The key to defeating HIV lies in understanding its secret hideouts.
The 2025 Conference on Retroviruses and Opportunistic Infections (CROI) brought together approximately 4,000 delegates in San Francisco, setting the stage for a critical deep dive into the molecular mysteries of HIV 5 .
Why has it been so difficult to cure HIV? The answer lies in the virus's complex life cycle. Upon infection, HIV inserts its genetic blueprint into the DNA of its host's cells, primarily CD4+ T cells of the immune system. For most cells, this leads to active virus production. However, in a small fraction of cells, the integrated virus falls silent, entering a "latent" state . These infected cells become invisible to the immune system and are untouched by standard antiretroviral therapy (ART), which only blocks new rounds of infection. This latent reservoir is the primary barrier to a cure 9 .
Researchers at CROI 2025 are moving beyond simply detecting this reservoir. They are now mapping its precise location within our vast genome and understanding the environmental factors that keep the virus quiet or allow it to reawaken. As Dr. Joseph J. Eron Jr. highlighted in a pre-conference podcast, the field is grappling with the critical distinction between a sterilizing cure (complete eradication of the virus) and a functional cure (long-term control without medication), with much research focused on the latter 9 .
Virus actively replicates in CD4+ T cells, producing new viral particles that infect other cells.
Virus integrates into host DNA but remains dormant, invisible to immune detection.
A key revelation is that HIV does not integrate into the human genome randomly. Its choice of neighbourhood within our DNA has profound implications for its own survival and our ability to find it.
In most people on ART, HIV tends to integrate into transcriptionally active genes marked by specific signals like H3K4me3 and open chromatin 5 . These are bustling areas of the genome, where the virus can easily activate and produce new particles if treatment stops.
In a fascinating contrast, studies of elite controllers—rare individuals who naturally control the virus without medication—reveal a different pattern. Research presented by Bushman (Abstract 13) showed that in these individuals, the persisting virus is heavily enriched in lamina-associated domains (LADs) and repressive chromatin regions marked by H3K9me3 and H3K27me3 5 .
This process, a form of immune editing, shapes the reservoir and offers clues for cure strategies. It implies that a successful cure might not need to eliminate every last infected cell, but could instead focus on driving the virus into these deep, silent sanctuaries where it cannot cause harm 5 .
One of the most detailed insights presented at CROI came from research unpacking exactly how HIV enters the nucleus of a cell—a crucial step in establishing a long-term infection. The study, presented by Jacques (Abstract 29), focused on the HIV capsid (CA), the protein shell that protects the viral genetic material 5 .
For years, scientists have known that HIV can infect non-dividing cells, a rarity among viruses. The capsid was known to be key, but the precise mechanism was a black box. The researchers designed a multi-faceted approach to open it:
Using purified CA proteins and components of the nuclear pore complex (NPC), the gateway to the nucleus, the team measured interactions with techniques like surface plasmon resonance (SPR) to determine binding affinity and speed 5 .
They introduced specific point mutations (e.g., N74D) into the capsid protein to disrupt a suspected hydrophobic binding pocket 5 .
The team then tested the mutant virus's ability to enter the nucleus of non-dividing cells by measuring the formation of 2-long terminal repeat (LTR) circles, a DNA byproduct of successful nuclear entry 5 .
Finally, they used cryo-electron tomography (cryo-ET) to visualize the interaction between the HIV capsid and the nuclear pore complex in stunning, near-atomic detail 5 .
The findings were striking. The HIV capsid does not merely passively drift into the nucleus. It actively mimics the cell's own import machinery, functioning as a "viral karyopherin."
Reduction in nuclear entry with capsid mutations
Perhaps most excitingly, the study showed that the investigational drug lenacapavir, a potent new capsid inhibitor, works by jamming this precise mechanism. It abrogates FG binding, effectively locking the virus out of the nucleus 5 . This not only confirms lenacapavir's sophisticated mechanism of action but also validates the capsid-nucleoporin interaction as a prime target for future antiviral drugs and potentially, cure strategies.
