HIV continues to be a debilitating and incurable disease, with 940 000 people losing their lives to the deadly disease in 2017 alone, and 35 million deaths overall. Antiretroviral (ARV) drugs have improved the lives of many sufferers worldwide, controlling the virus and preventing its spread. However, this treatment is not always suitable for infants and young children, while older patients may still suffer from frequent cardiovascular, renal, liver and neurologic diseases.
This may seem very doom and gloom, but never fear! Scientists are cooking up some advanced treatment options to banish the troublemaking virus for good!
HIV in a Nutshell
Human immunodeficiency virus (HIV) is an RNA virus capable of infecting and weakening the cells that make up the immune system. This lentivirus is transmitted via bodily fluids such as semen, blood, breast milk and vaginal fluid.
HIV can target CD4+ T cells, macrophages, and dendritic cells, as well as a range of other immune cells. However, its main site of infection is CD4+ T cells; the virus binds CD4 via its gp120 antigen, allowing it to release its RNA into the host cell. It uses a reverse transcriptase to produce the complementary strand and therefore proviral DNA which integrates into the genome of the helper T cell. When activated during an immune response, the T cells also transcribe the viral DNA and produce more virion particles which exit the cell and infect other immune cells.
Infected CD4+ T cells are slowly depleted by killer T cells and CD8+ T cells. The depletion of helper T cells creates a vulnerable immune system unable to defend the body against diseases it would usually quickly eliminate, such as tuberculosis, viral-induced cancers, and pneumonia. When these diseases are present, or the CD4+ T-cell count is below 200 cells/µl, the individual has Acquired Immunodeficiency Syndrome (AIDS).
Watch ASAP Science‘s fun animation to fully visualize the mechanisms of HIV and AIDS.
Antiretroviral Therapy (ART)
Current HIV treatment consists of Antiretroviral Therapy (ART); a combination of treatments able to prevent the virus from replicating and binding onto immune cells. Using this drug combination prevents HIV from gaining a resistance.
As ART slows down HIV, the immune system can recover and clear the virus as well as other opportunistic infections. However, only active forms of the virus are affected by this therapy.
ART can clear HIV to undetectable levels in the blood, relieving the patient of many symptoms and preventing spread to other people, but is not able to completely cure the individual. HIV sneakily hides away and remains dormant within inactive immune cells, ready to reawaken when the cell is activated; re-igniting symptoms in the patient.
HIV Cure Research 1: ‘Kick and Kill’
UC San Francisco (UCSF) Illustrates the workings of ‘Kick and Kill.’
Recently, five top UK institutions; Oxford University, University of Cambridge, Imperial College London, King’s College London, and University College London, collaborated in a study where dormant HIV-infected cells would be activated in fifty participants. Their intention was to produce a treatment which incorporated ART; able to eradicate both active and dormant forms of the virus. The study is known as RIVER: Research In Viral Eradication of HIV Reservoirs.
The clinical trial focuses on a drug called vorinostat, which awakens HIV-infected reservoir cells, (i.e. the ‘kick’). It is hoped that the immune system will then recognize and kill the infected cells with the help of two vaccines.
The first individual to complete the trial, a 44-year-old male, appeared to have no trace of the virus in his bloodstream. Unfortunately, the final study results suggest that the infected cells were not completely cleared, but RIVER researchers are hopeful that future studies may build on their findings.
HIV Cure Research 2: Hybrid Antibodies
Researchers at Duke University identified a rare antibody, able to target multiple strains of HIV-1, from the B cells of a chronically infected donor. The antibody is a variant of a DH511 antibody and due to its wide range of targets is known as a broadly neutralizing antibody (bnAb).
During their studies, researchers also discovered a closely related antibody in the plasma of the same patient; another variant of DH511, with very similar properties. Plasma antibodies do not usually attract much attention, as it is much harder to identify the initial genes from their protein structure than isolating genes that code bnAbs in B cells. In this study, the plasma antibody genes were identified by comparing their protein sequence to the genetic sequence of the related B cell antibodies.
