TRANSPLACENTAL TRANSMISSION OF A LEUKEMOGENIC MURINE LEUKEMIA-VIRUS

Recombinant inbred BXH-2 mice spontaneously produce a B-tropic murine leukemia virus (MuLV) beginning early in life and have a high incidenc e of spontaneous myeloid leukemia. These traits are not characteristic of the progenitor strains (C57BL/6J and C3H/HeJ) or of 11 other recom binant inbred BXH strains. Genetic analysis has shown that the virus i s not transmitted through the germ line, suggesting that the virus is passed from one generation to the next by horizontal transmission. An additional ecotropic proviral locus was detected in some mice of this strain after several generations of inbreeding. We show that BXH ecotr opic virus was transmitted to other strains when fostered on viremic B XH-2 mice and that these mice go on to develop tumors of hematopoietic origin. Our earlier finding that virus is expressed early in gestatio n suggested that the ecotropic MuLV is also transmitted in utero. In o rder to determine the stage at which the ecotropic MuLV is transmitted in utero, preimplantation stage embryos were transferred to the uteri of recipient ecotropic virus-negative mice. These mice were found to be negative for the presence of the ecotropic MuLV, suggesting that tr ansplacental transmission of the ecotropic virus readily occurs in BXH -2 mice. Although other viruses, including human lentiviruses, are tra nsmitted across the placental barrier, transplacental transmission of MuLV is a rare event. Thus, the BXH-2 mouse strain may contribute to o ur understanding of the mechanism of transplacental transmission and p athogenesis and offers a potential new model for use in drug therapy o f exogenously transmitted viruses related to lentiviruses.