The in vitro growth, heterotransplantation, and immunohistochemical characterization of the blastemal component of Wilms' tumor.

Wilms' tumor has been proposed to originate from a developmental abnormality of the metanephric blastema. This undifferentiated component of Wilms' tumors has previously eluded efforts for in vitro growth. Blastema from a "classical" Wilms' tumor was transplanted into nude mice and passaged through 12 generations of heterotransplantation. Tumors from heterotransplants were grown for 12 serial passages in a serum-free growth medium supplemented with hormones and conditioned media from human kidney proximal tubule cells. The blastema initially grew on a collagen-fetal calf serum matrix as multicellular spheroids, and the cells proliferating from the rim of the spheroids had a flattened shape. Pulse-labeling with bromodeoxyuridine (BrdU) identified the proliferating cell population as blastemal in origin. Except for a loss of extracellular matrix, ultrastructural studies demonstrated morphologic similarities in the cultured cells, compared with the primary tumor and heterotransplants. Lectin histochemical stains for the peanut lectin (PNA) and immunohistochemical stains for cytokeratin (CYTO), vimentin (VIM), and epithelial membrane antigen (EMA) were performed on the original tumor, successive heterotransplants, and cells grown in vitro. The PNA stained the surface of the blastemal cells after sialidase digestion in the original tumor, heterotransplants, and cultured cells. The blastema of the original tumors was negative for CYTO and EMA but reactive for vimentin. This lack of differentiation was maintained in heterotransplants through 12 passages. However, blastemal cells demonstrated coexpression of CYTO and VIM intermediate filaments when grown in a serum-free medium on a matrix material. These studies demonstrate that the blastemal component of Wilms' tumor can be successfully grown in culture, passaged in nude mouse heterotransplants, and shown to undergo early stages of blastemal differentiation in vitro by growth in serum-free medium. This in vitro system provides a model for testing the factors that influence the growth and differentiation of the blastemal component of Wilms' tumors.