10E8-like neutralizing antibodies against HIV-1 induced using a precisely designed conformational peptide as a vaccine prime

Small-molecule HIV-1 entry inhibitors targeting the epitopes of broadly neutralizing antibodies

Highly active antiretroviral therapy currently used for HIV/AIDS has significantly increased the life expectancy of HIV-infected individuals. It has also improved the quality of life, reduced mortality, and decreased the incidence of AIDS and HIV-related conditions. Currently, however, affected individuals are typically on a lifetime course of several therapeutic drugs, all with the potential for associated toxicity and emergence of resistance. This calls for development of novel, potent, and broad anti-HIV agents able to stop the spread of HIV/AIDS. Significant progress has been made toward identification of anti-HIV-1 broadly neutralizing antibodies (bNAbs). However, antibody-based drugs are costly to produce and store. Administration (by injection only) and other obstacles limit clinical use. In recent years, several highly promising small-molecule HIV-1 entry inhibitors targeting the epitopes of bNAbs have been developed. These newly developed compounds are the focus of the present article.

The development of HIV vaccines targeting gp41 membrane-proximal external region (MPER): challenges and prospects

A human immunodeficiency virus type-1 (HIV-1) vaccine which is able to effectively prevent infection would be the most powerful method of extinguishing pandemic of the acquired immunodeficiency syndrome (AIDS). Yet, achieving such vaccine remains great challenges. The membrane-proximal external region (MPER) is a highly conserved region of the envelope glycoprotein (Env) gp41 subunit near the viral envelope surface, and it plays a key role in membrane fusion. It is also the target of some reported broadly neutralizing antibodies (bNAbs). Thus, MPER is deemed to be one of the most attractive vaccine targets. However, no one can induce these bNAbs by immunization with immunogens containing the MPER sequence(s). The few attempts at developing a vaccine have only resulted in the induction of neutralizing antibodies with quite low potency and limited breadth. Thus far, vaccine failure can be attributed to various characteristics of MPER, such as those involving structure and immunology; therefore, we will focus on these and review the recent progress in the field from the following perspectives: (1) MPER structure and its role in membrane fusion, (2) the epitopes and neutralization mechanisms of MPER-specific bNAbs, as well as the limitations in eliciting neutralizing antibodies, and (3) different strategies for MPER vaccine design and current harvests.

Potential HIV-1 fusion inhibitors mimicking gp41-specific broadly neutralizing antibody 10E8: In silico discovery and prediction of antiviral potency

An integrated computational approach to in silico drug design was used to identify novel HIV-1 fusion inhibitor scaffolds mimicking broadly neutralizing antibody (bNab) 10E8 targeting the membrane proximal external region (MPER) of the HIV-1 gp41 protein. This computer-based approach included (i) generation of pharmacophore models representing 3D-arrangements of chemical functionalities that make bNAb 10E8 active towards the gp41 MPER segment, (ii) shape and pharmacophore-based identification of the 10E8-mimetic candidates by a web-oriented virtual screening platform pepMMsMIMIC, (iii) high-throughput docking of the identified compounds with the gp41 MPER peptide, and (iv) molecular dynamics simulations of the docked structures followed by binding free energy calculations. As a result, eight hits-able to mimic pharmacophore properties of bNAb 10E8 by specific and effective interactions with the MPER region of the HIV-1 protein gp41 were selected as the most probable 10E8-mimetic candidates. Similar to 10E8, the predicted compounds target the critically important residues of a highly conserved hinge region of the MPER peptide that provides a conformational flexibility necessary for its functioning in cell-virus membrane fusion process. In light of the data obtained, the identified small molecules may present promising HIV-1 fusion inhibitor scaffolds for the design of novel potent antiviral drugs.

Live attenuated Salmonella displaying HIV-1 10E8 epitope on fimbriae: systemic and mucosal immune responses in BALB/c mice by mucosal administration

The HIV-1 membrane proximal external region (MPER) that is targeted by several broadly neutralizing antibodies (BNAbs) has been considered a potential immunogen for vaccine development. However, to date the immunogenicity of these BNAb epitopes has not been made sufficiently adequate. In the present work, we used live attenuated Salmonella as a platform to present the HIV-1 MPER 10E8 epitope in the fimbriae. The insertion of the 10E8 epitope into the fimbriae had no significant influence on the expression and the absorption capacity of bacterial fimbriae, nor on the virulence and invasiveness of the attenuated Salmonella. After oral administration of the vaccine construct to mice followed by 10E8 epitope peptide boost, specific antibody responses in serum and mucosa as well as memory lymphocytes in spleen and plasma cells in bone marrow were induced. We also found that the live attenuated Salmonella vector directed the immunity toward Th1 bias, induced Th1 and Th2 cytokine responses and stimulated significant B cell differentiation into GC B, memory B and plasma cells. Therefore, we propose that the live attenuated Salmonella constitutively expressing HIV-1 BNAb epitopes on the fimbriae will be an effective approach to improving immune microenvironment and enhancing the immunogenicity of HIV-1 epitope vaccines.

Human Rhinovirus Presenting 4E10 Epitope of HIV-1 MPER Elicits Neutralizing Antibodies in Human ICAM-1 Transgenic Mice

Attempts at eliciting neutralizing antibodies against human immunodeficiency virus (HIV)-1 have generally failed. Computationally designed epitope-scaffold platforms allow transplantation of structural epitopes to scaffold proteins. Human rhinovirus (HRV) allows such engrafting of HIV-1 epitopes on the surface scaffold proteins. However, since HRV infects only humans and great apes, the efficacy of chimeric HRV-based live viral vaccines is difficult to assess in animal models. Here, we used human ICAM-1 transgenic (hICAM-1 Tg) mice that support productive HRV infection to assess the efficacy of chimeric HRV expressing the HIV-1 membrane proximal external region (MPER) epitope, 4E10. Intranasal immunization with chimeric HRV in transgenic mice effectively induced antibodies that recognized 4E10 peptide as well as HIV-1 Env trimer. Importantly, the immunized mouse sera were able to neutralize HIV strains including those belonging to clades B and C. Moreover, intranasal immunization could bypass pre-existing immunity to HRV. Thus, chimeric HRV appears to provide a viable vaccine vehicle for HIV-1 immunization in humans.

RNAe: an effective method for targeted protein translation enhancement by artificial non-coding RNA with SINEB2 repeat

In this study, a universal protein expression enhancement RNA tool, termed RNAe, was developed by modifying a recently discovered natural long non-coding RNA. At the moment, RNAe is the only technology for gene expression enhancement, as opposed to silencing, at the post-transcriptional level. With this technology, an expression enhancement of 50-1000% is achievable, with more than 200% enhancement achieved in most cases. This work identified the sufficient and necessary element for RNAe function, which was found to be merely 300 nucleotides long and was named minRNAe. It contains a 72-nt 5' pairing sequence which determines the specificity, a 167-nt short non-pairing interspersed nuclear element (SINE) B2 sequence which enhances ribosome recruitment to the target mRNA, and a poly(A) tail, provided together on a plasmid bearing the appropriate sequences. Cellular delivery of RNAe was achieved using routine transfection. The RNAe platform was validated in several widely-used mammalian cell lines. It was proven to be efficient and flexible in specifically enhancing the expression of various endogenous and exogenous proteins of diverse functions in a dose-dependent manner. Compared to the expression-inhibitory tool RNAi, the RNAe tool has a comparable effect size, with an enhancing as opposed to inhibitory effect. One may predict that this brand new technology for enhancing the production of proteins will find wide applications in both research and biopharmaceutical production.