Sequential immunization with V3 peptides from primary human immunodeficiency virus type 1 produces cross-neutralizing antibodies against primary isolates with a matching narrow-neutralization sequence motif

Design, synthesis, and bio-evaluation of novel triterpenoid derivatives as anti-HIV-1 compounds

Two betulinic acid derivatives, RPR103611 (2) and IC9564 (3) were previously reported to be potent HIV-1 entry inhibitors. In this current study, a SAR study of the triterpenoid moiety of 2 and 3 has been performed and an oleanolic acid derivative (4) was identified as a novel HIV-1 entry inhibitor. In addition, the combination of 4 with several-type of HIV-1 neutralizing antibodies provided significant synergistic effects. The synthetic utility of the CC double bond in the C-ring of 4 was also demonstrated to develop the 12-keto-type oleanolic acid derivative (5) as a potent anti-HIV compound. This simple transformation led to a significantly increased anti-HIV activity and a reduced cytotoxicity of the compound.

Peptides for Vaccine Development

This review discusses peptide epitopes used as antigens in the development of vaccines in clinical trials as well as future vaccine candidates. It covers peptides used in potential immunotherapies for infectious diseases including SARS-CoV-2, influenza, hepatitis B and C, HIV, malaria, and others. In addition, peptides for cancer vaccines that target examples of overexpressed proteins are summarized, including human epidermal growth factor receptor 2 (HER-2), mucin 1 (MUC1), folate receptor, and others. The uses of peptides to target cancers caused by infective agents, for example, cervical cancer caused by human papilloma virus (HPV), are also discussed. This review also provides an overview of model peptide epitopes used to stimulate non-specific immune responses, and of self-adjuvanting peptides, as well as the influence of other adjuvants on peptide formulations. As highlighted in this review, several peptide immunotherapies are in advanced clinical trials as vaccines, and there is great potential for future therapies due the specificity of the response that can be achieved using peptide epitopes.

Development and Evaluation of an Ebola Virus Glycoprotein Mucin-Like Domain Replacement System as a New Dendritic Cell-Targeting Vaccine Approach against HIV-1

The development of efficient vaccine approaches against HIV infection remains challenging in the vaccine field. Here, we developed an Ebola virus envelope glycoprotein (EboGP)-based chimeric fusion protein system and demonstrated that replacement of the mucin-like domain (MLD) of EboGP with HIV C2-V3-C3 (134 amino acids [aa]) or C2-V3-C3-V4-C4-V5-C5 (243 aa) polypeptides (EbGPΔM-V3 and EbGPΔM-V3-V5, respectively) still maintained the efficiency of EboGP-mediated viral entry into human macrophages and dendritic cells (DCs). Animal studies using mice revealed that immunization with virus-like particles (VLPs) containing the above chimeric proteins, especially EbGPΔM-V3, induced significantly more potent anti-HIV antibodies than HIV gp120 alone in mouse serum and vaginal fluid. Moreover, the splenocytes isolated from mice immunized with VLPs containing EbGPΔM-V3 produced significantly higher levels of gamma interferon (IFN-γ), interleukin 2 (IL-2), IL-4, IL-5, and macrophage inflammatory protein 1α (MIP-1α). Additionally, we demonstrated that coexpression of EbGPΔM-V3 and the HIV Env glycoprotein in a recombinant vesicular stomatitis virus (rVSV) vector elicited robust anti-HIV antibodies that may have specifically recognized epitopes outside or inside the C2-V3-C3 region of HIV-1 gp120 and cross-reacted with the gp120 from different HIV strains. Thus, this study has demonstrated the great potential of this DC-targeting vaccine platform as a new vaccine approach for improving immunogen delivery and increasing vaccine efficacy.

IMPORTANCE Currently, there are more than 38.5 million reported cases of HIV globally. To date, there is no approved vaccine for HIV-1 infection. Thus, the development of an effective vaccine against HIV infection remains a global priority. This study revealed the efficacy of a novel dendritic cell (DC)-targeting vaccination approach against HIV-1. The results clearly show that the immunization of mice with virus-like particles (VLPs) and VSVs containing HIV Env and a fusion protein composed of a DC-targeting domain of Ebola virus GP with HIV C2-V3-C3 polypeptides (EbGPΔM-V3) could induce robust immune responses against HIV-1 Env and/or Gag in serum and vaginal mucosa. These findings provide a proof of concept of this novel and efficient DC-targeting vaccine approach in delivering various antigenic polypeptides of HIV-1 and/or other emergent infections to the host antigen-presenting cells to prevent HIV and other viral infections.

Hybrids of Small-Molecule CD4 Mimics with Polyethylene Glycol Units as HIV Entry Inhibitors

CD4 mimics are small molecules that inhibit the interaction of gp120 with CD4. We have developed several CD4 mimics. Herein, hybrid molecules consisting of CD4 mimics with a long alkyl chain or a PEG unit attached through a self-cleavable linker were synthesized. In anti-HIV activity, modification with a PEG unit appeared to be more suitable than modification with a long alkyl chain. Thus, hybrid molecules of CD4 mimics, with PEG units attached through an uncleavable linker, were developed and showed high anti-HIV activity and low cytotoxicity. In investigation of pharmacokinetics in a rhesus macaque, a hybrid compound had a more effective PK profile than that of the parent compound, and intramuscular injection was a more useful administration route to maintain the high blood concentration of the CD4 mimic than intravenous injection. The presented hybrid molecules of CD4 mimics with a PEG unit would be practically useful when combined with a neutralizing antibody.

Peptides to combat viral infectious diseases

Viral infectious diseases have resulted in millions of deaths throughout history and have created a significant public healthcare burden. Tremendous efforts have been placed by the scientific communities, health officials and government organizations to detect, treat, and prevent viral infection. However, the complicated life cycle and rapid genetic mutations of viruses demand continuous development of novel medicines with high efficacy and safety profiles. Peptides provide a promising outlook as a tool to combat the spread and re-emergence of viral infection. This article provides an overview of five viral infectious diseases with high global prevalence: influenza, chronic hepatitis B, acquired immunodeficiency syndrome, severe acute respiratory syndrome, and coronavirus disease 2019. The current and potential peptide-based therapies, vaccines, and diagnostics for each disease are discussed.

Induction of cross-neutralizing antibodies by sequential immunization with heterologous papillomavirus L1VLPs and its implications for HPV prophylactic vaccines

Sequential immunization with antigens from different strains of HIV-1, influenza viruses or dengue viruses induced cross-neutralizing antibodies and enhanced the antibody responses against previous antigens. The characteristics of neutralizing antibodies induced by sequential immunization with different types of human papillomavirus (HPV) L1 virus-like particles (L1VLPs) are unclear. In this study, mice were primed with one or two types (HPV-16 or HPV16/18) of L1VLPs, then boosted sequentially with HPV6/18/45/11/31/58 or HPV6/45/11/31/58 L1VLPs, and sera were analyzed with HPV pseudovirus-based neutralization assay. The results showed that neutralizing activities against earlier immunized vaccine types were enhanced gradually by subsequent immunizations, and low levels of neutralizing activities against nonvaccine types (HPV33/35/52/59/68) were also observed. After absorbing the immune sera with vaccine-type (HPV16/18/45) L1VLPs, neutralizing activities against tested priming and boosting types (HPV16/18/58) decreased significantly, and that against nonvaccine type (HPV-33) was also partially eliminated. Moreover, neutralizing activities against vaccine types (HPV16/58) were significantly reduced after absorbing with nonvaccine-type VLPs (HPV33/52). These data suggest that cross-neutralizing epitopes exist among different HPV L1VLPs. The cross-neutralizing activities against nonvaccine types and the enhanced neutralizing activities against earlier immunized vaccine types may result from sequential boosting with these cross-neutralizing epitopes. These observations support early vaccination with more types of L1VLPs derived from HPVs that cause a serious threat to the population.

