Complement-dependent virolysis of HIV-1 with monoclonal antibody NM-01

Survivors Remorse: antibody-mediated protection against HIV-1

It is clear that antibodies can play a pivotal role in preventing the transmission of HIV-1 and large efforts to identify an effective antibody-based vaccine to quell the epidemic. Shortly after HIV-1 was discovered as the cause of AIDS, the search for epitopes recognized by neutralizing antibodies became the driving strategy for an antibody-based vaccine. Neutralization escape variants were discovered shortly thereafter, and, after almost three decades of investigation, it is now known that autologous neutralizing antibody responses and their selection of neutralization resistant HIV-1 variants can lead to broadly neutralizing antibodies in some infected individuals. This observation drives an intensive effort to identify a vaccine to elicit broadly neutralizing antibodies. In contrast, there has been less systematic study of antibody specificities that must rely mainly or exclusively on other protective mechanisms, although non-human primate (NHP) studies as well as the RV144 vaccine trial indicate that non-neutralizing antibodies can contribute to protection. Here we propose a novel strategy to identify new epitope targets recognized by these antibodies for which viral escape is unlikely or impossible.

Therapeutic antibodies as a treatment option for dengue fever

Dengue fever is the most prevalent mosquito-borne viral disease globally with about 100 million cases of acute dengue annually. Severe dengue infection can result in a life-threatening illness. In the absence of either a licensed vaccine or antiviral drug against dengue, therapeutic antibodies that neutralize dengue virus (DENV) may serve as an effective medical countermeasure against severe dengue. However, therapeutic antibodies would need to effectively neutralize all four DENV serotypes. It must not induce antibody-dependent enhancement of DENV infection in monocytes/macrophages through Fc gamma receptor (FcγR)-mediated phagocytosis, which is hypothesized to increase the risk of severe dengue. Here, we review the strategies and technologies that can be adopted to develop antibodies for therapeutic applications. We also discuss the mechanism of antibody neutralization in the cells targeted by DENV that express Fc gamma receptor. These studies have provided significant insight toward the use of therapeutic antibodies as a potentially promising bulwark against dengue.

Increased functional stability and homogeneity of viral envelope spikes through directed evolution

The functional HIV-1 envelope glycoprotein (Env) trimer, the target of anti-HIV-1 neutralizing antibodies (Abs), is innately labile and coexists with non-native forms of Env. This lability and heterogeneity in Env has been associated with its tendency to elicit non-neutralizing Abs. Here, we use directed evolution to overcome instability and heterogeneity of a primary Env spike. HIV-1 virions were subjected to iterative cycles of destabilization followed by replication to select for Envs with enhanced stability. Two separate pools of stable Env variants with distinct sequence changes were selected using this method. Clones isolated from these viral pools could withstand heat, denaturants and other destabilizing conditions. Seven mutations in Env were associated with increased trimer stability, primarily in the heptad repeat regions of gp41, but also in V1 of gp120. Combining the seven mutations generated a variant Env with superior homogeneity and stability. This variant spike moreover showed resistance to proteolysis and to dissociation by detergent. Heterogeneity within the functional population of hyper-stable Envs was also reduced, as evidenced by a relative decrease in a proportion of virus that is resistant to the neutralizing Ab, PG9. The latter result may reflect a change in glycans on the stabilized Envs. The stabilizing mutations also increased the proportion of secreted gp140 existing in a trimeric conformation. Finally, several Env-stabilizing substitutions could stabilize Env spikes from HIV-1 clades A, B and C. Spike stabilizing mutations may be useful in the development of Env immunogens that stably retain native, trimeric structure.

