HAART can successfully inactivate HIV-1, however the virus is able to persist within latent lymphoid, gut, and CNS reservoirs (5–8). This requires patients to remain adherent to the HAART regimen for the duration of their lifetime to prevent viral rebound (9). Since nanoparticles facilitate the sustained release of drugs, a group of researchers have developed a long-acting slow-effective release antiretroviral therapy (termed “LASER ART”), which utilizes nanoparticles for controlled release of HAART agents, thereby improving regimen adherence (37, 38). In a recent study, the same group of researchers demonstrated that a nanocrystallized product of lamivudine, a nucleoside reverse transcriptase inhibitor (NM23TC), maintained antiretroviral activity in HIV-1-infected monocyte-derived macrophages after viral challenge for up to 30 days. NM23TC was taken up by HIV-1-infected monocyte-derived macrophages and remained in high prodrug concentration in whole blood for 30 days after a single dose. In addition, at day 28, M23TC, a metabolized version of lamivudine, was detected at high levels in the liver, lymph nodes, and spleen (39), suggesting that this nanoplatform may improve delivery of the drug to HIV-1 niches. Other groups have also developed nanoparticles for improving HAART (40–43) (Table 1).

Latency-reversing agents (LRAs) are able to reactivate viral replication. LRAs are used in “shock and kill” treatment approaches, wherein the LRA-elicited viral replication is coupled to the actions of HIV-1 cell-specific cytotoxic agents or immune-mediated clearance (73). Several classes of molecules and macromolecules have been used as LRAs including protein kinase C (PKC) agonists, histone deacetylase inhibitors, and cytokines, and their mechanisms of latency reversal are well-described. For example, PKC agonists function via the NF-KB pathway. Activated PKC isoforms downregulate the inhibitor IKB, thereby releasing the transcription factor NF-KB, which translocates into the nucleus, and binds to the HIV-1 proviral long terminal repeats, thereby mediating viral transcription (74). Similar to HAART, nanoparticles have been utilized to improve the delivery of LRAs (Table 1). In one study, Kovochich et al. encapsulated bryostatin, a potent PKC agonist (75) and nelfinavir, an HIV-1 protease inhibitor, into nanoparticles. Their nanoplatform targeted CD4⁺ cells in a peripheral blood mononuclear cells (PBMC) culture, activated latent virus, and inhibited viral spread (76). In a more recent study, Cao et al. synthesized hybrid lipid-coated PLGA nanocarriers that incorporated diverse LRAs. These lipid-coated nanoparticles could selectively activate CD4⁺ T cells in nonhuman primate PBMCs as well as in murine lymph nodes with substantially reduced toxicity (44). Despite the fact that it is currently impossible to identify and target every HIV-1-infected cell in the latent reservoir (45), the ability of nanoparticles and nanocarriers to traffic and deliver LRAs to sites of latent HIV reservoirs can maximize their therapeutic benefit, and serve as an important component of successful shock and kill cure regimens. Other examples of nanoparticles for improving latency reversal appear in Table 1 (46, 47).

Traditional vaccines for HIV-1 have been difficult to develop, and clinical trials using HIV-1 vaccines have demonstrated poor efficacy (77, 78). Vaccines fail for several reasons including poor delivery to dendritic cells, reversion of a live attenuated virus to its virulent form, or if the vaccine is too weak to facilitate an immune response (68). Consequently, an ideal vaccine should be clinically safe, stable, and capable of inducing a potent immune response (79). Nanoparticles have been shown to overcome these limitations (80) by protecting antigens from proteolytic enzymes, promoting antigen uptake and processing by antigen-presenting cells (APCs), in addition to being biocompatible and biodegradable (81). Several groups have leveraged favorable properties of nanoparticles to develop nanovaccines for HIV-1 (Table 1).

