclear peritoneal exudate cells from BCG-treated mice were also found on addition of PPD to become cytotoxic to sarcoma cells. In vivo assays indicate that such cells may play a major role in the in vivo destruction of tumours at the site of a delayed hypersensitivity reaction.