Sequential immunization induces strong and broad immunity against all four dengue virus serotypes

A major challenge in dengue vaccine development is the need to induce immunity against four dengue (DENV) serotypes. Dengvaxia®, the only licensed dengue vaccine, consists of four variant dengue antigens, one for each serotype. Three doses of immunization with the tetravalent vaccine induced only suboptimal protection against DENV1 and DENV2. Furthermore, vaccination paradoxically and adversely primes dengue naïve subjects to more severe dengue. Here, we have tested whether sequential immunization induces stronger and broader immunity against four DENV serotypes than tetravalent-formulated immunization. Mice were immunized with four DNA plasmids, each encoding the pre-membrane and envelope from one DENV serotype, either sequentially or simultaneously. The sequential immunization induced significantly higher levels of interferon (IFN)γ- or tumor necrosis factor (TNF)α-expressing CD4⁺ and CD8⁺ T cells to both serotype-specific and conserved epitopes than tetravalent immunization. Moreover, sequential immunization induced higher levels of neutralizing antibodies to all four DENV serotypes than tetravalent vaccination. Consistently, sequential immunization resulted in more diversified immunoglobulin repertoire, including increased complementarity determining region 3 (CDR3) length and more robust germinal center reactions. These results show that sequential immunization offers a simple approach to potentially overcome the current challenges encountered with tetravalent-formulated dengue vaccines.

Specific Substitutions in Region V2 of gp120 env confer SHIV Neutralisation Resistance

A tier 2 SHIV-MK38 strain was obtained after two in vivo passages of tier 1 SHIV-MK1. SHIV-MK38#818, cloned from the MK38 strain, was neutralisation-resistant, like the parental MK38 strain, to SHIV-infected monkey plasma (MP), HIV-1-infected human pooled plasma (HPP), and KD247 monoclonal antibody (mAb) (anti-V3 gp120 env). We investigated the mechanisms underlying the resistance of #818, specifically the amino acid substitutions that confer resistance to MK1. We introduced amino acid substitutions in the MK1 envelope by in vitro mutagenesis and then compared the neutralisation resistance to MP, HPP, and KD247 mAb with #818 in a neutralisation assay using TZM-bl cells. We selected 11 substitutions in the V1, V2, C2, V4, C4, and V5 regions based on the alignment of env of MK1 and #818. The neutralisation resistance of the mutant MK1s with 7 of 11 substitutions in the V1, C2, C4, and V5 regions did not change significantly. These substitutions did not alter any negative charges or N-glycans. The substitutions N169D and K187E, which added negative charges, and S190N in the V2 region of gp120 and A389T in V4, which created sites for N-glycan, conferred high neutralisation resistance. The combinations N169D+K187E, N169D+S190N, and N169D+A389T resulted in MK1 neutralisation resistance close to that of #818. The combinations without 169D were neutralisation-sensitive. Therefore, N169D is the most important substitution for neutralisation resistance. This study demonstrated that although the V3 region sequences of #818 and MK1 are the same, V3 binding antibodies cannot neutralise #818 pseudovirus. Instead, mutations in the V2 and V4 regions inhibit the neutralisation of anti-V3 antibodies. We hypothesised that 169D and 190N altered the MK1 Env conformation so that the V3 region is buried. Therefore, the V2 region may block KD247 from binding to the tip of the V3 region.

Prediction of Contact Residues in Anti-HIV Neutralizing Antibody by Deep Learning

The monoclonal antibody 1C10 targets the V3 loop of HIV-1 and neutralizes a broad range of clade B viruses. However, the mode of interaction between 1C10 and the V3 loop remains unclear because crystallization of 1C10 and the V3 peptide was unsuccessful due to the flexible regions present in both 1C10 and the V3 peptide. In this study, we predicted the 1C10 amino acid residues that make contact with the V3 loop using a deep learning (DL)-based method. Inputs from ROSIE for docking simulation and FastContact, Naccess, and PDBtools, to approximate interactions were processed by Chainer for DL, and outputs were obtained as probabilities of contact residues. Using this DL algorithm, D95, D97, P100a, and D100b of CDRH3; D53, and D56 of CDRH2; and D61 of FR3 were highly ranked as contact residues of 1C10. Substitution of these residues with alanine significantly decreased the affinity of 1C10 to the V3 peptide. Moreover, the higher the rank of the residue, the more the binding activity diminished. This study demonstrates that the prediction of contact residues using a DL-based approach is a precise and useful tool for the analysis of antibody-antigen interactions.

Discovery and Development of Anti-HIV Therapeutic Agents: Progress Towards Improved HIV Medication

The history of the human immunodeficiency virus (HIV)/AIDS therapy, which spans over 30 years, is one of the most dramatic stories of science and medicine leading to the treatment of a disease. Since the advent of the first AIDS drug, AZT or zidovudine, a number of agents acting on different drug targets, such as HIV enzymes (e.g. reverse transcriptase, protease, and integrase) and host cell factors critical for HIV infection (e.g. CD4 and CCR5), have been added to our armamentarium to combat HIV/AIDS. In this review article, we first discuss the history of the development of anti-HIV drugs, during which several problems such as drug-induced side effects and the emergence of drug-resistant viruses became apparent and had to be overcome. Nowadays, the success of Combination Antiretroviral Therapy (cART), combined with recently-developed powerful but nonetheless less toxic drugs has transformed HIV/AIDS from an inevitably fatal disease into a manageable chronic infection. However, even with such potent cART, it is impossible to eradicate HIV because none of the currently available HIV drugs are effective in eliminating occult “dormant” HIV cell reservoirs. A number of novel unique treatment approaches that should drastically improve the quality of life (QOL) of patients or might actually be able to eliminate HIV altogether have also been discussed later in the review.

Peptide-Based Vaccination for Antibody Responses Against HIV

HIV-1 is responsible for a global pandemic of 35 million people and continues to spread at a rate of >2 million new infections/year. It is widely acknowledged that a protective vaccine would be the most effective means to reduce HIV-1 spread and ultimately eliminate the pandemic, whereas a therapeutic vaccine might help to mitigate the clinical course of the disease and to contribute to virus eradication strategies. However, despite more than 30 years of research, we do not have a vaccine capable of protecting against HIV-1 infection or impacting on disease progression. This, in part, denotes the challenge of identifying immunogens and vaccine modalities with a reduced risk of failure in late stage development. However, progress has been made in epitope identification for the induction of broadly neutralizing antibodies. Thus, peptide-based vaccination has become one of the challenges of this decade. While some researchers reconstitute envelope protein conformation and stabilization to conserve the epitope targeted by neutralizing antibodies, others have developed strategies based on peptide-carrier vaccines with a similar goal. Here, we will review the major peptide-carrier based approaches in the vaccine field and their application and recent development in the HIV-1 field.

Soluble-type small-molecule CD4 mimics as HIV entry inhibitors

Several small molecule CD4 mimics have been reported previously as HIV-1 entry inhibitors, which block the interaction between the Phe43 cavity of HIV-1 gp120 and the host CD4. Known CD4 mimics such as NBD-556 possess significant anti-HIV activity but are less soluble in water, perhaps due to their hydrophobic aromatic ring-containing structures. Compounds with a pyridinyl group in place of the phenyl group in these molecules have been designed and synthesized in an attempt to increase the hydrophilicity. Some of these new CD4 mimics, containing a tetramethylpiperidine ring show significantly higher water solubility than NBD-556 and have high anti-HIV activity and synergistic anti-HIV activity with a neutralizing antibody. The CD4 mimic that has a cyclohexylpiperidine ring and a 6-fluoropyridin-3-yl ring has high anti-HIV activity and no significant cytotoxicity. The present results will be useful in the future design and development of novel soluble-type molecule CD4 mimics.

Ibalizumab Targeting CD4 Receptors, An Emerging Molecule in HIV Therapy

The HIV infection is responsible for the most devastating global pandemic of the last century. More than 39 million people have died of HIV/AIDS since 1981. The development of the antiretroviral (ARV) treatment begins with the discovery of zidovudine a nucleoside reverse transcriptase inhibitor. This breakthrough was followed by other ARV drug classes and representatives. Presently, HIV treatment employs 27 ARV representatives belonging to five different classes. Despite the proven benefits of ARV treatment and its long-term control of the HIV infection, there is an increasing concern about the numerous adverse effects and resistance to current ARV drugs. Therefore, the new HIV treatment strategies focus on the development of new ARV agents with a high genetic barrier to resistance and low toxicity. Monoclonal antibodies (MAbs) belong to a new drug class with encouraging results in the treatment of cancer, autoimmune disorders and most recently against HIV infection. The advantages of using MAbs for HIV treatment are related to their antiviral effect, lack of toxicity, good resistance profile, additional synergy with other ARV drug classes and ability to restore CD4 T-cell responses. The current article is a short summary of ibalizumab, an anti-CD4 monoclonal antibody that interferes with HIV viral entry. Current studies on ibalizumab have underlined its antiviral potential, minimal adverse effects, and lack of crossed resistance with other ARV agents thus supporting its further therapeutic use in multidrug resistant HIV-infected patients.

