An Unidentified Virus which causes the Rapid Production of Tumours in Mice

Abstract

IN the course of routine passage of Moloney's leukæmogenic virus (MLV) plasma was collected from a leukæmic rat (Chester Beatty Institute outbred albino strain) which had been inoculated with MLV-containing mouse plasma when new-born. After storage at −70°C for three months the rat plasma was diluted 1 in 30 with Hanks's saline and passed through a ‘Selas 02’ filter, tested and found impervious to Esch. coli. The filtrate was injected into 15 new-born BALB/c mice, as a test of potency. Only 6 survived to weaning. On the 32nd day 5 had tumours at or near the injection site, and all had grossly enlarged spleens. Usually mice inoculated with MLV remain symptomless until they show the characteristic signs of leukæmia after 8 weeks.