Opportunities and challenges in achieving a functional cure for HIV

Abstract

The human immunodeficiency virus (HIV) epidemic poses a significant threat to global human health annually. Although antiretroviral therapy can control HIV viremia and delay disease progression, it cannot eliminate the viral reservoir. People living with HIV must rely on antiretroviral medication for their entire lifetime. HIV establishes a persistent viral latent reservoir, which remains an enormous challenge in eradicating HIV infection. With advancements in HIV research, many strategies have emerged to target cells harboring latent HIV. A functional cure for HIV has been proposed as a promising and pragmatic strategic objective. In this review, we provide an overview of current strategies and the latest research progress in the field of HIV cure development, highlighting the opportunities and challenges associated with finding a functional cure for HIV.

1. Introduction

The human immunodeficiency virus (HIV), a member of the retrovirus family, is the primary pathogen responsible for acquired immunodeficiency syndrome (AIDS) in humans. AIDS is a disease primarily characterized by the dysfunction and loss of CD4⁺ T cells. Currently, nearly 40 million people worldwide are living with HIV, with approximately 1 million new infections each year and close to 700,000 individuals dying annually from HIV-related complications.^[1]

Combined antiretroviral therapy (cART) is currently the most widely used treatment for HIV infection in clinical practice; it includes nucleoside and non-nucleoside reverse transcriptase inhibitors, as well as integrase and protease inhibitors, each targeting different steps in the life cycle of the virus.^[2] HIV integrates its viral genome into the host chromosome, generating a long-term stable viral reservoir. Despite the availability of cART, people living with HIV have approximately 0.1 to 10 latently infected cells with full replication capacity per million CD4⁺ T cells. These cells, which have a half-life of up to 44 months and the potential for clonal expansion in response to a variety of biological stimuli, are known as latent reservoirs.^[3,4]

Although cART effectively suppresses viral replication in people living with HIV, delays disease progression, and reduces AIDS-related mortality, it cannot completely eradicate HIV due to the persistence of a stable viral latent reservoir. The latent virus rebounds within weeks after cART interruption, causing new rounds of viremia.^[5] Therefore, people living with HIV must strictly adhere to lifelong cART to suppress viral rebound. However, long-term drug treatment causes serious side effects, promotes the emergence of viral mutations resistant to drugs, and has high financial costs, which translate into a heavy economic burden for society. Controlling viral rebound without cART remains a critical challenge in the pursuit of a cure for HIV infection.

To date, various strategies aimed at developing a functional cure for HIV infection have been investigated. These strategies can be classified into eight categories: shock-and-kill, block-and-lock, proviral gene editing, HIV broadly neutralizing antibody (bNAb) therapy, immunomodulatory agent therapy, stem cell–based transplantation, immune cell–based therapy, and therapeutic vaccines (Figure 1).

Figure 1.

The strategies for HIV functional cure. bNAb: Broadly neutralizing antibody; CAR T cell: Chimeric antigen receptor T cell; CCR5: C-C chemokine receptor 5; CD8: Cluster of differentiation 8; CRISPR: Clustered regularly interspaced short palindromic repeats; DC: Dendritic cell; HIV: Human immunodeficiency virus; IL-15: Interleukin-15; LNP: Lipid nanoparticle; LPA: Latency-promoting agents; LRA: Latency-reversing agent; NK cell: Natural killer cell; PD-L1: Programmed cell death ligand 1; TALEN: Transcription activator-like effector nucleases; ZFN: Zinc finger nucleases.

Natural HIV controllers exist, although they are exceedingly rare, accounting for <1% of cases of HIV infection. A few people living with HIV can spontaneously control HIV relapse without the need for cART; they are known as HIV elite controllers (ECs) or long-term non-progressors (LTNPs)^[6,7] and are considered models of functional cure for HIV. Additionally, post-treatment controllers (PTCs) can durably limit viremic rebound to very low levels after cART interruption.^[8] These reported proof-of-concept cases serve as valuable models for developing a functional cure for HIV infection.

In this study, we review recent progress and challenges in HIV functional cure research and explore novel therapies to achieve long-lasting HIV infection control.

