the cells should have a high loading capacity for the drugs or
nanomaterials and have the target tumor ability, for example,
monocytes/macrophages, mesenchymal stem cell [31], and neural
stem cell [32]. Typically, monocytes/macrophages are attractive
nanoparticle delivery vehicles because they are circulating cells
which can be easily obtained from patients [33,34]. Moreover,
macrophages can be readily loaded with therapeutic nanoparticles
based on the innate phagocytotic capability and each cell can serve
as a “Trojan Horse” delivery vector to reach otherwise inaccessible
tumor regions including the hypoxic areas [24e26].