If you want to grow primary HHV-6A/B isolates, you should use cord blood mononuclear cells (CBMC as these cells typically do not contain any HHV-6A/B. It is best to stimulate the CBMC with PHA (1-5 micrograms/ml) for 48 hours and then add 10-50 units of human IL-2. When the cells proliferate actively (3-4 days after PHA), spin and count the cells and infect the cell pellet for several hours (with mixing every hour) with HHV-6A/B at a MOI of approximately 0.1. Resuspend the cells at 500,000 cells/ml in culture medium with IL-2 (10-20 U/mL) and observe the cells on a daily basis. If the medium gets yellow, add some culture medium. After a few days, the appearance of large, multinucleated giant cells is a good indication that these are infected cel When infection is progressing nicely (>70% infected cells), expand by adding uninfected PHA-stimulated CBMC to the infected culture. Add 10 times more uninfected PHA-stimulated CBMC relative to the number of infected cells. When most cells are large and refractile (and infected), spin the cells at 4˚C. Collect supernatant and freeze-thaw the cell pellet 3 times using dry ice/methanol and 37˚C water bath. Spin at maximum speed and collect supernatant and mix with culture supernatant. At this point you can aliquot or centrifuge the culture supernatant to concentrate the virus if you desire.