In the fight against HIV, a number of therapeutic approaches are currently in development. But a major bottleneck remains: Finding suitable animal models to evaluate the clinical efficacy of novel compounds. Can humanized mice help us find a cure?
After almost 50 years, HIV is still a hot topic. The WHO estimates 36.9 million patients as of 2017, with 1.8 million new infections that same year. And there is no cure in sight. Fighting HIV is still limited to preventing the outbreak of immune deficiency (AIDS) symptoms by keeping the patient’s virus load under control.
To this end, the majority of HIV-positive patients must take antiretroviral therapy—every day, for the rest of their lives. So pharma companies are looking for long-acting formulations, such as a monthly regimen, to reduce side effects and improve patient compliance.The current standard of care for HIV is antiretroviral therapy. Although antiretrovial therapy has been shown to be effective, patients need to ensure they take their medication each and every day.
However, the combination of a long-term treatment and a fast-mutating virus creates a hotbed for resistance development, calling for combinatorial therapies with TCR-based immunotherapies or neutralizing antibodies.
As a retrovirus, HIV can integrate into the genome and re-emerge any time. Depletion of virus reservoirs is therefore another important area of research.
Why humanized mouse models are better suited for HIV research
For any of these therapeutic approaches, the efficacy of novel compounds must be demonstrated in animal models before moving to the clinical phase. Sebastien Tabruyn, CSO at the French CRO TransCure bioServices SAS based in Archamps, Rhône-Alpes, explains why he believes this is a major bottleneck:
“Sadly, most new anti-HIV drug candidates are still tested in primates. These experiments are not only ethically difficult and expensive, but also not fully comparable, as primates can only be infected with the simian immunodeficiency virus, not the real human virus.”Sebastien Tabruyn, CSO, TransCure bioServices
TransCure bioServices started off as a biotech startup looking for novel anti-HIV treatments. “We wanted to test our compounds in an animal model that was as close to the situation in humans as possible—and still economically feasible. Therefore, we developed a new approach that led to the foundation of TransCure bioServices by Prof. Patrick Nef, PhD” recalls Romain Gret, Director of Business Development at TransCure bioServices.
The result of the research efforts was a HIV humanized (hu-)mouse model featuring a fully functional human immune system that can be infected by HIV. Today, TransCure bioServices is the only commercial entity offering anti-HIV drug testing or profiling on HIV hu-mice to the pharmaceutical industry on a fee-for-service basis.
“With our long-standing expertise, we are able to reconstitute the full human immune system in severely immunodeficient mice,” Tabruyn explains. “These hu-mice are engrafted with highly enriched, quality-controlled CD34+ stem cells isolated from human cord blood for further infection with HIV.”
An optimized chemical treatment—or chemoablation—is applied to make room in the bone marrow for the human cells to engraft. After a maturation phase of 12-15 weeks, the human immune cell derived population is monitored and quality-controlled by flow cytometry to ensure 100% humanization.Using immune deficient mouse models, the scientific team at TransCure bioServices are able to produce mouse models containing a humanized immune system. Compared to SIV monkey models, these mice are cheaper, safer, and ethically acceptable.
Surprisingly, the hu-mice are perfectly healthy. “We have optimized our stem cell preparation to ensure that no immune cells are engrafted that could attack any murine cells, for example CD8+ cells,” Tabruyn says. “A typical experiment takes up to 15-20 weeks, which is perfectly fine since our mice maintain the full human immune system functional for at least 12-16 months,” he adds.
Advantages of TransCure’s hu-mice
Humanized mice can be used for analyzing all phases of the HIV life cycle. Protective compounds and vaccinations administered before infection, antiviral therapies to prevent replication, and compounds influencing relapse or resistance development have been successfully assessed.
“In the HIV hu-mouse models, even brain microglia are humanized. That’s a huge advantage when evaluating compounds to deplete the virus reservoir in the brain that causes HIV-related dementia”, Tabruyn adds.
The process is highly standardized, with about 350 hu-mice generated per month as of today. Customers can choose from a variety of infection routes—intravenous, intraperitoneal, or vaginal—and HIV strains. “In patients, we often find a mixed viral population that changes as the disease develops. Some subtypes are susceptible to antiretroviral drugs, while others require additional therapies,” Prof. Patrick Nef, CEO at TransCure, points outOther advantages of TransCure bioService’s mice are their high rate of humanization (up to 90%), lifelong humanized stability, and their reconstitution kinetics are fully established at 14 weeks.
The downside of the HIV hu-mouse models? Obviously, blood samples are smaller than those obtained from primates. “It can be challenging to determine the HIV detection limit in 100 microliter blood samples, even with our optimized qPCR methods. This might not fully correspond to the situation in humans, but it’s still the best model we have today. It is fully suitable to determine the best combination strategy for clinical studies and novel anti-HIV patient treatment paradigms,” Tabruyn says.
Not only HIV research
HIV was the first research area developed at TransCure bioServices. Meanwhile, the service offering has been extended to cancer/immuno-oncology, in particular for the analysis of checkpoint inhibitors and inflammation such as Crohn’s and ulcerative colitis diseases.
“As our next big project, we are trying to generate hu-mice with a fully humanized hepatocyte liver. We expect a major impact on toxicity studies, and also on the development of novel anti-hepatitis therapies. We’ll even be able to mimic the HIV / HBV co-infections found in many patients,” Tabruyn concludes.
Learn more about how humanized mice can be used as ideal models to address HIV and other diseases with highly unmet need.