Chimeric HIV-1 envelope glycoproteins with potent intrinsic granulocyte-macrophage colony-stimulating factor (GM-CSF) activity

CCL19 and CCL28 Assist Herpes Simplex Virus 2 Glycoprotein D To Induce Protective Systemic Immunity against Genital Viral Challenge

An effective HSV-2 vaccine should induce antigen (Ag)-specific immune responses against viral mucosal infection. This study reveals that chemokine CCL19 or CCL28 enhanced HSV-2 glycoprotein D ectodomain (gD-306aa)-induced immune responses against vaginal virus challenge.

Potent systemic immunity is important for recalled mucosal immune responses, but in the defense against mucosal viral infections, it usually remains low at mucosal sites. Based on our previous findings that enhanced immune responses can be achieved by immunization with an immunogen in combination with a molecular adjuvant, here we designed chemokine-antigen (Ag) fusion constructs (CCL19- or CCL28-herpes simplex virus 2 glycoprotein D [HSV-2 gD]). After intramuscular (i.m.) immunization with different DNA vaccines in a prime and boost strategy, BALB/c mice were challenged with a lethal dose of HSV-2 through the genital tract. Ag-specific immune responses and chemokine receptor-specific lymphocytes were analyzed to determine the effects of CCL19 and CCL28 in strengthening humoral and cellular immunity. Both CCL19 and CCL28 were efficient in inducing long-lasting HSV-2 gD-specific systemic immunity. Compared to CCL19, less CCL28 was required to elicit HSV-2 gD-specific serum IgA responses, Th1- and Th2-like responses of immunoglobulin (Ig) subclasses and cytokines, and CCR3⁺ T cell enrichment (>8.5-fold) in spleens. These findings together demonstrate that CCL28 tends to assist an immunogen to induce more potently protective immunity than CCL19. This work provides information for the application potential of a promising vaccination strategy against mucosal infections caused by HSV-2 and other sexually transmitted viruses.

IMPORTANCE An effective HSV-2 vaccine should induce antigen (Ag)-specific immune responses against viral mucosal infection. This study reveals that chemokine CCL19 or CCL28 enhanced HSV-2 glycoprotein D ectodomain (gD-306aa)-induced immune responses against vaginal virus challenge. In addition to eliciting robust humoral immune responses, the chemokine-Ag fusion construct also induced Th1- and Th2-like immune responses characterized by the secretion of multiple Ig subclasses and cytokines that were able to be recalled after HSV-2 challenge, while CCL28 appeared to be more effective than CCL19 in promoting gD-elicited immune responses as well as the migration of T cells to secondary lymph tissues. Of importance, both CCL19 and CCL28 significantly facilitated gD to induce protective mucosal immune responses in the genital tract. The above-described findings together highlight the potential of CCL19 or CCL28 in combination with gD as a vaccination strategy to control HSV-2 infection.

Immunization with HSV-2 gB-CCL19 Fusion Constructs Protects Mice against Lethal Vaginal Challenge

There is a lack of an HSV-2 vaccine, in part as the result of various factors that limit robust and long-term memory immune responses at the mucosal portals of viral entry. We previously demonstrated that chemokine CCL19 augmented mucosal and systemic immune responses to HIV-1 envelope glycoprotein. Whether such enhanced immunity can protect animals against virus infection remains to be addressed. We hypothesized that using CCL19 in a fusion form to direct an immunogen to responsive immunocytes might have an advantage over CCL19 being used in combination with an immunogen. We designed two fusion constructs, plasmid (p)gBIZCCL19 and pCCL19IZgB, by fusing CCL19 to the C- or N-terminal end of the extracellular HSV-2 glycoprotein B (gB) with a linker containing two (Gly4Ser)2 repeats and a GCN4-based isoleucine zipper motif for self-oligomerization. Following immunization in mice, pgBIZCCL19 and pCCL19IZgB induced strong gB-specific IgG and IgA in sera and vaginal fluids. The enhanced systemic and mucosal Abs showed increased neutralizing activity against HSV-2 in vitro. Measurement of gB-specific cytokines demonstrated that gB-CCL19 fusion constructs induced balanced Th1 and Th2 cellular immune responses. Moreover, mice vaccinated with fusion constructs were well protected from intravaginal lethal challenge with HSV-2. Compared with pgB and pCCL19 coimmunization, fusion constructs increased mucosal surface IgA(+) cells, as well as CCL19-responsive immunocytes in spleen and mesenteric lymph nodes. Our findings indicate that enhanced humoral and cellular immune responses can be achieved by immunization with an immunogen fused to a chemokine, providing information for the design of vaccines against mucosal infection by HSV-2 and other sexually transmitted viruses.

Enhanced immunogenicity of HIV-1 envelope gp140 proteins fused to APRIL

Current HIV-1 vaccines based on the HIV-1 envelope glycoprotein spike (Env), the only relevant target for broadly neutralizing antibodies, are unable to induce protective immunity. Env immunogenicity can be enhanced by fusion to costimulatory molecules involved in B cell activation, such as APRIL and CD40L. Here, we found that Env-APRIL signaled through the two receptors, BCMA and TACI. In rabbits, Env-APRIL induced significantly higher antibody responses against Env compared to unconjugated Env, while the antibody responses against the APRIL component were negligible. To extend this finding, we tested Env-APRIL in mice and found minimal antibody responses against APRIL. Furthermore, Env-CD40L did not induce significant anti-CD40L responses. Thus, in contrast to the 4-helix cytokines IL-21 and GM-CSF, the TNF-superfamily members CD40L and APRIL induced negligible autoantibodies. This study confirms and extends previous work and shows that fusion of Env-based immunogens to APRIL can improve Env immunogenicity and might help in designing HIV vaccines that induce protective humoral immunity.

