HIV-1/SIV Neutralizing Antibody Gene Delivery: A Novel Vaccination Approach
The human immunodeficiency virus (HIV) is the causative agent of acquired immunodeficiency syndrome (AIDS). Since there is no cure, creating an efficacious, safe, and affordable vaccine is of paramount importance. Several broadly neutralizing human antibodies (NAbs) have been identified that possess potent in vitro neutralization activity against diverse HIV-1 primary isolates. The challenge is how to deliver these NAbs as a prophylactic vaccine to millions of people.
Our approach is predicated on the ability to achieve sustained, high concentrations of NAbs in the systemic circulation by antibody gene transfer targeting skeletal muscle. Our laboratory previously demonstrated long-term expression of an anti-HIV-1 antibody in mice using recombinant adeno-associated virus serotype 2 (rAAV2). Unfortunately, the systemic expression levels were below that predicted to provide benefit in passive immunization studies in non-human primate challenge models. To improve serum antibody expression levels, we optimized multiple components of the expression platform to achieve significant improvement in secreted antibody levels (> 500-fold). Incremental increases were realized by using: (1) synthetic signal peptides; (2) second generation self-complementary rAAV vectors; (3) AAV serotype 1 which demonstrates robust skeletal muscle transduction; (4) genetic fusion constructs composed of single-chain Fv fragments fused to the hinge, C2, and C3 heavy chain domains from IgG1 and 2; and (5) selection of primates with absent or low pre-existing AAV binding antibodies prior to NAb gene vaccination. As a result of these iterative improvements, long-lasting transgene expression and in vitro neutralization activity were achieved in eight of nine vaccinated rhesus macaques at levels predicted to be therapeutically beneficial. Significantly, six of the vaccinated monkeys were completely protected against a virulent simian immunodeficiency virus (SIV) intravenous challenge. The three infected animals demonstrated significantly lower viral load set points. Interestingly, these 3 animals possessed anti-antibody humoral immune responses that may have blunted the activity of the expressed NAb resulting in SIV infection.
These data represent the first demonstration that NAb gene transfer can endow the host with protective humoral immunity and demonstrate the feasibility of using rAAV-mediated gene transfer into muscle tissue to achieve sufficient levels of circulating NAbs or inhibitors to either block or reduce the severity of challenge virus infection. This work provides a foundation to further explore the utility of this novel approach against an adversary that is unparalleled in evading natural mechanisms of protective host immunity.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:hiv 1 siv vaccine neutralizing antibody raav
Date of Publication:06/26/2009