Trace for 40 Years
In 2020, several researchers from the University of California, San Francisco and University of California, Davis created an unusual experiment: tracing HIV through molecular imaging equipment. At that time, 40 years had passed since the first AIDS case in humans was officially reported.
HIV viral load, i.e., the amount of HIV in blood, is an important basis for diagnosis and treatment of AIDS. The most commonly used method to measure it is the blood test. However, a blood test has a critical value. When the viral load is lower than the critical value, the virus won't be detected. Blood tests also can't determine virus distribution in the body. A lymph node biopsy with higher sensitivity can be used as a supplementary testing method, but it often takes samples of the patient's local tissues, and as a systemic disease, HIV is very likely to hide in unsampled tissue.
Viruses that can't be eradicated are like "time bombs." They always look for the right time for continuous replication in large numbers, and the incubation period can be as long as decades. Because of this, humans have been fighting HIV for 40 years. Cases of cured AIDS patients happen only by chance, and there are only 2 cases in the world so far that are acknowledged as cures.
The Visualization of HIV Viral Load in the Whole Body for the First Time
When conventional examination methods reach their limits, molecular imaging equipment that allows for the visualization of human body at the molecular level offer new options.
Molecular imaging has existed for decades, but hadn't yet been applied to HIV clinical testing because there is no tracer for HIV, and the equipment performance isn't good enough for high-definition imaging of virus in the patient's whole body. In 2019, University of California, Davis introduced the world's first Total-body PET/CT, the uEXPLORER®. This machine increased the axial field of view from the conventional 15cm to the subversive 2m, and increased the sensitivity by 40 times. It realized a total body scan from head to toe in one bed position for the first time, shortening the conventional MI examination time of 20 minutes to 1/40. It prolonged the imaging time to 9 half-lives and supported ultra-low-dose
imaging at 1/40 to 1/50 of the drug dose. As a result, it was called the "Hubble Telescope" that could observe the inside of human body, and it opened a new window for HIV research.
In the experiment, the researchers used a new type of antibody tracer - 89Zr-VRC01. VRC01 is a broad-spectrum antibody of HIV that can bind to HIV accurately. 89Zr that is used to label the antibody works as if lighting up a small lamp for each virus. These small lamps could then be accurately captured by PET/CT. The antibody tracers fully bound to the viruses 72 hours after the drug was injected into the body. Then, a patient who had taken antiretroviral therapy (ART) for 10 years was scanned by the total-body PET/CT uEXPLORER. A new picture never seen before appeared in front of the researchers for the first time: people directly and clearly saw the distribution of HIV in various parts of the body with the naked eye. This meant that we could determine the parts of the body with HIV infection and evaluate viral load through this method. There is huge potential for the equipment to be used in the clinical treatment and scientific research of AIDS.
Endless Possibilities of the Total-body PET/CT uEXPLORER
Research on HIV still continues in the University of California, Davis and University of California, San Francisco. Clinical trials on a larger scale are still due to be conducted.
Moreover, an infinite research space is being opened up. For example, for cutting-edge highly personalized clinical treatment methods such as immunotherapy, proton therapy, heavy ion therapy and cell therapy, total-body PET/CT will provide long-term tracking and verification of personalized treatment effects with the most accurate method and the lowest radiation. In terms of brain science research, it can directly show neural connections between various organs of human body, which will help people understand how the brain interacts with body organs, and will also promote research like depression, affective disorders, borderline personality, alcohol dependence and attention-deficit/hyperactivity disorder in children. In terms of R&D of new drugs, total-body PET/CT can perform the whole body pharmacokinetic testing, observe dynamic uptake of drugs by each organ and tissue in real time, and significantly shorten the R&D of new drugs through accurate measurement and analysis of drug flow and toxicology.