Morphology and in vivo growth characteristics of an atypical murine proliferative osseous lesion induced in vitro.

Mandibular condyles of late embryonic NMRI mice were used to study the effect of the FBR murine osteosarcoma virus in an in vitro tissue culture system. Chondroprogenitor cells and chondroblastic cells present in the condylar tissue normally undergo rapid differentiation in vitro which results in an advanced stage of bone formation. The infection of condyles with FBR murine osteosarcoma virus induced the transformation of bone progenitor cells and the formation of an atypical proliferative osseous lesion. In markedly disorganized tissue many spindle-like cells, giant cells, and pleomorphic cells were seen together with the formation of large bone spicules and the heavy mineralization of osteoid-like material and of the remaining cartilage. Fibroblast-like cells were found to penetrate from the perichondrial zone into the condylar mass and also into the underlying collagen sponge. The in vivo growth characteristics of FBR murine osteosarcoma virus-infected condyles after 3 days in culture were studied via s.c. transplantation into syngeneic mice. Control condyles developed normal trabecular bone, whereas the infected condyles induced a strong cellular response with the presence of atypical cells and newly formed connective tissue and bone in situ. These observations raise the possibility of a novel approach for further investigations related to numerous aspects of virus-induced osteosarcomagenesis.