Human Immunodeficiency Virus: Scientific Challenges Impeding Candidate Vaccines

Neutralizing antibodies induced by liposomal HIV-1 glycoprotein 41 peptide simultaneously bind to both the 2F5 or 4E10 epitope and lipid epitopes

OBJECTIVES

There is a need to develop HIV-1 vaccine formulations that incorporate inexpensive antigens and clinically acceptable potent adjuvants for inducing neutralizing antibodies. The purpose of this initial vaccine study was to produce peptide- and lipid-induced murine mAbs that replicate the characteristics of the 2F5 and/or 4E10 human antibodies in binding both to the membrane proximal external region (MPER) of glycoprotein 41 and the adjacent lipid bilayer for neutralizing HIV-1 infection of CD4 lymphocytes.

RESEARCH DESIGNS AND METHODS

Liposomes containing a synthetic MPER peptide as a peptide antigen, phosphatidylinositol-4-phosphate (PIP) as a lipid antigen, and monophosphoryl lipid A as a potent adjuvant were used as a formulation to immunize mice. mAbs were then produced and tested for binding to MPER, glycoprotein 41, and PIP and for the ability to neutralize HIV-1 infection of CD4 cells in a human peripheral blood mononuclear cell assay.

RESULTS

Polyclonal antisera contained antibodies that bound both to MPER and PIP. Immunoglobulin M mAbs were produced that bound both to the core MPER site of 2F5, or that overlapped with the 4E10 site, and that simultaneously bound PIP. High concentrations of these mAbs neutralized infection of peripheral blood lymphocytes by a primary infectious molecular clone of HIV-1.

CONCLUSION

Liposomes containing MPER peptide as an antigen, PIP as a lipid antigen, and lipid A as an adjuvant induce anti-MPER-specific multispecific antibodies that simultaneously bind glycoprotein 41 MPER and adjacent lipid and neutralize HIV-1 infection in a human peripheral blood mononuclear cell assay.

Elicitation of immunity to HIV type 1 Gag is determined by Gag structure

The gag gene of the human immunodeficiency virus type 1 (HIV-1) encodes for viral proteins that self-assemble into viral particles. The primary Gag gene products (capsid, matrix, and nucleocapsid) elicit humoral and cellular immune responses during natural infection, and these proteins are included in many preclinical and clinical HIV/AIDS vaccines. However, the structure (particulate or soluble) of these proteins may influence the immunity elicited during vaccination. In this study, mice were inoculated with four different HIV-1 Gag vaccines to compare the elicitation of immune responses by the same Gag immunogen presented to the immune system in different forms. The immunity elicited by particles produced in vivo by DNA plasmid (pGag) was compared to these same proteins retained intracellularly (pGag(DMyr)). In addition, the elicitation of anti- Gag immunity by Gag(p55) virus-like particles (VLPs) or soluble, nonparticulate Gag(p55) proteins was compared. Enhanced cellular responses, but almost no anti-Gag antibodies, were elicited with intracellularly retained Gag proteins. In contrast, DNA vaccines expressing VLPs elicited both anti-Gag antibodies and cellular responses. Mice vaccinated with purified Gag(p55) VLPs elicited robust humoral and cellular immune responses, which were significantly higher than the immunity elicited by soluble, nonparticulate Gag(p55) protein. Overall, purified particles of Gag effectively elicited the broadest and highest titers of anti-Gag immunity. The structural form of Gag influences the elicited immune responses and should be considered in the design of HIV/AIDS vaccines.