Inoculation of simian virus 40 into pregnant hamsters can induce tumors in offspring

Inoculation of 10(7) plaque-forming units of Simian virus 40 (SV40) into pregnant hamsters, a host in whom the virus cannot replicate, during the 8th or 12th day of gestation, produced subcutaneous tumors in offspring 4 to 10 months after birth. These tumors contained SV40 T antigen, and SV40 DNA was integrated into tumor cell DNA. Lower doses of virus or the same amount inoculated later in gestation had no effect. The same tumorogenic dose of virus inoculated at day 4 of gestation was associated with developmental delay and early death of offspring, but did not induce tumors. None of the inoculated mothers showed any effect of the virus. These findings indicate that SV40 can somehow cross the placenta of a nonpermissive host, the hamster, and induce tumors in susceptible offspring.