FIG. 6.

Rapid clearance of the defective virus in vaccinated animals. (A) Replication of the vaccine preparations in cyclophosphamide-treated mice was assayed by injecting two different doses of the defective virus vD4-prME (10⁶ or 10⁸ PFU/animal [d6 or d8]) and one dose of replicating virus varec280 (10⁶ PFU/animal [r6]). Virus was isolated from muscle preparations (site of inoculation) at the times indicated. Titration of the defective virus was done in the complementing cell line RK-D4R-44; the varec280 virus was titered in RK13 cells. Average titers obtained from three animals are shown. (B) Titer and genomic DNA load in the spleens of vaccinated animals. After injection of defective virus (10⁸ PFU/animal), spleens were isolated at the indicated times and the virus titer was determined (d8). From the same preparations, the amount of vaccinia DNA, given in genomic equivalents (ge), was determined by quantitative PCR. Titers below the detection limit (dashed line) are indicated by open symbols.