Two amino acid substitutions within the first external loop of CCR5 induce human immunodeficiency virus-blocking antibodies in mice and chickens

The Role of Natural Antibodies to CC Chemokine Receptor 5 in HIV Infection

The CC chemokine receptor 5 (CCR5) is responsible for immune and inflammatory responses by mediation of chemotactic activity in leukocytes, although it is expressed on different cell types. It has been shown to act as co-receptor for the human and simian immunodeficiency viruses (HIV-1, HIV-2, and SIV). Natural reactive antibodies (Abs) recognizing first loop (ECL1) of CCR5 have been detected in several pools of immunoglobulins from healthy donors and from several cohorts of either HIV-exposed but uninfected subjects (ESN) or HIV-infected individuals who control disease progression (LTNP) as well. The reason of development of anti-CCR5 Abs in the absence of autoimmune disease is still unknown; however, the presence of these Abs specific for CCR5 or for other immune receptors and mediators probably is related to homeostasis maintenance. The majority of anti-CCR5 Abs is directed to HIV binding site (N-terminus and ECL2) of the receptor. Conversely, it is well known that ECL1 of CCR5 does not bind HIV; thus, the anti-CCR5 Abs directed to ECL1 elicit a long-lasting internalization of CCR5 but not interfere with HIV binding directly; these Abs block HIV infection in either epithelial cells or CD4+ T lymphocytes and the mechanism differs from those ones described for all other CCR5-specific ligands. The Ab-mediated CCR5 internalization allows the formation of a stable signalosome by interaction of CCR5, β-arrestin2 and ERK1 proteins. The signalosome degradation and the subsequent de novo proteins synthesis determine the CCR5 reappearance on the cell membrane with a very long-lasting kinetics (8 days). The use of monoclonal Abs to CCR5 with particular characteristics and mode of action may represent a novel mode to fight viral infection in either vaccinal or therapeutic strategies.

Induction of Antihuman C-C Chemokine Receptor Type 5 Antibodies by a Bovine Herpesvirus Type-4 Based Vector

Bovine herpesvirus 4 (BoHV-4) is a promising vector for the delivery and intracellular expression of recombinant antigens and can thus be considered as a new prototype vaccine formulation system. An interesting, and actively pursued, antigen in the context of human immunodeficiency virus (HIV) infection prophylaxis (and therapy) is the C-C chemokine receptor type 5 (CCR5) co-receptor, whose blockage by specific antibodies has been shown to inhibit both viral entry and cell-to-cell transmission of the virus. Building on our previous work on the BoHV-4 vector system, we have engineered and tested a replication-competent derivative of BoHV-4 (BoHV-4-CMV-hCCR5ΔTK) bearing a human CCR5 (hCCR5) expression cassette. We show here that CCR5 is indeed expressed at high levels in multiple types of BoHV-4-CMV-hCCR5ΔTK-infected cells. More importantly, two intravenous inoculations of CCR5-expressing BoHV-4 virions into rabbits led to the production of anti-CCR5 antibodies capable of reacting with the CCR5 receptor exposed on the surface of HEK293T cells through specific recognition of the amino-terminal region (aa 14-34) of the protein. Given the growing interest for anti-CCR5 immunization as an HIV control strategy and the many advantages of virus-based immunogen formulations (especially for poorly immunogenic or self-antigens), the results reported in this study provide preliminary validation of BoHV-4 as a safe viral vector suitable for CCR5 vaccination.

The Membrane-Proximal Region of C-C Chemokine Receptor Type 5 Participates in the Infection of HIV-1

The initial infection and transmission of HIV-1 requires C-C chemokine receptor type 5 (CCR5). Here, we report that the membrane-proximal region (MPR, aa 22-38) of CCR5 participates in the infection of HIV-1. First, MPR-specific antibodies elicited in mice dose-dependently inhibited the infection of CCR5-tropic HIV-1. Second, substituting MPR with the same region from other co-receptors significantly impaired HIV-1 infection, while the key residues identified by alanine scanning mutagenesis formed an exposed leucine zipper-like structure. Moreover, a peptide derived from MPR could block the infection of a number of HIV-1 strains only before the formation of gp41 six-helix bundle, coincide with the early interaction between CCR5 and the gp120 protein during HIV-1 infection. These promising results ensured the potential of this previously uncharacterized domain as a starting point for the development of antiviral drugs, blocking antibodies, and HIV vaccines.

