Restriction factors are antiviral components of intrinsic immunity which constitute a first line of defense by blocking different steps of the human immunodeficiency virus (HIV) replication cycle. In immune cells, HIV infection is also sensed by several pattern recognition receptors (PRRs), leading to type I interferon (IFN-I) and inflammatory cytokines production that upregulate antiviral interferon-stimulated genes (ISGs). Several studies suggest a link between these two types of immunity. Indeed, restriction factors, that are generally interferon-inducible, are able to modulate immune responses. This review highlights recent knowledge of the interplay between restriction factors and immunity inducing antiviral defenses. Counteraction of this intrinsic and innate immunity by HIV viral proteins will also be discussed.

Our work highlights the role of HIV-1 unintegrated viral DNA in viral replication. A virus, resistant to strand-transfer inhibitors, has been selected in vitro . This virus highlights a mutation in the 3'PPT region and not in the integrase gene. This mutation modifies the reverse transcription step leading to the accumulation of 1-LTR circles and not the linear DNA. This accumulation of 1-LTR circles leads to viral replication without integration of the viral genome.

Integration of the HIV-1 DNA into the host genome is essential for viral replication and is catalyzed by the retroviral integrase. To date, the only substrate described to be involved in this critical reaction is the linear viral DNA produced in reverse transcription. However, during HIV-1 infection, two-long terminal repeat DNA circles (2-LTRcs) are also generated through the ligation of the viral DNA ends by the host cell's nonhomologous DNA end-joining pathway. These DNAs contain all the genetic information required for viral replication, but their role in HIV-1's life cycle remains unknown. We previously showed that both linear and circular DNA fragments containing the 2-LTR palindrome junction can be efficiently cleaved in vitro by recombinant integrases, leading to the formation of linear 3′-processed–like DNA. In this report, using in vitro experiments with purified proteins and DNAs along with DNA endonuclease and in vivo integration assays, we show that this circularized genome can also be efficiently used as a substrate in HIV-1 integrase-mediated integration both in vitro and in eukaryotic cells. Notably, we demonstrate that the palindrome cleavage occurs via a two-step mechanism leading to a blunt-ended DNA product, followed by a classical 3′-processing reaction; this cleavage leads to integrase-dependent integration, highlighted by a 5-bp duplication of the host genome. Our results suggest that 2-LTRc may constitute a reserve supply of HIV-1 genomes for proviral integration.

Integrase Strand Transfer Inhibitors (INSTIs) are currently used as the most effective therapy in the treatment of human immunodeficiency virus (HIV) infections. Raltegravir (RAL) and Elvitegravir (EVG), the first generation of INSTIs used successfully in clinical treatment, are susceptible to the emergence of viral resistance and have a high rate of cross-resistance. To counteract these resistant mutants, second-generation INSTI drugs have been developed: Dolutegravir (DTG), Cabotegravir (CAB), and Bictegravir (BIC). However, HIV is also able to develop resistance mechanisms against the second-generation of INSTIs. This review describes the mode of action of INSTIs and then summarizes and evaluates some typical resistance mutations, such as substitution and insertion mutations. The role of unintegrated viral DNA is also discussed as a new pathway involved in conferring resistance to INSTIs. This allows us to have a more detailed understanding of HIV resistance to these inhibitors, which may contribute to the development of new INSTIs in the future.

There is a strong demand for new and efficient antiviral compounds. A series of 2-hydroxy-1,4-naphthoquinone Mannich bases were screened for their HIV-1-RNase H inhibitory activity. An HIV-1-RNase H assay was used to study the RNase H inhibition by the test compounds. Docking of active derivatives into the active site of the enzyme was carried out. Compounds 1e and 2k showed distinctly higher HIV-1-RNase H inhibitory activity (IC₅₀ = 2.8–3.1 µM) than the known inhibitors RDS1759 and compound 13. The binding mode and possible interactions of 1e and 2k with the HIV-1-RNase H active site were determined using molecular docking, which led to the identification of salient and concealed pharmacophoric features of these molecules. The docking analysis revealed that there are significant differences in the binding mode of these compounds within the active site of the target enzyme. A selection of HIV-1-RNase H-inhibitory Mannich bases was tested for antiviral activity against HIV-1, and compound 2k showed the highest activity at low toxicity to host cells. The lawsone Mannich bases 1e and 2k also underwent a preliminary screening for activity against SARS-CoV-2, and compound 1e was found to inhibit SARS-CoV-2 replication (IC₅₀ = 11.2 µM).

Curcumin derivatives (curcuminoids) exhibit considerable antiparasitic and antiviral activities. In this study, EF24-like bis-2-fluorobenzylidene piperidone derivatives were synthesized and evaluated for antiprotozoal activity and inhibition of the human immunodeficiency virus (HIV)-1 reverse transcriptase (RT)-associated RNase H (HIV-1 RNase H). A series of bis-arylidene piperidones and tetrahydro(thio)pyranones bearing halogen or nitro substituents were tested against Leishmania major (promastigotes and amastigotes) and Toxoplasma gondii. L. major promastigotes were the most sensitive parasitic model, with several compounds exhibiting low-nanomolar IC₅₀ values, while ortho- or para-halogenated analogues demonstrated submicromolar activity against T. gondii. Among them, 3,4-dichlorophenyl (HPip-DC) and 4-bromophenyl (HPip-4Br) derivatives showed potent activity against L. major and HIV-1 RNase H. The entropy-uncorrected MM-GBSA effective binding energy estimates were −33.41, −9.29, −8.37, and −4.27 kcal/mol for the predicted L. major squalene monooxygenase–HPip-DC, bovine cytochrome bc₁–DiFiD (2,4-difluorophenyl derivative), RNase H–HPip-4NO (4-nitrophenyl derivative), and RNase H–HPip-DC complexes, respectively. During 300 ns simulations, the ligands remained associated with their binding pockets. The Arg557 residue was crucial for HPip-4NO-mediated RNase H inhibition while the inhibitory activity of HPip-DC was much less dependent on this amino acid. These findings identify EF24-like curcuminoids with potent in vitro antiprotozoal activity and biochemical inhibition of HIV-1 RNase H. Antiviral activity was observed but confounded by host cell toxicity.