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Use of irradiated mouse fibroblasts to improve the cloning and adaptation to culture of human melanoma cells

By using irradiated BALB/c 3T3 mouse fibroblasts as feeder cells, we obtained a marked increase in the cloning efficiency of the 9 human melanoma cell lines that were tested. Four of these melanoma lines had a cloning efficiency that was lower than 0.0007 in the absence of feeder cells. In the presence of irradiated 3T3 cells, their cloning efficiency ranged from 0.017 to 0.26. For most melanoma cell lines the growth rate of cultures that were seeded at a low cell density was also increased by the use of 3T3 feeder cells. In highdensity cultures, no effect was observed with most cell lines. The 3T3 effect was reversible. The pattern of surface antigens expressed by melanoma cells grown in the presence of 3T3 was similar to that observed without 3T3. The effect of feeder cells on the adaptation to culture of 5 primary melanomas was also tested. A definite improvement in cell yield was obtained with 4 of these melanomas.