HIV vaccine development

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Various approaches for HIV vaccine development Various approaches for HIV vaccine development.jpg
Various approaches for HIV vaccine development

An HIV vaccine is a potential vaccine that could be either a preventive vaccine or a therapeutic vaccine, which means it would either protect individuals from being infected with HIV or treat HIV-infected individuals.

Contents

It is thought that an HIV vaccine could either induce an immune response against HIV (active vaccination approach) or consist of preformed antibodies against HIV (passive vaccination approach). [1]

Two active vaccine regimens, studied in the RV 144 and Imbokodo trials, showed they can prevent HIV in some individuals.

However, the protection was in relatively few individuals, and was not long lasting. For these reasons, no HIV vaccines have been licensed for the market yet.

Difficulties in development

In 1984, after it was confirmed that HIV caused AIDS, the United States Health and Human Services Secretary Margaret Heckler declared that a vaccine would be available within two years. [2] However, priming the adaptive immune system to recognize the viral envelope proteins did not prevent HIV acquisition.

Many factors make the development of an HIV vaccine different from other classic vaccines (as of 1996): [3]

HIV structure

HIV structure cycle Hiv gross.png
HIV structure cycle

The epitopes of the viral envelope are more variable than those of many other viruses. Furthermore, the functionally important epitopes of the gp120 protein are masked by glycosylation, trimerisation and receptor-induced conformational changes making it difficult to block with neutralizing antibodies.

The ineffectiveness of previously developed vaccines primarily stems from two related factors:

The difficulties in stimulating a reliable antibody response has led to the attempts to develop a vaccine that stimulates a response by cytotoxic T-lymphocytes. [4] [5]

Another response to the challenge has been to create a single peptide that contains the least variable components of all the known HIV strains. [6]

It had been observed that a few, but not all, HIV-infected individuals naturally produce broadly neutralizing antibodies (BNAbs) which keep the virus suppressed, and these people remain asymptomatic for decades. Since the 2010s a core candidate is VRC01 and similar BNAbs, as they have been found in multiple unrelated people. [7] These antibodies mimic CD4 and compete for the conserved CD4 binding site. These antibodies all share a germline origin in the VH chain, where only a few human alleles of the IVIG1-2 gene are able to produce such an antibody. [8] Env is a protein on the HIV surface that enables to infect cells. Env extends from the surface of the HIV virus particle. The spike-shaped protein is "trimeric" — with 3 identical molecules, each with a cap-like region called glycoprotein 120 (gp120) and a stem called glycoprotein 41 (gp41) that anchors Env in the viral membrane. Only the functional portions of Env remain constant, but these are generally hidden from the immune system by the molecule's structure. X-ray analyses and low-resolution electron microscopy have revealed the overall architecture and some critical features of Env. But higher resolution imaging of the overall protein structure has been elusive because of its complex, delicate structure. Three new papers use stabilized forms of Env to gain a clearer picture of the intact trimer. An NCI research team led by Dr. Sriram Subramaniam used cryo-electron microscopy to examine the Env structure. The study appeared on October 23, 2013, in Nature Structural and Molecular Biology. [9]

Animal model

Young chimpanzees from Tchimpounga Sanctuary (Republic of the Congo) 2006-12-09 Chipanzees D Bruyere.JPG
Young chimpanzees from Tchimpounga Sanctuary (Republic of the Congo)

The typical animal model for vaccine research is the monkey, often the macaque. Monkeys can be infected with SIV or the chimeric SHIV for research purposes. However, the well-proven route of trying to induce neutralizing antibodies by vaccination has stalled because of the great difficulty in stimulating antibodies that neutralise heterologous primary HIV isolates. [10] Some vaccines based on the virus envelope have protected chimpanzees or macaques from homologous virus challenge, [11] but in clinical trials, humans who were immunised with similar constructs became infected after later exposure to HIV-1. [12]

There are some differences between SIV and HIV that may introduce challenges in the use of an animal model. The animal model can be extremely useful but at times controversial. [13]

There is a new animal model strongly resembling that of HIV in humans. Generalized immune activation as a direct result of activated CD4+ T cell killing - performed in mice allows new ways of testing HIV behaviour. [14] [15]

