Growth‐Promoting Factors in Neurofibroma Crude Extracts a

Crude extracts of neurofibromas from two unrelated neurofibromatosis (NF) patients were prepared by mincing, homogenizing, and ultracentrifugation in the absence of added solvents. Explant cultures of neurofibromas from other NF patients were grown at low density in culture medium with and without neurofibroma extract supplementation. Differences in growth were monitored by comparing monolayer densities, colony counts, or uptake of [3]H-thymidine. A consistent enhancement of growth rate was demonstrated, and titration curves showed an increasing effect with increasing dosage (ranging from 1.5 microliter/ml to 25 microliters/ml). However, the extract could not substitute for fetal bovine serum. As determined by microscopic examination of Giemsa-stained petri dishes, small spindle-shaped cells, distinct in morphology from ordinary fibroblasts, were the overwhelmingly predominant cell type in most extract-treated cultures. While the specific identity of the growth factor(s) involved is unknown, the following may be stated: The presence of one or more growth factors that may act in an autocrine or paracrine manner in neurofibromas in vivo is demonstrated. There is a preferential effect of such a factor on spindle-shaped cells (presumably Schwann cells), allowing for the selective enrichment of these cells in vitro. There is an enhanced yield of clones derived from single cells, allowing further analysis of the cellular heterogeneity of neurofibromas at the biochemical and molecular levels. These considerations should help to distinguish between those models for neurofibroma growth that emphasize secondary somatic mutations (including allelic exclusion) on the one hand, and cellular interaction on the other hand.