A study of the mechanism of endothelial proliferation induced by neoplastic lymphoid tissue

The growth of most solid neoplasms is accompanied by vascular proliferation from the host. A number of studies have shown that this vascular proliferation is induced by a soluble factor released from the tumour (tumour angiogenesis factor). Vascular proliferation is also a common feature of immunological reactions.In this study both in vivo and in vitro techniques have been used to study angiogenesis.In vivo studies:- The angiogenic capacity of various tissues,cells and extracts was tested on the chick embryo chorio-allantoic membrane (CAM). The vascular response was scored by naked eye examination and by histological sectioning. Angiogenesis was induced by a number of tumours, the most potent in this respect being Hodgkin's tissue, histiocytic lymphomas and malignant gliomas. Boiled or necrotic tumour tissue and normal mouse tissues did not induce angiogenesis.The angiogenic response to lymphoid cells was tested by implanting them in a millipore filter onto the CAM. T lymphocytes from peripheral blood and mitogen or allogeneically stimulated lymphocytes induced a strong vascular reaction as also did lymphoblastoid cell lines of T cell origin and a number of lymphoid cell lines derived' from neoplastic B cells of both human and mouse origin. Vascular proliferation was also induced by a fraction (M.W approximately 100,000) prepared by chromatography of a crude extract of malignant tumours. Similar extracts from lymphoid cell lines were negative.In association with the vascular reaction induced by the implantation of tumours, lymphocytes or angiogenic factor a dense infiltration of mononuclear cells was observed in the CAM. In vitro studies:- Attempts were made to culture endothelial cells from human umbilical cord veins. While it was possible to establish primary cultures these died after a few weeks and it was not possible to subculture them. Endothelial cells from adult bovine aortas have been established in culture and maintained for over a year. Primary cultures of human umbilical cord vein endothelial cells and early subcultures of bovine aortic endothelial cells seeded at low density and fed with medium containing only 2 per cent. serum were used for the assay. The response was measured by autoradiography, total DNA measurement or by cell count. It was not possible to produce a measurable increase in growth rate of these cells with tumour cells, lymphoid cells or tissue culture supernatants. Large doses (> 50jsg) of the angiogenic factor were toxic to endothelial cells while lower doses had no effect. Successful stimulation of bovine aortic endothelial cells was achieved by coculture with macrophages and by macrophage conditioned medium. Subsequent experiments have shown that the angiogenic factor is chemotactic for human mononuclear cells and guinea pig macrophages but not for neutrophil polymorphs. These results suggest that the angiogenesis induced by tumour implants is due to the release of a factor which is able to attract mononuclear cells to the site of the implant and that the vascular reaction is induced by macrophages which are able to sticulate vascular proliferationdirectly.