Characterization of recombinant BHK-21 endogenous particles: R-type particles.

R-particles are morphologically unique, non-infectious, virus-like particles present in Syrian hamster cells, including recombinant BHK-21 cells. Hybridization and induction studies were employed to confirm and extend literature observations on the genetic relationship between R-particles and intracisternal A particles (IAPs). Dot blot hybridization techniques using IAP probes were developed to estimate the concentration of R-particles in culture fluids and in-process fractions in the purification of recombinant Factor VIII. From these studies it was determined that R-particles are removed to undetectable levels at an early step in the purification process. It was concluded from these data, the known lability and the lack of evident biological activity, that R-particles do not present a safety hazard for the production of Factor VIII.