News

Published: 26 August 2024

Another failure of animal experimentation in AIDS research

More than 40 years after the discovery of the acquired immunodeficiency syndrome (AIDS), caused by the human immunodeficiency virus (HIV), predominantly animal-based HIV research has still not delivered a vaccine. In November 2023, another vaccine study was discontinued. The devastating results were presented at the ‘AIDS 2024’ conference in Munich. Not only did the vaccine combinations fail to protect against infection, but the vaccinated study participants actually became infected more frequently than those who were given a placebo.

1,512 healthy adults from southern and eastern Africa who are at increased risk of HIV infection participated in the PrEPVacc study. The participants were divided into four groups. Two groups received two different vaccine combinations, while the other two groups received a placebo. Additionally, all participants were provided with medications for pre-exposure prophylaxis (PrEP) and comprehensive counseling on infection prevention (1).

Due to these preventive measures, it was expected that relatively few participants would get infected with HIV. However, if the vaccines were effective, fewer HIV infections would be expected in the vaccine groups. But the opposite was the case: Among the vaccinated participants, depending on the group, 1.7 or 2.4 out of 100 participants became infected, while in the placebo groups only about 0.5 out of 100 participants were infected (2). The causes for this are not yet known. It could be a problem with the study design, where the small number of people who became infected during the study leads to low statistical significance. It could also be possible that the vaccines reduced the effectiveness of the pre-exposure prophylaxis.

However, it is clear that the tested vaccine combinations do not provide protection against HIV. Given the methods used to test HIV vaccines before human trials, this is not surprising: Research is conducted on animals that cannot even be infected with HIV (3). For instance, human immune cells must be implanted into mice to allow the virus to replicate. This involves, for example, using cells derived from human embryos. Non-human primates also cannot be infected with HIV. Instead, monkey-adapted viruses (SIV; simian immunodeficiency viruses; from simian = monkeys) are used. This creates an insurmountable conflict in trying to alter the virus to make it more similar to human HIV, while still being able to infect monkeys. Therefore, animal-based HIV research essentially revolves around optimizing so-called animal models and model viruses - which have nothing in common with the human infection (3).

The failed PrEPVacc study is part of a long list of failures. For example, the Mosaico study was discontinued at the beginning of 2023 due to a lack of effectiveness. The vaccine, which showed good results in trials on non-human primates, did not work in humans (4). According to virologist Hendrik Streeck, Director of the Institute of Virology at the University Hospital Bonn, there have already been 500 to 600 Phase 1 trials in which potential HIV vaccines—after promising trials on animals—were tested on humans for the first time. All of them have failed. In light of this track record, Streeck does not have high hopes for the 20 Phase 1 HIV vaccine trials currently underway (4).

Animal-based HIV research has primarily produced new 'animal models' in which animals are laboriously infected with HIV or similar 'model viruses.' However, it has so far not delivered a vaccine. To finally achieve a comprehensive understanding of the human infection, the use of human-based methods and models, such as those involving human blood cells, is necessary. Only in this way the development of effective treatments and vaccines against HIV will be possible.