2. Shock-and-kill strategy

As latently infected cells do not express viral proteins and remain in a state of transcriptional silence, the shock-and-kill strategy was developed to target them; latency-reversing agents (LRAs) are used to activate the cells, followed by the elimination of cells expressing viral proteins through virus-induced cytopathic effects, cytotoxic drugs, or the patient’s immune system, ultimately achieving a reduction or even elimination of the latent HIV reservoir.^[9]

The effectiveness of this strategy hinges on two key aspects: First, LRAs must effectively activate latent HIV within cells without inducing cytokine release syndrome.^[10] Second, a robust immune system is required to recognize and eliminate the activated target cells expressing viral proteins. Otherwise, the administration of exogenous drugs to induce the death of activated cells may be necessary.^[11,12]

So far, reported LRAs have included epigenetic modifiers, protein kinase C activators, NF-κB agonists, and toll-like receptor (TLR) agonists, which target different cellular signaling pathways to activate latent HIV.^[11] Due to differences in HIV proviral integration sites, epigenetic regulation in the HIV promoter, and other factors, some of the cells latently infected with HIV can be induced by currently available LRAs to produce viral proteins, known as the shallow viral reservoir; by contrast, others are non-inducible and called the deep viral reservoir.^[13]

Extensive studies have been conducted on epigenetic modifiers, such as histone deacetylase inhibitors, histone methyltransferase inhibitors, and DNA methyltransferase inhibitors. These modifiers have been shown to reactivate viral transcription in cells with latent infections by regulating gene expression.^[14–16] To date, disulfiram, an acetaldehyde dehydrogenase inhibitor, has been discovered to contribute to latent HIV reactivation through the PI3K/Akt signaling pathway.^[17] Arsenic trioxide was identified as an LRA that can effectively reduce the integrated simian immunodeficiency virus (SIV) DNA and restore CD4⁺ T cell counts, thereby suppressing viral rebound following cART interruption.^[18] It has also been proven to decrease the latent HIV reservoir by inducing apoptosis of SIV-infected CD4⁺ T cells and to block viral secondary infection by downregulating CD4 receptors and CCR5 co-receptors.^[19] HODHBt and isotretinoin, which are small molecules combined with IL-15, have been shown to increase HIV latency reversal and natural killer (NK) cell cytotoxicity, ultimately promoting the elimination of HIV reservoirs.^[20,21] Notably, the combination of acitretin (a retinoic-acid derivative) with an LRA, vorinostat (a histone deacetylase inhibitor) has been reported to promote HIV transcription, selectively induce apoptosis in virus-infected cells, and reduce viral reservoirs through the retinoic acid-inducible gene I signaling pathway.^[22] Similarly, TLRs, as a class of PRRs, play a critical role in HIV latency and immune modulation. TLR agonists have been found to control HIV infection by acting as moderately potent LRAs and enhancing immune response through activating HIV-specific CD8⁺ T cells and NK cells and supporting B cell maturation.

However, latent replication-competent HIV proviruses have low inducibility, with only 1.7% of intact proviruses capable of being induced to produce replication-competent virus from CD4⁺ T cells through a multiple stimulation viral outgrowth assay.^[23] Numerous clinical trials have also demonstrated that no existing LRAs, when administered alone, can effectively reduce the size of the latent reservoir in people living with HIV. Future research is expected to focus on developing more potent and reliable LRAs, either in combination with bNAb therapy or immunomodulatory agents or used as vaccine adjuvants.^[24–26]

3. Block-and-lock strategy

Unlike the shock-and-kill strategy, which aims to reactivate all latently infected cells, the block-and-lock strategy primarily focuses on suppressing HIV transcription and creating a stable, deep latent reservoir resistant to rebound, even after cessation of cART in people living with HIV.^[27] Due to limited success of shock-and-kill strategy, more and more interests shift to block-and-lock strategy.

Latency-promoting agents (LPAs) are used to suppress the permanent transcription of latent HIV to achieve a state of permanent viral silence.^[28] Available LPAs include HIV transactivators (Tat) of transcription inhibitors, NF-κB inhibitors, and epigenetic modifiers. Didehydro-Cortistatin A (dCA), a Tat inhibitor, effectively suppresses the transcription elongation and rebound of HIV by increasing nucleosome occupancy and preventing the host RNA polymerase II from binding to the HIV promoter. This has been demonstrated in in vivo experiments after cART interruption.^[29] Nevertheless, there was no significant decrease in HIV DNA detected under dCA treatment.^[29] Another small molecule, ZL0580, acts as a bromodomain-containing protein 4 modulator that suppresses HIV reactivation and transcription by inhibiting Tat transactivation and HIV transcription elongation. ZL0580 delays latent viral rebound in isolated peripheral blood mononuclear cells (PBMCs) from chronic HIV-infected participants up to 33 days; however, whether this efficacy could enable long-term suppression of latent virus release should be evaluated further, particularly through in vivo experiments.^[30] Hydrogen sulfide (H₂S) has been reported to prevent latent HIV reversal and block viral replication by enhancing mitochondrial bioenergetics, inhibiting the NF-κB pathway, and recruiting the epigenetic silencing factor YY1 to the HIV promoter. However, the safe concentration for the long-term administration of H₂S in vivo was not clearly defined in the study.^[31]

