Immune enhancement of the tumorigenicity of hamster brain tumor cells persistently infected with measles virus

Studies were conducted on the tumorigenicity of a hamster brain tumor (HBT) cell line persistently infected with measles virus (MV). This cell population, termed HBT‐M, exhibited decreased tumorigenicity in weanling hamsters when implanted intracutaneously. The lowered tumorigenicity of the HBT‐M cells could be counteracted by concurrent hydrocortisone treatment restoring the tumor‐producing capacity to levels comparable to those of the highly tumorigenic HBT cells. It was also determined that prior immunization of hamsters with MV resulted in enhancement of tumor formation from usually subtumorigenic doses of HBT‐M cells. This increase in tumorigenicity appeared to correlate with high titers of MV antibody. Treatment of hamsters with cyclophosphamide resulted in a reduction of MV antibody titers and effected a decrease of HBT‐M cell tumorigenicity to control levels. Preliminary studies with passive immunizations indicated that the enhancing factor could be transferred in the sera from hamsters hyperimmunized with MV. These data suggested that MV antibody may potentiate the development of neoplasia of cells persistently infected with MV in a manner similar to the enhancement of tumor growth by blocking antibody.