Establishment of Mouse Monoclonal Antibody LpMab-13 Against Human Podoplanin

Podoplanin (PDPN)/Aggrus is a type-I transmembrane sialoglycoprotein, which possesses a platelet aggregation-stimulating (PLAG) domain. The O-glycosylation on Thr52 of human PDPN (hPDPN) is critical for the interaction of hPDPN with C-type lectin-like receptor-2 (CLEC-2), resulting in platelet aggregation. Many anti-hPDPN monoclonal antibodies (MAbs) against PLAG domains and non-PLAG domains have been established; however, mouse anti-PLAG2/3 MAb, the epitope of which is consistent with rat anti-PLAG2/3 MAb NZ-1, has not been established. NZ-1 inhibits the hPDPN-CLEC-2 interaction and is also useful for anti-PA tag MAb. We recently established CasMab technology to produce MAbs against membranous proteins. Herein, we produced a novel anti-hPDPN MAb, LpMab-13, which binds to PLAG2/3 domains. LpMab-13 recognized endogenous hPDPN of cancer cells, including glioblastoma, oral cancer, lung cancer, and malignant mesothelioma, and normal cells such as lymphatic endothelial cells and podocytes of kidney in Western blot, flow cytometry, and immunohistochemistry. LpMab-13 recognized glycan-deficient hPDPN in flow cytometry, indicating that the interaction between LpMab-13 and hPDPN is independent of its glycosylation. The minimum epitope of LpMab-13 was identified as Ala42-Asp49 of hPDPN using Western blot and flow cytometry. The combination of different epitope-possessing MAbs could be advantageous for the hPDPN-targeting diagnosis and therapy.

Class B β-arrestin2-dependent CCR5 signalosome retention with natural antibodies to CCR5

CCR5 stimulation with natural ligands, such as RANTES, classically induces short-term internalization with transient activation of β-arrestins and rapidly recycling on the cell surface. Here we discovered that, in T cells, natural CCR5 antibodies induce a CCR5-negative phenotype with the involvement of β-arrestin2, which leads to the formation of a stable CCR5 signalosome with both β-arrestin2 and ERK1. The activation of β-arrestin2 is necessary to CCR5 signaling for the signalosome formation and stabilization. When all stimuli were washed out, β-arrestin1 silencing favors the activity of β-arrestin2 for the CCR5 signalosome retention. Interestingly, CCR5 turn from Class A trafficking pattern, normally used for its internalization with natural modulating molecules (i.e. RANTES), into a long lasting Class B type specifically induced by stimulation with natural anti-CCR5 antibodies. This new CCR5 pathway is relevant not only to study in depth the molecular basis of all pathologies where CCR5 is involved but also to generate new antidody-based therapeutics.

High-efficiency antibody discovery achieved with multiplexed microscopy

The analysis of secreted antibody from large and diverse populations of B cells in parallel at the clonal level can reveal desirable antibodies for diagnostic or therapeutic applications. By immobilizing B cells in microdroplets with particulate reporters, decoding and isolating them in a microscopy environment, we have recovered panels of antibodies with rare attributes to therapeutically relevant targets. The ability to screen up to 100 million cells in a single experiment can be fully leveraged by accessing primary B-cell populations from evolutionarily divergent species such as chickens.