Unique binding modes for the broad neutralizing activity of single-chain variable fragments (scFv) targeting CD4-induced epitopes

Background

The CD4-induced (CD4i) epitopes in gp120 includes the co-receptor binding site, which are formed and exposed after interaction with CD4. Monoclonal antibodies (mAbs) to the CD4i epitopes exhibit limited neutralizing activity because of restricted access to their epitopes. However, small fragment counterparts such as single-chain variable fragments (scFvs) have been reported to neutralize a broad range of viruses compared with the full-size IgG molecule. To identify the CD4i epitope site responsible for this broad neutralization we constructed three scFvs of anti-CD4i mAbs from a human immunodeficiency virus type 1 (HIV-1)-infected elite controller, and investigated the neutralization coverage and precise binding site in the CD4i epitopes.

Results

We constructed scFvs from the anti-CD4i mAbs, 916B2, 4E9C, and 25C4b and tested their neutralization activity against a panel of 66 viruses of multi-subtype. Coverage of neutralization by the scFvs against this panel of pseudoviruses was 89% (59/66) for 4E9C, 95% (63/66) for 25C4b and 100% (66/66) for 916B2. Analysis using a series of envelope glycoprotein mutants revealed that individual anti-CD4i mAbs showed various dependencies on the hairpin 1 (H1) and V3 base. The binding profiles of 25C4b were similar to those of 17b, and 25C4b bound the region spanning multiple domains of H1 and hairpin 2 (H2) of the bridging sheet and V3 base. For 4E9C, the V3-base dependent binding was apparent from no binding to mutants containing the ΔV3 truncation. In contrast, binding of 916B2 was dependent on the H1 region, which is composed of β2 and β3 strands, because mutants containing the H1 truncation did not show any reactivity to 916B2. Although the H1 region structure is affected by CD4 engagement, the results indicate the unique nature of the 916B2 epitope, which may be structurally conserved before and after conformational changes of gp120.

Conclusions

Identification of a unique structure of the H1 region that can be targeted by 916B2 may have an important implication in the development of small molecules to inhibit infection by a broad range of HIV-1 for the purpose of HIV treatment and prevention.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-017-0369-y) contains supplementary material, which is available to authorized users.

Maternal Binding and Neutralizing IgG Responses Targeting the C-Terminal Region of the V3 Loop Are Predictive of Reduced Peripartum HIV-1 Transmission Risk

The development of an effective maternal HIV-1 vaccine that could synergize with antiretroviral therapy (ART) to eliminate pediatric HIV-1 infection will require the characterization of maternal immune responses capable of blocking transmission of autologous HIV to the infant. We previously determined that maternal plasma antibody binding to linear epitopes within the variable loop 3 (V3) region of HIV envelope (Env) and neutralizing responses against easy-to-neutralize tier 1 viruses were associated with reduced risk of peripartum HIV infection in the historic U.S. Woman and Infant Transmission Study (WITS) cohort. Here, we defined the fine specificity and function of the potentially protective maternal V3-specific IgG antibodies associated with reduced peripartum HIV transmission risk in this cohort. The V3-specific IgG binding that predicted low risk of mother-to-child-transmission (MTCT) was dependent on the C-terminal flank of the V3 crown and particularly on amino acid position 317, a residue that has also been associated with breakthrough transmission in the RV144 vaccine trial. Remarkably, the fine specificity of potentially protective maternal plasma V3-specific tier 1 virus-neutralizing responses was dependent on the same region in the V3 loop. Our findings suggest that MTCT risk is associated with neutralizing maternal IgG that targets amino acid residues in the C-terminal region of the V3 loop crown, suggesting the importance of the region in immunogen design for maternal vaccines to prevent MTCT.IMPORTANCE Efforts to curb HIV-1 transmission in pediatric populations by antiretroviral therapy (ART) have been highly successful in both developed and developing countries. However, more than 150,000 infants continue to be infected each year, likely due to a combination of late maternal HIV diagnosis, lack of ART access or adherence, and drug-resistant viral strains. Defining the fine specificity of maternal humoral responses that partially protect against MTCT of HIV is required to inform the development of a maternal HIV vaccine that will enhance these responses during pregnancy. In this study, we identified amino acid residues targeted by potentially protective maternal V3-specific IgG binding and neutralizing responses, localizing the potentially protective response in the C-terminal region of the V3 loop crown. Our findings have important implications for the design of maternal vaccination strategies that could synergize with ART during pregnancy to achieve the elimination of pediatric HIV infections.

Humanized Immunoglobulin Mice: Models for HIV Vaccine Testing and Studying the Broadly Neutralizing Antibody Problem

A vaccine that can effectively prevent HIV-1 transmission remains paramount to ending the HIV pandemic, but to do so, will likely need to induce broadly neutralizing antibody (bnAb) responses. A major technical hurdle toward achieving this goal has been a shortage of animal models with the ability to systematically pinpoint roadblocks to bnAb induction and to rank vaccine strategies based on their ability to stimulate bnAb development. Over the past 6 years, immunoglobulin (Ig) knock-in (KI) technology has been leveraged to express bnAbs in mice, an approach that has enabled elucidation of various B-cell tolerance mechanisms limiting bnAb production and evaluation of strategies to circumvent such processes. From these studies, in conjunction with the wealth of information recently obtained regarding the evolutionary pathways and paratopes/epitopes of multiple bnAbs, it has become clear that the very features of bnAbs desired for their function will be problematic to elicit by traditional vaccine paradigms, necessitating more iterative testing of new vaccine concepts. To meet this need, novel bnAb KI models have now been engineered to express either inferred prerearranged V(D)J exons (or unrearranged germline V, D, or J segments that can be assembled into functional rearranged V(D)J exons) encoding predecessors of mature bnAbs. One encouraging approach that has materialized from studies using such newer models is sequential administration of immunogens designed to bind progressively more mature bnAb predecessors. In this review, insights into the regulation and induction of bnAbs based on the use of KI models will be discussed, as will new Ig KI approaches for higher-throughput production and/or altering expression of bnAbs in vivo, so as to further enable vaccine-guided bnAb induction studies.

Progress toward active or passive HIV-1 vaccination

AIDS is a preventable disease. Nevertheless, according to UNAIDS, 2.1 million individuals were infected with HIV-1 in 2015 worldwide. An effective vaccine is highly desirable. Most vaccines in clinical use today prevent infection because they elicit antibodies that block pathogen entry. Consistent with this general rule, studies in experimental animals have shown that broadly neutralizing antibodies to HIV-1 can prevent infection, suggesting that a vaccine that elicits such antibodies would be protective. However, despite significant efforts over the last 30 years, attempts to elicit broadly HIV-1 neutralizing antibodies by vaccination failed until recent experiments in genetically engineered mice were finally successful. Here, we review the key breakthroughs and remaining obstacles to the development of active and passive HIV-1 vaccines.

Sequential Immunization Elicits Broadly Neutralizing Anti-HIV-1 Antibodies in Ig Knockin Mice

A vaccine that elicits broadly neutralizing antibodies (bNAbs) against HIV-1 is likely to be protective, but this has not been achieved. To explore immunization regimens that might elicit bNAbs, we produced and immunized mice expressing the predicted germline PGT121, a bNAb specific for the V3-loop and surrounding glycans on the HIV-1 spike. Priming with an epitope-modified immunogen designed to activate germline antibody-expressing B cells, followed by ELISA-guided boosting with a sequence of directional immunogens, native-like trimers with decreasing epitope modification, elicited heterologous tier-2-neutralizing responses. In contrast, repeated immunization with the priming immunogen did not. Antibody cloning confirmed elicitation of high levels of somatic mutation and tier-2-neutralizing antibodies resembling the authentic human bNAb. Our data establish that sequential immunization with specifically designed immunogens can induce high levels of somatic mutation and shepherd antibody maturation to produce bNAbs from their inferred germline precursors.

