Phagocytosis of Mycobacterium bovis BCG organisms by murine S180 sarcoma cells

Instillation of BCG vaccine directly into the bladder of patients suffering from superficial bladder tumours represents the major clinical application of this material. The mode of action is by no means clearly defined but it is known that the BCG cells need to be in close proximity to the tumours and may be capable of directly targeting the tumour cells through a fibronectin/fibronectin receptor interaction. In addition to cellular adherence there is a local stimulation of macrophages which is known to phagocytose mycobacteria. Use of a murine S180 sarcoma model facilitated the quantitative measurement of antitumour activity of BCG and BCG isolates. Ultrastructural examination of the BCG/sarcoma interaction confirmed that, in fact, these tumour cells do phagocytose and subsequently kill the BCG cells. The relationship between this phenomenon and the subsequent tumour cell death is not currently clear, although a strong tumoricidal agent has recently been isolated from BCG cells.