ERK1-Based Pathway as a New Selective Mechanism To Modulate CCR5 with Natural Antibodies

Natural human Abs, recognizing an epitope within the first extramembrane loop of CCR5 (the main HIV coreceptor), induce a long-lasting internalization (48 h) of the protein, whereas all known CCR5 modulating molecules show a short-term kinetics (60-90 min). Despite extensive studies on the regulation of CCR5 signaling cascades, which are the effect of concomitant CCR5 internalization by exogenous stimuli such as Abs, downstream signaling continues to be poorly understood. In this article, we report a hitherto unrecognized mechanism of CCR5 modulation mediated by G protein-dependent ERK1 activity. We further demonstrate that ERK1 is localized mainly in the cytoplasmic compartment and that it interacts directly with the CCR5 protein, thus provoking possible CCR5 degradation with a subsequent de novo synthesis, and that re-expression of CCR5 on the cell membrane required several days. In contrast, the RANTES treatment induces a recovery of the receptor on the cell membrane in short-term kinetics without the involvement of de novo protein synthesis. The said new pathway could be relevant not only to better understand the molecular basis of all pathologic conditions in which CCR5 is involved but also to generate new tools to block viral infections, such as the use of recombinant Abs.

Induction of HIV-blocking anti-CCR5 IgA in Peyers's patches without histopathological alterations

The chemokine receptor CCR5 is essential for HIV infection and is thus a potential target for vaccine development. However, because CCR5 is a host protein, generation of anti-CCR5 antibodies requires the breaking of immune tolerance and thus carries the risk of autoimmune responses. In this study, performed in mice, we compared 3 different immunogens representing surface domains of murine CCR5, 4 different adjuvants, and 13 different immunization protocols, with the goal of eliciting HIV-blocking activity without inducing autoimmune dysfunction. In all cases the CCR5 sequences were presented as fusions to the Flock House virus (FHV) capsid precursor protein. We found that systemic immunization and mucosal boosting elicited CCR5-specific antibodies and achieved consistent priming in Peyer's patches, where most cells showed a phenotype corresponding to activated B cells and secreted high levels of IgA, representing up to one-third of the total HIV-blocking activity. Histopathological analysis revealed mild to moderate chronic inflammation in some tissues but failed in reporting signs of autoimmune dysfunction associated with immunizations. Antisera against immunogens representing the N terminus and extracellular loops 1 and 2 (Nter1 and ECL1 and ECL2) of CCR5 were generated. All showed specific anti-HIV activity, which was stronger in the anti-ECL1 and -ECL2 sera than in the anti-Nter sera. ECL1 and ECL2 antisera induced nearly complete long-lasting CCR5 downregulation of the receptor, and especially, their IgG-depleted fractions prevented HIV infection in neutralization and transcytosis assays. In conclusion, the ECL1 and ECL2 domains could offer a promising path to achieve significant anti-HIV activity in vivo.

IMPORTANCE

The study was the first to adopt a systematic strategy to compare the immunogenicities of all extracellular domains of the CCR5 molecule and to set optimal conditions leading to generation of specific antibodies in the mouse model. There were several relevant findings, which could be translated into human trials. (i) Prime (systemic) and boost (mucosal) immunization is the best protocol to induce anti-self antibodies with the expected properties. (ii) Aluminum is the best adjuvant in mice and thus can be easily used in nonhuman primates (NHP) and humans. (iii) The Flock House virus (FHV) system represents a valid delivery system, as the structure is well known and is not pathogenic for humans, and it is possible to introduce constrained regions able to elicit antibodies that recognize conformational epitopes. (iv) The best CCR5 vaccine candidate should include either extracellular loop 1 or 2 (ECL1 or ECL2), but not N terminus domains.