A vaccine is needed to prevent HIV/AIDS but eliciting potent neutralizing antibodies (Abs) against primary isolates has been a major stumbling block. The target of HIV-1 neutralizing antibodies is the native envelope glycoprotein (Env) trimer that is displayed on the surface of the virus. Virion associated Env typically elicits antibodies that cannot neutralize primary viruses. However, because native Env trimers can dissociate and coexist with non-fusogenic forms of Env interpreting these results are difficult. Here, we used directed evolution to select for virions that display native Env with increased stability and homogeneity. HIV-1 virions were subjected to increasingly harsh treatments that destabilize Env trimers, and the variants that survived each treatment were expanded. We could identify seven different mutations in Env that increased its stability of function in the face of multiple destabilizing treatments. When these mutations were combined, the resulting mutant Env trimers were far more stable than the original Env protein. Incorporating trimer-stabilizing mutations into Env-based immunogens should facilitate vaccine research by mitigating the confounding effects of non-native byproducts of Env decay. A similar approach may be used on other pathogens with potential vaccine targets that are difficult to isolate and maintain in a native form.

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.

Isolation and characterization of novel human monoclonal antibodies possessing neutralizing ability against rabies virus

Rabies is a fatal viral encephalitis which is transmitted by exposure to the bite of rabid animals. Human and equine rabies immunoglobulins are indispensable pharmacological agents for severe bite exposure, as is vaccine. However, several disadvantages, including limited supply, adverse reactions, and high cost, hamper their wide application in developing countries. In the present study, two novel huMabs which neutralize rabies virus were established from vaccinated hyperimmune volunteers using the Epstein-Barr virus transformation method. One MAb (No. 254), which was subclass IgG3, effectively neutralized fixed rabies viruses of CVS, ERA, HEP-Flury, and Nishigahara strains and recognized a well-conserved epitope located in antigenic site II of the rabies virus glycoprotein. No. 254 possessed 68 ng/ml of FRNT₅₀ activity against CVS, 3.7 × 10⁻⁷ M of the Kd value, and the enhancing effect of complement-dependent virolysis. In addition, No. 254 showed effective neutralization potency in vivo in the mouse challenge test. The other MAb, 4D4, was subclass IgM and showed neutralizing activity against CVS and Nishigahara strains. 4D4 recognized a novel antigenic site which is associated with the neurovirulence of rabies, a glycoprotein located between antigenic site I and VI. Both human MAbs against rabies are expected to be utilized as a tool for future post-exposure prophylaxis.

Monoclonal antibody hNM01 in HIV-infected patients: a phase I study

BACKGROUND

hNM01 is a humanized monoclonal antibody that binds to the V(3) region of the HIV-1 envelope protein gp120. This binding leads to the activation of complement and the disruption of the viral envelope.

OBJECTIVES AND STUDY DESIGN

The aim of this study was to investigate the clinical responses of the individuals when treated with the humanized antibody NMO1. In this phase I study, four HIV-1 infected patients with CD4 counts between 50 and 500 cells/mul received a total of four doses of hNM01 in an intrapatient dose escalation fashion: day 1-0.2 mg/kg, day 15-1 mg/kg, day 29-5 mg/kg, and day 43-5mg/kg. Patients were required to have virus that reacted to hNM01 by a virion capture assay and to have a viral load > or =15,000 copies/mL.

RESULTS AND CONCLUSION

The antibody was well-tolerated; no significant adverse events were observed even at the highest dose tolerated. None of the patient developed either human anti-hNM01 (anti-idiotype) or human anti-rat antibodies. The mean elimination half-life was 153 h (6.4 days). During hNMO1 therapy effects were observed on CD4 cell counts and plasma viral loads and further dose finding trials are necessary to better determine the therapeutic activity of hNM01 in HIV-infected individuals.

Virolysis and in vitro neutralization of HIV-1 by humanized monoclonal antibody hNM-01

Antibody humanization by transplanting the complimentarity determining region (CDR) to a human framework aims to reduce the response of the human immune system against a foreign molecule during passive immunization. We transferred the CDR from the murine monoclonal antibody (MAb) NM-01 to a human IgG frame. The humanized NM-01 (hNM-01) recognizes the same epitope on Human Immunodeficiency Virus type 1 (HIV-1) envelope as its murine progenitor, but with greater efficiency, and shows enhanced neutralization of HIV-1. We have shown that this increase in reactivity may be attributed to residue 4 of the humanized kappa chain, where the presence of a methionine residue rather than the murine leucine appears to promote a more advantageous conformation of the antigen-binding site, perhaps via packing interactions with the V(kappa) CDR1. The capacity of humanized NM-01 to neutralize direct clinical isolates was also examined with the expectation that hNM-01 will prove suitable for development as a therapeutic agent. This reshaped antibody reacted with several clinical isolates of HIV-1 tested. Moreover, we proved the ability of this antibody of its activation of complement by flow cytometry and electron microscopy analysis. Although hNM-01 alone was capable of neutralizing HIV-1, the presence of complement enhanced neutralization. The enhancement of complement activation was also observed in hNM-01 than murine progenitor. This finding supports a potential role for antibody-dependent complement-mediated virolysis and more effective neutralization in HIV-1 therapy.