NIAID-funded SIV research has shown that challenging monkeys with a cytomegalovirus (CMV)-based SIV vaccine results in containment of virus. Typically, virus replication and dissemination occurs within days after infection, whereas vaccine-induced T cell activation and recruitment to sites of viral replication take weeks. Researchers hypothesized that vaccines designed to maintain activated effector memory T cells might impair viral replication at its earliest stage.[ citation needed ]

Specific vaccines may also need specialized animal models. For example, vaccines designed to produce VRC01-type antibodies require human-like VH alleles to be present. For organisms like mice, the human allele must be inserted into their genome to produce a useful mimic. [16] Murines are also experimental animals in AIDS and also murine AIDS and human AIDS are similar. Immunological analysis and genetic studies reveal resistant gene(s) in the H-2 complex of mice, an indication that genetic differences in mice could modify features of HIV disease. The defective murine leukemia virus is the major etiologic agent of MAIDS, which seems to be able to induce disease in the absence of virus replication. Target cell proliferation and oligoclonal expansion are induced by the virus, which suggests repressed immunity seen in mice thus referred to as paraneoplastic syndrome. This is further supported by the good response(s) of MAIDS mice to antineoplastic agents. This animal model is useful in demonstrating the emergence of novel hypotheses about AIDS, including the roles of defective HIV and HIV replication in the progression of the disease, and also the importance of identifying the HIV targeted cells in vivo. [17]

Clinical trials

Several vaccine candidates are in varying phases of clinical trials.

Phase I

Most initial approaches have focused on the HIV envelope protein. At least thirteen different gp120 and gp160 envelope candidates have been evaluated, in the US predominantly through the AIDS Vaccine Evaluation Group. Most research focused on gp120 rather than gp41/gp160, as the latter is generally more difficult to produce and did not initially offer any clear advantage over gp120 forms. Overall, they have been safe and immunogenic in diverse populations, have induced neutralizing antibody in nearly 100% recipients, but rarely induced CD8+ cytotoxic T lymphocytes (CTL). Mammalian derived envelope preparations have been better inducers of neutralizing antibody than candidates produced in yeast and bacteria. Although the vaccination process involved many repeated "booster" injections, it was challenging to induce and maintain the high anti-gp120 antibody titers necessary to have any hope of neutralizing an HIV exposure.[ citation needed ]

The availability of several recombinant canarypox vectors has provided interesting results that may prove to be generalizable to other viral vectors. Increasing the complexity of the canarypox vectors by including more genes/epitopes has increased the percent of volunteers that have detectable CTL to a greater extent than did increase the dose of the viral vector. CTLs from volunteers were able to kill peripheral blood mononuclear cells infected with primary isolates of HIV, suggesting that induced CTLs could have biological significance. Besides, cells from at least some volunteers were able to kill cells infected with HIV from other clades, though the pattern of recognition was not uniform among volunteers. The canarypox vector is the first candidate HIV vaccine that has induced cross-clade functional CTL responses. The first phase I trial of the candidate vaccine in Africa was launched early in 1999 with Ugandan volunteers. The study determined the extent to which Ugandan volunteers have CTL that are active against the subtypes of HIV prevalent in Uganda, A and D. In 2015, a Phase I trial called HVTN 100 in South Africa tested the combination of a canarypox vector ALVAC and a gp120 protein adapted for the subtype C HIV common in sub-Saharan Africa, with the MF59 adjuvant. Those who received the vaccine regimen produced strong immune responses early on and the regimen was safe. [18]

Other strategies that have progressed to phase I trials in uninfected persons include peptides, lipopeptides, DNA, an attenuated Salmonella vector, p24, etc. Specifically, candidate vaccines that induce one or more of the following are being sought:

In 2011, researchers in National Biotech Centre in Madrid unveiled data from the Phase I clinical trial of their new vaccine, MVA-B. The vaccine induced an immunological response in 92% of the healthy subjects. [20]

In 2016, results were published of the first Phase I human clinical trial of a killed whole-HIV-1 vaccine, SAV001. HIV used in the vaccine was chemically and physically deadened through radiation. The trial, conducted in Canada in 2012, demonstrated a good safety profile and elicited antibodies to HIV-1. [21] According to Dr. Chil-Yong Kang of Western University's Schulich School of Medicine & Dentistry in Canada, the developer of this vaccine, antibodies against gp120 and p24 increased to 8-fold and 64-fold, respectively after vaccination. [22]

