Broadly neutralizing, anti-HIV-1 gp120 mAbs have been isolated from infected individuals, and there is considerable interest in developing these reagents for Ab-based immunoprophylaxis and treatment. As a means to identify potentially new anti-HIV Abs, we exploited humanized NOD-scid IL2rgamma(null) mice systemically infected with HIV-1 to generate a wide variety of Ag-specific human mAbs. The Abs were encoded by a diverse range of variable gene families and Ig classes, including IgA, and several showed significant levels of somatic mutation. Moreover, the isolated Abs not only bound target Ags with similar affinity as broadly neutralizing Abs, they also demonstrated neutralizing ability against multiple HIV-1 clades. The use of humanized mice will allow us to use our knowledge of HIV-1 gp120 structure and function, and the immune response targeting this protein, to generate native human prophylactic Abs to reduce the infection and spread of HIV-1.

HIV vaccine efforts tend to focus on the induction of IgG neutralizing antibodies. In part, this may stem from the observations that most HIV infected individuals fail to produce significant mucosal IgA. However, this is unlike most other infections and in turn it can be argued that mucosal IgA with appropriate function and specificity may contribute significantly to the prevention of HIV transmission. To explore this, we previously isotype switched F425A1g8, an anti-HIV CD4i human monoclonal antibody that binds to epitopes exposed upon CD4 binding (CD4i) The VH and VL chains were amplified from the IgG hybridoma and inserted into IgA1 or IgA2 and IgKappa vectors respectively. Stable cells lines were produced and antibody was collected and purified. Initial results showed that the IgA1 variant neutralized a number of HIV-1 isolates better than its parental form IgG1. We believe the increased neutralization of HIV is mainly due to the structural differences between IgG1 and IgA1. We hypothesize that the extended hinge of IgA1 may increase segmental flexibility and change the interaction of antibody with CD4i epitopes of the HIV, resulting in greater avidity. To look at this further, we have generated monomeric and dimeric IgA1 and IgA2 variants of three different CD4i antibodies: F425A1g8, 17b and E51. All antibody variants will be tested for immumoreactivity, HIV neutralization, prevention of transmission and ADCVI activity. Consistent with our previous results, there are significant differences in functional activity of the other CD4i antibodies with IgA1 more effective than the IgA2 variants. Additional activities will contribute to the hypothesis that the extended hinge region of the IgA1 antibody increases the antibodies ability to access the CD4i epitopes upon HIV-1 binding to CD4. These studies should impact on the design of active and passive immunotherapy and the prevention of HIV transmission.

Background: Despite the length of time HIV has been wreaking havoc on its victims, improvements in the prevention and treatment of HIV are needed. Anti-retroviral therapy can be effective but is expensive and not entirely accessible for people infected in third world countries. Several promising broadly neutralizing antibodies have been isolated from infected individuals; we propose that generating antigen specific human monoclonal antibodies using humanized mice further represents a promising approach to engineer prophylactic antibodies to reduce spread and infection of HIV. Methods: Immunodeficient mice were engrafted with fetal liver and thymus (BLT) prior to infection with different HIV isolates. HIV infection of the mice was monitored by viral load and antibody response followed by ELISA using gp120, gp41 or gp120/CD4 complex as antigens. Approximately 8-12 weeks post infection, spleens were harvested and splenocytes fused with human fusion partner HMMA 2.5 to isolate antibody-expressing hybridomas. Lead clones were scaled and purified for testing in functional assays such as TZM-bl neutralization assays as well as ADCVI to determine neutralizing and cytotoxic ability of the antibodies. Antibody sequences were also determined for analysis. Results: A robust, specific antibody response, of both IgG and IgA isotypes, was generated in response to HIV infection. Over 60 hybridomas were created that were not only immunoreactive with env antigens, but also had neutralization activity. Moreover, variable family usage was not limited and somatic mutation was clearly evident. Conclusions: These findings suggest that humanized BLT mice are a novel source for well-characterized, stable human monoclonal antibodies to HIV.