A SIMPLE PROCEDURE TO DETERMINE THE BIOLOGICAL TITER OF RECOMBINANT RETROVIRAL VECTORS

Retroviral vectors are widely used to deliver genetic material to live cells both in experimental and clinical settings. The ability of thes e vectors to transduce target cells is an important aspect of their cl inical applicability and one of the factors determining their transduc tion efficiency is Vector functional titer. Current methods for titrat ing retroviral vectors involve measuring the number of target cells in culture transduced by a given volume of vector solution. In this repo rt, we describe a new procedure which allows one to estimate the actua l number of infectious particles capable of transducing a permissive c ell type. Vector biological titer is calculated from the fractional de cline in transduction efficiency observed when a given volume of vecto r solution is sequentially added to multiple dishes containing permiss ive cells. Values determined this way are greater than those obtained from a single transduction experiment, with the difference being inver sely proportional to the degree of cell permissiveness for vector entr y. The present procedure is simple, reliable and expeditious. It will be useful to standardize vector biological titers determined in differ ent laboratories, and help implement strategies for efficient gene del ivery protocols.