Cross-Neutralization Activity of Single-Chain Variable Fragment (scFv) Derived from Anti-V3 Monoclonal Antibodies Mediated by Post-Attachment Binding

The V3 loop in the envelope (Env) of HIV-1 is one of the major targets of neutralizing antibodies. However, this antigen is hidden inside the Env trimer in most isolates and is fully exposed only during CD4-gp120 interaction. Thus, primary HIV-1 isolates are relatively resistant to anti-V3 antibodies because IgG is too large to access the V3 loop. To overcome this obstacle, we constructed single-chain variable fragments (scFvs) from anti-V3 monoclonal antibodies 0.5γ, 5G2, and 16G6. Enhanced neutralization by 0.5γ and 5G2 scFvs was observed in strains resistant to their IgG counterparts. Neutralization coverage by 0.5γ scFv reached up to 90% of the tested viruses (tier 2 and 3 classes). The temperature-regulated neutralization assay revealed that extensive cross-neutralization of 0.5γ scFv can be explained by post-attachment neutralization. Neutralization assay involving viruses carrying an inter-subunit disulfide bond (SOS virus) showed that the neutralization-susceptible timeframe after attachment was 60 to 120 min. These results indicate that the scFvs efficiently access the V3 loop and subsequently neutralize HIV-1, even after virus attachment to the target cells. Based on its broad and potent neutralizing activity, further development of anti-V3 scFv for therapeutic and preventive strategies is warranted.

Small-Molecule CD4 Mimics Containing Mono-cyclohexyl Moieties as HIV Entry Inhibitors

CD4 mimics are small molecules that inhibit the protein-protein interaction between gp120 and CD4, which is a key interaction for the entry of human immunodeficiency virus (HIV) into host immune cells. In the present study, mono-cyclohexyl-type CD4 mimics were designed to form hydrophobic and electrostatic interactions with Val430 and Asp368 located in the entrance of the Phe43 cavity of gp120, the interaction site of CD4. YIR-329, a novel 1-azaspiro[5.5]undecane derivative with a cyclohexyl ring attached to the piperidine ring, exhibited only slightly weaker anti-HIV activity than a previously described lead HAR-171, and modeling results indicated the formation of advantageous interactions by the para-chlorophenyl moiety of YIR-329. To introduce an electrostatic interaction with Asp368, derivatives with a guanidino group on the piperidine nitrogen atom were synthesized. Mono-cyclohexyl-type CD4 mimics with a guanidino group, such as YIR-819 (N(1) -(4-chlorophenyl)-N(2) -(1-(2-(N-(amidino)glycinamide)ethyl)-2-cyclohexylpiperidin-4-yl)oxalamide) and YIR-821 (1-(2-(5-guanidinovaleramide)ethyl derivative of YIR-819), were identified that exhibit approximately fivefold more potent anti-HIV activity than YIR-329. In combination with a neutralizing antibody, their anti-HIV activities were augmenting. Modeling results suggest that these compounds interact effectively with Val430 and either Asp368 or Asp474 in the gp120 Phe43 cavity. YIR-819 and YIR-821 represent useful lead compounds for the further development of HIV-1 entry inhibitors and could potentially be useful for co-administration with neutralizing antibodies for the treatment of HIV infection and AIDS.

Generation of a neutralization-resistant CCR5 tropic simian/human immunodeficiency virus (SHIV-MK38) molecular clone, a derivative of SHIV-89.6

Previously, we reported that a new genetically diverse CCR5 (R5) tropic simian/human immunodeficiency virus (SHIV-MK38) adapted to rhesus monkeys became more neutralization resistant to SHIV-infected plasma than did the parental SHIV-KS661 clone. Here, to clarify the significance of the neutralization-resistant phenotype of SHIV in a macaque model, we initially investigated the precise neutralization phenotype of the SHIVs, including SHIV-MK38 molecular clones, using SHIV-MK38-infected plasma, a pooled plasma of human immunodeficiency virus (HIV)-infected individuals, soluble CD4 and anti-HIV-1 neutralizing mAbs, the epitopes of which were known. The results show that SHIV-KS661 had tier 1 neutralization sensitivity, but monkey-adapted R5 tropic SHIV-MK38 acquired neutralization resistance similar to that of tier 2 or 3 as a clone virus. Sequence analysis of the env gene suggested that the neutralization-resistant phenotype of SHIV-MK38 was acquired by conformational changes in Env associated with the net charge and potential N-linked glycosylation sites. To examine the relationship between neutralization phenotype and stably persistent infection in monkeys, we performed in vivo rectal inoculation experiments using a SHIV-MK38 molecular clone. The results showed that one of three rhesus monkeys exhibited durable infection with a plasma viral load of 105 copies ml- 1 despite the high antibody responses that occurred in the host. Whilst further improvements are required in the development of a challenge virus, it will be useful to generate a neutralization-resistant R5 tropic molecular clone of the SHIV-89.6 lineage commonly used for vaccine development - a result that can be used to explore the foundation of AIDS pathogenesis.

A minimally cytotoxic CD4 mimic as an HIV entry inhibitor

Several CD4 mimics have been reported as HIV-1 entry inhibitors which can block the interaction between the viral envelope glycoprotein gp120 and the cell surface protein CD4. We previously found a lead compound 2 (YYA-021) with high anti-HIV activity and low cytotoxicity. Pharmacokinetic analysis however showed compound 2 to have wide tissue distribution and relatively high distribution volumes in rats and rhesus macaques. In the present study we searched for more hydrophilic CD4 mimics with a view to reducing tissue distribution. A new compound (5) with a 1,3-benzodioxolyl moiety was found to have relatively high anti-HIV activity and no significant cytotoxicity. Compound 5 is more hydrophilic than compound 2 and the pharmacokinetics of the intravenous administration of compound 5 in a rhesus macaque showed that compound 5 has lower tissue distribution than compound 2, suggesting that compound 5 possesses a better profile.

Incompatible Natures of the HIV-1 Envelope in Resistance to the CCR5 Antagonist Cenicriviroc and to Neutralizing Antibodies

Cenicriviroc is a CCR5 antagonist which prevents human immunodeficiency virus type 1 (HIV-1) from cellular entry. The CCR5-binding regions of the HIV-1 envelope glycoprotein are important targets for neutralizing antibodies (NAbs), and mutations conferring cenicriviroc resistance may therefore affect sensitivity to NAbs. Here, we used the in vitro induction of HIV-1 variants resistant to cenicriviroc or NAbs to examine the relationship between resistance to cenicriviroc and resistance to NAbs. The cenicriviroc-resistant variant KK652-67 (strain KK passaged 67 times in the presence of increasing concentrations of cenicriviroc) was sensitive to neutralization by NAbs against the V3 loop, the CD4-induced (CD4i) region, and the CD4-binding site (CD4bs), whereas the wild-type (WT) parental HIV-1 strain KKWT from which cenicriviroc-resistant strain KK652-67 was obtained was resistant to these NAbs. The V3 region of KK652-67 was important for cenicriviroc resistance and critical to the high sensitivity of the V3, CD4i, and CD4bs epitopes to NAbs. Moreover, induction of variants resistant to anti-V3 NAb 0.5γ and anti-CD4i NAb 4E9C from cenicriviroc-resistant strain KK652-67 resulted in reversion to the cenicriviroc-sensitive phenotype comparable to that of the parental strain, KKWT. Resistance to 0.5γ and 4E9C was caused by the novel substitutions R315K, G324R, and E381K in the V3 and C3 regions near the substitutions conferring cenicriviroc resistance. Importantly, these amino acid changes in the CCR5-binding region were also responsible for reversion to the cenicriviroc-sensitive phenotype. These results suggest the presence of key amino acid residues where resistance to cenicriviroc is incompatible with resistance to NAbs. This implies that cenicriviroc and neutralizing antibodies may restrict the emergence of variants resistant to each other.

