Evaluation of the anti-HIV activity of natalizumab, an antibody against integrin alpha4

Mucosal integrin α4β7 blockade fails to reduce the seeding and size of viral reservoirs in SIV-infected rhesus macaques

Cellular viral reservoirs are rapidly established in tissues upon HIV‐1/SIV infection, which persist throughout viral infection, even under long‐term antiretroviral therapy (ART). Specific integrins are involved in the homing of cells to gut‐associated lymphoid tissues (GALT) and inflamed tissues, which may promote the seeding and dissemination of HIV‐1/SIV to these tissue sites. In this study, we investigated the efficacy of prophylactic integrin blockade (α4β7 antibody or α4β7/α4β1 dual antagonist TR‐14035) on viral infection, as well as dissemination and seeding of viral reservoirs in systemic and lymphoid compartments post‐SIV inoculation. The results showed that blockade of α4β7/α4β1 did not decrease viral infection, replication, or reduce viral reservoir size in tissues of rhesus macaques after SIV infection, as indicated by equivalent levels of plasma viremia and cell‐associated SIV RNA/DNA to controls. Surprisingly, TR‐14035 administration in acute SIV infection resulted in consistently higher viremia and more rapid disease progression. These findings suggest that integrin blockade alone fails to effectively control viral infection, replication, dissemination, and reservoir establishment in HIV‐1/SIV infection. The use of integrin blockade for prevention or/and therapeutic strategies requires further investigation.

New Diagnosis of Acquired Immunodeficiency Syndrome in a Patient With Crohn's Disease

There are limited data on the natural history of Crohn's disease (CD) in the presence of human immunodeficiency virus infection and the safety of available treatments. We report a patient with CD who presented with pneumocystis pneumonia secondary to newly diagnosed acquired immunodeficiency syndrome. One month before his admission, his gastrointestinal symptoms were well controlled without treatment but gradually reappeared after antiretroviral therapy was initiated. Clinical remission was achieved with vedolizumab treatment. We review the management challenges of CD in a patient with human immunodeficiency virus and describe the unique mechanism of anti-α4β7 integrin therapy in this setting.

Extracellular Matrix Proteins Mediate HIV-1 gp120 Interactions with α4β7

Gut-homing α₄β₇^high CD4⁺ T lymphocytes have been shown to be preferentially targeted by human immunodeficiency virus type 1 (HIV-1) and are implicated in HIV-1 pathogenesis. Previous studies demonstrated that HIV-1 envelope protein gp120 binds and signals through α₄β₇ and that this likely contributes to the infection of α₄β₇^high T cells and promotes cell-to-cell virus transmission. Structures within the second variable loop (V2) of gp120, including the tripeptide motif LDV/I, are thought to mediate gp120-α₄β₇ binding. However, lack of α₄β₇ binding has been reported in gp120 proteins containing LDV/I, and the precise determinants of gp120-α₄β₇ binding are not fully defined. In this work, we report the novel finding that fibronectins mediate indirect gp120-α₄β₇ interactions. We show that Chinese hamster ovary (CHO) cells used to express recombinant gp120 produced fibronectins and other extracellular matrix proteins that copurified with gp120. CHO cell fibronectins were able to mediate the binding of a diverse panel of gp120 proteins to α₄β₇ in an in vitro cell binding assay. The V2 loop was not required for fibronectin-mediated binding of gp120 to α₄β₇, nor did V2-specific antibodies block this interaction. Removal of fibronectin through anion-exchange chromatography abrogated V2-independent gp120-α₄β₇ binding. Additionally, we showed a recombinant human fibronectin fragment mediated gp120-α₄β₇ interactions similarly to CHO cell fibronectin. These findings provide an explanation for the apparently contradictory observations regarding the gp120-α₄β₇ interaction and offer new insights into the potential role of fibronectin and other extracellular matrix proteins in HIV-1 biology.IMPORTANCE Immune tissues within the gut are severely damaged by HIV-1, and this plays an important role in the development of AIDS. Integrin α₄β₇ plays a major role in the trafficking of lymphocytes, including CD4⁺ T cells, into gut lymphoid tissues. Previous reports indicate that some HIV-1 gp120 envelope proteins bind to and signal through α₄β₇, which may help explain the preferential infection of gut CD4⁺ T cells. In this study, we demonstrate that extracellular matrix proteins can mediate interactions between gp120 and α₄β₇ This suggests that the extracellular matrix may be an important mediator of HIV-1 interaction with α₄β₇-expressing cells. These findings provide new insight into the nature of HIV-1-α₄β₇ interactions and how these interactions may represent targets for therapeutic intervention.