Rational epitope design for protein targeting

We present a new multidisciplinary strategy integrating computational biology with high-throughput microarray analysis aimed to translate molecular understanding of protein-antibody recognition into the design of efficient and selective protein-based analytical and diagnostic tools. The structures of two proteins with different folds and secondary structure contents, namely, the beta-barrel FABP and the α-helical S100B, were used as the basis for the prediction and design of potential antibody-binding epitopes using the recently developed MLCE computational method. Starting from the idea that the structure, dynamics, and stability of a protein-antigen play a key role in the interaction with antibodies, MLCE integrates the analysis of the dynamical and energetic properties of proteins to identify nonoptimized, low-intensity energetic interaction-networks on the surface of the isolated antigens, which correspond to substructures that can aptly be recognized by a binding partner. The identified epitopes were next synthesized as free peptides and used to elicit specific antibodies in rabbits. Importantly, the resulting antibodies were proven to specifically and selectively recognize the original, full-length proteins in microarray-based tests. Competition experiments further demonstrated the specificity of the molecular recognition between the target immobilized proteins and the generated antibodies. Our integrated computational and microarray-based results demonstrate the possibility to rationally discover and design synthetic epitopes able to elicit antibodies specific for full-length proteins starting only from three-dimensional structural information on the target. We discuss implications for diagnosis and vaccine development purposes.

Study on CCR5 analogs and affinity peptides

The G protein-coupled receptor of human chemokine receptor 5 (CCR5) is a key target in the human immunodeficiency virus (HIV) infection process due to its major involvement in binding to the HIV type 1 (HIV-1) envelope glycoprotein gp120 and facilitating virus entry into the cells. The identification of naturally occurring CCR5 mutations (especially CCR5 delta-32) has allowed us to address the CCR5 molecule as a promising target to prevent or resist HIV infection in vivo. To obtain high-affinity peptides that can be used to block CCR5, CCR5 analogs with high conformational similarity are required. In this study, two recombinant proteins named CCR5 N-Linker-E2 and CCR5 mN-E1-E2 containing the fragments of the CCR5 N-terminal, the first extracellular loop or the second extracellular loop are cloned from a full-length human CCR5 cDNA. The recombinant human CCR5 analogs with self-cleavage activity of the intein Mxe or Ssp in the vector pTwinI were then produced with a high-yield expression and purification system in Escherichia coli. Experiments of extracellular epitope-activity identification (such as immunoprecipitation and indirective/competitive enzyme-linked immunosorbent assay) confirmed the close similarity between the epitope activity of the CCR5 analogs and that of the natural CCR5, suggesting the applicability of the recombinant CCR5 analogs as antagonists of the chemokine ligands. Subsequent screening of high-affinity peptides from the phage random-peptides library acquired nine polypeptides, which could be used as CCR5 peptide antagonists. The CCR5 analogs and affinity peptides elucidated in this paper provide us with a basis for further study of the mechanism of inhibition of HIV-1 infection.

Immunization with HIV-1 gp41 subunit virosomes induces mucosal antibodies protecting nonhuman primates against vaginal SHIV challenges

Human immunodeficiency virus (HIV)-1 is mainly transmitted mucosally during sexual intercourse. We therefore evaluated the protective efficacy of a vaccine active at mucosal sites. Macaca mulatta monkeys were immunized via both the intramuscular and intranasal routes with an HIV-1 vaccine made of gp41-subunit antigens grafted on virosomes, a safe delivery carrier approved in humans with self-adjuvant properties. Six months after 13 vaginal challenges with simian-HIV (SHIV)-SF162P3, four out of five vaccinated animals remained virus-negative, and the fifth was only transiently infected. None of the five animals seroconverted to p27gag-SIV. In contrast, all 6 placebo-vaccinated animals became infected and seroconverted. All protected animals showed gp41-specific vaginal IgAs with HIV-1 transcytosis-blocking properties and vaginal IgGs with neutralizing and/or antibody-dependent cellular-cytotoxicity activities. In contrast, plasma IgGs totally lacked virus-neutralizing activity. The protection observed challenges the paradigm whereby circulating antiviral antibodies are required for protection against HIV-1 infection and may serve in designing a human vaccine against HIV-1-AIDS.

