New strategy targets rare B cells to develop effective HIV vaccine

According to a recently published study, Nature Immunology Epitope-scaffolded nanoparticles targeting germ cells are rare and widespread Neutralizing antibodies (bnAb) precursor to human immunodeficiency virus (HIV).

investigation: Vaccination induces broadly neutralizing antibody precursors against HIV gp41Image credit: Salov Evgeniy/Shutterstock.com

background

Broad vaccine protection against antigenically diverse viruses, such as betacoronaviruses, hepatitis C virus, HIV, and influenza viruses, requires bnAbs directed against conserved epitopes on variable membranes. GlycoproteinsAlthough monoclonal bnAbs have been identified against these viruses, strategies to derive bnAbs with predefined binding specificities and genetic characteristics are needed.

In germline targeted vaccine design, a priming immunogen induces responses from rare bnAb precursor B cells that possess the genetic characteristics required for bnAb development. After priming, successive boosts with immunogens that resemble native glycoproteins induce B cell maturation to generate bnAbs against the target epitope.

This approach has been demonstrated with VRC01-class bnAbs against the human HIV envelope CD4-binding site, although most VRC01-class bnAbs show heavy chain complementarity-determining region 3 (HCDR3)-dominated interactions.

HCDR3-dominant bnAbs against the membrane-proximal external region (MPER) of the HIV envelope protein (Env) are of great importance because such bnAbs (e.g., DH511, LN01, and 10E8) have a large breadth of neutralization.

Research and Results

In this study, the researchers developed germline-targeting epitope scaffold nanoparticles to induce 10E8 class HCDR3-dominant bnAb precursor responses. First, they selected one of the epitope scaffolds of MPER, namely T117v2, for optimization.

This scaffold bound strongly to mature 10E8 but failed to bind other 10E8-class precursors identified by next-generation sequencing (NGS) database searches (NGS precursors).

Next, the team aimed to develop an immunogen based on T117v2 that has the following features: affinity of ≥10 μM for the unmutated common ancestor (UCA) of 10E8 and NGS precursors, an affinity gradient for 10E8-class antibodies, multivalent display on self-assembled single-component nanoparticles, and an N-linked glycosylation site.

Therefore, iterative optimization of T117v2 binding to 10E8 putative germline, NGS precursor, and UCA generated a series of immunogens (10E8-GT).

These 10E8-GT scaffolds were multimerized by fusion with self-assembled nanoparticles derived from hyperthermophilic bacteria, and N-linked glycosylation sites were added to the scaffold surface to mitigate off-target responses.

These scaffolds stabilized MPER in a 10E8-bound conformation and bound to 10E8-class HCDR3, resembling 10E8 glycoprotein 41 (gp41) interactions.Next, the team assessed the ability of naive B cell receptor (BCR) repertoires to respond to the 10E8-GT immunogen.

On average, 10E8-GT12, 10E8-GT10.1, and 10E8-GT9.2 bound to 0.7%, 0.8%, and 0.05% of naive B cells (from HIV-seronegative donors).

Of these epitope scaffold-binding cells, 97%, 94%, and 81% did not bind to the 10E8 epitope knockout (KO) version of the corresponding 10E8-GT construct and were referred to as epitope-specific BCRs.

BCR sequencing showed that epitope-specific BCRs were enriched in long HCDR3s and HCDR3 binding motifs (YxFW) compared to the unsorted control dataset.

In total, 16%, 23%, and 18% of epitope-specific BCRs were classified as 10E8-GT12, 10E8-GT10.1, and 10E8-GT9.2, respectively, and fulfilled the criteria for 10E8-class HCDR3.

Next, the researchers synthesized monoclonal antibodies (mAbs) from B cells that were classified as 10E8-GT12, 10E8-GT10.1, or 10E8-GT9.2 and had HCDR3s of either the 10E8 class or non-10E8 class. They found that 60 of the 70 10E8-like mAbs had affinity for each classification probe.

Additional experiments demonstrated that the 10E8-GT scaffold selectively binds to naive BCRs bearing 10E8-class HCDR3s and efficiently binds 10E8-class HCDR3s. alive B cell activation.

Next, the team investigated whether the 10E8-GT immunogen would elicit a 10E8-class response in mice with diverse 10E8-class progenitor cells._HSix mice were developed in which the mouse JH1-JH4 and DQ52 segments were replaced with human J._H6 and D_H3-3 segments each.

These mice were immunized with adjuvanted proteins 10E8-GT10.2 12mer, 10E8-GT12 24mer, 10E8-GT12 12mer, mRNA lipid nanoparticle (LNP)-encoded 10E8-GT12 24mer, or control 10E8-GT9-KO 12mer.

Six weeks later, immunogen-specific BCR for immunoglobulin D (IgD)^–) IgM^– B cells were sequenced. All immunogens except for the control induced 10E8 class HCDR3s, which were enriched for YxFw motifs and long HCDR3s.

LN01-class HCDR3 was detected in all mice immunized with the 10E8-GT12 12mer or 10E8-GT10.2 12mer and in 11 mice immunized with the 10E8-GT12 24mer.

Thus, 10E8-GT12 was delivered as a protein or LNP-induced response from diverse and rapid 10E8 and LN01 class precursors. alive.

The researchers then immunized rhesus macaques with the 10E8-GT10.2 12mer and a saponin/monophosphoryl A lipid A nanoparticle (SMNP) adjuvant in a 14-day dose-escalating regimen.

Control macaques received a stabilized HIV-1 Env trimer lacking the MPER.⁺CD38^– B cell responses were observed in germinal centers (GCs) by week 10. In particular, the 10E8-GT10.2 12mer elicited strong epitope-specific GC responses.

In macaques immunized with the 10E8-GT10.2 12mer, 10E8-class HCDR3 was detected on CD71.⁺CD38^– GC and IgD^–CD20⁺ Memory B cells in peripheral blood. In contrast, one 10E8-like HCDR3 was detected in more than 9000 BCRs in the control group.

Finally, the researchers assessed binding of postprime antibodies to 10E8-B1, a fully native epitope scaffold with one mutation (lytic), which lacked affinity for members of the early 10E8 lineage but showed very high affinity for mature 10E8.

10E8-B1 bound to 10% of the 10E8 class antibodies induced by 10E8-GT nanoparticles and 25% of the antibodies primed by the 10E8-GT10 12mer.

Conclusion

The researchers developed an immunogen through germline targeting, epitope scaffolding, and nanoparticles. The immunogen consistently elicited 10E8 class HIV bnAb precursors in two mouse models and in rhesus macaques. Thus, this finding indicates that epitope scaffolds can be designed to trigger responses from rare bnAb precursors and select for favorable maturation.

Taken together, the researchers believe that the 10E8-GT nanoparticles are a priming immunogen for the MPER vaccine. The epitope scaffold bound to naive bnAb precursors isolated from human peripheral blood.

Furthermore, mRNA-LNP delivery of the 10E8-GT12 24mer elicited similar responses to SMNP-adjuvanted protein immunization, supporting the possibility of rapid clinical trials.