Cell Types Found in the Harding and Passey Mouse Melanoma Grown in vitro

Abstract

The growing of melanoma tissue in vitro has presented a good method for identifying the various cells found in this tumor. In sections of the tumor the study of the cells is more difficult because of the heavy pigmentation. In tissue cultures cells migrate from the margin of the explant, retain their specific morphology and are easily identified.

Previously, attempts had been made to grow this tumor in vitro but without success. At the beginning of our experiments we found that the fragments of explants rendered the medium alkaline and as long as this alkalinity was maintained no growth occurred. We found that we could best counteract the alkalinity by implanting pieces of normal tissues in the same medium. The growth of the normal tissues produces an acidity sufficient to counteract the alkalinity. Under these conditions good healthy growths were obtained. It was also found that fragments of the tumor will grow by themselves, provided that the margins of the fragments contain relatively non-pigmented macrophages because these cells begin to migrate and their continuous growth causes the medium to become less alkaline.

Three types of cells appear in the outgrowths—macrophages, fibroblasts and melanoblasts. The macrophages can be differentiated into actively moving, sparsely laden cells, and swollen, sluggish cells densely filled with melanin granules. The fibroblasts have oval nuclei and are frequently spindle-shaped. The melanoblasts have spherical nuclei and are highly dendritic and are of 2 kinds morphologically: small cells with slender, uniform dendrites, and large cells with stouter dendrites possessing knobbed swellings along their lengths.

The melanin granules in the various types of cells are distributed as follows: In the macrophages they are usually packed in irregular clumps throughout the entire protoplasm; in the fibroblasts they are massed about the nucleus and are sparse or absent in the pseudopodia; in the melanoblasts they occur in the dendritic processes and in the periphery of the main cell body.