attP-CC (5'-GTGCCCCAACTGGGGTAACCTccGAGTTCTCTCAGTTGGGGG-3') is an engineered integrase target site generated by mutating the central TT nucleotide of attP to CC. attP-CC is compatible with the engineered attB-CC site and the phiC31:int integrase. phiC31:int can mediate exchange between attP-CC and attB-CC, resulting in genetic modification, the nature of which is influenced by the relative orientation (direct or inverted), and location of the two target sites. The recombination event results in the formation of hybrid sites (attL[CC] and attR[CC]) that are no longer a substrate of the phiC31:int integrase, and thus the exchange reaction driven by phiC31:int is unidirectional. The attP-CC/attB-CC site pair are orthogonal to the attP/attB site pair; no recombination between attB-CC (donor plasmid) and attP (docking site) or between attB (donor plasmid) and attP-CC (docking site) was seen in vivo (FBrf0239922).