Characteristic growth of human choriocarcinoma xenografts in nude mice

In order to investigate the mechanisms and regulation of trophoblast vessel invasion, we established a model using malignant trophoblast cells grown in nude mice. The human choriocarcinoma cell line Jeg-3 established fast-growing tumours within 2 weeks after subcutaneous injection into nude mice. Interestingly, instead of neoangiogenesis the tumours were characterized by large blood-filled lacunae. Staining for hCG-beta and for mouse panendothelial antigen revealed that the majority of the lacunae were lined by trophoblast cells. The blood supply of the lacunae resulted from invasion of the choriocarcinoma cells into the host vessels at the junctional zone between tumour and mouse tissue. These large blood-filled lacunae led to a much faster expansion of tumours with less necrotic areas compared to tumours of non-trophoblastic origin (Hec-1A and HeLa), which revealed neovascularization. Jeg-3 choriocarcinoma cells eroded host vessels and replaced the endothelial lining in a similar way to trophoblast cells during the establishment of a haemochorial placenta. This model can be useful in investigating the cell biological mechanisms of trophoblast vessel invasion and replacement of the endothelium by trophoblast cells.