Particles with characteristics of leukoviruses in cultures of marrow cells from leukemic patients in remission and relapse.

An enzyme activity with the characteristics of RNA-directed DNA polymerase (reverse transcriptase) was detected in marrow from patients with leukemia in relapse and in firm hematological remission. Material having the enzyme activity, when analyzed in sucrose gradients, appeared as two distinct homogeneous bands of particles with densities of about 1.17 and 1.23 g/ml. The enzyme activity was stimulated by exogenous template poly(rC).(dG)(12-18) but not by (dT)(12-18). The enzyme activities in these bands also increased (1.7- to 24-fold) after culture, and both bands with enzyme activity were obtained from the cultured cells and from the supernatant medium. Electron microscopic studies showed that the two bands contained particles resembling leukoviruses or their cores.