Forty-four primary feline vaccine-associated fibrosarcomas and 16 recurrences were examined histologically for detailed morphologic characterization with emphasis on tumor grade, presence of neoplastic multinucleated giant cells, presence and proportion of T and B lymphocytes within the tumor, and thin and intermediate filament contents of neoplastic and stromal cells. The microvascularity and proliferation rates of central and peripheral areas of the tumors were also quantified by computerized image analysis. For primary fibrosarcomas, 11 of 44 (25%) were grade I, 21 of 44 (47.7%) were grade II, and 12 of 44 (27.3%) were grade III. The recurrences followed a similar pattern: 4 of 16 (25%) were grade I, 8 of 16 (50%) were grade II, and 4 of 16 (25%) were grade III. A positive correlation was found between the presence of neoplastic multinucleated giant cells and tumor grade. These cells were present in 9 of 12 (75%) of grade III and none of the grade I tumors. Prominent peritumoral lymphoid aggregates or follicles were present in 59% of the tumors, and many contained high proportions of T lymphocytes, varying from 19 to 87%. All fibrosarcomas were immunoreactive for vimentin and 28 of 44 (64%) were reactive for alpha-smooth muscle actin. The actin-positive cells were either part of the tumor or formed a capsule around tumor nodules. The peripheral vascularity was significantly higher than the central vascular density but no difference was found in tumor cell proliferation rates between the two areas. Centrally located, fluid-filled micro- or macrocavitations were frequently observed in the large vaccine sarcomas and probably formed secondary to rapid tumor growth and central necrosis.

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Bovine papillomaviral DNA was detected in essentially all sarcoids examined. There appears to be regional variation in the prevalence of viral types in these tumors. The fact that we detected viral DNA in normal skin samples from horses with sarcoids suggests the possibility of a latent viral phase. Viral latency may be 1 explanation for the high rate of recurrence following surgical excision of sarcoids.

Twenty feline vaccine-associated sarcomas were examined by transmission electron microscopy. Tumors contained pleomorphic spindle cells, histiocytoid cells, and giant cells. Most tumors contained myofibroblasts, which had morphologic features similar to those of fibroblasts. These cells were further distinguished by subplasmalemmal dense plaques and thin cytoplasmic actin myofilaments organized as elongated bundles concentrated at irregular intervals forming characteristic dense bodies. Intracellular crystalline particulate material was found in 5 of the 20 tumors. Energy dispersive X-ray spectroscopy was used to identify the crystalline material within one tumor as aluminum-based. One tumor from a feline leukemia virus-infected cat contained budding and immature retroviral particles.

Purpose: Measles virus (MV) causes the regression of human lymphoma xenografts. The purpose of this study was to determine if canine lymphoid cells could be infected in vitro with MV or canine distemper virus (CDV, the canine Morbillivirus equivalent of MV) and determine if in vitro viral infection leads to apoptotic cell death. Experimental Design: Reverse transcriptase-PCR was used to examine the expression of both signal lymphocyte activation molecule (CD150) and membrane cofactor molecule (CD46) mRNA. An attenuated CDV expressing enhanced green fluorescent protein was used to infect canine cells in vitro. Both flow cytometry and reverse transcriptase-PCR was used to document CDV infection. Cell death was examined using a propidium iodide staining assay and Annexin V binding. Results: Canine lymphoid cell lines and neoplastic B and T lymphocytes collected from dogs with spontaneous lymphoma expressed the Morbillivirus receptor CD150 mRNA. In contrast, only neoplastic lymphocytes expressed detectable levels of CD46 mRNA. Although MV did not infect canine cells, CDV efficiently infected between 40% and 70% of all three canine lymphoid lines tested. More importantly, CDV infected 50% to 90% of neoplastic lymphocytes isolated from dogs with both B and T cell lymphoma. Apoptosis of CDV-infected cell lines was documented. Conclusions: Attenuated CDV may be a useful treatment for canine lymphoma. As such, dogs with lymphoma may represent a biologically relevant large animal model to investigate the feasibility, safety, and efficacy of Morbillivirus therapy in a clinical setting with findings that may have direct applicability in the treatment of human non-Hodgkin's lymphoma.