The VRC01 line of research produced an "eOD-GT8" antigen which specifically exposes the CD4 binding site for immunization, refined over time to expose less of the other sites. [23] As it turns out that most (but not all) [8] humans do have the required alleles, the problem shifted to the method of delivery. In 2021, after promising results in tests with mice and primates, scientists announced that they plan to conduct a Phase 1 trial of an mRNA vaccine against HIV if a further developed (via their 'env–gag VLP mRNA platform' which contains eOD-GT8 [24] ) vaccine is confirmed safe and effective. [25] [26] On January 17, 2022 IAVI and Moderna launched a phase I trial of a HIV vaccine with mRNA technology. [27] On March 14, 2022 the National Institutes of Health reported that it had launched a "clinical trial of three mRNA HIV vaccines". The phase one trial is expected to conclude July 2023.[ citation needed ]

Phase II

Preventive HIV vaccines

Therapeutic HIV vaccines

Biosantech developed a therapeutic vaccine called Tat Oyi, which targets the tat protein of HIV. It was tested in France in a double-blind Phase I/II trial with 48 HIV-positive patients who had reached viral suppression on Highly Active Antiretroviral Therapy and then stopped antiretrovirals after getting the intradermal Tat Oyi vaccine. [38]

Phase III

Preventive HIV vaccines

There have been no passive preventive HIV vaccines to reach Phase III yet, but some active preventive HIV vaccine candidates have entered Phase III.

Therapeutic HIV vaccines

No therapeutic HIV vaccine candidates have reached phase 3 testing yet.

Economics

A July 2012 report of the HIV Vaccines & Microbicides Resource Tracking Working Group estimates that $845 million was invested in HIV vaccine research in 2011. [44]

Economic issues with developing an HIV vaccine include the need for advance purchase commitment (or advance market commitments) because after an AIDS vaccine has been developed, governments and NGOs may be able to bid the price down to marginal cost. [45]

Classification of possible vaccines

Theoretically, any possible HIV vaccine must inhibit or stop the HIV virion replication cycle. [46] The targets of a vaccine could be the following stages of the HIV virion cycle:

Therefore, the following list comprises the current possible approaches for an HIV vaccine:

Filtering virions from blood (Stage I)

Approaches to catching the virion (Stage I-III, VI, VII)

Approaches to destroying or damaging the virion or its parts (Stage I-VII)

Here, "damage" means inhibiting or stopping the ability of virion to process any of the Phase II-VII. Here are the different classification of methods:

Blocking replication (Stage V)

Biological, chemical or physical approaches to inhibit the process of phases

Inhibiting the functionality of infected cells (Stage VI-VII)

Inhibiting the life functions of infected cells:

Future work

There have been reports that HIV patients coinfected with GB virus C (GBV-C), also called hepatitis G virus, can survive longer than those without GBV-C, but the patients may be different in other ways. GBV-C is potentially useful in the future development of an HIV vaccine. [51]

Live attenuated vaccines are highly successful against polio, rotavirus and measles, but have not been tested against HIV in humans. Reversion to live virus has been a theoretical safety concern that has to date prevented clinical development of a live attenuated HIV-1 vaccine. Scientists are researching novel strategies to develop a non-virulent live attenuated HIV-1 vaccine. For example, a genetically modified form of HIV has been created in which the virus's codons (a sequence of three nucleotides that form genetic code) are manipulated to rely on an unnatural amino acid for proper protein translation, which allows it to replicate. Because this amino acid is foreign to the human body, the virus cannot reproduce. [52] Recent evidence suggests using universal CAR NK cells against HIV [53] [54]

See also

Related Research Articles

<span class="mw-page-title-main">HIV</span> Human retrovirus, cause of AIDS

The human immunodeficiency viruses (HIV) are two species of Lentivirus that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive. Without treatment, the average survival time after infection with HIV is estimated to be 9 to 11 years, depending on the HIV subtype.

<i>Adenoviridae</i> Family of viruses

Adenoviruses are medium-sized, nonenveloped viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from their initial isolation from human adenoids in 1953.

This is a list of AIDS-related topics, many of which were originally taken from the public domain U.S. Department of Health Glossary of HIV/AIDS-Related Terms, 4th Edition.

