Vertical transmission of murine leukemia virus through successive generations.

lower incidences and with increasingly longer latency periods to leukemia death (7). The incidence of leukemia in the origi nal, virus-infected females (injected at birth) was low (35%) with an average latency period of 240 days. The incidence of leukemia in 4 successive generations dropped from 22% to 4%, and the latency periods increased from 372 to 462 days. The incidence of Friend virus disease, induced by Friend virus transmitted vertically, was greatly reduced, and the la tency period to death increased in the first generation, as corn pared to the incidence and latency obtained in virus-injected animals (9). However, the low incidence and long latency were maintained through the next 2 generations. Incidences ranged from 9 to 17% with latencies of 5†" 6.5 months in the first 3 generations, as compared with 83% in 2.5 months in the origi nal virus-inoculated litter. In this experiment, the mothers of the first generation offspring were injected as adults, and trans mission occurred only when litters had been suckled on mothers that eventually developed Friend virus disease. The Moloney leukemia virus has been transmitted vertically through successive generations of three C3H sublines and the RF mouse strains for 13†" 15generations without decrease in incidence of leukemia or increase in latency period to death with leukemia (8). However, on several occasions a generation has become leukemia-free and this state has been maintained through successive generations; the change was abrupt rather than progressive through successive generations. Vertical trans mission of Moloney virus in Swiss mice, on the other hand, resulted in a gradual reduction in leukemia incidence in sub sequent generations (6). This report presents data on the vertical transmission of 334C murine leukemia virus through 5 successive generations of Swiss mice without decrease in leukemia incidence or in crease in latency to leukemia death. This virus, isolated from Hauschka ICR (Ha/ICR) Swiss mice and carried in our labora tory for several years (1, 3), is transmitted from mother to offspring in the mother's milk following injection of the mother at birth with virus (2). The incidence of leukemia in litters born to and nursed by their infected mothers was al most as great as that which occurred in Swiss mice injected with virus at birth (70†" 80%at 8†" 9months of age). MATERIALS AND METhODS SUMMARY The 334C murine leukemia virus, isolated from Ha/ICR Swiss mice, has been transmitted vertically …