At this stage, the adaptive immune system is not yet developed, therefore, human cells can be tolerated by the host. The transparency of zebrafish embryos also enabled us to monitor the distribution of human cells, which were stained with a vital fluorescent dye. Xenotransplanted embryos were treated with AUY922 (500 nM) and 5b (500 nM) for 48 h, whereas DMSO was used as a negative control. No toxicity of drugs at the given concentration was noticed on the development of xenotransplanted embryos. We then determined the number of MOLT4 cells in each treated group using flow cytometry.