| Technique | Acronym | Primary Function |
|---|---|---|
| Chromatin Immunoprecipitation Sequencing | ChIP-seq | Maps where proteins interact with DNA across the entire genome. |
| Assay for Transposase-Accessible Chromatin with high-throughput sequencing | ATAC-seq | Identifies "open" and accessible regions of the genome, indicating active regulatory areas. |
| Linear Amplification-Mediated PCR | LAM-PCR | A highly sensitive method to locate where HIV has integrated into the host DNA. |
| Cryo-Electron Tomography | Cryo-ET | Creates 3D visualizations of cellular structures and viruses at near-atomic resolution. |
| Surface Plasmon Resonance | SPR | Measures the binding affinity and kinetics between two molecules (e.g., a viral protein and a host factor). |
Decoding HIV requires a powerful arsenal of research tools. Many of these are made available to the global scientific community through repositories like the Centre for AIDS Reagents (CFAR) in Europe, which houses over 6,500 unique reagents 7 .
| Reagent / Tool Category | Examples & Specifics | Function in Research |
|---|---|---|
| Virus Strains & Isolates | Historic HIV strains, novel subtypes from recent infections. | Used to study viral diversity, antibody neutralization, and drug resistance. |
| Cell Lines & Primary Cells | CD4+ T-cell lines, primary macrophages. | Provide the cellular models to study HIV infection, replication, and latency. |
| Molecular Clones & Vectors | Infectious molecular clones, lentiviral vectors. | Allow for controlled genetic studies of specific viral genes and their functions. |
| Host Factor Reagents | Recombinant proteins like CPSF6, LEDGF/p75, Nucleoporins. | Critical for studying how HIV hijacks host machinery for nuclear entry and integration 5 . |
| Sensors & Assay Kits | CARD8 inflammasome activation assays, ELISA kits for cytokines. | Enable measurement of immune responses to HIV infection and cell death pathways 5 . |
The importance of these tools is highlighted by another study presented at CROI (Abstract 30), which showed that host proteins CPSF6 and LEDGF/p75 form liquid-liquid phase-separated condensates to guide HIV integration to specific genomic neighbourhoods 5 . Research like this, which relies on high-quality reagents, is fundamental to understanding and eventually manipulating the HIV reservoir.
The basic science track at CROI showcased a diverse range of innovative approaches targeting HIV persistence.
Hughes and colleagues (Abstract 134) demonstrated how the host protein CARD8 acts as an innate immune sensor for HIV. They found that certain mutations in the HIV Gag protein can trigger premature activation of the protease, which CARD8 detects, leading to inflammasome formation and death of the infected cell. This reveals a potential vulnerability that could be exploited to force the virus to expose and eliminate itself 5 .
While not a cure, the development of long-acting therapies is a major focus. Gilead presented Phase 2 data on a twice-yearly regimen combining lenacapavir with two broadly neutralizing antibodies (bNAbs), teropavimab and zinlirvimab. This approach, which received FDA Breakthrough Therapy Designation, could revolutionize treatment and prevention, improving adherence and accessibility 1 .
(Data from CROI & EACS 2025)
| Modality | Dosing Frequency | Stage of Development | Reported Efficacy / Key Finding |
|---|---|---|---|
| Lenacapavir + bNAbs (Teropavimab & Zinlirvimab) | Twice-Yearly | Phase 2 (Progressing to Phase 3) | 96% virologically suppressed at Week 26; well-tolerated 1 3 . |
| Islatravir + Lenacapavir | Once-Weekly (Oral) | Phase 2 | 100% (Missing=Excluded) maintained viral suppression at 96 weeks 3 . |
| Lenacapavir for PrEP | Twice-Yearly (Injection) | Approved in U.S./E.U. | Demonstrates safety with common medications like statins 3 . |
The basic science presented at CROI 2025 paints a picture of a field moving from detection to deep understanding. Researchers are no longer just looking for the hidden virus; they are creating high-resolution maps of its genomic hideouts, uncovering the sophisticated tricks it uses to enter and nest within our DNA, and identifying new ways to smoke it out.
Identifying where HIV integrates in the genome
Revealing how HIV enters the nucleus
Creating targeted approaches to eliminate reservoirs
The synergistic work on the HIV capsid's nuclear entry, the immune editing of the reservoir in elite controllers, and the triggering of innate sensors like CARD8, all point toward a future where multi-pronged, targeted therapies could finally overcome HIV's persistence. As these foundational discoveries in basic science continue to mature, the hope for a future without HIV burns brighter than ever.