Neutralizing and Targeting Properties of a New Set of α4β7-Specific Antibodies Are Influenced by Their Isotype

The homing of lymphocytes to the mucosa is mainly controlled by α4β7 integrin, and it is amplified during gut chronic inflammation, as occurs with HIV and/or inflammatory bowel diseases. We designed and applied an improved immunization strategy based on an innovative selection process to isolate new α4β7 lymphocyte-specific monoclonal antibodies that are able to prevent their migration into inflamed gut tissues and/or to counteract HIV infection in vitro. First, 5 monoclonal antibodies (1 IgA, 1 IgM, and 4 IgGs) were selected based on their capacity to recognize α4 or β7 homodimers and α4β7 heterodimers in transfected human cells. Their ability to block gp120/α4β7 or MAdCAM-1/α4β7 interactions was then measured in vitro with human T and B lymphocytes. In vitro, the anti-α4β7 IgA isotype was found to have the highest affinity for the α4β7 heterodimer, and it significantly reduced HIV replication in retinoic acid-treated α4β7 CD4 human T cells. This α4β7-specific IgA also displayed a high avidity for human and mouse α4β7 lymphocytes in both mouse and human inflammatory colitis tissues. These new antibodies, and in particular those with mucosa-targeting isotypes such as IgA, could therefore be potential novel therapeutic tools for treating HIV and inflammatory bowel disease.

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.

[Targeting and role of α4β7 integrin in the pathophysiology of IBD and HIV infection]

Integrins are a large family of heterodimeric cell adhesion molecules that are key regulators in multiple biological functions. They orchestrate cell-cell and cell-extracellular matrix (ECM) adhesive interactions from embryonic development to mature tissue function, and are thus involved in cell migration, proliferation, differentiation, and survival. As such, they are also involved in human diseases, such as thrombotic diseases, inflammation, cancer, fibrosis and infectious diseases. Integrins are exciting pharmacological targets because they are exposed on the cell surface. Indeed, several compounds have been developed that block integrins function, and five have been approved as therapeutic drugs for use in clinic. This review will detail the role of α4β7, an integrin of particular relevance for mucosal diseases such as IBD (inflammatory bowel disease) and also, as reported more recently, HIV infection.

Integrin α4β7 Expression Increases HIV Susceptibility in Activated Cervical CD4+ T Cells by an HIV Attachment-Independent Mechanism

BACKGROUND

CD4 T cells are crucial for the establishment and dissemination of HIV in mucosal tissues during acute infection. Studies indicate that integrin α4β7 CD4 T cells are preferentially infected by HIV in vitro and during acute SIV infection. The integrin α4β7 is thought to promote HIV capture by target cells; however, the role of integrin α4β7 in HIV transmission remains controversial. In this study, we characterized immune phenotypes of human cervical T cells and examined HIV preference in integrin α4β7 CD4 T cells. In vitro all-trans retinoic acid-differentiated peripheral CD4 T cells (atRA-differentiated cells) were included as a comparison.

RESULTS

In both peripheral and cervical cells, the majority of HIV p24 cells were activated CD4 T cells expressing integrin α4β7. Among infected atRA-differentiated cells, the frequency of CCR5 expression was higher in HIV p24 cells than in HIV p24 cells; no such difference was observed in cervical cells. Neither the cyclic hexapeptide CWLDVC nor a monoclonal antibody against integrin α4β7 blocked HIV attachment or gp120 binding to target cells regardless of the presence of CD4, indicating that integrin α4β7 did not facilitate HIV capture by target cells.

CONCLUSIONS

Integrin α4β7 expression increases HIV susceptibility, but the mechanism is not through promoting HIV binding to target cells.

Review article: the intersection of mucosal pathophysiology in HIV and inflammatory bowel disease, and its implications for therapy

BACKGROUND

The immunopathology of inflammatory bowel diseases (IBD) and HIV in the gastrointestinal (GI) tract can be viewed as ends of a spectrum with IBD being associated with 'immune excess' and HIV with 'immune paucity' within the GI tract.

AIM

To review the pathophysiology of IBD and HIV as they intersect in the gut immune system.

METHODS

A search was conducted in PubMed using defined keywords 'IBD, inflammatory bowel disease, Crohn's disease, ulcerative colitis, HIV, innate immunity, mucosal layer, macrophage, cytokine, dendritic cells, adaptive immunity, CD4, T cells, Th1, Th2, natural killer T cells (NKT)'.

RESULTS

Both the mucosal innate defence and adaptive immunity are profoundly affected by IBD and HIV. The pathophysiology of IBD and HIV with regard to mucosal barrier, macrophages, dendritic cells, NK cells, NKT cells and T-cell subsets is distinct yet closely interwoven. There is limited information on the clinical manifestations of patients who have both IBD and HIV. However, recent studies suggest that the clinical course of IBD may be attenuated by concurrent HIV infection - a premise that is reasonably supported by what is known of their pathophysiology.

