Alirocumab, a Therapeutic Human Antibody to PCSK9, Does Not Affect CD81 Levels or Hepatitis C Virus Entry and Replication into Hepatocytes

PLoS One. 2016 Apr 26;11(4):e0154498. doi: 10.1371/journal.pone.0154498. eCollection 2016.


Background: Proprotein convertase subtilisin/kexin type 9 (PSCK9) is secreted mainly from the liver and binds to the low-density lipoprotein receptor (LDLR), reducing LDLR availability and thus resulting in an increase in LDL-cholesterol. While the LDLR has been implicated in the cell entry process of the hepatitis C virus (HCV), overexpression of an artificial non-secreted, cell membrane-bound form of PCSK9 has also been shown to reduce surface expression of CD81, a major component of the HCV entry complex, leading to concerns that pharmacological inhibition of PCSK9 may increase susceptibility to HCV infection by increasing either CD81 or LDLR availability. Here, we evaluated effects of PCSK9 and PCSK9 blockade on CD81 levels and HCV entry with a physiologically relevant model using native secreted PCSK9 and a monoclonal antibody to PCSK9, alirocumab.

Methods and results: Flow cytometry and Western blotting of human hepatocyte Huh-7 cells showed that, although LDLR levels were reduced when cells were exposed to increasing PCSK9 concentrations, there was no correlation between total or surface CD81 levels and the presence and amount of soluble PCSK9. Moreover, inhibiting PCSK9 with the monoclonal antibody alirocumab did not affect expression levels of CD81. In an in vitro model of HCV entry, addition of soluble PCSK9 or treatment with alirocumab had no effect on the ability of either lentiviral particles bearing the HCV glycoproteins or JFH-1 based cell culture virus to enter hepatocytes. Consistent with these in vitro findings, no differences were observed in hepatic CD81 levels using in vivo mouse models, including Pcsk9-/- mice compared with wild-type controls and hyperlipidemic mice homozygous for human Pcsk9 and heterozygous for Ldlr deletion, treated with either alirocumab or isotype control antibody.

Conclusion: These results suggest that inhibition of PCSK9 with alirocumab has no effect on CD81 and does not result in increased susceptibility to HCV entry.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / administration & dosage*
  • Antibodies, Monoclonal / pharmacology
  • Antibodies, Monoclonal, Humanized
  • Cell Line
  • Clinical Trials, Phase III as Topic
  • Disease Models, Animal
  • HEK293 Cells
  • Hepacivirus / physiology*
  • Hepatitis C / metabolism*
  • Hepatocytes / cytology
  • Hepatocytes / drug effects*
  • Hepatocytes / metabolism
  • Humans
  • Mice
  • Proprotein Convertase 9 / antagonists & inhibitors
  • Proprotein Convertase 9 / metabolism*
  • Receptors, LDL / metabolism
  • Tetraspanin 28 / metabolism*
  • Virus Internalization
  • Virus Replication


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Receptors, LDL
  • Tetraspanin 28
  • PCSK9 protein, human
  • Proprotein Convertase 9
  • alirocumab

Grant support

This study was funded by Sanofi and Regeneron Pharmaceuticals, Inc. Regeneron Pharmaceuticals Inc. provided support in the form of salaries, stock option and/or stock for authors [AR, VG, NS, AGB, CAK]. The specific roles of these authors are articulated in the "author contributions" section. Sanofi and Regeneron Pharmaceuticals, Inc. funded materials for conduct of the study, and were involved in the study design, data collection and analysis, decision to publish, and preparation of the manuscript.