Remarkably, an epigenetic reader, GS-9822, which is one of small-molecule integrase inhibitors, disrupts HIV integration by targeting the HIV integrase and host cofactor LEDGF/p75 interaction; it has been shown to reduce HIV replication and hinder latent viral reactivation, even when using LRAs, by preventing HIV DNA from integrating into transcriptionally active regions of the genome in target cells in vitro.^[32] Preclinical trials have demonstrated that GS-9822 possesses potent antiviral properties and suitable pharmacokinetics. However, it has been reported to result in serious urothelial toxicity, severely limiting its clinical application.^[33]

This strategy focuses on inducing viral transcriptional silence or establishing a repressive epigenetic environment at the HIV promoter through histone methylation, acetylation/deacetylation, DNA methylation, or repressive chromatin interactions. LPAs should induce an irreversible state of latent HIV silencing to effectively prevent viral rebound. Currently, the strategy remains limited to basic research, and the results come from in vitro experiments. Furthermore, LPAs’ penetration into lymph tissue, which serves as a vital latent HIV reservoir, bioavailability, drug toxicity, pharmacokinetics, and potential side effects all warrant careful consideration in clinical settings.

4. Proviral gene editing

The HIV proviral gene-editing strategy uses advanced gene-editing technologies, such as transcription activator-like effector nucleases, zinc finger nucleases, and novel clustered regularly interspaced short palindromic repeats (CRISPR/CRISPR-associated protein [Cas]), to knock out or inactivate the proviral gene sequences integrated into the host genome via mutagenesis. This approach aims to achieve permanent inactivation of latently infected HIV cells by targeting proviral DNA directly.^[34]

CRISPR/Cas9, a novel gene-editing technology, has been engineered to target the highly conserved LTR U3 region of HIV. It has been shown to completely disrupt integrated proviral DNA in vitro, demonstrating high specificity and efficiency.^[35] A library of guide RNAs (gRNAs), designed on the basis of 4004 HIV strains, simultaneously targeted 5 HIV exons as multiclade viral consensus sequences that were conserved and overlapping to effectively excise a broad range of HIV proviral DNAs.^[36] Another study has shown that synthetic gRNA/Cas9 ribonucleoprotein targeting HIV proviral polymerase and vpr/tat genes can efficiently suppress infectious virus production and induce specific sequence cleavages in latently infected HIV cell lines.^[37]

Similarly, a different CRISPR/Cas13a can cleave newly synthesized HIV RNA in cells with latent infection and inhibit HIV infection by destroying viral RNA within viral particles. However, the system exerted off-target effects by cleaving similar RNA sequences. This showed a short-term effect that was observed for only 72 h in HIV latency models. The limited efficiency of latent reservoir clearance, with an approximately 50% reduction in HIV gag mRNA, is another crucial consideration.^[38] Cas12b nuclease, which has a smaller size, has also been reported to be sensitive to mismatches between gRNA and the target HIV proviral DNA; unlike Cas9, which requires two gRNAs, it only needs a single gRNA to achieve HIV inactivation according to this report.^[39] The CRISPR/Cas12b system caused larger deletions and fewer off-target effects than did the CRISPR/Cas9 system in cell cultures with long-term HIV replication; an in vivo experiment is expected in animal models in further studies.^[39]

CRISPR/Cas-based gene-editing technology provides a novel and promising therapeutic approach. However, challenges, such as potential off-target effects due to frequent escape mutations in proviral DNA, hepatotoxicity or immunogenicity of systemic administration (e.g., intravenous injection), and difficulty delivering exogenous gene-editing systems to Latent HIV reservoirs in vivo, especially immune privileged zones, highlight the need for further exploration before clinical therapies based on this strategy can be successfully applied.^[40]

5. Broadly neutralizing antibodies

HIV bNAbs not only bind to the HIV envelope glycoprotein (Env) to inhibit virus entry into target cells but also enhance the eradication of infected cells through antibody-dependent cellular cytotoxicity (ADCC).^[41] Currently, numerous clinical investigations have shown that bNAbs can significantly delay viral rebound in people living with HIV after cART is discontinued.

