The development of a prophylactic hepatitis C vaccine faces significant challenges, according to a Justin R. Bailey, MD, of Johns Hopkins University, Baltimore, and his colleagues.
luiscar/Thinkstock
Barriers to developing a prophylactic HCV vaccine include the great diversity of the virus, the limited models that are available for vaccine testing, and the currently incomplete understanding of protective immune responses, according to their review published in Gastroenterology.
Functionally, the inability to culture HCV, until recently, and continuing limitations of HCV culture systems pose challenges to standard production of a live-attenuated or inactivated whole HCV vaccine. In addition, there is the risk of causing HCV infection with live-attenuated vaccines.
On a practical level for all forms of vaccine development, a principal challenge “is the extraordinary genetic diversity of the virus. With 7 known genotypes and more than 80 subtypes, the genetic diversity of HCV exceeds that of human immunodeficiency virus-1,” according to the authors (Gastroenterology 2019;156[2]:418-30).
With regard to vaccine testing, there are also significant difficulties: There is a lack of in vitro systems and immunocompetent small-animal models useful for determining whether vaccination induces protective immunity. Although a use of an HCV-like virus, the rat Hepacivirus, provides a new small-animal model for vaccine testing, this virus has limited sequence analogy to HCV.
The development of immunity to HCV in humans is complex and under broad investigation. However, decades of research have revealed that HCV-specific CD4+ helper T cells, CD8+ cytotoxic T cells, and antibodies all play a role in protection against persistent HCV infection, according to the authors, and vaccine strategies to induce all three adaptive immune responses are in development.
“A prophylactic HCV vaccine is an important part of a successful strategy for global control. Although development is not easy, the quest is a worthy challenge,” the authors concluded.
Dr. Bailey and his colleagues reported that they had no conflicts.
SOURCE: Bailey JR et al. Gastroenterology 2019(2);156:418-30.