HIV-1 Env-specific memory and germinal center B cells in C57BL/6 mice

Continued efforts to define the immunogenic properties of the HIV-1 envelope glycoproteins (Env) are needed to elicit effective antibody (Ab) responses by vaccination. HIV-1 is a highly neutralization-resistant virus due to conformational and glycan shielding of conserved Ab determinants on the virus spike. Elicitation of broadly neutralizing Abs that bind poorly accessible epitope regions on Env is therefore extremely challenging and will likely require selective targeting of specific sub-determinants. To evaluate such approaches there is a pressing need for in vivo studies in both large and small animals, including mice. Currently, most mouse immunization studies are performed in the BALB/c strain; however, the C57BL/6 strain offers improved possibilities for mechanistic studies due to the availability of numerous knock-out strains on this genetic background. Here, we compared Env immunogenicity in BALB/c and C57BL/6 mice and found that the magnitude of the antigen-specific response was somewhat lower in C57BL/6 than in BALB/c mice by ELISA but not significantly different by B cell ELISpot measurements. We then established protocols for the isolation of single Env-specific memory B cells and germinal center (GC) B cells from immunized C57BL/6 mice to facilitate future studies of the elicited response at the monoclonal Ab level. We propose that these protocols can be used to gain an improved understanding of the early recruitment of Env-specific B cells to the GC as well as the archiving of such responses in the memory B cell pool following immunization.

Development of broadly neutralizing antibodies from autologous neutralizing antibody responses in HIV infection

PURPOSE OF REVIEW

Detailed genetic and structural characterization has revealed that broadly neutralizing antibodies (bnAbs) against HIV-1 have unusually high levels of somatic hypermutation, long CDRH3 domains, and the ability to target one of four sites of vulnerability on the HIV-1 envelope (Env) glycoproteins. A current priority is to understand how bnAbs are generated during natural infection, and translate this information into immunogens that can elicit bnAb following vaccination.

RECENT FINDINGS

Strain-specific neutralizing antibodies can acquire broad neutralizing capacity when the transmitted/founder Env or a specific Env variant is recognized by an unmutated rearranged germline that has the capacity to develop bnAb-like features. This event could be relatively infrequent, as only certain germlines appear to possess inherent features needed for bnAb activity. Furthermore, the glycosylation pattern and diversity of circulating HIV-1 Envs, as well as the state of the B-cell compartment, may influence the activation and maturation of certain antibody lineages.

SUMMARY

Collectively, studies over the last year have suggested that the development of HIV-1 Env immunogens that bind and activate bnAb-like germlines is feasible. However, more information about the features of Env variants and the host factors that lead to breadth during natural infection are needed to elicit bnAbs through immunization.

Autoantibodies induced by chimeric cytokine-HIV envelope glycoprotein immunogens

Cytokines are often used as adjuvants to increase the immunogenicity of vaccines because they can improve the immune response and/or direct it into a desired direction. As an alternative to codelivering Ags and cytokines separately, they can be fused into a composite protein, with the advantage that both moieties act on the same immune cells. The HIV-1 envelope glycoprotein (Env) spike, located on the outside of virus particles and the only relevant protein for the induction of neutralizing Abs, is poorly immunogenic. The induction of anti-Env Abs can be improved by coupling Env proteins to costimulatory molecules such as a proliferation inducing ligand (APRIL). In this study, we evaluated the immunogenicity of chimeric molecules containing uncleaved Env gp140 fused to the species-matched cytokines IL-21 or GM-CSF in rabbits and mice. Each cytokine was either fused to the C terminus of Env or embedded within Env at the position of the variable loops 1 and 2. The cytokine components of the chimeric Env-GM-CSF and Env-IL-21 molecules were functional in vitro, but none of the Env-cytokine fusion proteins resulted in improved Ab responses in vivo. Both the Env-GM-CSF and the Env-IL-21 molecules induced strong anticytokine Ab responses in both test species. These autoimmune responses were independent of the location of the cytokine in the chimeric Env molecules in that they were induced by cytokines inserted within the variable loops 1 and 2 of Env or fused to its C terminus. The induction of undesired autoimmune responses should be considered when using cytokines as costimulatory molecules in fusion proteins.

An HIV-1 envelope glycoprotein trimer with an embedded IL-21 domain activates human B cells

Broadly neutralizing antibodies (bNAbs) that target the HIV-1 envelope glycoproteins (Env) can prevent virus acquisition, but several Env properties limit its ability to induce an antibody response that is of sufficient quantity and quality. The immunogenicity of Env can be increased by fusion to co-stimulatory molecules and here we describe novel soluble Env trimers with embedded interleukin-4 (IL-4) or interleukin-21 (IL-21) domains, designed to activate B cells that recognize Env. In particular, the chimeric Env_IL-21 molecule activated B cells efficiently and induced the differentiation of antibody secreting plasmablast-like cells. We studied whether we could increase the activity of the embedded IL-21 by designing a chimeric IL-21/IL-4 (ChimIL-21/4) molecule and by introducing amino acid substitutions in the receptor binding domain of IL-21 that were predicted to enhance its binding. In addition, we incorporated IL-21 into a cleavable Env trimer and found that insertion of IL-21 did not impair Env cleavage, while Env cleavage did not impair IL-21 activity. These studies should guide the further design of chimeric proteins and Env_IL-21 may prove useful in improving antibody responses against HIV-1.