Natural anti-CCR5 antibodies in HIV-infection and -exposure

Natural antibodies constitute a first-line of defence against pathogens; they may also play other roles in immune regulation and homeostasis, through their ability to bind host antigens, surface molecules and receptors. Natural anti-CCR5 antibodies can be decisive in preventing HIV infection in mucosal tissues and offer prompt and effective protection just at major sites of virus entry. Among natural anti-CCR5 antibodies, IgG and IgA to the ECL1 domain have been shown to block HIV effectively and durably without causing harm to the host. Their biological properties and their uncommon generation in subsets of HIV-infected and HIV-exposed individuals (so called ESN) will be introduced and discussed, with the aim at exploiting their potential in therapy and prevention.

CCR5: From Natural Resistance to a New Anti-HIV Strategy

The C-C chemokine receptor type 5 (CCR5) is a key player in HIV infection due to its major involvement in the infection process. Investigations into the role of the CCR5 coreceptor first focused on its binding to the virus and the molecular mechanisms leading to the entry and spread of HIV. The identification of naturally occurring CCR5 mutations has allowed scientists to address the CCR5 molecule as a promising target to prevent or limit HIV infection in vivo. Naturally occurring CCR5-specific antibodies have been found in exposed but uninfected people, and in a subset of HIV seropositive people who show long-term control of the infection. This suggests that natural autoimmunity to the CCR5 coreceptor exists and may play a role in HIV control. Such natural immunity has prompted strategies aimed at achieving anti-HIV humoral responses through CCR5 targeting, which will be described here.

Protective versus pathogenic anti-CD4 immunity: insights from the study of natural resistance to HIV infection

HIV-1 exposure causes several dramatic unbalances in the immune system homeostasis. Here, we will focus on the paradox whereby CD4 specific autoimmune responses, which are expected to contribute to the catastrophic loss of most part of the T helper lymphocyte subset in infected patients, may display the characteristics of an unconventional protective immunity in individuals naturally resistant to HIV-1 infection. Reference to differences in fine epitope mapping of these two oppositely polarized outcomes will be presented, with particular reference to partially or totally CD4-gp120 complex-specific antibodies. The fine tuning of the anti-self immune response to the HIV-1 receptor may determine whether viral exposure will result in infection or, alternatively, protective immunity.

Along this line, an efficacious anti-HIV strategy can rely on the active (i.e., through immunization) or passive targeting of cryptic epitopes of the CD4-gp120 complex, including those harboured within the CD4 molecule. Such epitopes are expected to be safe from genetic drift and thus allow for broad spectrum of efficacy. Moreover, since these epitopes are not routinely exposed in uninfected individuals, they are expected to become targets of neutralizing antibodies or other specifically designed molecules only after viral exposure, with a predictable low impact in terms of potentially harmful anti-CD4 self-reactivity.

The experimentum naturae of naturally resistant individuals indicates a strategy to design innovative strategies to neutralize HIV-1 by acting on the sharp edge between harmful and protective self-reactivity.

A Gag peptide encompassing B- and T-cell epitopes of the caprine arthritis encephalitis virus functions as modular carrier peptide

Short synthetic peptides are important tools in biomedical research permitting to generate hapten specific polyclonal sera for analytical purposes or functional studies. In this paper we provide proof of principle that a peptide located in a highly conserved portion of the Gag protein of the caprine arthritis encephalitis virus and carrying an immunodominant T helper cell epitope functions as an efficient carrier peptide, mediating a strong antibody response to a peptidic hapten encompassing a well-characterized B cell epitope of Env. The carrier and hapten peptides were collinearly synthesized permutating their molecular arrangement. While the antibody response to the hapten was similar for both constructs, the antibody response to a B cell epitope overlapping the T helper cell epitope of the Gag carrier peptide was considerably different. This permits a modular use of the carrier peptide to generate antibody directed exclusively to the hapten peptide or a strong humoral response to both carrier- and hapten-peptide. Finally, we have mapped the epitopes involved in this polarized antibody response and discussed the potential immunological implications.