Southern blotting of the retrovirally transduced lymphocytes after the ex vivo culture (day 10). Ten micrograms of DNA from transduced lymphocytes was digested with KpnI, which released the proviral sequence at the length of 6.0 kb (see Fig 1), separated on an agarose gel, and transferred to a nylon membrane followed by hybridization with the neo DNA probe. The proviral sequence in the transduced lymphocyte genome was detected in all 4 monkeys. The positive controls (lanes 6 through 10) were made from dilutions of the G1PLII-retroviral producer DNA into control rhesus lymphocyte DNA.