The genome and proteins of HIV (human immunodeficiency virus) have been the subject of extensive research since the discovery of the virus in 1983. "In the search for the causative agent, it was initially believed that the virus was a form of the Human T-cell leukemia virus (HTLV), which was known at the time to affect the human immune system and cause certain leukemias. However, researchers at the Pasteur Institute in Paris isolated a previously unknown and genetically distinct retrovirus in patients with AIDS which was later named HIV." Each virion comprises a viral envelope and associated matrix enclosing a capsid, which itself encloses two copies of the single-stranded RNA genome and several enzymes. The discovery of the virus itself occurred two years following the report of the first major cases of AIDS-associated illnesses.

<span class="mw-page-title-main">Envelope glycoprotein GP120</span> Glycoprotein exposed on the surface of the HIV virus

Envelope glycoprotein GP120 is a glycoprotein exposed on the surface of the HIV envelope. It was discovered by Professors Tun-Hou Lee and Myron "Max" Essex of the Harvard School of Public Health in 1984. The 120 in its name comes from its molecular weight of 120 kDa. Gp120 is essential for virus entry into cells as it plays a vital role in attachment to specific cell surface receptors. These receptors are DC-SIGN, Heparan Sulfate Proteoglycan and a specific interaction with the CD4 receptor, particularly on helper T-cells. Binding to CD4 induces the start of a cascade of conformational changes in gp120 and gp41 that lead to the fusion of the viral membrane with the host cell membrane. Binding to CD4 is mainly electrostatic although there are van der Waals interactions and hydrogen bonds.

Antigenic variation or antigenic alteration refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters the proteins or carbohydrates on its surface and thus avoids a host immune response, making it one of the mechanisms of antigenic escape. It is related to phase variation. Antigenic variation not only enables the pathogen to avoid the immune response in its current host, but also allows re-infection of previously infected hosts. Immunity to re-infection is based on recognition of the antigens carried by the pathogen, which are "remembered" by the acquired immune response. If the pathogen's dominant antigen can be altered, the pathogen can then evade the host's acquired immune system. Antigenic variation can occur by altering a variety of surface molecules including proteins and carbohydrates. Antigenic variation can result from gene conversion, site-specific DNA inversions, hypermutation, or recombination of sequence cassettes. The result is that even a clonal population of pathogens expresses a heterogeneous phenotype. Many of the proteins known to show antigenic or phase variation are related to virulence.

Entry inhibitors, also known as fusion inhibitors, are a class of antiviral drugs that prevent a virus from entering a cell, for example, by blocking a receptor. Entry inhibitors are used to treat conditions such as HIV and hepatitis D.

HIV superinfection is a condition in which a person with an established human immunodeficiency virus infection acquires a second strain of HIV, often of a different subtype. These can form a recombinant strain that co-exists with the strain from the initial infection, as well from reinfection with a new virus strain, and may cause more rapid disease progression or carry multiple resistances to certain HIV medications.

Env is a viral gene that encodes the protein forming the viral envelope. The expression of the env gene enables retroviruses to target and attach to specific cell types, and to infiltrate the target cell membrane.

<span class="mw-page-title-main">Antibody-dependent enhancement</span> Antibodies rarely making an infection worse instead of better

Antibody-dependent enhancement (ADE), sometimes less precisely called immune enhancement or disease enhancement, is a phenomenon in which binding of a virus to suboptimal antibodies enhances its entry into host cells, followed by its replication. The suboptimal antibodies can result from natural infection or from vaccination. ADE may cause enhanced respiratory disease, but is not limited to respiratory disease. It has been observed in HIV, RSV virus and Dengue virus and is monitored for in vaccine development.

CD4 immunoadhesin is a recombinant fusion protein consisting of a combination of CD4 and the fragment crystallizable region, similarly known as immunoglobulin. It belongs to the antibody (Ig) gene family. CD4 is a surface receptor for human immunodeficiency virus (HIV). The CD4 immunoadhesin molecular fusion allow the protein to possess key functions from each independent subunit. The CD4 specific properties include the gp120-binding and HIV-blocking capabilities. Properties specific to immunoglobulin are the long plasma half-life and Fc receptor binding. The properties of the protein means that it has potential to be used in AIDS therapy as of 2017. Specifically, CD4 immunoadhesin plays a role in antibody-dependent cell-mediated cytotoxicity (ADCC) towards HIV-infected cells. While natural anti-gp120 antibodies exhibit a response towards uninfected CD4-expressing cells that have a soluble gp120 bound to the CD4 on the cell surface, CD4 immunoadhesin, however, will not exhibit a response. One of the most relevant of these possibilities is its ability to cross the placenta.

