Alternative protocol components	Advantages	Disadvantages
Four-plasmid packaging system (Dull et al. 1998)	Less chance of replication- competent lentivirus (RCL) formation	Requires extra optimization and plasmid preps. No reports of RCL with three- plasmid system
Cell factories to replace HYPERFlasks	Easier to change medium, available with larger culture areas	More expensive per unit area, require more incubator space
Calcium phosphate transfection	Less expensive	Less reliable, requires more plasmid, necessitates more washing during medium changes to remove precipitate