Our investigation indicates that transcriptionally active HBV genomes are present in various geographic areas among patients with liver cancer who are negative for hepatitis B surface antigen. This observation is consistent with an etiologic role for the virus in the development of these tumors.

Generation of replicative defective viruses is frequently observed during viral infections. We now report that encapsidation and reverse transcription of spliced viral RNA is an additional mechanism for synthesis of defective viral particles. We have investigated the in vivo synthesis of a spliced hepatitis B virus (HBV) RNA. By using the polymerase chain reaction with different sets of primers on DNA purified from infected livers and the HepG2 HBV cell line, we detected a subgenomic HBV DNA complementary to the spliced viral RNA. Its nucleotide sequence was found to be identical to that previously described for the spliced RNA. This HBV RNA is packaged and reverse transcribed in vivo, the cDNA being incorporated into circulating particles. This finding establishes the synthesis of spliced HBV RNA in vivo and indicates that its reverse transcription can give rise to defective viruses.

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The polymerase chain reaction was evaluated as a diagnostic tool in 72 chronic hepatitis B virus carriers. Hepatitis B virus DNA was detectable in the serum of HBsAg-positive virus carriers using aliquots as small as 100 al. The detection limit for cloned hepatitis B virus DNA was 100 ag. Primer pairs for different regions of the HBV genome resulted in different sensitivity. Detection of the amplified hepatitis B virus DNA by Southern blotting and subsequent scintillation counting or densitometry allowed a semiquantitative assay. Using several primer pairs in parallel for optimal detection, all HBeAg-positive HBsAg carriers, 80% of HBe antibody-positive symptomatic HBsAg carriers and 57% of asymptomatic HBe antibody-positive HBsAg carriers were found to have hepatitis B virus DNA in the serum. During antiviral therapy hepatitis B virus DNA disappeared by the polymerase chain reaction assay in patients who became HBeAg negative, but polymerase chain reaction detected a relapse earlier than did the conventional dot blot. Pre-S antigens were assayed in serum and liver samples from most chronic carriers by enzyme-linked immunosorbent assay and/or immunoblot. Although most viremic carriers were strongly positive for pre-S1 and pre-S2 antigens, some hepatitis B virus DNA-positive HBsAg carriers did not have detectable pre-S antigens, and vice versa. Our data show that assay of hepatitis B virus DNA in the serum by polymerase chain reaction is by far more proficient than by dot blot and that it cannot be replaced by serological assays of HBeAg or pre-S antigen.

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