Hepatitis A virus (HAV) is the major pathogen responsible for acute
infectious hepatitis A, a disease that is prevalent worldwide. Although HAV immunization effectively prevents
infection, primary immunizations must be administered at least 2 weeks prior to HAV exposure. In contrast, passive immunization with pooled human
immunoglobulin (Ig) can provide immediate and rapid protection from HAV
infection. Because the use of human sera-derived Igs carries the risk of contamination, we sought to develop recombinant HAV-neutralizing human
antibodies. We prepared a combinatorial phage display library of recombinant human
anti-HAV antibodies from
RNA extracted from the blood lymphocytes of a convalescent
hepatitis A patient. Two recombinant human
IgG antibodies, HAIgG16 and HAIgG78, were screened from the antibody library by their ability to bind with high affinity to purified, inactivated HAV virions. These
antibodies recognized different
epitopes of the HAV virion capsid, and competed with both patient sera and well-characterized neutralizing mouse
monoclonal antibodies. A cocktailed mixture of HAIgG16 and HAIgG78 at a 3:1 ratio was prepared to compare its combined biological activity with that conferred by each antibody individually. The cocktailed
antibodies displayed a stronger neutralizing activity in vitro than that observed with either HAIgG16 and HAIgG78 alone. To determine the in vivo neutralizing abilities of these
antibodies, rhesus monkeys were inoculated with cocktailed
antibodies and challenged with HAV. Whereas control animals developed
hepatitis A and seroconverted to the HAV antibody, animals receiving cocktailed
antibodies were protected either from
viral infection or from developing clinical
hepatitis. These results demonstrate that recombinant human antibody preparations could be used to prevent or treat early-stage HAV
infection.