Identification of New Regions in HIV-1 gp120 Variable 2 and 3 Loops that Bind to α4β7 Integrin Receptor

Background

The gut mucosal homing integrin receptor α4β7 present on activated CD4⁺ T cells interacts with the HIV-1 gp120 second variable loop (V2). Case control analysis of the RV144 phase III vaccine trial demonstrated that plasma IgG binding antibodies specific to scaffolded proteins expressing the first and second variable regions (V1V2) of HIV envelope protein gp120 containing the α4β7 binding motif correlated inversely with risk of infection. Subsequently antibodies to the V3 region were also shown to correlate with protection. The integrin receptor α4β7 was shown to interact with the LDI/V motif on V2 loop but recent studies suggest that additional regions of V2 loop could interact with the α4β7. Thus, there may be several regions on the V2 and possibly V3 loops that may be involved in this binding. Using a cell line, that constitutively expressed α4β7 receptors but lacked CD4, we examined the contribution of V2 and V3 loops and the ability of V2 peptide-, V2 integrin-, V3-specific monoclonal antibodies (mAbs), and purified IgG from RV144 vaccinees to block the V2/V3-α4β7 interaction.

Results

We demonstrate that α4β7 on RPMI8866 cells bound specifically to its natural ligand mucosal addressin cell adhesion molecule-1 (MAdCAM-1) as well as to cyclic-V2 and cyclic-V3 peptides. This binding was inhibited by anti-α4β7-specific monoclonal antibody (mAb) ACT-1, mAbs specific to either V2 or V3 loops, and by purified primary virions or infectious molecular clones expressing envelopes from acute or chronic subtypes A, C, and CRF01_AE viruses. Plasma from HIV-1 infected Thai individuals as well as purified IgG from uninfected RV144 vaccinees inhibited (0–50%) the binding of V2 and V3 peptides to α4β7.

Conclusion

Our results indicate that in addition to the tripeptide LDI/V motif, other regions of the V2 and V3 loops of gp120 were involved in binding to α4β7 receptors and this interaction was blocked by anti-V2 peptide, anti-V2 integrin, and anti-V3 antibodies. The ability of purified IgG from some of the uninfected RV144 vaccinees to inhibit α4β7 raises the hypothesis that anti-V2 and anti-V3 antibodies may play a role in blocking the gp120-α4β7 interaction after vaccination and thus prevent HIV-1 acquisition.

Impact of HIV-1 backbone on neutralization sensitivity: neutralization profiles of heterologous envelope glycoproteins expressed in native subtype C and CRF01_AE backbone

Standardized assays to assess vaccine and antiviral drug efficacy are critical for the development of protective HIV-1 vaccines and drugs. These immune assays will be advanced by the development of standardized viral stocks, such as HIV-1 infectious molecular clones (IMC), that i) express a reporter gene, ii) are representative of globally diverse subtypes and iii) are engineered to easily exchange envelope (env) genes for expression of sequences of interest. Thus far, a subtype B IMC backbone expressing Renilla luciferase (LucR), and into which the ectodomain of heterologous env coding sequences can be expressed has been successfully developed but as execution of HIV-1 vaccine efficacy trials shifts increasingly to non-subtype B epidemics (Southern African and Southeast Asia), non-subtype B HIV-1 reagents are needed to support vaccine development. Here we describe two IMCs derived from subtypes C and CRF01_AE HIV-1 primary isolates expressing LucR (IMC.LucR) that were engineered to express heterologous gp160 Envs. 18 constructs expressing various subtypes C and CRF01_AE Envs, mostly acute, in subtype-matched and -unmatched HIV backbones were tested for functionality and neutralization sensitivity. Our results suggest a possible effect of non-env HIV-1 genes on the interaction of Env and neutralizing antibodies and highlight the need to generate a library of IMCs representative of the HIV-1 subtype spectrum to be used as standardized neutralization assay reagents for assessing HIV-1 vaccine efficacy.

Magnitude and breadth of the neutralizing antibody response in the RV144 and Vax003 HIV-1 vaccine efficacy trials

BACKGROUND

A recombinant canarypox vector expressing human immunodeficiency virus type 1 (HIV-1) Gag, Pro, and membrane-linked gp120 (vCP1521), combined with a bivalent gp120 protein boost (AIDSVAX B/E), provided modest protection against HIV-1 infection in a community-based population in Thailand (RV144 trial). No protection was observed in Thai injection drug users who received AIDSVAX B/E alone (Vax003 trial). We compared the neutralizing antibody response in these 2 trials.