As single bNAb therapy often results in the emergence of HIV escape mutations, combined therapy using multiple bNAbs has become essential.^[42] bNAb 3BNC117 targets Env CD4-binding epitopes, while 10-1074 targets the Env V3 loop. Phase Ι clinical trials have shown that after three infusions of these two bNAbs, people living with HIV who discontinued cART experienced a significant delay in viral rebound that lasted up to 30 weeks.^[43] Nonetheless, this therapy seemed only effective against specific HIV strains recognized by these two antibodies. VRC07-523LS, as a regenerate bNAb, was derived from first-generation VRC01. A phase Ι randomized clinical trial demonstrated that VRC07-523LS has superior potency, increased breadth, and a longer half-life (42 days) compared to VRC01 (15 days) during the 30-month follow-up in healthy volunteers without HIV.^[44,45] One challenge for this therapy is the low bioavailability following subcutaneous and intramuscular administration, possibly indicating insufficient mucosal immune responses, the main route of HIV infection. Furthermore, bNAbs have suboptimal efficacy (only 73%) against primary HIV isolates and a short half-life (30 days) in people living with HIV.^[46]

Moreover, due to the short half-life of bNAbs and the challenges in their induction by a stimulus, an adeno-associated viral vector 8 (AAV8) was developed to deliver them. A phase Ι clinical trial has demonstrated that AAV8 enabled the durable production of bNAb VRC07 in people living with HIV; however, this therapy did not show a significant change in CD4 T cell count and viral load, and some patients presented a non-idiotypic response against VRC07.^[47]

As single or dual bNAbs are prone to causing viral escape, a clinical trial evaluated a combination of PGDM1400, PGT121, and VRC07-523LS bNAb therapy; the results showed that the therapy was safe and well tolerated, and it could reduce viral RNA in plasma from five HIV-infected individuals. Unfortunately, viral rebound occurred within 20 days in all participants after cART stopped due to the emergence of bNAb-resistant variants and a significant decline in bNAb concentration.^[46]

It should be noted that in people living with HIV who have undergone multiple bNAb reinfusion sessions, the viral envelope glycoprotein has developed escape mutations, rendering the original antibody ineffective. Therefore, current bNAb-based therapies alone cannot eliminate the latent HIV reservoir.

6. Immunomodulatory agents

Immunomodulatory agents mainly involve immune checkpoint inhibitors, cytokines, and small molecule drugs that facilitate the immune functions of T cells and NK cells.

In immune checkpoint inhibitor therapy, antibodies targeting immune checkpoint receptors on T cells, such as anti-PD1 antibody combined with bryostatin, an LRA, enhanced latent HIV production within CD4⁺ T cells. Meanwhile, the combination did not result in T cell activation ex vivo, but the safety, tolerance, and efficacy in people living with HIV remain unknown.^[48] ASC22, an anti-PD-L1 antibody used to enhance CD8⁺ T cells function, can be combined with chidamide, an LRA and histone deacetylase inhibitor, to significantly increase cell associated HIV RNA levels; however, it failed to reduce integrated HIV DNA level or improve the function of HIV-specific CD8⁺ T cells in a phase II clinical trial.^[49] Furthermore, combinations of multiple antibodies against immune checkpoint receptors, such as LAG-3, CTLA-4, and TIGIT, not only increased HIV latent reactivation but also enhanced the function of HIV-specific T cells.^[50–52]

Additionally, a phase I clinical trial showed that an IL-15 superagonist (N-803) led to an HIV RNA increase in plasma (from 0.700 to 12.16; fold change: 11.35) and a reduction in inducible HIV proviruses, which were sustained for up to 6 months. The proliferation and activation of NK and CD8⁺ T cells were significantly increased, whereas the antiviral function of NK cells was not evaluated. The results demonstrated that N-803 was safe and well tolerated, although the study was based on a small sample size (11 HIV-infected patients completed three doses of N-803 administered intravenously). In addition, the HIV reservoir was not evaluated in lymph tissues.^[53] The combination of N-803 with AZD5582 (an antagonist of inhibitor of apoptosis proteins) and four SIV Env-specific monoclonal antibodies could effectively induce latency reversal in SIV-infected rhesus macaques under cART suppression; it could also reduce the viral reservoir within the lymph nodes. However, the viral reservoirs in the peripheral blood and spleen were not reduced. Of note, cART interruption was not conducted in the study, so the effect on delaying viral rebound after cART cessation remains unclear. The clinical efficacy of this therapy should be evaluated carefully in the future.^[54]

