Downregulation of the retinoblastoma gene expression in the progression of malignant melanoma.

The retinoblastoma gene is a cell cycle regulator preventing cells from entering into S-phase. An altered expression of the retinoblastoma gene has been reported in the majority of human malignancies. The main aim of this study was to investigate retinoblastoma gene expression in the full spectrum of melanoma progression from naevus to melanoma metastases by applying immunohistochemistry and RT-PCR. All naevi with and without dysplasia showed high expression of the retinoblastoma gene. In primary melanomas, Rb-positive cells were found in 82 out of 106. Loss of expression correlated with an increase in Clark level and shorter survival rates. An independent prognostic role of the retinoblastoma gene was confirmed by Cox multivariate analyses (p < 0.01). In melanoma metastases, retinoblastoma gene expression (at the RNA level) was found in 18 out of 26 melanoma lymphatic metastases, and in 2 out of 5 liver metastases. Our results indicate a downregulation of the retinoblastoma gene in the progression of melanocytic tumours.

Monoclonal antibody defining fibroblasts appearing in fetal and neoplastic tissues.

VIF3 is a hybridoma-derived mouse IgG monoclonal antibody (MoAb) generated in a fusion with the use of a malignant fibrous histiocytoma as the immunizing agent and shown to recognize a 70-kilodalton antigen expressed within connective tissues. Of 55 human tissue culture cell lines tested by indirect immunofluorescence, VIF3 was shown to bind to 20 of 35 (57%) sarcomas, 4 of 9 (44%) normal fibroblasts, and none of 11 carcinomas and other neoplasm-derived cell lines. A panel of over 259 human frozen tissue sections obtained from surgical pathology specimens, postmortem studies, and elective abortions was used to further determine the histopathologic specificity of VIF3. MoAb VIF3 was found to bind to 15 of 19 (79%) human sarcoma tissue sections tested. It was also shown to recognize an antigen expressed on a subset of fibroblasts dispersed within the stroma of carcinomas obtained from all 46 patients tested, as well as a subset of cells within 3 of 10 benign hyperplastic tissues (30%). VIF3-positive cells were detected in all 60 fetal tissues tested including amniotic membranes, placentas, and umbilical cords. In contrast, fibroblasts of normal adult tissues tested stained infrequently (22/97 or 23%) with this reagent. The results confirm that this MoAb is directed against a human connective tissue-specific marker. VIF3 detects a marker appearing on fetal fibroblasts that is typically not present in normal adult tissues, but reappears in association with neoplastic diseases. MoAb VIF3 therefore defines a fibroblast-oncofetal antigen and as such may serve as a probe for immunopathologic studies.

Monoclonal antibodies to human sarcoma and connective tissue differentiation antigens.

The use of monoclonal antibodies to distinguish human sarcoma from carcinoma cells has been explored. Spleen cells from a BALB/c mouse immunized with a human malignant fibrohistiocytoma were fused with cells of the mouse P3U1 plasmacytoma cell line. Antibodies were then screened for reactivity against human sarcoma and carcinoma cells growing in culture. This work has yielded 2 immunoglobulin G monoclonal antibodies VIE4 and VIF3 which, respectively, reacted with 85% (17 of 20) and 90% (18 of 20) of sarcoma lines tested but with none of eight carcinoma cell line preparations. Reactivity against normal fibroblasts was also demonstrated. By immunofluorescence, the antigens detected by the two antibodies appear to have distinctive intracellular distributions. Immunoprecipitation with VIF3 has shown that it is detecting a protein with a molecular weight of 70,000. When tested against pathological frozen tissue sections, VIF3 reacted with four of 11 and VIE4 with three of 11 human sarcomas but with none of ten carcinomas tested. VIF3 occasionally bound to normal adult connective tissues, whereas no such reactivity was seen with VIE4. These antibodies appear to be directed to fibroblastic markers associated with sarcomas and connective tissue differentiation antigens.