Lecture 24: HIV (3) Flashcards
What are the differences between cure and remission?
What is the model for each?
What is the likelihood of both?
Cure: ‘infectious disease model’
* eradication of all HIV-infected cells
* ‘sterilising cure’
* likely to be very difficult in HIV
2. Remission: ‘cancer model’ - its the pathway to a HIV cure
* long term health in the absence of cART
* HIV still present at low levels
* ‘functional cure’
* rare, but not impossible
What are the major barriers to a cure for HIV?
- Latently infected T cells
Residual viral replication
Anatomical reservoirs
What are the new concepts in HIV persistence and latency?
- Reservoir activity
- Proliferation
- Position matters
- Defective and intact virus
- Evade immunity
- Primed to survive
What single cell technologies are transforming our understanding of HIV latency?
- Phenotypic and pro-viral sequencing (PheP-Seq)
- Focused interrogation of cells by nucleic acid detection and sequencing (FIND-seq)
What is the importance of HIV integration sites?
- Integration sites determine the likelihood of a virus being active or silent
- New techniques determine the integration site, sequence, and transcription in the same cell
- In a subset of people, intact virus is only found in gene deserts meaning limited or no HIV transcription
What is the latent reservoir?
Many resting CD4+ T cells that are infected with HIV:
Predominantly:
* Central Memory T cells
Also:
* Thymic T cells
* Naïve T cells
* Effector T cells
HAART can not target these cells
Describe anatomical reservoirs of HIV
List some
Certain parts of the body are sequestered from the drugs and the immune system
* Brain
* Lymph nodes
* GIT
* Testis
HAART can not target the infected cells in these organs
What are the strategies for a HIV cure?
Activating latently infected cells
Make cells resistant to HIV
Eliminate residual virus replication
Enhance HIV-specific immunity
What are some agents of latent infection reactivation?
HDACi (e.g. Vorinostat)
Cytokines: IL-7
Disulfiram
Describe the function of HDACi
(Histone deacetylase inhibitors)
‘Turns genes on’; reactivates latently infected cells
HDACi deacetylates the histones of the HIV DNA
Expression of HIV genes
Cell may die
What is observed in most patients when cART is stopped?
Rapid rebound of HIV RNA in serum
What is residual replication?
How often is it observed?
Observed in 1/3rd of people with HIV infection
cART is not effective at blocking replication of HIV in some T cells
What is Vorinostat?
Describe its function
It is a Histone deacetylase inhibitor (HDACi)
Function:
* Acetylation of HIV genes integrated into host genome → genes turned ON
→ Activates latent HIV in vivo
Evidence:
Has been shown to greatly increase gag copies in patients (evidence of gene expression)
What are some strategies to target HIV?
- Very early ART
- Latency reversal
- Pro-apoptotic drugs
- Immunotoxins
- Latency silencing
- Gene editing
What are some strategies to target the immune system?
- Broadly neutralising antibodies (bNAbs)
- T-cell vaccines
- Immunomodulation
- CAR T-cells
Give an overview of some methods of making cells resistant to HIV
Gene therapy
Blockage of HIV protein action
* RNA interference
Expression of an anti-viral factor
* Mutant APOBEC 3G
Elimination of integrated HIV
* LTR
Removal of an essential host factor
* CCR5
What does HIV latency reversal involve? What is the difference between it and ART?
HIV latency reversal, also known as “shock and kill,” is a potential strategy for curing HIV infection. While antiretroviral therapy (ART) can effectively suppress active virus replication, it cannot eliminate latent HIV reservoirs.
Overall, the goal of the shock and kill strategy is to eliminate latent HIV reservoirs by combining LRAs that reactivate the virus with approaches that target and eliminate infected cells.
What is the shock and kill part of HIV latency reversal?
The “shock” part of the shock and kill approach involves the use of agents, called latency-reversing agents (LRAs), to reactivate latent HIV from its dormant state. LRAs target the transcriptional silencing of HIV, which is mediated by epigenetic mechanisms, and aim to activate the virus so that it can be recognized and eliminated by the immune system or targeted by antiretroviral drugs. LRAs that have been studied in clinical trials include histone deacetylase (HDAC) inhibitors, protein kinase C (PKC) agonists, and cytokines such as interleukin-2.
The “kill” part of the strategy involves the elimination of the reactivated HIV-infected cells. One potential approach is to rely on the immune system to recognize and eliminate these cells. Another approach involves using cytotoxic agents, such as monoclonal antibodies, to target and kill HIV-infected cells selectively. Pro-apoptotic drugs
What are immune checkpoints?