METHODS

Neutralization was assessed with tier 1 and tier 2 strains of virus in TZM-bl and A3R5 cells.

RESULTS

Neutralization of several tier 1 viruses was detected in both RV144 and Vax003. Peak titers were higher in Vax003 and waned rapidly in both trials. The response in RV144 was targeted in part to V3 of gp120.vCP1521 priming plus 2 boosts with gp120 protein was superior to 2 gp120 protein inoculations alone, confirming a priming effect for vCP1521. Sporadic weak neutralization of tier 2 viruses was detected only in Vax003 and A3R5 cells.

CONCLUSION

The results suggest either that weak neutralizing antibody responses can be partially protective against HIV-1 in low-risk heterosexual populations or that the modest efficacy seen in RV144 was mediated by other immune responses, either alone or in combination with neutralizing antibodies.

Strong cellular and humoral anti-HIV Env immune responses induced by a heterologous rhabdoviral prime-boost approach

Recombinant rhabdovirus vectors expressing human immunodeficiency virus (HIV) and/or simian immunodeficiency virus (SIV) proteins have been shown to induce strong immune responses in mice and rhesus macaques. However, the finding that such responses protect rhesus macaques from AIDS-like disease but not from infection indicates that further improvements for these vectors are needed. Here, we designed a prime-boost schedule consisting of a rabies virus (RV) vaccine strain and a recombinant vesicular stomatitis virus (VSV) both expressing HIV Envelope (Env). Mice were primed and boosted with the two vaccine vehicles by different routes and in different combinations. Mucosal and systemic humoral responses were assessed using enzyme linked immunosorbent assay (ELISA) while the cellular immune response was determined by an IFN-gamma ELISPOT assay. We found that an immunization combination of RV and VSV elicited the highest titers of anti-Env antibodies and the greatest amount of Env-specific IFN-gamma secreting cells pre- and post-challenge with a recombinant vaccinia virus expressing HIV(89.6) Env. Furthermore, intramuscular immunization did not induce antigen-specific mucosal antibodies while intranasal inoculation stimulated vector-specific IgA antibodies in vaginal washings and serum. Our results show that it is feasible to elicit robust cellular and humoral anti-HIV responses using two different live attenuated Rhabdovirus vectors to sequentially prime and boost.

Specific antibody responses to vaccination with bivalent CM235/SF2 gp120: detection of homologous and heterologous neutralizing antibody to subtype E (CRF01.AE) HIV type 1

HIV-1 CRF.AE-01 (formerly subtype E) infection is highly prevalent in Southeast Asia. Despite success with public health measures, the development of an effective CRF01.AE vaccine is critical to the control of this epidemic. Sera from the open-label arms of the first clinical trial of a bivalent HIV gp120 SF2/CM235 (subtypes B and CRF.AE-01, respectively) vaccine were evaluated for the presence of gp120-specific binding (BAb) and neutralizing antibody (NAb). Twelve pre- and postvaccination sera pairs were tested for CM235 BAb; anti-gp120 CM235 BAb was found in all postvaccination samples. The 12 pre- and postvaccination (1 month after third vaccination) serum pairs were evaluated in several neutralization formats: heterologous T cell line adapted (TCLA) NP03/H9, homologous CM235/PBMC, CM235/dendritic cell, and CM235M4-C4.6/A3R5. A3R5 is a CCR5+ T cell line, and CM235M4-C4.6 is the homologous CM235 virus adapted to growth in A3R5 cells. All volunteers developed BAb, but meaningful NAb was not demonstrable against primary isolate CM235. Using the TCLA CRF01.AE virus NP03 in H9 cells, 9 of 12 persons had NAb with a geometric mean titer (GMT) of 46. The CM235M4-C4.6 virus in A3R5 cells also detected NAb in 9 of 12 persons, with a GMT of 41. CM235M4-C4.6/A3R5 detected NAb in two persons with negligible NAb to NP03/H9 and vice versa. Whether the NAb detected by the CM235M4-C4.6/A3R5 system is qualitatively different from those in more traditional NP03/H9 assays will require further study.