Nevertheless, this strategy has demonstrated insufficient efficacy in either reactivating latent HIV reservoir or boosting immune cell antiviral activity when used alone, and it has been associated with potentially serious side effects.^[55–57] Its clinical application requires further optimization. Advanced interventions suggest that immunomodulatory agents combined with other regimens, such as LRAs, bNAbs, or chimeric antigen receptor (CAR) T cell therapy, may better contribute to eliminating HIV reservoirs.^[58]

7. Stem cell–based transplantation

Stem cell-based transplantation mainly involves hematopoietic stem cell transplantation (HSCT) and umbilical cord blood transplantation (UCBT). This strategy is based on the principle that allogeneic HSCT from a donor with homozygous 32-base pair deletions in the CCR5 allele (CCR5 ∆32/Δ32) leads to dysfunction of CCR5, the co-receptor used by HIV for cell entry; the transplant into HIV-infected individuals replaces the original hematopoietic system with CCR5 ∆32/Δ32 cells, resulting in viral reservoir eradication and viral rebound resistance after cART interruption.^[59] To date, five individuals have successfully achieved a functional cure for HIV through this strategy.

Among these cases, the Berlin patient was the first in the world to achieve complete suppression of the Latent HIV reservoir after undergoing chemotherapy and receiving human leukocyte antigen (HLA)-matched hematopoietic stem cells with CCR5 ∆32/Δ32 through bone marrow transplantation. Significantly, no HIV rebound was detected for more than 10 years after cART interruption.^[60] Subsequently, the London patient, an adult with HIV infection and Hodgkin’s lymphoma, underwent allogeneic CCR5 ∆32/Δ32 HSCT, similar to the Berlin patient. However, unlike the latter, the London patient did not undergo irradiation and still achieved long-term HIV remission.^[61] HIV was maintained under control without cART for up to 9 years in another individual (the Dusseldorf patient) with HIV infection and acute myeloid leukemia (AML) following allogeneic CCR5 Δ32/Δ32 HSCT.^[62] Furthermore, a woman with HIV infection and AML (the New York patient) was the first female reported to achieve a cure for HIV. In this case, the patient received stem cells with a wild-type CCR5 allele from a haploidentical donor, followed by UCBT containing CCR5 Δ32/Δ32 homozygous cells. cART was interrupted 37 months after transplantation, and the plasma viral load remained below detectable levels for 18 months.^[63] This case suggests a potential functional cure approach using CCR5 Δ32/Δ32 cells from umbilical cord blood stem cells when hematopoietic stem cells are unavailable. Likewise, a 63-year-old man diagnosed with HIV and AML accepted allogeneic CCR5 ∆32/Δ32 HSCT, and HIV was suppressed up to 35 months after cART discontinuation. He is the oldest patient who has achieved a functional cure for HIV so far (the City of Hope patient).^[64]

As healthy individuals with CCR5 ∆32/Δ32 mutation are extremely rare, compatible HLA genotypes are equally critical. Gene-editing technology to artificially generate CCR5 mutations is a promising alternative. Hu Chen reported transfusing CRISPR/Cas9-edited CCR5-disrupted hematopoietic stem cells into a patient with HIV and acute lymphoblastic leukemia. The patient achieved complete remission with full donor chimerism, and the gene-edited CCR5-ablated hematopoietic stem cells were maintained for more than 19 months without adverse events. However, the percentage of CCR5-ablated lymphocytes was only 5% during the follow-up period. Due to the low efficiency of gene editing, the patient did not achieve a functional cure for HIV.^[65] Recently, a case report showed that a male achieved HIV remission over 32 months without cART after allogeneic HSCT with wild-type CCR5 donor cells, although the CD4⁺ T cells remained permissive to HIV infection.^[66]

Unfortunately, allogeneic HSCT, even when using CCR5 ∆32/Δ32 HSCT donors, has not always been successful as a treatment for HIV infection. Sixteen HIV-infected patients with hematologic malignancies underwent allogeneic HSCT, including five individuals who received CCR5 Δ32/Δ32 HSCT. The frequency of CD4⁺ T cell activation peaked at 40% between months 2 and 3 post-HSCT, which was vulnerable to HIV reseeding. Moreover, the immune reconstitution was slow, and HIV-specific CD8⁺ T cell responses persisted at a low level during a period of up to 7 years follow-up.^[67]

Currently, CCR5 ∆32/Δ32 cell-based HSCT or UCBT is considered the only therapy that has successfully eradicated the latent HIV reservoir and achieved a functional cure. However, this strategy is only suitable for HIV-infected patients who also have leukemia or lymphoma. While it eliminates the risk of causing acute leukemia in these patients and demonstrates the safety of gene-editing technology in humans, the potential risks of HSCT or USCT and the low efficiency of current gene-editing methods have prevented the clinical achievement of an HIV cure.

