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Human immunodeficiency virus (HIV) remains one of the most formidable challenges in global public health. Despite four decades of research, an effective prophylactic vaccine has remained elusive. With approximately 39.9 million people living with HIV worldwide and around 1.3 million new infections annually, the development of a safe, effective, and accessible preventive vaccine remains the most promising strategy to end the epidemic.
HIV belongs to the Lentivirus genus of the Retroviridae family. As a retrovirus, HIV alternates between a single-stranded RNA genome within the virion and a double-stranded DNA form integrated into the host genome. Two distinct types have been identified: HIV-1, responsible for the global pandemic and classified into four groups (M, N, O, P) with group M further divided into subtypes A–K and numerous circulating recombinant forms (CRFs); and HIV-2, which is less pathogenic, less transmissible, and largely confined to West Africa.
Fig. 1 HIV virion
The viral particle measures approximately 120 nm in diameter and consists of a conical capsid (p24) enclosing two copies of positive-sense genomic RNA and essential enzymes. The gag gene encodes structural proteins including the matrix (p17), capsid (p24), nucleocapsid (p7), and p6; the env gene encodes the envelope glycoproteins gp120 and gp41, which mediate viral entry; and the pol gene encodes reverse transcriptase, integrase, and protease—enzymes critical for viral replication. Additionally, the genome contains regulatory genes (tat, rev) and accessory genes (vif, vpr, vpu, nef) that modulate host cell functions, enhance viral replication, and facilitate immune evasion. The long terminal repeats (LTRs) at both ends of the genome contain promoter and enhancer elements essential for viral transcription.
The envelope glycoprotein complex is of particular relevance to vaccine design. Each Env spike consists of three gp120 subunits non-covalently associated with three gp41 transmembrane subunits. The gp120 exterior subunit contains five variable loops (V1–V5) interspersed with conserved regions, while gp41 anchors the complex in the viral membrane and mediates membrane fusion. The extraordinary sequence diversity of Env, driven by immune pressure and the error-prone replication machinery, represents the primary obstacle to antibody-mediated protection.
The HIV replication cycle comprises six sequential steps, each representing a potential target for therapeutic and vaccine intervention. Understanding this cycle in molecular detail is essential for rational vaccine design, as the immune system must intercept the virus before productive infection is established.
Fig. 2 HIV replication cycle
Attachment and Entry: The gp120 glycoprotein, organized as trimers on the viral surface, binds sequentially to the CD4 receptor and a chemokine coreceptor—primarily CCR5 (for macrophage-tropic, R5 viruses) or CXCR4 (for T-cell-tropic, X4 viruses). This dual-receptor engagement triggers conformational changes in gp41, exposing its N-terminal fusion peptide, which inserts into the host cell membrane. Subsequent refolding of the heptad repeat regions (HR1 and HR2) into a six-helix bundle drives membrane fusion and viral entry.
Uncoating: Following fusion, the viral capsid disassembles in the cytoplasm—a process mediated by host factors including cyclophilin A and CPSF6—releasing the RNA genome and associated replication enzymes into the cytosol.
Reverse Transcription: Viral reverse transcriptase, an RNA-dependent DNA polymerase with RNase H activity, synthesizes a complementary DNA (cDNA) strand from the RNA template, then degrades the RNA and synthesizes the second DNA strand. This process is error-prone, contributing significantly to viral diversity.
Integration: The pre-integration complex, containing viral cDNA and integrase, translocates to the nucleus. Viral integrase catalyzes the insertion of the proviral DNA into the host genome, preferentially targeting actively transcribed genes. Once integrated, the provirus can remain transcriptionally silent (latent) for years, forming a persistent reservoir that complicates both cure and vaccine strategies.
Protein Synthesis and Assembly: Host RNA polymerase II transcribes the proviral DNA into full-length and spliced viral RNAs. These are exported to the cytoplasm, where host ribosomes translate Gag and Gag-Pol polyproteins. Viral protease then cleaves these precursors into functional proteins. New virions assemble at the plasma membrane, where Gag recruits genomic RNA and envelope glycoproteins.
Budding and Maturation: Immature virions bud from the cell, acquiring a lipid envelope studded with Env trimers. Viral protease then catalyzes the maturation of the capsid, transforming the virion from a non-infectious to an infectious state—a process essential for subsequent rounds of infection.
Core Challenge: The envelope glycoprotein (Env) is the primary target of neutralizing antibodies, yet it exhibits extraordinary genetic diversity—with amino acid variation reaching 30% within subtypes and 42% between subtypes.
Several interrelated biological and logistical factors have impeded vaccine development:
Genetic Diversity: HIV's error-prone reverse transcriptase generates mutations at a rate of approximately 3 × 10⁻⁵ per base per replication cycle. Combined with high replication rates (10⁹–10¹⁰ virions produced daily in an infected individual) and frequent recombination, this generates a vast swarm of quasi-species. Designing immunogens capable of eliciting antibodies that neutralize this global diversity remains a central challenge.
Immune Evasion: The Env trimer is decorated with a dense shield of N-linked glycans that occlude conserved epitopes from antibody recognition. Additionally, the trimer adopts multiple conformational states (closed, partially open, fully open), allowing the virus to sample conformations that resist antibody binding. The CD4-induced conformational changes further mask vulnerable epitopes.
