What is the difference between a p24 and qPCR titer?

A p24 ELISA detects the lentiviral p24 Gag protein. It is not specific for function lentiviral vector particles; it measures free p24, p24 associated with non-functional vector particles, and p24 in functional vector particles. Thus, traditional p24 ELISA titrations overestimate the functional titer. And because the ratio of free p24, p24 associated with non-functional vector particles, and p24 associated with functional vector particles can vary greatly between each lentiviral vector lot, the titers are inherently inaccurate.

In contrast, qPCR titration quantifies the number of integrated lentiviral genome copies per cell in a population of transduced cells. Thus, qPCR titers yield a functional and more accurate titer, though they often appear lower than p24 titers. All Imanis lentiviral vectors are titered by qPCR.