Fig. 3. Inhibition of the CXCR4-dependent transduction of HOS.CXCR4 cells by the S3 vector with (A) soluble SDF-1α and (B) an anti-SDF-1 antibody. Transduction assays were performed using the S3 (black bars) and AM (gray bars) vectors in the presence of the indicated concentrations of SDF-1α or after pretreatment of the vector with the indicated concentrations of the antibody. Percent transduction titers relative to those obtained in the absence of the inhibitors are shown: S3, 6.1 and 4.6 × 10³ c.f.u./ml for (A) and (B), respectively; and AM, 6.6 and 6.9 × 10⁶ c.f.u./ml for (A) and (B), respectively.