Describe the process of lentiviral vector production for gene delivery.

Lentiviral production involves transient co-transfection of HEK293T cells with multiple plasmids: the transfer vector containing the gene of interest, packaging plasmids (gag-pol, rev), and envelope plasmid (usually VSV-G for broad tropism). Third-generation systems split packaging elements for safety. Cells produce viral particles for 48-72 hours post-transfection. Supernatant is harvested, filtered (0.45um), and concentrated by ultracentrifugation or precipitation. Viral titer is determined by qPCR, p24 ELISA, or functional assays (GFP expression, antibiotic selection). Safety considerations include biosafety level 2 practices and avoiding replication-competent lentivirus generation.