8. Immune cell–based therapy

The sources of HLA-matched hematopoietic stem cells are extremely scarce, and HSCT or UCBT poses significant risks to people living with HIV. Thus, immune cell–based therapy has emerged in recent years. Immune cells, such as T cells and NK cells, are engineered with bNAb-derived CAR moiety or boosted with viral antigens and cytokines to enhance the capacity of immune cells to recognize and kill HIV-infected cells. They are then transfused back into the patients to control HIV rebound without cART in the long term.^[68,69]

Among these approaches, Liu et al. developed a VRC01-based autologous CAR T cell therapy that combined the advantages of HIV bNAbs and CAR T cells. These engineered CAR T cells can specifically lyse target cells expressing the HIV envelope in an MHC-independent manner, significantly suppress HIV rebound.^[70] Furthermore, the results from a phase I clinical trial demonstrated that a single administration of bNAb-based CAR T cells was safe, well tolerated, and capable of delaying viremia rebound for up to 10 weeks after cART discontinuation. Although this therapy imposed selective pressure and reduced the viral reservoir, it failed to suppress viremia rebound upon cART interruption; this was likely due to preexisting resistance or new mutations that resulted in viral escape.^[71,72]

Another phase Ι clinical trial tested multifunctional CAR T cells, known as M10 cells, which were based on the combination of HIV bNAbs with the chemokine receptor CXCR5. bNAbs mediate the elimination of HIV-infected cells through cytotoxicity and the neutralization of viral particles released from chidamide as a class of LRAs to reactivate latent HIV. Meanwhile, CXCR5 drives lymphocyte migration into B-cell follicles, which have been identified as immunologically privileged sites harboring the HIV latent reservoir. Two allogeneic M10 cell transfusions were followed by the administration of two doses of chidamide, and the size of the inducible viral reservoir was significantly reduced with cART treatment. However, the deep reservoir persisted, and resistant mutations emerged as a result of the selective pressure exerted during M10 cell administration.^[73] In the future, this treatment should be further optimized, not only eradicate shallow latent viral reservoir, but also confine the deep reservoir rebound without the continuation of cART.

Not only CAR T cell therapy but also HIV multi-antigen-specific T cell therapy was shown to be well tolerated and safe in six individuals living with HIV suppressed on ART; these participants received two treatments of autologous expanded polyfunctional T cells targeting multiple HIV-conserved epitopes.^[74] This phase I clinical trial was designed to harness HIV-specific T cell responses and restrain HIV immune escape variants. However, as intact proviruses did not significantly decrease, and the participants did not stop with cART during the follow-up period, further improvements are needed to increase the efficacy of this therapy.

In addition to T cell–based therapy, NK cell–based therapy has shown significant promise in the development of a functional cure for HIV.^[75–77] Recently, a phase Ι clinical trial has shown that a single infusion of haploidentical NK cells along with IL-2 or IL-15 decreased HIV production in lymphatic tissues from people living with HIV. Adoptively transferred NK cells persisted in PBMCs for up to 8 days and in the lymph nodes and rectum for up to 28 days post-infusion, while the frequency of transferred NK cells peaked at < 10%. However, the efficacy of NK cells was limited, as HIV-producing cells in the lymph nodes showed only a moderate decrease; intact proviral DNA was also not analyzed due to the limited number of available cells.^[78]

Compared to bNAbs administration alone, bNAb-based CAR T or NK cells possess multifunctional properties, including virus neutralization, specific cytotoxicity, and ADCC. Unfortunately, viral escape mutations are generally the primary reason for the failure of bNAb-based CAR cell adoptive transfer to eliminate latent reservoirs. Given that MHC restriction is a major concern for T cell–based therapy, NK cell–based therapy may be a suitable alternative.^[79] Nonetheless, the combination of immune cell–based therapy with LRAs, bNAbs, or immunomodulatory agents warrants further exploration.

9. Therapeutic vaccine approach

The HIV therapeutic vaccine offers a promising and innovative strategy for effectively preventing HIV transmission.^[1] Therapeutic vaccine has been developed for inducing potent immune responses, such as HIV-specific T-cell responses or triggering the precursors of bNAbs through HIV-specific immunogens, so as to confine HIV rebound in absence of cART.

