Effect of thymectomy on polyoma tumor induction in CF 1 mice

Summary In CF1 mice thymectomized and inoculated with polyoma virus at birth, tumor formation was markedly accelerated; by 70 to 82 days after polyoma virus inoculation, tumors developed in 100% of neonatally thymectomized mice, while less than 20% of control mice developed tumors. Furthermore, grossly apparent polyoma tumors were produced in neonatally thymectomized CF1 mice when inoculated with polyoma virus at 21 days of age: of 18 neonatally thymectomized and polyoma virus inoculated-weanling mice, 3 were found to have grossly apparent tumors 100 to 150 days after the virus inoculation. No tumors were found in so treated sham-thymectomized mice, during the same observation period.Polyoma virus recovery from kidneys and antipolyoma virus antibody were almost equal in neonatally thymectomized mice and control mice. The data may indicate that anti-polyoma virus antibody has little influence on the production of polyoma tumors, and that neonatal thymectomy causes a higher incidence of polyoma tumors because of the reduced capacity of homograft immunity.By varying the days of operation and of virus inoculation after birth, it was found that operation two days after birth was as effective as thymectomy at birth, and inoculation of polyoma virus into neonatally thymectomized mice as late as 7 days after birth was as effective as inoculation at birth.The accelerating effect of neonatal thymectomy on polyoma tumor formation is suggestive that so operated mice may be used as hosts in search for oncogenic viruses.