Evidence for an RNA tumor viruses in human milk.

Certain human milks have been shown to contain particles that have the biochemical and biophysical properties that are diagnostic of the known RNA tumor viruses of animals. These properties include 1) a particle density of 1.16-1.19 g/ml 2) a viral reverse transcriptase (RNA-directed DNA polymerase), and 3) a high molecular weight (HMW) 60-70S RNA that contains polyadenylic regions of 200 nucleotides in length. Inner cores, or nucleoids, of these particles have been isolated. They have a density of 1.26-1.27 g/ml and contain the viral reverse transcriptase and 60-70S RNA. Using molecular hybridization, a specific homology was demonstrated between radioactive DNA synthesized from the RNA of the human milk particle and the RNA from human malignant breast tumors. RNA from benign breast tumors and other human tissues were negative in these tests.