A clinical trial tested an autologous dendritic cell (DC)–based vaccine pulsed with inactivated virus particles to fight against HIV infection. Despite the strong capacity of DCs to take up and present HIV antigens, this therapy yielded only a modest reduction in plasma viral load and elicited more vigorous HIV-specific T cell responses.^[80]

The mRNA-based vaccine is considered an innovative strategy for HIV, particularly considering the rapid development of severe acute respiratory syndrome coronavirus 2 vaccines. Two clinical trials were conducted with an mRNA-based HIV vaccine made up of naked mRNAs containing DC activation signal and HIV immunogen conserved sequences. The results indicated that the approach was safe, well tolerated, and capable of enhancing HIV-specific immune responses in people living with HIV.^[81,82] A synthetic lipid nanoparticle-encapsulated mRNA vaccine was reported to elicit high levels of HIV-specific neutralizing antibodies in animal models.^[83,84] In addition, certain factors characteristic of mRNA-based vaccines should be considered, including mRNA modification, purity, stability, and adverse events.

Additionally, the combination of a T cell immunogen-based vaccine and a TLR7 agonist was demonstrated to be safe, eliciting robust T cell responses. However, all participants experienced viral rebound after cART interruption, and the size of the viral reservoir was comparable between experimental and placebo recipients in a phase 2a clinical trial.^[85]

To date, various studies have used Env as a dominant immunogen, but its diverse mutations and high levels of glycosylation pose challenges for the design of an HIV therapeutic vaccine. As a result, existing vaccine designs are largely ineffective in inducing durable bNAbs against HIV; their efficacy in reducing the size of the HIV latent reservoir and controlling viremia rebound remains inadequate, severely limiting their clinical applications.^[1,86]

10. HIV controllers

Interest has been directed toward understanding the mechanisms and determinants responsible for HIV control in ECs, LTNPs, and PTCs. Numerous studies have revealed that HIV controllers exhibit distinct virological characteristics, genetic differences, and immunological profiles. These discoveries will significantly advance the development of a functional cure for HIV.^[87]

Virologically, HIV strains isolated from ECs exhibit lower viral fitness, which reduces virus entry, and weak replicative capacity.^[88] In addition, the intact proviral genome integrates into specific locations which along with distinct epigenetic characteristics in ECs. In ECs, HIV is frequently integrated into heterochromatin, a transcriptionally silent region that restricts viral gene expression.^[13,89,90] These discoveries provide important insights for research on vulnerable sites in HIV and LPA development.

In terms of host factors, differences in genetic and immunological profiles are the main considerations.^[6] From a genetic perspective, ECs tend to express protective HLA alleles, including HLA-B57 and HLA-B27, which can induce polyfunctional CD8⁺ T cells and thus restrict viral replication.^[91,92] The deficiency of HLA-B46 has also been linked to increased NK cell activation, contributing to the deceleration of HIV disease progression.^[93] Moreover, NK cell antiviral activity and frequency have been reported to have positive correlations with slow HIV infection progression in ECs.^[75,94] EPTC112 has been identified in PTCs. It targets the glycan-V3 loop of the HIV envelope, exhibiting potent neutralization and ADCC effects.^[95] Identification of protective HLA alleles may be helpful in distinguishing HIV controllers and appraising the immunologic function of HIV-infected patients. In addition, these investigations have dramatically promoted immune cell–based therapy and bNAb development.

HIV controllers provide natural blueprints for combination therapeutic strategies. They not only target viruses by reducing viral fitness and restricting HIV transcription in euchromatin but also enhance host immunity by inducing HIV-specific CD8⁺ T cell responses, enhancing NK cell antiviral activity, and developing HIV bNAb. These discoveries encourage researchers to pursue a universal therapy aimed at achieving the goal of a functional cure for HIV.

11. Conclusions and perspectives

The development of a functional cure for HIV is a cutting-edge approach to containing the HIV pandemic. Despite the significant progress achieved in this area in recent years, many challenges remain in attaining this goal (Table 1).

Table 1.

