EFFECTS OF LYMPHOCYTES AND FIBROBLASTS ON THE GROWTH OF HUMAN MAMMARY-CARCINOMA CELLS STUDIED IN SHORT-TERM PRIMARY CULTURES

Breast carcinomas commonly contain varying amounts of fibrous stroma and infiltrates of lymphoid cells. Dickson and Lippman (Endocrine Rev., 8,29, 1987) have proposed a model of growth regulation in breast cancer involving interactions between stroma and carcinoma cells. This model is based on results obtained with established cell lines. In an effort to bring experimentation closer to the clinical situation we have used short-term primary cultures from human breast cancer in co-cultures with lymphocytes and fibroblasts. Cultures were established in a chemically defined serum-free medium (CDM3). Cell types were characterized on the basis of live morphology and expression of vimentin and keratin 18. A semi-quantitative system was developed for measuring growth of epithelial cells, thus defining two indices: maximal growth index (GI-max) and growth rate (GR). Moderate-to-good growth was obtained from 34 out of 46 carcinoma samples (74%) and 30 out of 38 parallel samples of non-cancerous tissue (79%). Success in culture was negatively correlated with the amount of hard stroma but unrelated to age of patient or clinical status. Malignant epithelium was clearly identified in 12 out of 34 (35%) carcinoma samples. For the evaluation of responses of epithelial cells in co-cultures, the cultures from each sample were ranked according to GI-max. From 20 co-culture experiments using carcinoma samples, the following results were obtained: the highest GI-max was found in 11 of the co-cultures with lymphocytes; in six of the co-cultures with fibroblasts; in one case in the control culture without partner cells; and in two experiments there was no difference between controls and co-cultures. The corresponding values for non-cancerous samples were: 5 out of 17, 2/17, 2/17, and 8/17. Control experiments performed without partner cells confirmed that these differences in GI-max between cultures were beyond random variations. Four samples displayed particularly vigorous responses to lymphocytes, and two samples responded extensively to fibroblasts. In four of these six samples cancer cells proliferated. We conclude that it is feasible to use primary cultures of breast carcinomas for experimentation. Fibroblasts did not have very marked effects on epithelial cell growth, but, contrary to expectation, there was a clear tendency for lymphocytes to stimulate growth.