CONCLUSIONS

It is apparent that through specific pathophysiological mechanisms, HIV is capable of attenuating inflammation in IBD. In the absence of experimental models, further clinical studies are necessary to better understand patients with concurrent disease and decipher the clinical and mechanistic relationship between HIV and IBD at mucosal surfaces. Such studies are critical to guide therapeutic decisions in the management of patients with IBD infected with HIV.

Partial rescue of V1V2 mutant infectivity by HIV-1 cell-cell transmission supports the domain's exceptional capacity for sequence variation

BACKGROUND

Variable loops 1 and 2 (V1V2) of the HIV-1 envelope glycoprotein gp120 perform two key functions: ensuring envelope trimer entry competence and shielding against neutralizing antibodies. While preserving entry functionality would suggest a high need for V1V2 sequence optimization and conservation, shielding efficacy is known to depend on a high flexibility of V1V2 giving rise to its substantial sequence variability. How entry competence of the trimer is maintained despite the continuous emergence of antibody escape mutations within V1V2 has not been resolved. Since HIV cell-cell transmission is considered a highly effective means of virus dissemination, we investigated whether cell-cell transmission may serve to enhance infectivity of V1V2 variants with debilitated free virus entry.

RESULTS

In a detailed comparison of wt and V1V2 mutant envelopes, V1V2 proved to be a key factor in ascertaining free virus infectivity, with V1V2 mutants displaying significantly reduced trimer integrity. Despite these defects, cell-cell transmission was able to partially rescue infectivity of V1V2 mutant viruses. We identified two regions, encompassing amino acids 156 to 160 (targeted by broadly neutralizing antibodies) and 175 to 180 (encompassing the α4β7 binding site) which were particularly prone to free virus infectivity loss upon mutation but maintained infectivity in cell-cell transmission. Of note, V1V2 antibody shielding proved important during both free virus infection and cell-cell transmission.

CONCLUSIONS

Based on our data we propose a model for V1V2 evolution that centers on cell-cell transmission as a salvage pathway for virus replication. Escape from antibody neutralization may frequently result in V1V2 mutations that reduce free virus infectivity. Cell-cell transmission could provide these escape viruses with sufficiently high replication levels that enable selection of compensatory mutations, thereby restoring free virus infectivity while ensuring antibody escape. Thus, our study highlights the need to factor in cell-cell transmission when considering neutralization escape pathways of HIV-1.

Early infection HIV-1 envelope V1-V2 genotypes do not enhance binding or replication in cells expressing high levels of α4β7 integrin

It has been postulated that HIV-1 envelope properties, such as shorter and less-glycosylated V1-V2 loops commonly observed among non-subtype B early-transmitted viruses, promote utilization of the gut homing integrin α4β7. This property potentially confers an advantage to some HIV-1 variants early after acquisition. We found that replication-competent recombinant viruses incorporating HIV-1 subtype A compact and less-glycosylated early versus chronic phase V1-V2 loops demonstrated no significant difference in binding to α4β7 high CD8⁺ T cells or replication in α4β7 high CD4⁺ T cells. Integrin α4β7 usage does not select for shorter less-glycosylated envelopes during transmission.

Transmitted/founder and chronic subtype C HIV-1 use CD4 and CCR5 receptors with equal efficiency and are not inhibited by blocking the integrin α4β7

Sexual transmission of human immunodeficiency virus type 1 (HIV-1) most often results from productive infection by a single transmitted/founder (T/F) virus, indicating a stringent mucosal bottleneck. Understanding the viral traits that overcome this bottleneck could have important implications for HIV-1 vaccine design and other prevention strategies. Most T/F viruses use CCR5 to infect target cells and some encode envelope glycoproteins (Envs) that contain fewer potential N-linked glycosylation sites and shorter V1/V2 variable loops than Envs from chronic viruses. Moreover, it has been reported that the gp120 subunits of certain transmitted Envs bind to the gut-homing integrin α4β7, possibly enhancing virus entry and cell-to-cell spread. Here we sought to determine whether subtype C T/F viruses, which are responsible for the majority of new HIV-1 infections worldwide, share biological properties that increase their transmission fitness, including preferential α4β7 engagement. Using single genome amplification, we generated panels of both T/F (n = 20) and chronic (n = 20) Env constructs as well as full-length T/F (n = 6) and chronic (n = 4) infectious molecular clones (IMCs). We found that T/F and chronic control Envs were indistinguishable in the efficiency with which they used CD4 and CCR5. Both groups of Envs also exhibited the same CD4+ T cell subset tropism and showed similar sensitivity to neutralization by CD4 binding site (CD4bs) antibodies. Finally, saturating concentrations of anti-α4β7 antibodies failed to inhibit infection and replication of T/F as well as chronic control viruses, although the growth of the tissue culture-adapted strain SF162 was modestly impaired. These results indicate that the population bottleneck associated with mucosal HIV-1 acquisition is not due to the selection of T/F viruses that use α4β7, CD4 or CCR5 more efficiently.