Advantages, limitations and current advances of HIV functional cure strategies

Strategies	Advantages	Limitations	Current advances
Shock-and-kill	Removing shallow HIV reservoir	Low inducibility of HIV latency; Limited efficacy when used alone	Combined therapy undergoing clinical trials
Block-and-lock	Blocking HIV reactivation	Limited penetration; Bioavailability; Potential drug side effects	Preclinical study
Provirus gene editing	Inactivation HIV provirus	Delivery system feasibility; Long-term safety; Scarce cells harboring proviral	Preclinical study
bNAbs	Neutralization; ADCC	HIV escape mutations; Short half-life	Undergoing clinical trials
Immunomodulatory agents	Promote viral rebound; Boost immunity	Limited efficacy when used alone; Short half-life	Combined therapy undergoing clinical trials
Stem cell-based transplantation	Control HIV rebound without cART	Transplant-related side effects; Rare donors source	Successful cure cases
Immune cell-based therapy	Elicit specific immune responses; Delay HIV rebound off cART	HIV escape mutations; T-cell exhaustion	Combined therapy undergoing clinical trials
Therapeutic vaccines approach	Elicit specific immune responses; Delay HIV rebound off cART	Delivery system feasibility; Long-term safety; Limited efficacy	Combined therapy undergoing clinical trials

ADCC: Antibody-dependent cellular cytotoxicity; bNAb: Broadly neutralizing antibody; cART: Combined antiretroviral therapy; HIV: Human immunodeficiency virus.

The existence of anatomical sanctuaries (e.g., the central nervous system, gut-associated lymphoid tissue, and the reproductive tract) that are difficult to reach by standard antiviral therapeutic agents, and thus contributes to HIV evading the attack from immune system. The absence of specific latency biomarkers is an additional difficulty in targeting cells with latent HIV. Immune dysfunction due to chronic viral infection also requires urgent attention.

Considering these challenges, personalized combination regimens according to individual immune profiles should be given priority (Figure 2). For example, CD8⁺ T cells from HIV-infected individuals present an exhaustion phenotype, making them suitable for anti-PD-1 antibody and IL-15 superagonist therapies combined with CAR-T cell therapy. The advancement of long-acting delivery platforms and targeted nanotechnologies also significantly facilitate the delivery of LPAs and gene-editing drugs to viral latent reservoirs in immunologically privileged sanctuaries. Moreover, the identification of robust biomarkers to monitor immune responses is essential, as these biomarkers predict the consequences of HIV infection, such as the immunological characteristics of HIV controllers, evaluate therapeutic efficacy and potential viral relapse, and further guide treatment decisions.

Figure 2.

Combinatorial strategies for HIV functional cure. (A) LRA is able to reactivated latent viruses that can be neutralized by bNAbs, recognized and killed by CAR T cells with CXCR5 overexpression which facilitate the entry of anatomical sanctuaries. (B) Therapeutic vaccines to induce durable bNAbs and HIV-specific T cells and then clear HIV latent cells reactivated by LRA. (C) Immunomodulatory agents combined with CAR T cells to enhance cytotoxicity to LRA reactivated latently infected cells. (D) CRISPR technology can knock out the CCR5 and HLA gene of stem cells and then conduct HSCT or UCBT. bNAb: Broadly neutralizing antibody; Cas9/sgRNA: CRISPR-associated protein 9/single guide RNA; CAR T cell: Chimeric antigen receptor T cell; CCR5: C-C chemokine receptor 5; CXCR5: Chemokine C-X-C motif receptor 5; HIV: Human immunodeficiency virus; HLA: Human leukocyte antigen; IL-15: Interleukin-15; LNP: Lipid nanoparticle; LRA: Latency-reversing agent; PD-L1: Programmed cell death ligand 1.

The purposes of a functional cure for HIV are to maintain viral suppression, restore immune homeostasis, and eliminate reliance on lifelong medication regimens. The integration of precision interventions, technological breakthroughs, and translational enablers is necessary to realize a functional cure for HIV. Although many preclinical studies have demonstrated substantial therapeutic effects, the translational routes from preclinical success to clinical implementation acknowledge the regulatory, logistical, and ethical considerations that will shape the development of scalable, durable HIV-1 cure strategies.

Author Contributions

Linghua Li led the study’s conceptualization and design, and supervised the manuscript writing. Wanying Zhang, Mo Zhou, Jingliang Chen, Yizi He collaboratively managed literature analysis, draft preparation, and data interpretation, with overlapping responsibilities in the progress. All four also contributed significantly to the manuscript’s discussion section and ensured compliance with submission standards. Wanying Zhang contributed to the writing of the manuscript and to significant revisions of its content. All authors reviewed and approved the final version of the manuscript.

Conflicts of Interest

None.

Funding Statement

This work was supported by the China Postdoctoral Science Foundation (2024M760664); the National Natural Science Foundation of China (82302513), GuangDong Basic and Applied Basic Research Foundation (2024A1515013281, 2022A1515110546), and Science and Technology Project of Guangzhou (2025A04J5143, 2023A03J0801).