A nucleic acid amplification procedure, the polymerase chain reaction (PCR), has been used to establish a diagnostic assay for the identification of cytomegalovirus (CMV) immediateearly sequences in clinical specimens. Preliminary testing against virus-infected cell cultures indicated that the PCR assay was highly CMV-specific, recognizing both wild-type and laboratory strains of CMV. There was no cross-reactivity with human DNA or with DNA from other herpes viruses. The sensitivity of the assay, using cloned CMV AD169 Eco RI fragment-J as template, was 1 viral genome per 40,000 cells. In a prospective study of CMV infection in bone marrow transplant recipients, the PCR assay correctly identified four patients with confirmed CMV infection. In three of these patients who were followed longitudinally, correlation of DNA reactivity with CMV culture and CMV antibody status over time indicated that DNA was the most sensitive marker for the diagnosis of CMV infection.

DNA hybridization and cell separation techniques were used to determine which blood components contained hepatitis B viral DNA sequences. Free monomer-length hepatitis B virus was found in large amounts in the polymorphonuclear leukocyte cell fraction in two of five HBsAG-positive patients. In these two patients, viral DNA sequences were not detected in the plasma or platelet fraction, whereas the mononuclear cell DNA contained small amounts of a 7.2 kb size unintegrated hepatitis B genome. These studies indicate that the major reservoir of unit-length viral DNA in the asymptomatic hepatitis B carriers studied here was in the polymorphonuclear leukocyte fraction. The basis for the presence of the viral DNA within these cells is presently unknown, but may relate to viral replication within, or phagocytosis of virus by, these cells.