One effective strategy is utilizing nanovaccines to activate dendritic cells (DCs), which in turn cause T cell activation (82). To this end, Rostami et al. decorated antigens onto the surface of nanoparticles to facilitate greater interaction with the APCs due to the high surface area to volume ratio of the nanoparticles (48). Specifically, a flagellin molecule sequence derived from Pseudomonas aeruginosa (FLiC), a toll-like receptor 5 agonist, was conjugated to an HIV-1 p24-NeF peptide, and encapsulated within PLGA nanoparticles. The FLiC-p24-NeF-encapsulated nanoparticle elicited higher levels of lymphocyte proliferation and cytotoxic T cell activity compared to controls (48), suggesting its potential use in an HIV-1 vaccination strategy. In a more recently study by Tokatlian et al., nanoparticles encapsulating HIV-1 antigens were observe to localize to the lymph nodes more than corresponding soluble antigen counterparts, and remained localized there for up to 4 weeks (49). In another study, Lori et al. showed that their nanoplatform “DermaVir” could administer HIV-1 antigens to Langerhans cells, which resulted in a potent immunogenic response (50). DermaVir is currently undergoing a phase 3 clinical trial evaluation based on excellent responses observed in Phase I/II clinical trials (83). Together, these studies along with others summarized in Table 1 (51–56), clearly suggest the importance of nanovaccines for treating HIV-1.

Targeting the HIV replication cycle by inhibiting the ability of HIV-1 to fuse and/or enter a target cell has been the focus of several published studies (Table 1). Fusion or entry inhibition leads to inhibition of viral activity and viral cytotoxicity. In one approach, Lara et al. showed that silver nanoparticles are antiviral and prophylactic against HIV-1 fusion to target cells (57). Silver nanoparticles exert anti-HIV activity at an early stage of viral replication, likely as a virucidal agent or as an inhibitor of viral entry. Silver nanoparticles bind to gp120 in a manner that prevents CD4-dependent virion binding, fusion, and infectivity, acting as an effective virucidal agent against cell-free and cell-associated virus. Further, silver nanoparticles inhibit post-entry stages of the HIV-1 life cycle (57).

Another approach utilized semen-derived enhancer of viral infection (SEVI), which is a type of amyloid fibril present in human semen that enhances HIV-1 infection of target cells by capturing HIV-1 virions, resulting in increased viral fusion (84). SEVI serves as a mediator for HIV-1 viral attachment due to its highly cationic nature (84, 85). In their study, Sheik et al., synthesized a hydrophobic polymeric nanoparticle to reduce SEVI fibril-mediated infection (58). The hydrophobicity of the nanoparticle interferes with Aβ amyloid structure, forming amorphous aggregates, thereby disrupting the amyloid HIV-1 trafficking protein to target cells (86–88). Thus, the hydrophobic nanoparticles were able to reduce HIV-1 virion binding affinity toward their target cells (58).

Biomimicry approaches, such as plasma membrane-coated nanoparticles, represent a unique strategy to target a variety of human pathologies (89). A pivotal study showed the efficacy of coating a nanoparticle with a cell membrane to imitate and model endogenous cell activity. HIV-1 infection begins when an exposed HIV-1 surface protein, gp120, interacts with CD4 receptor and chemokine receptor type 5 (CCR5) co-receptor on target cells (90). Wei et al. coated polymeric nanoparticles with a CD4⁺ T cell membrane, causing the modified membrane-coated nanoparticle to preferentially interact with HIV-1. This preferential binding ultimately neutralized HIV-1 viral activity in PBMCs in vitro (59), illustrating the potential of biomimicking nanoparticle approaches to reduce HIV-1 viral spread by blocking viral fusion to T cells.

