Table 1.

Approaches to post-exit modification of R/LV vector surfaces.

Type	Virus/vector	Modification	Objective	References
Covalent chemical
Iodination	(AV), VSV, RV	Radionuclides	L	[8]
Reductive amination	RV	Lactose	R	[9]
Conjugation	LV	Poly (ethylene) glycol	H	[10]
Biotinylation	RV, HV	Biotin, different secondary	R	[11, 12]
PAL chemistry*	RV	Biotin, Alexa fluorophore	P, L	[13]
Membrane-topic
FSL	VSV, MV, IV	Fluorescein, Biotin	L	[14]
Molecular painting	RV, LV, HV, IV	CD59, GFP	L, H	[7, 15]
Membrane-traversing**	HV	Radionuclides	L	[16]
Synthetic GPI**	n.a.	n.a.	n.a.	[17]
Oleyl/PEG**	n.a.	Streptavidin, GFP, mAB	L	[18]
Myristyl/peptide**	n.a.	CD59	(H)	[19]
Adaptor-based
(Strept)avidin (soluble)	RV	Streptavidin, MHC	R	[20]
(Strept)avidin (membr.)***	LV, BV	Biotinylated radionuclids, antibodies and ligands	L, R	[4]
Biotinylation	See above
Biotin acceptor peptide***	LV, BV	Biotin, different secondary	P, R	[21–24]
Bridging molecules	RV, HV	Heregulin EGF, VEGF AntiCEA	R	[25–28]
Bispecific antibodies**	(AV)	AntiCD40 AntiEndoglin	R, H	[29, 30]
Antibody binding (membr.)***	RV	AntiHER2 AntiP-GP	R	[31, 32]
“Clickable” Adaptors**	(AV)	TAMRA	(L)	[33]
Split inteins∗∗/∗∗∗	n.a.	GFP	(L)	[34]

*Mostly pre-exit, **not tried on R/LV, ***requires genetic modifications (transfection/transduction) to deliver part of the system. RV: retrovirus, LV: lentivirus, VSV: vesicular stomatitis virus, MV: measles virus, IV: influenza virus, HV: herpes virus, BV: baculovirus, AV: adenovirus. Lenti/retroviruses are in bold and underlined, viruses in brackets are naked viruses. P: preparation, L: labeling, H: host responses, R: range of infectivity. Objectives in brackets have not been carried out on enveloped viruses. CD59 protectin, GFP green fluorescent protein, MHC major histocompatibility complex, EGF epidermal growth factor, VEGF vascular endothelial growth factor, CEA carcinoembryonic antigen, HER human epidermal growth factor receptor 2, P-GP permeability glycoprotein, TAMRA Carboxytetramethylrhodamine.