The main target of these bnAbs is the epitope gp41 on HIV-1; specifically the distal portion of the membrane-proximal external region (MPER). However, structural analyses also showed that these antibodies bind the marker more closely to the plasma membrane than any other bnAb currently known, at a distinct orientation. The former characteristic is especially ideal for inhibiting the viral life cycle.
From these two potent bnAbs, many chimeric antibodies were constructed. The most powerful hybrid neutralized up to 90% of HIV-1 strains (i.e. 206 out of 209). The hybrid antibody was optimized to incorporate the best features of the B cell and plasma antibodies; ensuring it binds adjacent to the membrane and to as many HIV-1 strains as possible.
Problems to overcome
One problem to overcome for this potential vaccine is autoreactivity. Due to the viral membrane being similar to that of human cells, the immune system will delete antibodies which appear to target its membranes, such as the new chimera.
To overcome this tolerance, researchers will need to learn more about the common ancestor of these antibodies and their ontogeny. This research should provide a better understanding of how the antibodies function and their interactions with other molecules, enabling researchers to cleverly adapt the hybrid antibody, so that it can go undetected by the patient’s immune system.
Original Paper: http://immunology.sciencemag.org/content/2/7/eaal2200
HIV Cure Research 3: CRISPR
UMASS Medical School smoothly guides you through CRISPR editing.
Back in 2016, researchers at the Lewis Katz School of Medicine at Temple University and the University of Pittsburgh used CRISPR-Cas9 to eliminate HIV-1 DNA from most tissues in both transgenic mice and rats.
They successfully inactivated HIV-1 in transgenic mice; reducing RNA expression by 60-95%. Following on from this, the researchers acutely infected mice with EcoHIV, the equivalent of human HIV-1 in mice. The results showed 96% excision efficiency of the virus.
As well as this, the investigators were able to recreate a latent HIV-1 infection in humanized mice; engrafted with human immune cells. The HIV-1 in these mice lay dormant in the genomes of the engrafted T cells; where usually they would usually remain out of the reach of the immune system. When these mice were treated a single time with CRISPR-Cas9, these concealed sections of viral DNA were removed from the T cells’ genome.
CRISPR Delivery & HIV Detection
The researcher’s technique was based on the use of the adeno-associated viral (rAAV) vector delivery system, specifically AAV-DJ/8, which uses multiple serotypes/strains to target a wider range of cells for CRISPR-Cas9 delivery. On top of this, the CRISPR-Cas9 system used incorporated four guide RNAs, preventing mutational escape by the HIV-1.
Their detection system employed bioluminescence to measure the RNA levels of HIV-1, which allowed them to view the location of HIV-1-infected cells in real-time and locate reservoirs of the virus.
Successful Cure Cases: Bone Marrow Transplant and CRISPR
So far there have only been two unique cases of cures; the Berlin patient and the use of CRISPR in California.
The Berlin Patient
Timothy Ray Brown underwent a bone marrow transplant in Berlin, receiving stem cells from an HIV-resistant donor. The donor had a deletion in their CCR5 gene, which encodes for a co-receptor that HIV binds to enter the CD4+ T cell. This mutation is only present in 1% of Europeans, making them less likely to contract the virus.
To this day Mr. Brown appears to be clear of both HIV and Leukemia (which he was also suffering from). However, this method of treatment is hazardous, and the virus may still be present in other untested cells. It is also personalized treatment, with very high costs involved. The Berlin Patient offers many crucial lessons and may be the first step towards personalized treatment for all.
In California, CRISPR was used to remove the HIV genome from the DNA of Matt Chappell’s CD4+ T cells. Co-expression of the CRISPR/Cas9 system protected edited cells from re-infection, while CRISPR-Cas9 delivered by lentivirus reduced replication of HIV in infected primary CD4+ T cells. Unfortunately, his trial was only involved a small number of patients, so we can’t get too excited yet!