TLR7 Activation of Macrophages by Imiquimod Inhibits HIV Infection through Modulation of Viral Entry Cellular Factors

Abstract

The Toll-like receptor (TLR) 7 is a viral sensor for detecting single-stranded ribonucleic acid (ssRNA), the activation of which can induce intracellular innate immunity against viral infections. Imiquimod, a synthetic ligand for TLR7, has been successfully used for the topical treatment of genital/perianal warts in immunocompetent individuals. We studied the effect of imiquimod on the human immunodeficiency virus (HIV) infection of primary human macrophages and demonstrated that the treatment of cells with imiquimod effectively inhibited infection with multiple strains (Bal, YU2, and Jago) of HIV. This anti-HIV activity of imiquimod was the most potent when macrophages were treated prior to infection. Infection of macrophages with pseudotyped HIV NL4-3-ΔEnv-eGFP-Bal showed that imiquimod could block the viral entry. Further mechanistic studies revealed that while imiquimod had little effect on the interferons (IFNs) expression, its treatment of macrophages resulted in the increased production of the CC chemokines (human macrophage inflammatory protein-1 alpha (MIP-1α), MIP-1β, and upon activation regulated normal T cells expressed and secreted (RANTES)), the natural ligands of HIV entry co-receptor CCR5, and decreased the expression of CD4 and CCR5. The addition of the antibodies against the CC chemokines to macrophage cultures could block imiquimod-mediated HIV inhibition. These findings provide experimental evidence to support the notion that TLR7 participates in the intracellular immunity against HIV in macrophages, suggesting the further clinical evaluation of imiquimod for its additional benefit of treating genital/perianal warts in people infected with HIV.

Activation of Toll‐like receptor 3 inhibits HIV infection of human iPSC‐derived microglia

“…Total cellular RNAs were extracted from iMg with Tri-reagent (Sigma-Aldrich) according to the manufacturer's instruction and were subjected to reverse transcription reaction using the random primer, dNTPs, AMV reverse transcriptase and RNase inhibitor (Promega Co.) to generate complementary DNA (cDNA), which was then used as a template for real-time PCR with Powerup SYBR Green Master Mix (Applied Biosystems) as previously described. 20 The mRNA level of GAPDH was used as an endogenous reference to normalize the quantities of the target mRNAs. The sequences of oligonucleotide primers for tested mRNAs are available upon request.…”

“…Among PRRs, Toll‐like receptor 3 (TLR3) in conjunction with TLR7 and TLR9 constitutes an efficient system to monitor viral infections. TLR3 recognizes viral double‐stranded RNA, 17 while TLR7 and TLR9 can be triggered by single‐stranded RNA and cytosine phosphate guanine DNA, respectively 18–21 . Although HIV is a single‐strained RNA virus, it can form double‐stranded RNAs during its replication, which can be recognized by TLR3 22,23 .…”

“…TLR3 recognizes viral double-stranded RNA, 17 while TLR7 and TLR9 can be triggered by single-stranded RNA and cytosine phosphate guanine DNA, respectively. [18][19][20][21] Although HIV is a single-strained RNA virus, it can form double-stranded RNAs during its replication, which can be recognized by TLR3. 22,23 TLR3 activation can induce the production of both type I and type III IFNs as well as IFN-stimulated genes (ISGs).…”

Viral-Host Dependency Factors as Therapeutic Targets to Overcome Antiviral Drug-Resistance: A Focus on Innate Immune Modulation

“…Imiquimod (brand name Aldara ™ ) is FDA-approved TLR7/8a (mainly a TLR7a) that is currently in use for the treatment of HPV-and HSV-induced genital and perianal warts (111). In vitro antiviral activity of Imiquimod against HIV-1 has also been reported in pretreated human macrophages in a mechanism involving the downregulation of HIV entry coreceptors CCR5 and CD4 (123). Imiquimod derivative resiquimod (R848) has been proposed for its use in combination to nucleoside analogues for the treatment of noroviruses (124) as well as adjuvant in HIV-1 vaccines using HIV abortive RNAs seeking priming of DCs (125).…”

Discovery of new TLR7 agonists by a combination of statistical learning-based QSAR, virtual screening, and molecular dynamics

“…Imiquimod (compound 9) is a tricyclic nitrogen molecule belonging to the imidazo[4,5-c]quinoline series, which indirectly inhibits viral replications of certain viruses such as herpes simplex virus type 2 (HSV-2), Sendai virus, human papillomavirus (HPV), Rift Valley fever virus (RVFV), hepatitis C virus (HCV), Banzi virus, poxvirus (molluscum contagiosum disease) by induction of IFN-α [ 6 ]. Typically, imidazoquinolines like resiquimod can activate TLR7 and TLR8 simultaneously [ 7 ], but some of them, like imiquimod, can act as a TLR7-specific agonist [ 8 ]. Aldara® (5% cream) and Zyclara® (3.75% cream) are two commercially available FDA-approved imiquimod-containing products for the treatment of actinic keratosis, superficial basal cell carcinoma, external genital, and perianal warts in people of 12 years of age or older [ 9 ].…”