Inhibition of growth of certain human tumour cell lines by a factor derived from human fibroblast-like cell lines. I. Demonstration by mixed culture and by use of cell washings.

The growth of 7/9 Burkitt's lymphoma (BL) cell lines and 5/6 human melanoma cell lines was inhibited by certain human fibroblast-like cell lines, especially human myofibroblast cell lines. In contrast to BL lines, 3/5 lymphoblastoid cell lines were less susceptible and 3/4 human leukaemic lines were resistant. The effect was time- and concentration-dependent. Co-cultivation led to inhibition of tumour-cell growth within 3 days, but after removal from the fibroblasts, washing, and resuspending in fresh medium some tumour cells recovered and growth improved. The inhibitory activity was also demonstrated with washings of fibroblast-like cell lines, and was sensitive to pronase. The biological significance of this factor remains to be defined.