Sera of individuals chronically infected with hepatitis B virus (HBV) contain diverse RNA types produced by HBV replication or derived from integrated HBV DNA
This study aimed to better characterize the repertoire of serum HBV RNAs during chronic HBV infection in humans, which remains understudied. Using RT-PCR, qPCR, RNA-sequencing and immuno-precipitation, we found that (i) >50% of serum samples bore different amounts of HBV replication-derived RNAs (rd-RNAs); (ii) a few samples contained RNAs transcribed from integrated HBV DNA including 5'-HBV-human-3' RNAs (integrant-derived RNAs or id-RNAs) and 5'-human-HBV-3' transcripts as a minority of serum HBV RNAs; (iii) spliced HBV RNAs were abundant in <50% of analyzed  samples; (iv) most serum rd-RNAs were polyadenylated via conventional HBV polyadenylation signal; (v) pre-genomic RNA (pgRNA) was the major component of the pool of serum RNAs; (vi) area of HBV positions 1531-1739 had very high RNA reads coverage and thus should be used as a target for detecting serum HBV RNAs; (vii) vast majority of rd-RNAs and pgRNA were associated with HBV virions, but not with unenveloped capsids, exosomes, classic microvesicles or apoptotic vesicles and bodies; (viii) considerable rd-RNAs presence in the circulating immune complexes was found in a few samples; and (ix) serum rcDNA and rd-RNAs should be quantified simultaneously to evaluate HBV replication status and efficacy of anti-HBV therapy with nucleos(t)ide analogs.  In summary, sera contain various HBV RNA types of different origin, which are likely secreted via different mechanisms. In addition, since we previously showed that id-RNAs were abundant or predominant HBV RNAs in many of liver and hepatocellular carcinoma tissues comparing to rd-RNAs, there is likely a mechanism favoring the egress of the replication-derived RNAs. Overall design: The serum samples collected from individuals chronically infected with HBV were analyzed for serum HBV RNA species using RNA-seq