Molecular recognition of human ephrinB2 cell surface receptor by an emergent African henipavirus

The discovery of African henipaviruses (HNVs) related to pathogenic Hendra virus (HeV) and Nipah virus (NiV) from Southeast Asia and Australia presents an open-ended health risk. Cell receptor use by emerging African HNVs at the stage of host-cell entry is a key parameter when considering the potential for spillover and infection of human populations. The attachment glycoprotein from a Ghanaian bat isolate (GhV-G) exhibits <30% sequence identity with Asiatic NiV-G/HeV-G. Here, through functional and structural analysis of GhV-G, we show how this African HNV targets the same human cell-surface receptor (ephrinB2) as the Asiatic HNVs. We first characterized this virus-receptor interaction crystallographically. Compared with extant HNV-G-ephrinB2 structures, there was significant structural variation in the six-bladed β-propeller scaffold of the GhV-G receptor-binding domain, but not the Greek key fold of the bound ephrinB2. Analysis revealed a surprisingly conserved mode of ephrinB2 interaction that reflects an ongoing evolutionary constraint among geographically distal and phylogenetically divergent HNVs to maintain the functionality of ephrinB2 recognition during virus-host entry. Interestingly, unlike NiV-G/HeV-G, we could not detect binding of GhV-G to ephrinB3. Comparative structure-function analysis further revealed several distinguishing features of HNV-G function: a secondary ephrinB2 interaction site that contributes to more efficient ephrinB2-mediated entry in NiV-G relative to GhV-G and cognate residues at the very C terminus of GhV-G (absent in Asiatic HNV-Gs) that are vital for efficient receptor-induced fusion, but not receptor binding per se. These data provide molecular-level details for evaluating the likelihood of African HNVs to spill over into human populations.

Passive transfer of neutralizing mAb KD-247 reduces plasma viral load in patients chronically infected with HIV-1

OBJECTIVE

Neutralizing antibodies against HIV-1 such as a humanized mAb KD-247 can mediate effector functions that attack infected cells in vitro. However, the clinical efficacy of neutralizing antibodies in infected individuals remains to be determined. We evaluated the safety, tolerability and pharmacokinetics of KD-247 infusion and its effect on plasma HIV-1 RNA load and CD4 T-cell count.

DESIGN AND METHODS

KD-1002 is a phase Ib, double-blind, placebo-controlled, dose-escalation study of KD-247 in asymptomatic HIV-1 seropositive individuals who did not need antiretroviral therapy. Individuals were randomized to 4, 8 or 16 mg/kg KD-247 or placebo, and received three infusions over a 2-week period.

RESULTS

Patients were randomized to receive one of the three doses of KD-247 and the treatment was well tolerated. We observed a significant decrease in HIV RNA in the 8 and 16 mg/kg KD-247 cohorts, with two individuals who achieved more than 1 log reduction of HIV RNA. Two patients in the 16 mg/kg cohort had selections and/or mutations in the V3-tip region that suggested evasion of neutralization. Long-term suppression of viral load was observed in one patient despite a significant decrease in plasma concentration of KD-247, suggesting effects of the antibody other than neutralization or loss of fitness of the evading virus.

CONCLUSION

The results indicate that KD-247 reduces viral load in patients with chronic HIV-1 infection and further clinical trials are warranted.

Complementary and synergistic activities of anti-V3, CD4bs and CD4i antibodies derived from a single individual can cover a wide range of HIV-1 strains

Antibodies with modest neutralizing activity and narrow breadth are commonly elicited in HIV-1. Here, we evaluated the complementary and synergistic activities of a set of monoclonal antibodies (MAb) isolated from a single patient, directed to V3, CD4 binding site (CD4bs), and CD4 induced (CD4i) epitopes. Despite low somatic hypermutation percentages in the variable regions, these MAbs covered viral strains from subtypes B, C, A and CRF01_AE and transmitted/founder viruses in terms of binding, neutralizing and antibody-dependent cell-mediated cytotoxicity (ADCC) activities. In addition, a combination of the anti-V3 and CD4bs MAbs showed a synergistic effect over the neutralization of HIV-1JR-FL. A humoral response from a single patient covered a wide range of viruses by complementary and synergistic activities of antibodies with different specificities. Inducing a set of narrow neutralizing antibodies, easier to induce than the broadly neutralizing antibodies, could be a strategy for developing an effective vaccine against HIV-1.

Structural basis of clade-specific HIV-1 neutralization by humanized anti-V3 monoclonal antibody KD-247

Humanized monoclonal antibody KD-247 targets the Gly(312)-Pro(313)-Gly(314)-Arg(315) arch of the third hypervariable (V3) loop of the HIV-1 surface glycoprotein. It potently neutralizes many HIV-1 clade B isolates, but not of other clades. To understand the molecular basis of this specificity, we solved a high-resolution (1.55 Å) crystal structure of the KD-247 antigen binding fragment and examined the potential interactions with various V3 loop targets. Unlike most antibodies, KD-247 appears to interact with its target primarily through light chain residues. Several of these interactions involve Arg(315) of the V3 loop. To evaluate the role of light chain residues in the recognition of the V3 loop, we generated 20 variants of KD-247 single-chain variable fragments with mutations in the antigen-binding site. Purified proteins were assessed for V3 loop binding using AlphaScreen technology and for HIV-1 neutralization. Our data revealed that recognition of the clade-specificity defining residue Arg(315) of the V3 loop is based on a network of interactions that involve Tyr(L32), Tyr(L92), and Asn(L27d) that directly interact with Arg(315), thus elucidating the molecular interactions of KD-247 with its V3 loop target.

The presence of glutamine at position 315 but not epitope masking predominantly hinders HIV subtype C neutralization by the anti-V3 antibody B4e8

Antibody B4e8 exhibits modest cross-neutralizing activity, with preference for HIV subtype B. This preference might be explained by B4e8׳s extensive interaction with Arg315, which occurs at the center of most subtype B V3 sequences but is replaced by Gln in subtype C. The extent to which B4e8׳s ability to neutralize subtype C strains is hindered by Gln315 and/or other factors, e.g. epitope masking, is unclear. We confirmed here that an Arg315-to-Gln substitution in a subtype B virus abrogates B4e8 neutralizing activity. Conversely, B4e8-resistant subtype C viruses were rendered sensitive upon Gln 315-to-Arg substitution. V2 region swapping between B4e8-sensitive and- resistant subtype C strains revealed a role for V2 in limiting B4e8 access, but this was less significant than the absence of Arg315. Our findings, while illustrating the importance of Arg315 for B4e8, suggest that some subtype C strains may be vulnerable to B4e8 derivatives capable of binding stronger to Gln315-containing sequences.

Impact of maraviroc-resistant and low-CCR5-adapted mutations induced by in vitro passage on sensitivity to anti-envelope neutralizing antibodies

The aim of this study was to generate maraviroc (MVC)-resistant viruses in vitro using a human immunodeficiency virus type 1 subtype B clinical isolate (HIV-1KP-5) to understand the mechanism(s) of resistance to MVC. To select HIV-1 variants resistant to MVC in vitro, we exposed high-chemokine (C-C motif) receptor 5 (CCR5)-expressing PM1/CCR5 cells to HIV-1KP-5 followed by serial passage in the presence of MVC. We also passaged HIV-1KP-5 in PM1 cells, which were low CCR5 expressing to determine low-CCR5-adapted substitutions and compared the Env sequences of the MVC-selected variants. Following 48 passages with MVC (10 µM), HIV-1KP-5 acquired a resistant phenotype [maximal per cent inhibition (MPI) 24%], whilst the low-CCR5-adapted variant had low sensitivity to MVC (IC50 ~200 nM), but not reduction of the MPI. The common substitutions observed in both the MVC-selected and low-CCR5-adapted variants were selected from the quasi-species, in V1, V3 and V5. After 14 passages, the MVC-selected variants harboured substitutions around the CCR5 N-terminal-binding site and V3 (V200I, T297I, K305R and M434I). The low-CCR5-adapted infectious clone became sensitive to anti-CD4bs and CD4i mAbs, but not to anti-V3 mAb and autologous plasma IgGs. Conversely, the MVC-selected clone became highly sensitive to the anti-envelope (Env) mAbs tested and the autologous plasma IgGs. These findings suggest that the four MVC-resistant mutations required for entry using MVC-bound CCR5 result in a conformational change of Env that is associated with a phenotype sensitive to anti-Env neutralizing antibodies.