Unlike synthetic nanoparticles, extracellular vesicles (EVs) are naturally occurring nanoscale structures that carry cargo (e.g., proteins, lipids, nucleic acids) and can be released from both healthy and apoptotic cells (91). Recently, Palomino et al. discovered that EVs released by Lactobacillus in the healthy vaginal microbiota prevented HIV-1 attachment to target cells and thereby inhibited HIV-1 infection (60). In a recent study by Welch et al., EVs extracted from semen inhibited HIV-1 in vitro regardless of HIV infection status of the donor, while EVs extracted from the blood and semen of ART-treated subjected inhibited HIV-1 in vivo (61). These studies suggest a potential avenue for bacterial and/or EV-based treatment strategies in preventing HIV-1 viral spread.

Gene therapy technologies have been explored for HIV-1 cure strategies (Table 1). Clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR-Cas9) is a gene editing platform wherein genes can be added, removed, or altered at given genetic loci (92). CRISPR-Cas9 is a faster and more efficient technique than other genetic editing platforms using other viral vectors or the Cre-Lox system, although current CRISPR-Cas9 delivery techniques use electroporation to facilitate DNA entry into living cells, which is difficult to control and can generate cytotoxicity (92, 93). Previously, gene-editing tools have knocked out CCR5 in CD4⁺ T cells to block HIV-1 viral entry (94, 95). However, gold nanoparticles (AuNPs) have a unique ability to safely deliver CRISPR-Cas9 components to their targets (96). AuNPs have large surface area to volume ratios and are biocompatible with low toxicity (5). Shahbazi et al. developed AuNPs with layer-by-layer surface conjugation of CRISPR components (AuNP/CRISPR), targeting two locations within the hematopoietic stem and progenitor cell (HSPC) genome, CCR5 and the gamma-globin gene promoter. Genetic deficiency in CCR5 is linked to HIV-1 resistance through the elimination of viral anchoring and entry through its CCR5 co-receptor (62, 97). AuNP/CRISPR was able to penetrate into CD34⁺ hematopoietic cell line, which is difficult to transfect. At micromolar concentrations, AuNP/CRISPR exhibited an overall low amount of gene editing and homologous directed repair (HDR) at the CCR5 and the gamma-globin promoter locus. This demonstrates that AuNP/CRISPR functioned with low efficacy. However, genetic editing and HDR via AuNP/CRISPR was higher than the electroporation-driven process. This suggests that AuNP/CRISPR could be effective in delivering gene editing for HIV-1 therapy (62).

With the promising innovations of LASER ART and CRISPR-Cas9, Dash et al. combined the two methodologies to evaluate a potentially synergistic functionality. Two of seven HIV-1-infected mice that received LASER ART followed by subsequent AAV₉-CRISPR-Cas9 treatment targeting a fragment of the HIV-1 genome were cured of viral rebound and experienced a restoration of their CD4⁺ T cells, suggesting HIV-1 regression/elimination (63). Additionally, HIV-1 RNA levels diminished to undetectable levels in the plasma, spleen, liver, gut, and brain in the cured mice. Further, naïve humanized mice that were challenged with adoptively transferred cells isolated from the cured mice showed no detectable HIV-1 viral loads. This study demonstrates the possibility of eliminating HIV-1 in plasma and infectious tissues through this novel combination approach (63).

Recent studies show promising effects of cell therapies for treating HIV-1 (98–100). Here, autologous or allogenic immune cells are transferred to the patient after ex vivo expansion and/or modification to clear HIV-1 infected cells. Nanoparticles may offer the ability to enhance the ability of immune cells to target and kill target cells in the context of HIV-1. In their study, Sweeney et al. generated a PLGA nanoplatform that co-encapsulated an LRA and a target cell-specific antibody to improve NK cell effector function in an in vitro cell model of latent HIV-1 (64). The nanoplatform was able to increase NK cell cytotoxicity of the target cells, thereby illustrating an example of nanoparticles enhancing immune cell function in the context of latent HIV-1 (64). In another studies, Jones et al. demonstrated that cytotoxic T lymphocytes (CTLs) were made more potent by conjugating drug-loaded lipid nanoparticles to their surface (65). HIV-1-specific CTLs were able to specifically target HIV-1-infected cells and deliver the nanoparticle-encapsulated payload (65).