A neutralizing antibody (NAb) is an antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically. Neutralization renders the particle no longer infectious or pathogenic. Neutralizing antibodies are part of the humoral response of the adaptive immune system against viruses, bacteria and microbial toxin. By binding specifically to surface structures (antigen) on an infectious particle, neutralizing antibodies prevent the particle from interacting with its host cells it might infect and destroy.

RV 144, or the Thai trial, was an HIV vaccine clinical trial that was conducted in Thailand between 2003 and 2006. It used a combination of two HIV vaccines that had each failed in earlier trials. Participants were vaccinated over the course of 24 weeks beginning in October 2003 and were then tested for HIV until July 2006. The results of the study were publicized in September 2009. The initial report showed that the rate of HIV infection among volunteers who received the experimental vaccine was 31% lower than the rate of HIV infection in volunteers who received the placebo. This reduction was not large enough for the Ministry of Public Health in Thailand to support approving the vaccine; it would have licensed it if the reduction had been 50% or more.

The STEP Study was a Phase IIb clinical trial intended to study the efficacy of an experimental HIV vaccine based on a human adenovirus 5 (HAdV-5) vector. The study was conducted in North and South America, the Caribbean, and Australia. A related study using the same experimental vaccine was conducted simultaneously in South Africa. These trials were co-sponsored by Merck, the HIV Vaccine Trials Network (HVTN), and the National Institute of Allergy and Infectious Diseases (NIAID), and had an Oversight Committee consisting of representatives from these three organizations. In South Africa the trial was overseen by the South African AIDS Vaccine Initiative.

MVA-B, or Modified Vaccinia Ankara B, is an HIV vaccine created to give immune resistance to infection by the human immunodeficiency virus. It was developed by a team of Spanish researchers at the Spanish National Research Council's Biotechnology National Centre headed by Dr. Mariano Esteban. The vaccine is based on the Modified vaccinia Ankara (MVA) virus used during the 1970s to help eradicate the smallpox virus. The B in the name "refers to HIV-B, the most common HIV subtype in Europe". It has been stated by Dr. Esteban that, in the future, the vaccine could potentially reduce the virulence of HIV to a "minor chronic infection akin to herpes".

SAV001-H is the first candidate preventive HIV vaccine using a killed or "dead" version of the HIV-1 virus.

<span class="mw-page-title-main">HIV/AIDS research</span> Field of immunology research

HIV/AIDS research includes all medical research that attempts to prevent, treat, or cure HIV/AIDS, as well as fundamental research about the nature of HIV as an infectious agent and AIDS as the disease caused by HIV.

<span class="mw-page-title-main">Susan Zolla-Pazner</span> American research scientist

Susan Zolla-Pazner is an American research scientist who is a Professor of Medicine in the Division of Infectious Diseases and the Department of Microbiology at Mount Sinai School of Medicine and a guest investigator in the Laboratory of Molecular Immunology at The Rockefeller University, both in New York City. Zolla-Pazner's work has focused on how the immune system responds to the human immunodeficiency virus (HIV) and, in particular, how antibodies against the viral envelope develop in the course of infection.

Intrastructural help (ISH) is where T and B cells cooperate to help or suppress an immune response gene. ISH has proven effective for the treatment of influenza, rabies related lyssavirus, hepatitis B, and the HIV virus. This process was used in 1979 to observe that T cells specific to the influenza virus could promote the stimulation of hemagglutinin specific B cells and elicit an effective humoral immune response. It was later applied to the lyssavirus and was shown to protect raccoons from lethal challenge. The ISH principle is especially beneficial because relatively invariable structural antigens can be used for the priming of T-cells to induce humoral immune response against variable surface antigens. Thus, the approach has also transferred well for the treatment of hepatitis B and HIV.

<span class="mw-page-title-main">Viral vector vaccine</span> Type of vaccine

A viral vector vaccine is a vaccine that uses a viral vector to deliver genetic material (DNA) that can be transcribed by the recipient's host cells as mRNA coding for a desired protein, or antigen, to elicit an immune response. As of April 2021, six viral vector vaccines, four COVID-19 vaccines and two Ebola vaccines, have been authorized for use in humans.

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