Towards an HIV cure: science and debate from the International AIDS Society 2013 symposium

The International AIDS Society convened the multi-stakeholder “Towards an HIV Cure” symposium in Kuala Lumpur, Malaysia in 2013 to address the significant research challenges posed by the search for a cure for HIV infection. Current antiretroviral regimens select for a small reservoir of cells that harbour latent HIV provirus, produce few or no HIV virions, and resist detection or clearance by host immunity. The symposium examined basic molecular science and animal model data, and emerging and ongoing clinical trial results to prioritise strategies and determine the viral and immune responses that could lead to HIV remission without ART. Here we review the presentations that scrutinized the molecular mechanisms controlling virus expression from proviral DNA, and the intrinsic cellular restriction and immune mechanisms preventing viral production. Insights from the basic science have translated into new therapeutic strategies seeking HIV remission without ongoing therapy, and much interest was focused on these ongoing trials. We also summarise the emerging ethical issues and patient expectations as concepts move into the clinic.

Generation of a replication-competent simian-human immunodeficiency virus, the neutralization sensitivity of which can be enhanced in the presence of a small-molecule CD4 mimic

Simian-human immunodeficiency virus (SHIV) carrying the envelope from the clade B clinical human immunodeficiency virus type 1 (HIV-1) isolate MNA, designated SHIV MNA, was generated through intracellular homologous recombination. SHIV MNA inherited biological properties from the parental HIV-1, including CCR5 co-receptor preference, resistance to neutralization by the anti-V3 loop mAb KD-247 and loss of resistance in the presence of the CD4-mimic small-molecule YYA-021. SHIV MNA showed productive replication in rhesus macaque PBMCs. Experimental infection of a rhesus macaque with SHIV MNA caused a transient but high titre of plasma viral RNA and a moderate antibody response. Immunoglobulin in the plasma at 24 weeks post-infection was capable of neutralizing SHIV MNA in the presence but not in the absence of YYA-021. SHIV MNA could serve a model for development of novel therapeutic interventions based on CD4-mimic-mediated conversion of envelope protein susceptible to antibody neutralization.

Clinical development of monoclonal antibody-based drugs in HIV and HCV diseases

Today there are many licensed antiviral drugs, but the emergence of drug resistant strains sometimes invalidates the effects of the current therapies used in the treatment of infectious diseases. Compared to conventional antiviral drugs, monoclonal antibodies (mAbs) used as pharmacological molecules have particular physical characteristics and modes of action, and, therefore, they should be considered as a distinct therapeutic class. Despite being historically validated, antibodies may represent a novel tool for combatting infectious diseases. The current high cost of mAbs' production, storage and administration (by injection only) and the consequent obstacles to development are outweighed by mAbs' clinical advantages. These are related to a low toxicity combined with high specificity and versatility, which allows a specific antibody to mediate various biological effects, ranging from the virus neutralization mechanisms to the modulation of immune responses.This review briefly summarizes the recent technological advances in the field of immunoglobulin research, and the current status of mAb-based drugs in clinical trials for HIV and HCV diseases. For each clinical trial the available data are reported and the emerging conceptual problems of the employed mAbs are highlighted.This overview helps to give a clear picture of the efficacy and challenges of the mAbs in the field of these two infectious diseases which have such a global impact.

Preparation of biologically active single-chain variable antibody fragments that target the HIV-1 gp120 V3 loop

KD-247 is a humanized monoclonal antibody that targets the third hypervariable (V3) loop of gp120. It can efficiently neutralize a broad panel of clade B, but not non-clade B, HIV-1 isolates. To overcome this limitation, we are seeking to prepare genetically-engineered single-chain variable fragments (scFvs) of KD-247 that will have broader neutralizing activity against both clade B and non-clade B HIV-1 isolates. Initial attempts of optimizing the expression of KD-247 scFv have resulted in the formation of insoluble protein. Therefore, we have established purification protocols to recover, purify, and refold the KD-247 scFv from inclusion bodies. The protocol involved step-wise refolding of denatured scFv by dilution, dialysis, and on-column nickel-affinity purification. Monomeric scFv was further purified by size-exclusion chromatography. Using far UV circular dichroism (CD) spectroscopy we confirmed the expected beta-sheet profile of the refolded KD-247 scFv. Importantly, the refolded KD-247 scFv showed neutralizing activity against replication-competent HIV-1 BaL and JR-FL Env pseudotyped HIV-1, at potency comparable to that of the native full-size KD-247 antibody. Ongoing studies focus on the application of this system in generating KD-247 scFv variants with the ability to neutralize clade B and non-clade B HIV-1 isolates.

Candidate antibody-based therapeutics against HIV-1

Antibody-based therapeutics have been successfully used for the treatment of various diseases and as research tools. Several well characterized, broadly neutralizing monoclonal antibodies (bnmAbs) targeting HIV-1 envelope glycoproteins or related host cell surface proteins show sterilizing protection of animals, but they are not effective when used for therapy of an established infection in humans. Recently, a number of novel bnmAbs, engineered antibody domains (eAds), and multifunctional fusion proteins have been reported which exhibit exceptionally potent and broad neutralizing activity against a wide range of HIV-1 isolates from diverse genetic subtypes. eAds could be more effective in vivo than conventional full-size antibodies generated by the human immune system. Because of their small size (12∼15 kD), they can better access sterically restricted epitopes and penetrate densely packed tissue where HIV-1 replicates than the larger full-size antibodies. HIV-1 possesses a number of mechanisms to escape neutralization by full-size antibodies but could be less likely to develop resistance to eAds. Here, we review the in vitro and in vivo antiviral efficacies of existing HIV-1 bnmAbs, summarize the development of eAds and multispecific fusion proteins as novel types of HIV-1 inhibitors, and discuss possible strategies to generate more potent antibody-based candidate therapeutics against HIV-1, including some that could be used to eradicate the virus.

Dynamic appearance of antigenic epitopes effective for viral neutralization during membrane fusion initiated by interactions between HIV-1 envelope proteins and CD4/CXCR4

HIV-1 entry into cells is mediated by interactions between the envelope (Env) gp120 and gp41 proteins with CD4 and chemokine receptors via an intermediate called the viral fusion complex (vFC). Here, mAbs were used to find the dynamic changes in expression of antigenic epitopes during vFC formation. A CD4-specific mAb (R275) and anti-vFC mAbs, designated F12-1, F13-6 and F18-4 that recognize the epitopes only appeared by the co-culture of env-transfected 293FT and CD4-transfected 293 cells, were developed by immunizing ganp-gene transgenic mice with an vFC-like structure formed by the same co-culture. The epitopes recognized by the mAbs appeared at different time points during vFC formation: F18-4 appeared first, followed by F13-6, and finally F12-1. The anti-vFC mAbs had little effect on vFC formation or virus neutralization; however, interestingly F12-1 and F18-4 increased exposure of the OKT4-epitope on the domain 3 in the extracellular region of CD4. R275, which recognizes the epitope closely associated with the OKT4-determinant on the domain 3, showed the marked inhibition of vFC formation and viral neutralization activity. The Ab binding to the epitopes appeared during viral membrane fusion might reinforce the appearance of the target epitopes for effective neutralization activity.

Regulation of the susceptibility of HIV-1 to a neutralizing antibody KD-247 by nonepitope mutations distant from its epitope

OBJECTIVE

A humanized neutralizing antibody, KD-247, targets the V3 loop of HIV-1 Env. HIV-1 bearing the GPGR sequence at the V3 loop is potentially susceptible to KD-247. However, not all GPGR-positive HIV-1 isolates are neutralized by KD-247. We examined the potential mechanism by which the susceptibility of HIV-1 to KD-247-mediated neutralization is regulated.

DESIGN

We searched for nonepitope neutralization regulatory (NNR) mutations that sensitize GPGR-bearing HIV-1AD8 to KD-247 and mapped the locations of such mutations relative to the V3 loop.

METHODS

: We generated a functional HIV-1AD8 Env library, and evaluated the viral susceptibility to KD-247 by measuring the half-inhibitory concentration (IC50) to KD-247 on TZM-bl cell assay.

RESULTS

We identified nine KD-247-sensitizing NNR mutations from 30 mutations in various regions of gp120, including the V1/V2 loop, C2, V3 loop, C4, and C5. They specifically affected KD-247-mediated neutralization, as they did not affect the b12-mediated neutralization. When combined, the KD-247-sensitizing NNR mutations additively sensitized the virus to KD-247 by up to 10 000 folds. The KD-247-sensitizing NNR mutations increased KD-247 binding to the virion. Notably, the NNR mutation in C4 coincides with the CD4-binding site of gp120.

