It’s the outside that counts

In 2008, Françoise Barré-Sinoussi and Luc Montagnier (from France) were awarded the Nobel Prize in Physiology and Medicine for their discovery of human immunodeficiency virus (HIV) in the 80s. Basically, this pathogen destroys the host immune system, making it sensitive to multiple infections that lead to death if they are not treated.

One of the ways of transmitting HIV is from mother to offspring during pregnancy, childbirth and lactation. Without medical assistance, there is a 35% of probability of transmission, which can be produced through birth, post-partum period, including breastfeeding.

Juan Pablo Jaworski, CONICET assistant researcher at the “Research Centre of Veterinary and Agronomic Sciences” (CICVYA) of the National Institute of Agricultural Technology (INTA), shows that it is possible to stop the advance and eliminate the virus of one-month-old primate’s organisms.

“This working model with primates resembles what happens to humans with HIV virus, but faster. It is an accelerated model of immunodeficiency similar to what happens to men in terms of interaction between host and virus, viral replication, immune response and development of the disease”, Jaworsky explains.

During Jaworsky’s post-doctoral studies at the University of Oregon, US, the researchers worked with SHIV (simian HIV) as it is a model that maintains the natural dynamics of the virus and has the HIV envelope protein, the focus of the research.

The structure of the envelope protein is unsteady, like jelly. Furthermore, this protein can mutate constantly through the strains and cell cycles, and is one of the most variable of the virus. Despite that, it maintains a well-preserved portion called CD4 binding site.

That binding site allows the virus to enter CD4 T lymphocytes, the type of white blood cells that are their target. Without that site, which interacts with the membrane receptors of CD4 T lymphocytes, the virus will not be able to enter, infect these cells or replicate inside them.

“The fact that there are antibodies that can neutralize the virus and have different targets has been known for many years. A great proportion of them is oriented to the union zone to CD4”, Jaworsky explains. This site, a kind of key that allows the virus to enter CD4, is hidden inside the envelope protein.

“At the moment of the first virus-cell interaction this region is exposed but when the virus is free in the organism, it is occluded” Jaworsky explains and provides an example: “Different studies show that the antibodies that are directed to this binding site can neutralize more than 90% of the HIV virus in the world.”

The scientists worked with one-month-old macaques (M. Mulatta) to replicate what happens with the virus transmission in humans, from mother to offspring, during breastfeeding. For this reason, the virus was administered through the mouth and soon the results were surprising.

“Through previous studies we learnt quickly that within two weeks we would have a peak of viremia [concentration of virus in the blood]. What we did not know was that one day after ingesting the virus, it would be all spread throughout the body. We were surprised because 24 hours later it was already in peripheral lymph nodes and in considerable quantities”, the researcher comments.

The next day, the scientists applied the antibodies directed against the binding site. And 48 hours after the virus infection, the results showed that the animals that had not received the treatment on the previous day had the virus spread throughout the body. Conversely, those that had received the vaccine had fewer replications of the virus.

The total treatment comprised four doses on days 1, 4, 7 and 10 after the treatment. Two weeks later, the animals that were treated had no traces of the virus.

But, how can we prove these results? How do we know if it was not a lack of sensibility of the diagnostic test and that once the treatment is over the infection would not come back?
“In order to prove it, we analyzed first if there were traces of the infection in the immune system; and then we noticed that if we inhibited certain type of lymph, the infection would not come back”, Jaworsky states.

For the first verification, the researchers carried out a follow up of the treated animals for six months in order to see if they had some kind of adaptive immune response. This happens when an animal is infected and its body mounts an immune response. Then, when the animals receive antiretrovirals, viral load often reaches undetectable levels but then what remains is the specific response residue, a sort of ‘print’ or mark on the immune system that can be detected in vitro.

“The animals we treated with the antibodies had no traces of infection. The virus did not leave marks in the immune system. It is as if the virus had never been to that body, but we saw it”, the veterinarian describes.

For the second stage of the verification, the researchers took the animals that have been treated and eliminated a specific type of white blood cells, CD8 + T lymphocytes, one of the main cell types that are involved in the defense of the body against HIV.

“When the body has no CD8, one would expect that if there are hidden viruses after the treatment, they would be able to escape, replicate and therefore be detected.

Nevertheless, even without CD8, the virus did not appear meaning that, indeed, it was not  in the body as far as we can observe”, the scientist says.

For Jaworsky, there is still a long way to go in order to find a treatment for humans. “These studies were performed in macaques, and despite the fact that they have many similarities with humans, it is necessary to conduct more research”, the scientist concludes.