Abstract
Cultured cell lines of osteosarcoma and normal skin fibroblasts were derived from tissues of five patients with localized osteosarcoma. Testing of pretreatment patient sera in an indirect immunofluorescence assay against both autologous normal fibroblasts and autologous osteosarcoma cells showed cytoplasmic staining. Quantitative absorption of patient sera with human fetal cells removed all reactivity against autologous fibroblasts, but fetal-absorbed sera showed cytoplasmic, membrane, and nuclear fluorescence when tested against autologous osteosarcoma. Testing the five patient sera against all five cell lines showed staining of allogeneic fibroblasts and osteosarcoma by nonabsorbed sera. Following fetal absorption, all reactivity against fibroblasts was removed, with the retention of specific staining of all osteosarcoma cell lines by all five patient sera. Additional testing of sera from normal patients, patients with soft tissue sarcomas, and patients with melanoma showed staining of allogeneic cultured fibroblasts and tumor cells derived from a patient with osteosarcoma. All staining against fibroblasts and tumor cells was eliminated by fetal absorption of the allogeneic sera. Results suggested that fetal neoantigens are expressed in cultured normal and malignant cell lines and that such fetal antigens are recognized by natural antibodies. Absorption of antifetal reactivity allowed demonstration of specific serum reactivity against osteosarcoma cells.
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