Complement-Mediated Anti-HIV-1 Effect Induced by Human IgM Monoclonal Antibody Against Ganglioside GM2

HIV-infected cells aberrantly express a high level of antigenic glycosidic structures such as GM2 and Gg4. Some normal sera containing natural IgM Abs to GM2 and/or Gg4 cause C-mediated cytolysis of HIV-infected cells. In the present study we demonstrated that a human IgM anti-GM2 mAb (L55 Ab) can induce cytolysis of HIV-infected cells. Increased GM2 expression by HIV-1 infection of a human T cell line (MOLT4), a human monocyte cell line (U937), and human lymphoblastoid cells was confirmed by immunofluorescence staining with L55 Ab. These infected cells were readily lysed by L55 Ab in the presence of fresh human serum as a C source that alone did not cause cytolysis. L55 Ab also had the ability to destroy HIV-1 particles via C-mediated lysis. By adding L55 Ab together with human C to mixed culture of HIV-infected cells and naive cells, HIV-1 replication was significantly suppressed, and this effect was synergistic when L55 Ab was combined with a reverse transcriptase inhibitor and a proteinase inhibitor. Therefore, a human IgM anti-GM2 mAb may be effective in treating HIV-infected patients, especially when used together with chemotherapeutic agents.

Mutations of the HIV type 1 V3 loop under selection pressure with neutralizing monoclonal antibody NM-01

Variants of human immunodeficiency virus type 1 (HIV-1) were selected for resistance to the neutralizing monoclonal antibody (MAb) NM-01. MAb NM-01 recognizes the center of the third hypervariable domain (V3 loop) of the envelope gp120, and neutralizes diverse HIV-1 strains. In the continuous presence of MAb NM-01, transmission and propagation of molecularly cloned HIV-1 were performed in vitro to isolate escape variants. The polymerase chain reaction-single-strand conformation polymorphism and sequence analyses of these variants indicated that the antigenic change against MAb NM-01 is due to a single base substitution resulting in one amino acid interchange within the recognition site of MAb NM-01 in the V3 loop. Mutational analyses also demonstrated a nonrandom event of variability and the existence of mutational hot spots in the V3 loop. The bias of variability could be interpreted by the specificity of error-prone replication by HIV-1 reverse transcriptase. Furthermore, the results suggest that distribution of mutability might correlate closely with the stability of the secondary structure of RNA encoding the V3 loop region.

Quantification of the CD55 and CD59, membrane inhibitors of complement on HIV-1 particles as a function of complement-mediated virolysis

Previous studies have demonstrated that the murine monoclonal antibody (MoAb) NM-01 activates the human complement classical pathway resulting in lysis of human immunodeficiency virus (HIV). The present study was performed to determine the availability of the V3-loop of gp120 relative to the complement regulatory proteins, CD55 (DAF) and CD59 (HRF20) molecules on HIV. The results demonstrate that CD55 and CD59 exist on HIV virions, along with gp120 molecules. These findings suggest that activation of human complement on free viral particles is induced by MoAb NM-01 and that this occurs regardless of the presence of CD55 and CD59 molecules. The destruction of viral particles was demonstrated by a decrease in infectivity. The involvement of human complement in this process was confirmed with an immunoelectron microscopy technique by the presence of a human C9 to prove membrane attack complex (MAC). The results indicate that NM-01 can induce complement activation because of the ratios of CD55 and CD59 to gp120 molecules on HIV virions. The availability of the gp120 V3 domain on the virion is sufficient for binding of NM-01 and thereby the formation of MAC that results in virolysis.