A model for primitive neuroectodermal tumors in transgenic neural transplants harboring the SV40 large T antigen.

Using retrovirus-mediated transfer of the SV40 virus large T antigen into neural transplants, we have observed a high incidence of primitive neuroectodermal tumors (PNET). These neoplasms developed in 8 of 14 (57%) neural grafts after latency periods of 176 to 311 days. Histopathologically, the tumors exhibited features of human PNET such as formation of neuroblastic rosettes and immunocytochemical evidence for neuronal differentiation, synaptogenesis, and focal astrocytic differentiation. All neoplasms showed a striking migratory potential. The presence of the large T gene in the tumors was demonstrated by polymerase chain reaction-mediated amplification of a specific 242 bp segment of large T and DNA sequence analysis. Large T antigen was identified in tissue sections using an immunocytochemical reaction with the monoclonal antibody Pab 108. Cell lines were established from several tumors and subjected to G418 selection. Secondary tumors induced by intracerebral transplantation of these cells retained the characteristic morphological and immunocytochemical properties of PNETs. These experiments demonstrate a considerable transforming potential of SV40 large T antigen for neural precursor cells. The long latency period suggests that neoplastic transformation initiated by the large T gene requires additional spontaneous mutations of cooperating cellular genes. Because the mechanism of transformation by large T antigen appears to involve complex formation with and inactivation of cellular tumor suppressor gene products, these cell lines may serve as an interesting tool to search for novel neural tumor suppressor genes.