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Subcutaneous hamster tumors induced by Simian adenovirus SA7, strains C8, B105 and C626, were found to be poorly differentiated sarcomas having morphological features which distinguish them from tumors induced at the same site by papovaviruses and the Rous sarcoma virus. In general, the adenovirus-induced tumors were morphologically alike, C8-induced sarcomas showing some differences. Tumors induced by this strain in the subcutaneous tissue, muscles, peritoneum and mediastinum were morphologically identical. Tumors found in the brain were mainly malignant ependymomas and choroid plexus carcinomas, generally originating in neuroectoderm. The oncogenicity of adenovirus SA7 (C8) in meso- and ectodermal cells has thus been demonstrated.

Preparations of simian adenovirus SA7, strain C8, highly oncogenic for hamsters, contain a mixture of large- and small-plaque variants. The variants do not differ in their adsorption rates, virus yield per cell, sensitivity to sulfated agar polysaccharides or antigenic properties, as determined by neutralization tests. However, the small-plaque variant releases infectious virus from cells at a slower rate than the large-plaque variant. It is also more oncogenic for hamsters than the large-plaque variant, but the tumors induced by the two variants do not differ morphologically. The variants seem to induce a transplantation antigen of similar or related antigenicity. Fewer cells are required for transplantation of tumors induced by the original virus and the small-plaque variant than for transplantation of tumors induced by the large-plaque variant.