Lack of Correlates of Protection: Unlike pathogens such as hepatitis B or measles, where neutralizing antibody titers reliably predict protection, the immune correlates required to prevent HIV acquisition remain incompletely defined.
Animal Model Limitations: No animal model fully recapitulates human HIV pathogenesis. Chimpanzees are susceptible to HIV-1 infection but are no longer used for invasive research. Rhesus macaques can be infected with simian immunodeficiency virus (SIV) or chimeric simian-human immunodeficiency virus (SHIV), providing valuable but imperfect surrogates for human vaccine evaluation.
Mucosal Immunity: HIV primarily establishes infection at mucosal surfaces. Generating durable, high-affinity mucosal antibody responses (particularly IgA) through systemic vaccination has proven difficult, as most injectable vaccines poorly induce mucosal immunity.
Informed by decades of clinical experience, the field has pivoted toward novel immunogen designs and delivery platforms that address the biological barriers identified through failed trials:
Computational algorithms now generate mosaic antigens—synthetic proteins engineered to maximize coverage of global HIV diversity by computationally tiling natural sequences. The Janssen Ad26.Mos4.HIV candidate incorporated mosaic inserts for Gag, Pol, and Env, designed to elicit cross-clade cellular responses. While the Mosaico trial did not demonstrate efficacy, the mosaic concept continues to inform T-cell-based vaccine designs, particularly when combined with novel delivery vectors.
Advances in cryo-electron microscopy and protein engineering have enabled the design of stable, soluble SOSIP trimers (e.g., BG505 SOSIP.664, MD39) that faithfully mimic the native, closed conformation of the Env spike. These trimers present multiple broadly neutralizing antibody (bNAb) epitopes—including the CD4 binding site, V1/V2 apex, V3 glycan patch, and gp41 membrane-proximal external region (MPER)—while shielding non-neutralizing epitopes. In non-human primates, SOSIP trimers have elicited tier-2 autologous neutralization, and human trials are now evaluating their immunogenicity.
Fig. 3 bNAb binding sites on Env trimer
Building on the transformative success of SARS-CoV-2 mRNA vaccines, nucleic acid platforms encoding HIV immunogens are now in early-phase clinical evaluation. Self-amplifying mRNA (saRNA) formulations encoding conserved Gag and Pol regions have induced durable CD4+ and CD8+ T-cell responses in preclinical models. Moderna's mRNA-1644 (encoding eOD-GT8 and Core-g28v2 60mer nanoparticles) and mRNA-1574 (encoding native-like Env trimers) are currently under evaluation in Phase I trials, with initial data expected in the coming years. The mRNA platform offers rapid manufacturing, flexible antigen design, and the potential for repeated boosting without vector-specific immunity limitations.
A transformative strategy involves germline-targeting immunogens designed to engage naive B-cell precursors of bNAbs, followed by sequential boosting immunogens that guide affinity maturation toward broadly reactive specificities. Early clinical data from the eOD-GT8 60mer nanoparticle vaccine have demonstrated successful priming of VRC01-class precursors.
Parallel to active vaccination, passive administration of broadly neutralizing antibodies is being explored as a prevention strategy. The AMP studies demonstrated that VRC01 prevented acquisition of antibody-sensitive viral strains, validating the concept that bNAbs can block infection. Long-acting bNAb formulations (e.g., lenacapavir combinations) and bispecific antibodies are now being evaluated in prevention trials, potentially bridging the gap until an effective vaccine is developed. These approaches may also inform immunogen design by defining the precise epitopes that must be targeted for protection.
The HIV vaccine field stands at a critical juncture. While no candidate has yet achieved the efficacy threshold required for licensure, the convergence of structural biology, systems immunology, and advanced delivery platforms offers renewed optimism.
Future success will likely require a multipronged approach: combining durable humoral immunity (via native-like trimers and germline-targeting strategies) with robust cellular responses (through conserved-element immunogens and novel vectors). As the global community continues to invest in HIV prevention research, the ultimate goal—a world without new HIV infections—remains within reach.
| Cat. No. | Product Name | Species Reactivity | Application | Detection Sample | |
| DEIA2359 | Human HIV 1&2 Ag/Ab ELISA Kit | Human | Qualitative | Serum, plasma | Inquiry |
| DEIA3571 | Lentivirus Titer Kit, HIV-1 p24 ELISA Kit | Virus | Quantitative | Tissue culture supernatants | Inquiry |
| IVDEIA002 | Human anti-HIV 1+2 ELISA Kit | Human | Qualitative | Serum, plasma | Inquiry |
| DEIA10155 | HIV-1 p24 ELISA Kit | Human | Quantitative | Tissue culture supernatants | Inquiry |
| DEIASL616 | HIV-1 gp120 Clade C ELISA Development Kit | Human | Quantitative | Serum, cell culture supernatants | Inquiry |
| DEIA064 | Antibody to Human Immunodeficiency Virus(1+2) ELISA Kit | Human | Qualitative | Serum, plasma | Inquiry |
| DEIA066 | Human Immunodeficiency Virus (1+2) Antigen and Antibody ELISA Kit | Human | Qualitative | Serum, plasma | Inquiry |
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