**4. Non-tumor, xenograft models**

As tumor cells often produce a multitude of factors which may cooperate in inducing angiogenesis and lymphangiogenesis, these models are considered to be relatively "dirty" and unsuitable for studying the effects of just one or a few factors. In order to overcome this problem, a xenograft model for non-tumor angiogenesis has been developed. In this model, a matrigel plug is grafted onto the mouse which can be mixed with recombinant angiogenic factors prior to grafting.

### **4.1 Matrigel plug assay**

Matrigel consist of purified basement membrane components (collagens, proteoglycans and laminin) and, while it is liquid at temperatures just above 0 degrees, it forms a gel when it is warmed to 37 °C. Thus, the material can be cooled and then injected in the mice, where it will form a three dimensional gel, in which host blood vessels can invade. Matrigel itself is a poor inducer of angiogenesis, but it can be mixed with angiogenic growth factors and/or cells prior to injection leading to a controllable induction of blood vessel growth into the plug. Plug vessels are usually evaluated 7-21 days after implantation by gross examination/photography as well as immunohistochemical staining as described above (Akhtar et al, 2002). If the plug contains functional vessels, the blood (red) vessels can be identified from the photograph. Alternatively, by using mice which express GFP in the endothelium, immunohistochemical staining can be avoided. Also in this model, intravenous dye injection can be performed to evaluate vessel perfusion and leakiness.