CONCLUSION

Given that most of the KD-247-sensitizing NNR mutations are remote from V3 loop, it is reasonable to hypothesize that the steady-state, local conformation of the V3 loop is regulated by the interdomain contact of gp120. Our mutational analysis complements crystallographic studies by helping provide a better understanding of the steady-state conformation and the functional geometry of Env.

Immunotherapeutic restoration in HIV-infected individuals

While the development of combined active antiretroviral therapy (cART) has dramatically improved life expectancies and quality of life in HIV-infected individuals, long-term clinical problems, such as metabolic complications, remain important constraints of life-long cART. Complete immune restoration using only cART is normally unattainable even in cases of sufficient plasma viral suppression. The need for immunologic adjuncts that complement cART remains, because while cART alone may result in the complete recovery of peripheral net CD4+ T lymphocytes, it may not affect the reservoir of HIV-infected cells. Here, we review current immunotherapies for HIV infection, with a particular emphasis on recent advances in cytokine therapies, therapeutic immunization, monoclonal antibodies, immune-modulating drugs, nanotechnology-based approaches and radioimmunotherapy.

Comparative reactivity of serum samples from Argentinean HIV-infected patients with V3 peptides from subtype B or BF recombinants

To analyze humoral cross-reactivity to V3 peptides from subtype B and BF recombinant forms, plasma samples from 50 HIV-1-infected patients were characterized by sequencing fragments of the env and pol genes. An in-house EIA was performed using peptides corresponding to the 15 central amino acids of the V3 loop of gp120 from subtypes B (MN, SF2) and F1 and a consensus peptide from Argentinean BF recombinants. No differences were found with respect to the infecting subtype, but significant differences were found among the peptides. Reactivity was higher against the MN and BF peptides in both groups infected with subtype B (n = 28) and BF (n = 22) recombinants than against subtype F1 and SF2 peptides.

Enhanced exposure of human immunodeficiency virus type 1 primary isolate neutralization epitopes through binding of CD4 mimetic compounds

N-(4-Chlorophenyl)-N'-(2,2,6,6-tetramethyl-piperidin-4-yl)-oxalamide (NBD-556) is a low-molecular-weight compound that reportedly blocks the interaction between human immunodeficiency virus type 1 (HIV-1) gp120 and its receptor CD4. We investigated whether the enhancement of binding of anti-gp120 monoclonal antibodies (MAbs) toward envelope (Env) protein with NBD-556 are similar to those of soluble CD4 (sCD4) by comparing the binding profiles of the individual MAbs to Env-expressing cell surfaces. In flow cytometric analyses, the binding profiles of anti-CD4-induced epitope (CD4i) MAbs toward NBD-556-pretreated Env-expressing cell surfaces were similar to the binding profiles toward sCD4-pretreated cell surfaces. To investigate the binding position of NBD-556 on gp120, we induced HIV-1 variants that were resistant to NBD-556 and sCD4 in vitro. At passage 21 in the presence of 50 microM NBD-556, two amino acid substitutions (S375N in C3 and A433T in C4) were identified. On the other hand, in the selection with sCD4, seven mutations (E211G, P212L, V255E, N280K, S375N, G380R, and G431E) appeared during the passages. The profiles of the mutations after the selections with NBD-556 and sCD4 were very similar in their three-dimensional positions. Moreover, combinations of NBD-556 with anti-gp120 MAbs showed highly synergistic interactions against HIV-1. We further found that after enhancing the neutralizing activity by adding NBD-556, the contemporaneous virus became highly sensitive to antibodies in the patient's plasma. These findings suggest that small compounds such as NBDs may enhance the neutralizing activities of CD4i and anti-V3 antibodies in vivo.

An optimally constrained V3 peptide is a better immunogen than its linear homolog or HIV-1 gp120

Synthetic peptides offer an attractive option for development of a V3-directed vaccine. However, immunization with flexible linear peptides may result in an immune response to multiple conformations, many of which differ from the native conformation of the corresponding region in the protein. Here we show that optimization of the location of a disulfide bond in peptides constrained to mimic the beta-hairpin conformation of the V3, yields an immunogen that elicits a 30-fold stronger HIV-1 neutralizing response in rabbits compared with the homologous linear V3 peptide. The HIV-1 neutralizing response elicited by the optimally constrained peptide is also significantly stronger than that elicited by a gp120 construct in which the V3 is exposed. Neutralization of an HIV-1 strain that shares only 72% identity with the immunizing peptide was demonstrated. The most effective immunogen was also able to neutralize primary isolates that are more resistant to neutralization such as SS1196 and 6535.

Human immunodeficiency virus type 1 evasion of a neutralizing anti-V3 antibody involves acquisition of a potential glycosylation site in V2

It has been reported that the addition of a potential N-linked glycosylation site (PNGS) to the gp120 human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein provides protection against neutralizing antibodies (NAbs) by acting as a 'glycan shield'. In this study, we induced insertion of a PNGS into the V2 region of HIV-1(BaL) with the KD-247 anti-V3 neutralizing monoclonal antibody. In the presence of KD-247 (200 microg ml(-1)) at passage five, viruses with 3 aa mutations in the C2 (T240S and I283T) and V3 (T319A) regions expanded from pre-existing variants. After six passages with KD-247 (>300 microg ml(-1)), a PNGS emerged in the V2 region in addition to C2 (T240S) and V3 mutations (R315K and F317L). A variant with a PNGS insertion in V2, but no V3 mutations was sensitive to KD-247, whereas a clone with a V2 PNGS insertion and mutations in V3 demonstrated a high level of resistance to KD-247. Replication kinetic analysis revealed that the F317L mutation in V3 played a compensatory role for fitness-loss caused by the PNGS insertion in V2. The evading HIV-1 variant did not revert back to the wild-type virus after 14 passages without KD-247. These findings demonstrate that the virus with fitness-loss mutations can replicate equally as well as the wild-type virus to acquire some key mutations in the V3 stem and the C2 region, and the compensated variants containing PNGS do not revert back to the ancestral virus even in the absence of NAb.

Postinfection passive transfer of KD-247 protects against simian/human immunodeficiency virus-induced CD4+ T-cell loss in macaque lymphoid tissue

BACKGROUND

Preadministration of high-affinity humanized anti-HIV-1 mAb KD-247 by passive transfer provides sterile protection of monkeys from heterologous chimeric simian/human immunodeficiency virus infection.

METHODS

Beginning 1 h, 1 day, or 1 week after simian/human immunodeficiency virus-C2/1 challenge (20 50% tissue culture infective dose), mature, male cynomolgus monkeys received multiple passive transfers of KD-247 (45 mg/kg) on a weekly basis for approximately 2 months. Concentrations and viral loads were measured in peripheral blood, and CD4 T-cell counts were examined in both peripheral blood and various lymphoid tissues.

RESULTS

Pharmacokinetic examination revealed similar plasma maintenance levels ranging from 200 to 500 microg/ml of KD-247 in the three groups. One of the six monkeys given KD-247 could not maintain these concentrations, and elicitation of anti-KD-247 idiotype antibody was suggested. All monkeys given KD-247 exhibited striking postinfection protection against both CD4 T-cell loss in various lymphoid tissues and atrophic changes in organs compared with control group animals treated with normal human immunoglobulin G. The KD-247-treated groups were also partially protected against plasma viral load elevation in peripheral blood samples, although the complete protection previously reported with preadministration of this mAb was not achieved.

CONCLUSION

Postinfection passive transfer of humanized mAb KD-247 with strong neutralizing capacity against challenged virus simian/human immunodeficiency virus-C2/1 protected CD4 T cells in lymphoid organs.

