Another interesting example is a recombinant version of a ricin nanoparticle (T22-mRTA-H6) containing the T22 peptide, an efficient ligand of the cell surface marker CXCR4 (a cytokine receptor selectively overexpressed in metastatic cells of many cancer types) at the amino terminus followed by a mutated version of the ricin A chain and a hexahistidine tail at the carboxy terminus [284]. The gene discussed is CXCR4; the disease is cancer.