For example, the success rate of the PDX model could be improved by the application of severe combined immunodeficiency mice such as NOG (NOD/Shi-scid/IL-2Rγnull), NCG (NOD-Prkdcem26Il2rgem26Nju), and NSG (NOD.Cg-PrkdcscidIl2rgtm1Wjl/SzJ) [60, 61]. Here, CTSG is linked to immune system disorder.