If left untreated, an infection with human immunodeficiency virus (HIV) leads to AIDS and eventually death of the patient. Current treatment modalities can prevent this by suppressing HIV replication in the body. Nevertheless, however, this antiretroviral therapy (ART) does not cure the disease and must therefore be administered for life. It is connected with adverse events, especially in long-term use. Currently, HIV cannot be cured due to the ability of the virus to enter latency. This means that, as a provirus, HIV has the ability to stably integrate itself into cells' genome and to reside there for a long-time, "invisible" to the immune system. Especially after therapy discontinuation, the patient's viral load increased rapidly again due to reactivation of the latently infected cells. Permanent provirus integration is therefore considered the greatest obstacle to finding a cure for HIV/AIDS. This cooperation project will investigate in great detail the mechanistic basis of HIV integration and latency development. Based on this, new therapeutic approaches aimed at curing HIV/AIDS by eliminating the provirus or the HIV co-receptor CCR5 are being developed.
Antiretroviral therapy (ART) suppresses HIV plasma viral load to undetectable levels in most patients, thereby reducing morbidity and mortality. However, treatment interruption causes rapid rebound of virus loads to pretreatment levels. The failure of ART to cure HIV infection is based on the fact that HIV persists in cellular reservoirs that harbor integrated transcriptionally silenced proviruses. These latent viruses are not susceptible to antiretroviral treatment or immune effector mechanisms. Thus, HIV cure is not feasible without either activating infected cells, for subsequent immune clearance, or directly eradicating latent proviral genomes.
Current advanced cure strategies are mainly based on either “shock-and-kill” approaches or on the inactivation of integrated proviruses. In shock-and-kill approaches, the latent provirus is reactivated in infected cells by induced stress. Consecutively, the infected cells should become “visible” for the immune system, resulting in their final elimination. Meanwhile, this approach is tested in first clinical trials.
It is generally believed that successful cure of latent HIV infection will require a combination of several approaches including shock-and-kill immunotherapy, therapeutic vaccination, administration of HIV-neutralizing antibodies (see project 04.812/broadly neutralizing antibodies for HIV, LINK) and genome editing for provirus excision/inactivation. Accordingly, TTU HIV pursues different strategies that may eventually be combined once fully validated.
With respect to genome editing, this project focuses on two arms: either the excision or destruction of the integrated HIV genome, or the knock-out of the HIV co-receptor CCR5, which is essential for entry of the virus into cells in the first place. For both attempts, designer enzymes like TALENs, CRISPR/Cas9, or tailored Cre-derived recombinases (i.e. Brec1) are developed and tested for their ability to destroy the silent HIV provirus or the co-receptor. Moreover, advanced transport systems based on Adeno-Associated Virus (AAV), i.e. a nonpathogenic virus that has been extensively validated in >100 clinical trials, are developed for the delivery of the respective designer enzymes into the infected patient cells.
The aims of this project are:
- Analysis of HIV integration sites in the infected cells of HIV-positive patients and in animal models (humanized mice) in order to better understand the mechanisms of viral latency.
- Removal/inactivation of HIV or the proviruses from the genome of the infected host cell, and/ or turning off the receptor CCR5, which the human immunodeficiency virus requires for entry into cells. Special designer enzymes (Brec1, CRISPR/Cas and TALEN) are being developed and tested for provirus inactivation and/or inhibition of HIV co-receptor.
- Developing special AAV-based transport systems to facilitate the introduction of the designer enzymes into the infected cells. Particular attention is paid to the development of systems that would enable the side-effect free administration of both these innovative therapies and approaches to a cure; therefore guaranteeing the highest safety for the patients.