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Chronic HBV infection results in various clinical manifestations due to different levels of immune response. In recent years, hepatitis B treatment has improved by long‐term administration of nucleos(t)ide analogues (NUCs) and peg‐interferon. Nucleic acid polymers (NAPs; REP 2139‐Ca and REP 2139‐Mg) are new antiviral drugs that block the assembly of subviral particles, thus preventing the release of HBsAg and allowing its clearance and restoration of functional control of infection when combined with various immunotherapies. In the REP 102 study (NCT02646189), 9 of 12 patients showed substantial reduction of HBsAg and seroconversion to anti‐HBs in response to REP 2139‐Ca, whereas 3 of 12 patients did not show responses (>1 log reduction of HBsAg and HBV DNA from baseline). We characterized the dynamic changes of HBV quasispecies (QS) within the major hydrophilic region (MHR) of the 'pre‐S/S' open reading frame including the 'a' determinant in responders and nonresponders of the REP 102 study and four untreated matched controls. HBV QS complexity at baseline varied slightly between responders and nonresponders (P = .28). However, these responders showed significant decline in viral complexity (P = .001) as REP 2139‐Ca therapy progressed but no significant change in complexity was observed among the nonresponders (P = .99). The MHR mutations were more frequently observed in responders than in nonresponders and matched controls. No mutations were observed in 'a' determinant of major QS population which may interfere with the detection of HBsAg by diagnostic assays. No specific mutations were found within the MHR which could explain patients' poor HBsAg response during REP 2139‐Ca therapy. [ABSTRACT FROM AUTHOR]

Summary: The treatment of patients suffering from HBeAg‐positive chronic hepatitis B with REP 2139‐Ca resulted in potent reductions in HBsAg and HBV DNA, seroconversion to anti‐HBs and the establishment of functional control of infection. In this cohort of 12 patients, we investigated whether differences between HBsAg sequences might explain the lack of response to REP 2139‐Ca observed in 3 of 12 patients. We also assessed if the reduction or complete loss of HBsAg in serum observed during therapy were caused by mutations in the "a" determinant preventing the detection of HBsAg by standard diagnostic assays. The complete pre‐S/S open reading frame (ORF) was sequenced and pre‐S1, pre‐S2 and S amino acid sequences were analysed. We found no major differences between pre‐S1, pre‐S2 and S sequences in responders and nonresponders correlated with low reduction in HBsAg. In addition, we found no mutations in the "a" determinant that would significantly affect the reactivity of HBsAg in diagnostic assays. These results demonstrate that the amino acid sequence of complete pre‐S/S ORF has no direct influence on response to REP 2139‐Ca therapy. [ABSTRACT FROM AUTHOR]