DNA Vaccine Molecular Adjuvants SP-D-BAFF and SP-D-APRIL Enhance Anti-gp120 Immune Response and Increase HIV-1 Neutralizing Antibody Titers

Abstract

Broadly neutralizing antibodies (bNAbs) specific for conserved epitopes on the HIV-1 envelope (Env) are believed to be essential for protection against multiple HIV-1 clades. However, vaccines capable of stimulating the production of bNAbs remain a major challenge. Given that polyreactivity and autoreactivity are considered important characteristics of anti-HIV bNAbs, we designed an HIV vaccine incorporating the molecular adjuvants BAFF (B cell activating factor) and APRIL (a proliferation-inducing ligand) with the potential to facilitate the maturation of polyreactive and autoreactive B cells as well as to enhance the affinity and/or avidity of Env-specific antibodies. We designed recombinant DNA plasmids encoding soluble multitrimers of BAFF and APRIL using surfactant protein D as a scaffold, and we vaccinated mice with these molecular adjuvants using DNA and DNAprotein vaccination strategies. We found that immunization of mice with a DNA vaccine encoding BAFF or APRIL multitrimers, together with interleukin 12 (IL-12) and membrane-bound HIV-1 Env gp140, induced neutralizing antibodies against tier 1 and tier 2 (vaccine strain) viruses. The APRIL-containing vaccine was particularly effective at generating tier 2 neutralizing antibodies following a protein boost. These BAFF and APRIL effects coincided with an enhanced germinal center (GC) reaction, increased anti-gp120 antibody-secreting cells, and increased anti-gp120 functional avidity. Notably, BAFF and APRIL did not cause indiscriminate B cell expansion or an increase in total IgG. We propose that BAFF and APRIL multitrimers are promising molecular adjuvants for vaccines designed to induce bNAbs against HIV-1. IMPORTANCERecent identification of antibodies that neutralize most HIV-1 strains has revived hopes and efforts to create novel vaccines that can effectively stimulate HIV-1 neutralizing antibodies. However, the multiple immune evasion properties of HIV have hampered these efforts. These include the instability of the gp120 trimer, the inaccessibility of the conserved sequences, highly variable protein sequences, and the loss of HIV-1-specific antibody-producing cells during development. We have shown previously that tumor necrosis factor (TNF) superfamily ligands, including BAFF and APRIL, can be multitrimerized using the lung protein SP-D (surfactant protein D), enhancing immune responses. Here we show that DNA or DNA-protein vaccines encoding BAFF or APRIL multitrimers, IL-12p70, and membrane-bound HIV-1 Env gp140 induced tier 1 and tier 2 neutralizing antibodies in a mouse model. BAFF and APRIL enhanced the immune reaction, improved antibody binding, and increased the numbers of anti-HIV-1 antibody-secreting cells. Adaptation of this vaccine design may prove useful in designing preventive HIV-1 vaccines for humans.

Binding Studies of TNF Receptor Superfamily (TNFRSF) Receptors on Intact Cells

“…First, strong receptor activation by poorly active soluble ligand trimers can be restored by multimerization, e.g. by oligomerization with antibodies recognizing an epitope/tag not interfering with receptor binding or by genetically enforced formation of hexameric, nonameric, or dodecameric molecules (14,19,22,23,(25)(26)(27)(28)(29)(30). Second, inefficient receptor activation by soluble ligand trimers can be overcome by binding to the extracellular matrix or by artificial cell surface immobilization using genetically engineered trimeric variants of soluble TNF ligands (31).…”

Antibody responses to prime–boost vaccination with an HIV-1 gp145 envelope protein and chimpanzee adenovirus vectors expressing HIV-1 gp140

“…Other pre-clinical vaccine studies have also elicited NAbs; tier 1 and tier 2 PV neutralization was achieved with a DNA vaccine expressing gp160 given together with particles displaying the membrane proximal external region of Env [34]. Similar results were obtained with an adjuvanted DNA vaccine followed by a protein boost, as well as with a DNA prime/protein boost regimen using constructs that expressed diverse polyvalent heterotrimeric Envs [35,36]. Careful design of immunogens and adjuvants thus allows for the induction of cross-reactive NAbs to HIV-1, which upon passive transfer have been shown to protect nonhuman primates against challenge with an HIV-1/simian immunodeficiency virus (SIV) chimera and to reduce viral loads in chronically infected individuals in human trials [29,30,37].…”

APRIL:TACI axis is dispensable for the immune response to rabies vaccination

“…Increased expression of APRIL in RABV-infected primary murine B cells suggested that APRIL expression in the context of RABV-based vaccines could augment immunogenicity. Indeed, previous HIV vaccine studies have successfully employed APRIL as an adjuvant (Gupta et al, 2015; Kanagavelu et al, 2012; Melchers et al, 2012). …”