Frank: Studies to Maximize Immunogenicity
The research team lead by Dr. Michael Frank will explore two avenues for generating an effective HIV vaccine: 1) slowing the clearance of the HIV Env antigen and 2) increasing the vulnerability of HIV to complement attack.
For an antigen to be effective as an immunogen, it must remain intact long enough to stimulate an immune response. Vaccines are commonly compounded with adjuvant to prolong stimulation of the immune system. Clearance of viral envelope glycoproteins occurs, in part, because these proteins often have sugars on their surface (ie mannose, galactose) and spleen cells have mannose binding receptors such as L-sign (mice) or DC-sign (humans) that can bind and remove the high mannose proteins from circulation. Liver cells have asialoglycoprotein recpetors that bind and remove degrading host proteins as well as viral envelope proteins that have terminal galactose residues. Other mechanisms of protein degradation include protyolysis by enzymes or chemical oxidation.
It is well known that complement plays a crucial role in the control of many viral and bacterial infections by opsonizing organisms, by phagocytosis or by directly lysing them. Pathogens such as HIV have evolved strategies to avoid complement attack. However, the role of complement in the generation of an effective HIV vaccine is poorly understood and represents the most novel and potentially groundbreaking aspect of the proposal. HIV-1 Env is an excellent antigen with which to examine this question, because: 1) so much is known about the glycosylation patterns of HIV and structural features and 2) complement binding to HIV has been controversial and the role in inducing a strong and effective immune response is not clear.
The team lead by Dr. Frank will investigate if slowing clearance of HIV by the liver and/or spleen contributes to a weak antibody response. They will attempt to do this by stabilizing the Env antigen via chemical means using cross linking agents or by the removal of N-linked carbohydrates (ie selective or global removal of mannose residues). They will also examine the role of complement binding by Env by making protein conjugates, modifying glycosylation patterns or by MBL binding.
1. Stabilizing HIV-1 envelope gp140 by chemical means or by binding mannose binding protein (MBP) such that Env is neither rapidly removed from the circulation nor quickly degraded, allowing it to enter well defined spleenic antigen processing pathways and enhance immunogenicity.
2. Improve complement binding to Env by making protein conjugates, modifying glycosylation patterns or by MBL binding.
3. Testing the immunogenicity of the newly derived gp140 immunogens in mice and guinea pigs to determine whether the researchers have achieved the goal of appropriate antigen processing. This includes entry of antigen into the marginal zone of secondary lymphoid tissues, subsequent transfer into follicles and generation of germinal centers in secondary lymphoid tissues. Through these alterations, Env may induce a long lived, polymeric antibody response that neutralizes a range of HIV-1 clade B tier 1 and tier 2 viral isolates. If successful, the researchers then propose testing the antibodies in pre-clinical Rhesus macaque immunogenicity studies.