FIG 5.

Multicycle replication of rB/HPIV3 vectors in vitro in the presence or absence of RSV-neutralizing antibodies. LLC-MK2 cells were infected with empty rB/HPIV3 vector (A), DS-Cav1 vector (B), or DS-Cav1/B3TMCT vector (C) at an MOI of 0.01 TCID₅₀ per cell. After adsorption for 1 h, cells were washed three times with cell culture medium and then incubated, in the absence of added complement, with culture medium containing 10% of one of the following sera (which had been previously heated at 56°C for 30 min): preimmune hamster serum (blue) or pooled sera from hamsters infected with wt RSV (red) or with empty rB/HPIV3 vector (black). The hamster sera were from the experiment in Fig. 1. The different treatments were performed in triplicate. An aliquot of medium was taken daily for 3 consecutive days after infection and flash-frozen, and viral titers were determined. The significance of difference between the replication in the presence of the preimmune serum (blue) and RSV immune serum (red) was determined by Student’s t tests. *, P < 0.05; **, P < 0.01.