Cell fusion responsible for horizontal oncogenesis by human tumors in nude mice

Enhanced lung colonization and tumorigenicity of fused cells isolated from primary MCA tumors

Cells derived from cell-cell fusion events were clonally isolated from primary methylcholanthrene (MCA)-induced tumors in allophenic mice. Compared with non-fused cells isolated from the same cultures, the fused cells had markedly greater experimental metastasizing (lung colonizing) activity, but only slightly greater tumorigenicity and the same cloning efficiency in soft agar. Cell-cell fusion may thus contribute to the generation of tumor heterogeneity that underlies the process of tumor progression.

Cell fusion in tumor development and progression: occurrence of cell fusion in primary methylcholanthrene-induced tumorigenesis

Definitive evidence for the occurrence of cell fusion in tumorigenesis was sought in methylcholanthrene-induced sarcomas. This was approached by using allophenic mice generated from strains differing for electrophoretic variants of the ubiquitous, dimeric enzyme glucose phosphate isomerase, with fusion assessed by heterodimer formation. Eight-three carefully trimmed primary tumor samples (from 23 individual tumors in allophenic mice) were analyzed, as were 1,140 clones derived from them. In all primary tumor samples, zymograms exhibited one GPI homopolymeric band. Expression of a hybrid band (indicative of a fusion event) was not observed in these samples. However, 9 (0.8%) of the tumor clones demonstrated a distinct and reproducible hybrid band which was uniformly lost upon recloning. Our data suggest that cell fusion, although uncommon, occurs in the clonogenic cell fraction during primary MCA tumorigenesis and is followed rapidly by chromosome segregation.

Development of lymphosarcoma lines with high metastatic ability to lymph nodes and visceral organs in BALB/c mice

A metastatic tumor population was isolated in BALB/c mice during routine s.c. passage of the colon 26 adenocarcinoma. The tumor metastasized to lymph nodes, liver, spleen, ovary and kidney. A primary culture established from the s.c. growing tumor was composed of both adherent and nonadherent cells. These two cell types were successfully separated from the primary culture and designated CMS (suspension cells) and CMA (adherent cells). The CMS and CMA cell lines are morphologically distinct in culture; however both formed similar histopathologic tumors when inoculated s.c. Furthermore, both tumor lines showed identical metastatic patterns in BALB/c mice with involvement of lymph node, liver, spleen, ovary and kidney. CMS and CMA expressed T-antigen as revealed by FITC-labeled-anti-Thy 1.2 antibody. Chromosome analysis and morphologic studies by light and electron microscopy indicated that the present metastatic lines have no relationship with the colon 26 adenocarcinoma and seem to be non-thymic T-cell lymphosarcomas which developed spontaneously in BALB/c mice.

Monoclonal antibodies produced by in vitro immunization with sera of human-xenotransplant-bearing mice

In vitro immunization procedures, using sera of athymic mice bearing human WOC ovarian tumors or CM III mammary tumors as immunizing antigen, induced a highly efficient formation of mABs (44% of antibody-producing clones) reacting with human ovarian and/or mammary tumor cells. More than half of these mABs showed cross-reactivity with mouse cell lines. Immunogenicity of normal mouse components in the sera from tumor bearers can be excluded since control immunization with sera of normal athymic mice yielded no mABs reacting with mouse or human cell lines. Furthermore, immunization with sera from tumor bearers did not induce mABs only reacting with mouse cells since 20% of the antibody-producing clones showed an exclusive specificity for the human tumor cells. On the basis of these results we concluded that the human-mouse cross-reacting mABs were induced by circulating human TAA with epitopes shared by mouse cellular components.