Lentivirus vector based on the human immunodeficiency virus-1 (HIV-1) has become a promising vector for gene transfer studies. A popular feature of the lentivirus vector is its ability of gene transfer and integration into both dividing and non-dividing cells. The pseudotyped envelope with vesicular stomatitis virus envelope G (VSV-G) protein broadens the target cell range.
Knowing the concentration, or titer, of a recombinant lentivirus is important in ensuring good gene expression. The most published method for titering lentiviral samples is an assay for p24, a nucleocapsid protein encoded by the lentiviral gag gene. What many researchers don’t realize is that this quantitation method not only detects lentiviral-associated p24, but it also detects free p24. This is important because during lentiviral packaging, 293T cells overexpress free matrix proteins, envelope proteins, and viral core proteins including p24, which are then assembled into the recombinant lentivirus containing the desired gene of interest. The vast majority of overexpressed p24 never gets assembled into a viral particle; therefore the total p24 level (lentiviral p24 plus free p24) in a supernatant cannot be used to accurately determine lentiviral concentration.
Cell Biolabs’ QuickTiter™ Lentivirus Titer Kit (Lentivirus-Associated HIV p24) is an ELISA developed for quantitation of the p24 core protein specifically found in lentiviral particles. This kit minimizes the overestimation of lentiviral titer common to traditional p24 assays. Proprietary reagents found only in this kit form complexes with the lentiviral particles, allowing them to be removed from solution while free p24 remains in the supernatant. The amount of lentivirus-associated p24 can then be measured by a standard ELISA procedure.