Most new HIV-1 infections worldwide are caused by the sexual transmission of subtype C viruses, which are prevalent in Asia and southern Africa. While chronically infected individuals harbor a genetically diverse set of viruses, most new infections are established by single variants, termed transmitted/founder (T/F) viruses. This raises the question whether certain viral variants have particular properties allowing them to more efficiently overcome the transmission bottleneck. Preferential binding of the viral envelope (Env) to the integrin α4β7 has been hypothesized as one important feature of transmitted viruses. Here, we compared Envs from subtype C viruses that were transmitted to those that were prevalent in chronic infections for efficiency in utilizing α4β7, CD4 and CCR5 for cell entry and replication. We found that transmitted and chronic Envs engaged CD4 and CCR5 with equal efficiency, and that blocking the interaction between Env and α4β7 failed to inhibit replication of T/F as well as control viruses. While the search for determinants of transmission fitness remains an important goal, preferential CD4, CCR5 or α4β7 interactions do not appear to represent distinguishing features of T/F viruses.

Adenovirus vector-specific T cells demonstrate a unique memory phenotype with high proliferative potential and coexpression of CCR5 and integrin alpha4beta7

BACKGROUND

The Step Study was a randomized trial to reduce HIV infection through vaccination with an adenovirus type 5 (Ad5)-based gag/pol/nef construct; analysis following early cessation of the trial revealed an excess of HIV seroconversion in Ad5 seropositive men. This led to the suggestion that the Ad based vector may boost the number of CD4 chemokine receptor 5 (CCR5) T cells, target cells for HIV infection.

OBJECTIVES

We sought to determine the immunophenotype and proliferative capacity of Ad5-specific T cells in the peripheral blood of adult donors to determine whether stimulation with replication defective Ad5 vectors could result in the significant expansion of a CD4 CCR5 T-cell subset.

METHODS

Ad5-specific T cells were identified in the peripheral blood of healthy donors by interferon-gamma secretion assay and proliferative response was measured by carboxyfluorescein succinimidyl ester labelling. Cells were analyzed by flow cytometry to determine T-cell differentiation marker, CCR5 and alpha4beta7 expression on memory and proliferated cells.

RESULTS

Ad5-specific CD4 T cells within healthy adult donors exhibit a unique minimally differentiated memory phenotype with coexpression of CD45RA, CD45RO and CCR7. Stimulation with Ad vector leads to rapid expansion in vitro and a switch to an effector memory phenotype. Both short-term reactivated and proliferating Ad5-specific CD4 T cells express the HIV coreceptor CCR5 and the HIV gp120-binding integrin alpha4beta7.

CONCLUSION

Ad5-specific T cells demonstrate a phenotype and proliferative potential that would support HIV infection; these results are pertinent to the findings of the Step Study and future use of Ad5 as a vaccine vector.

Different selection patterns of resistance and cross-resistance to HIV-1 agents targeting CCR5

OBJECTIVES

Identification of CCR5 as an antiretroviral target led to the development of several CCR5 antagonists in clinical trials and the approval of maraviroc. Evaluating the mechanism of drug resistance to CCR5 agents may have implications in the clinical development of this class of agents. We have analysed the resistance profile of two R5 HIV-1 strains [BaL and a clinical isolate (CI)] after long-term passage in cell culture in the presence of TAK-779, the first developed non-peptidic small molecule targeting CCR5.

METHODS

Genotypic and phenotypic tests were used to evaluate the resistance of virus isolated from cell culture in the presence of the CCR5 inhibitor TAK-779.

RESULTS

Mutations conferring resistance appeared in the gp120 sequence but were not confined to the V3 loop region, and both strains had a different mutation pattern. Recombination of the env gene of the BaL-derived resistant virus into the HIV-1 HXB2 wild-type backbone conferred resistance to TAK-779 and cross-resistance to maraviroc, with 63- and 11-fold changes in their EC(50) (50% effective concentration), respectively, together with an apparent reduction of the maximal plateau inhibition (MPI) of TAK-779 but not of maraviroc. Conversely, the resistant CI viruses showed an approximately 50% reduction in MPI for both TAK-779 and maraviroc.

CONCLUSIONS

We confirm that different pathways to the generation of CCR5 drug resistance/cross-resistance may occur that strongly depend on cell culture conditions, CCR5 availability and the genetic background of the HIV strain. Our study provides complementary information to understand the complexity of resistance to CCR5 antagonists.