CXCR4 and neoplasm: However, the horseshoe crab derivative CXCR4 ligand T22 [15] is one of the few tumor-homing peptides that shows high affinity for CXCR4 in a recombinant form, being also capable of promoting selective uptake of macro-molecular complexes and NPs inside CXCR4 overexpressing cells [16].