Recombinant Mycobacterium bovis BCG vector system expressing SIV Gag protein stably and persistently induces antigen-specific humoral immune response concomitant with IFN gamma response, even at three years after immunization

A vaccine against HIV-1 infection absolutely needs the ability to effectively elicit virus-specific immunity over a long term; nevertheless, there have been few studies indicating that the immunoinductivity of such a candidate vaccine has been researched for several years running. In a previous report, we demonstrated that recombinant BCG (rBCG) expressing the full-length gag gene of simian immunodeficiency virus (SIV) (rBCG-SIVgag) induced Gag-specific delayed-type hypersensitivity, T cell proliferation, gamma interferon (IFN gamma), and serum IgG responses in guinea pigs immunized intradermally (i.d.) with 0.1 mg for the 1-year period of study. Especially, the production of long-lasting Gag-specific serum IgG in the vaccinated animals perhaps reflects the persistent antigenic stimulation by rBCG-SIVgag. How long, we questioned, will such immune responses to Gag engendered by the rBCG-SIVgag vaccination persist without booster immunizations? To learn this, we examined Gag-specific IgG production in sera and Gag-specific IFN gamma mRNA expression in peripheral blood mononuclear cells (PBMC) in guinea pigs vaccinated with rBCG-SIVgag i.d. (0.1 mg) or orally (80 mg x 2) during a 3-year period. As a result, Gag-specific serum IgG was highly generated for 3 years at similar levels between the i.d. and the orally immunized guinea pigs (IgG2>IgG1). The enhancement of IFN gamma mRNA expression by in vitro restimulation with Gag antigen was also detected in PBMC from the two immunization groups throughout the 3-year observation period. In guinea pigs immunized i.d. with rBCG-SIVgag, a high level of Gag-specific IFN gamma response was observed at 1 year after vaccination, whereas the response has waned gradually. The current study indicates that i.d. and oral inoculations of rBCG-SIVgag elicit stable, strong, Gag-specific serum IgG production while exhibiting the different kinetics of Gag-specific IFN gamma responses between i.d. and oral vaccination routes. This suggests that the rBCG vector system expressing an appropriate size of foreign antigen gene should be suited for the induction of the antigen-specific humoral immunity concomitant with an IFN gamma response.

Analysis of the neutralization breadth of the anti-V3 antibody F425-B4e8 and re-assessment of its epitope fine specificity by scanning mutagenesis

The identification of cross-neutralizing antibodies to HIV-1 is important for designing antigens aimed at eliciting similar antibodies upon immunization. The monoclonal antibody (mAb) F425-B4e8 had been suggested previously to bind an epitope at the base of V3 and shown to neutralize two primary HIV isolates. Here, we have assessed the neutralization breadth of mAb F425-B4e8 using a 40-member panel of primary HIV-1 and determined the epitope specificity of the mAb. The antibody was able to neutralize 8 clade B viruses (n=16), 1 clade C virus (n=11), and 2 clade D viruses (n=6), thus placing it among the more broadly neutralizing anti-V3 antibodies described so far. Contrary to an initial report, results from our scanning mutagenesis of the V3 region suggest that mAb F425-B4e8 interacts primarily with the crown/tip of V3, notably Ile(309), Arg(315), and Phe(317). Despite the somewhat limited neutralization breadth of mAb F425-B4e8, the results presented here, along with analyses from other cross-neutralizing anti-V3 mAbs, may facilitate the template-based design of antigens that target V3 and permit neutralization of HIV-1 strains in which the V3 region is accessible to antibodies.

Impact of V2 mutations on escape from a potent neutralizing anti-V3 monoclonal antibody during in vitro selection of a primary human immunodeficiency virus type 1 isolate

KD-247, a humanized monoclonal antibody to an epitope of gp120-V3 tip, has potent cross-neutralizing activity against subtype B primary human immunodeficiency virus type 1 (HIV-1) isolates. To assess how KD-247 escape mutants can be generated, we induced escape variants by exposing bulked primary R5 virus, MOKW, to increasing concentrations of KD-247 in vitro. In the presence of relatively low concentrations of KD-247, viruses with two amino acid mutations (R166K/D167N) in V2 expanded, and under high KD-247 pressure, a V3 tip substitution (P313L) emerged in addition to the V2 mutations. However, a virus with a V2 175P mutation dominated during passaging in the absence of KD-247. Using domain swapping analysis, we demonstrated that the V2 mutations and the P313L mutation in V3 contribute to partial and complete resistance phenotypes against KD-247, respectively. To identify the V2 mutation responsible for the resistance to KD-247, we constructed pseudoviruses with single or double amino acid mutations in V2 and measured their sensitivity to neutralization. Interestingly, the neutralization phenotypes were switched, so that amino acid residue 175 (Pro or Leu) located in the center of V2 was exchanged, indicating that the amino acid at position 175 has a crucial role, dramatically changing the Env oligomeric state on the membrane surface and affecting the neutralization phenotype against not only anti-V3 antibody but also recombinant soluble CD4. These data suggested that HIV-1 can escape from anti-V3 antibody attack by changing the conformation of the functional envelope oligomer by acquiring mutations in the V2 region in environments with relatively low antibody concentrations.

Resistance profile of a neutralizing anti-HIV monoclonal antibody, KD-247, that shows favourable synergism with anti-CCR5 inhibitors

BACKGROUND

The high-affinity humanized monoclonal antibody (MAb) KD-247 reacts with a tip region in gp120-V3 and cross-neutralizes primary isolates with a matching neutralization sequence motif.

METHODS

We induced an HIV-1 variant that was resistant to KD-247 by exposing the JR-FL virus to increasing concentrations of KD-247 in PM1/CCR5 cells, which expressed high levels of CCR5 in vitro. We determined the amino acid sequence of the gp120-encoding region of the JR-FL escape mutant from KD-247. To confirm that this substitution was responsible for the KD-247-resistance, a single-round replication assay was performed. We further evaluated the anti-HIV-1 interactions between KD-247 and various CCR5 inhibitors in vitro.

RESULTS

At passage 8 of the culture in the presence of 1000 mug/ml KD-247, one amino acid substitution, Gly to Glu at position 314 (G314E), was identified in the V3-tip of gp120. A pseudotyped virus with the G314E mutation was highly resistant to KD-247. Unexpectedly, this mutant virus was sensitive to CCR5 inhibitors, RANTES, recombinant human soluble CD4 (rsCD4) and an anti-CCR5 MAb, but resistant to an anti-CD4 MAb, compared with the wild-type virus. We also found that combinations of KD-247 and CCR5 inhibitors were highly synergistic.

CONCLUSIONS

The present data suggest that KD-247 has certain advantages for possible passive immunotherapy. They are: high concentrations of KD-247 are needed for viral acquisition of KD-247 resistance; the escape variants are more sensitive to CCR5 inhibitors and rsCD4; and there are high levels of synergism between KD-247 and CCR5 inhibitors at all concentrations tested.

Anti-V3 humanized antibody KD-247 effectively suppresses ex vivo generation of human immunodeficiency virus type 1 and affords sterile protection of monkeys against a heterologous simian/human immunodeficiency virus infection

In an accompanying report (Y. Eda, M. Takizawa, T. Murakami, H. Maeda, K. Kimachi, H. Yonemura, S. Koyanagi, K. Shiosaki, H. Higuchi, K. Makizumi, T. Nakashima, K. Osatomi, S. Tokiyoshi, S. Matsushita, N. Yamamoto, and M. Honda, J. Virol. 80:5552-5562, 2006), we discuss our production of a high-affinity humanized monoclonal antibody, KD-247, by sequential immunization with V3 peptides derived from human immunodeficiency virus type 1 (HIV-1) clade B primary isolates. Epitope mapping revealed that KD-247 recognized the Pro-Gly-Arg V3 tip sequence conserved in HIV-1 clade B isolates. In this study, we further demonstrate that in vitro, KD-247 efficiently neutralizes CXCR4- and CCR5-tropic primary HIV-1 clade B and clade B' with matching neutralization sequence motifs but does not neutralize sequence-mismatched clade B and clade E isolates. Monkeys were provided sterile protection against heterologous simian/human immunodeficiency virus challenge by the passive transfer of a single high dose (45 mg per kg of body weight) of KD-247 and afforded partial protection by lower antibody doses (30 and 15 mg per kg). Protective neutralization endpoint titers in plasma at the time of virus challenge were 1:160 in animals passively transferred with a high dose of the antibody. The antiviral efficacy of the antibody was further confirmed by its suppression of the ex vivo generation of primary HIV-1 quasispecies in peripheral blood mononuclear cell cultures from HIV-infected individuals. Therefore, KD-247 promises to be a valuable tool not only as a passive immunization antibody for the prevention of HIV infection but also as an immunotherapy for the suppression of HIV in phenotype-matched HIV-infected individuals.