- Immune checkpoints = proteins expressed on the cell surface of T-cells and when they bind to antigen-presenting cells this alters T cell function and largely dampens down the response to the T cell
What is the relationship between immune checkpoints and HIV latency?
- PD-1 and CTLA-4, dampen the immune response and are expressed on exhausted T cells in treated and untreated HIV
- Latent HIV is enriched in PD-1+ cells in blood and lymph nodes from people on ART and in both PD-1+ and CTLA4+ cells in non-human primates on ART
- Case reports of anti-PD1 in HIV infected individuals on ART with cancer show a decline in infected cells
What is an example of pro-apoptotic drugs?
BCL-2 antagonists
* Venetoclax is a BCL-2 antagonist and a license treatment for chronic lymphocytic leukemia
* Ex vivo, venetoclax leads to the enhanced selective death of latently infected cells
What are some immunotherapies under investigation for HIV cure?
Broadly neutralising antibodies
Therapeutic HIV vaccines
Immune checkpoint blockages
Toll-like receptor agonists
Immunomodulatory drugs
CAR T-cells
Interferon therapy
Cytokines: IL-15, anti-IL-10
Which monkeys develop AIDS when exposed to HIV?
Rhesus Macaques:
* develop AIDS when exposed to SIV
Sooty Mangabeys:
* have very high levels of the virus, but remain healthy
Compare CD4+ T cell decline in the various monkeys
RM: depletion
SM: no depletion
Compare immune activation in the various monkeys
RM: increased
SM: low
Compare CD4+ T cell depletion in the GIT in the various monkeys
RM: depleted
SM: normal
What is the role of pDC in the immune response to HIV?
Plasmacytoid dendritic cells (pDCs) are a type of dendritic cell that plays a critical role in the immune response to HIV. They are specialized in recognizing viral pathogens through the detection of viral nucleic acids, such as single-stranded RNA, and are major producers of type I interferons (IFN-α and IFN-β) in response to viral infections.
In the case of HIV infection, pDCs can recognize viral RNA through the endosomal Toll-like receptors (TLRs) TLR7 and TLR8, which trigger the production of type I interferons and other pro-inflammatory cytokines.
Explain how anti-PD1 induces virus control off ART in a monkey model
Anti-PD-1 (programmed cell death protein 1) is a type of immunotherapy that works by blocking the PD-1 receptor on T cells. PD-1 is an immune checkpoint receptor that downregulates T cell function when it binds to its ligands PD-L1 and PD-L2, which are often upregulated in tumors and chronic viral infections such as HIV. By blocking the PD-1 receptor, anti-PD-1 antibodies can enhance T cell activity and promote immune-mediated control of tumors or viruses.
The study found that a combination of anti-PD-1 therapy and a therapeutic vaccine was able to induce durable control of viral replication in some animals, even after discontinuation of ART.
In particular, they found that anti-PD-1 therapy increased the proliferation and functional capacity of HIV-specific CD8+ T cells, leading to increased control of viral replication.
What are the targets and strategies of gene therapy?
- Attack: enhance anti-HIV immune responses
- Protect: engineer uninfected cells to be resistant to HIV
- Purge: directly eliminate the virus itself
Delivery of gene therapy a major challenge : ex vivo (gene editing of cells outside the body) or in vivo (gene editing in the body)
What is the relationship between gene therapy and the CCR5 gene?
One target for gene therapy in HIV is the CCR5 gene, which encodes a protein that HIV uses to enter immune cells. Some people are naturally resistant to HIV because they have a mutation in the CCR5 gene that prevents the virus from entering their cells. Based on this knowledge, researchers have attempted to replicate this mutation in other individuals through gene therapy.
The most common approach to CCR5 gene therapy involves using a virus to deliver a modified version of the CCR5 gene/cutting the CCR5 gene out to a patient’s own immune cells. Once the cells are modified to lack functional CCR5 receptors, they become resistant to HIV infection.
What is the In vivo gene therapy for SIV/HIV with CRISPR-Cas9?
Involves using the CRISPR-Cas9 system to edit the genes of infected cells in the body of an animal or a human. This method is designed to specifically target and disrupt the viral DNA of SIV/HIV in infected cells, thereby preventing the virus from replicating and spreading.
The CRISPR-Cas9 system uses a guide RNA to direct the Cas9 enzyme to a specific location on the viral genome, where it cuts the DNA and induces a DNA repair process that results in the inactivation of the viral genes. This approach is particularly useful in targeting latent viral reservoirs, which are difficult to eliminate using current antiretroviral therapies.
