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The hunt for a HIV vaccine has a long history, and one dotted with failures. In fact, various characteristics of the virus make it difficult to achieve the goal and World AIDS Day, like every year, was an opportunity to take stock of what is probably the longest and most dramatic epidemic of the modern era. An assessment inevitably made of lights and shadows. With efforts that should be multiplied in terms of preventionsince i new cases of HIV unfortunately continue to increase, especially in the poorer areas of the planet. But which also sees continuous successes on the therapeutic level: today the life expectancy of a HIV positive in therapy antiretroviral it is in fact comparable to that of a healthy person; and new drugs long acting are finally revolutionizing the daily life of patients. Where research continues to struggle, however, is in the development of a vaccinea goal that would perhaps represent the only true way to arrive to eradication of the disease. Even in this field, however, something seems to be moving: on the latest issue of Science one has just been presented new vaccination strategy which seems, finally, to give promising results. Let’s see what it is.
A difficult goal
Hiv is a retrovirusesi.e. a pathogen capable of inserting its own genetic material into the DNA of our cells, where it can lie dormant for months or years, and where it is nearly impossible to get rid of. In short, once the infection has begun, there is no vaccine that holds. A vaccine against HIV to be useful must therefore necessarily be a vaccine sterilizing, i.e. capable of eliminating the risk of infection (and not only of avoiding the disease or mitigating its symptoms). And as we found out with the vaccines against covid 19it is not at all easy to obtain such a vaccine.
The fact that HIV is a retrovirus also makes it highly variable. Its peculiar replication mechanisms in fact cause the virus to quickly accumulate a high number of mutationswhich help him escape the action of the system immune. As happens with other extremely changeable viruses, such as the flu, developing a vaccine that continues to work despite the mutations that the pathogen undergoes is really complicated. Furthermore, in the case of HIV, it is not considered safe to use one of the more traditional and effective vaccination strategies, i.e. the one based on live attenuated viruses. In fact, live attenuated vaccines always have a minimal risk of causing the disease they want to protect against. And since HIV infection is a chronic and extremely dangerous infection, it is not considered safe to have it. In the face of so many problems, of course, research continues to work. And the one described on the pages of Science is one of the new vaccination strategies considered most promising in recent years, defined by specialists germline targeting.
A multi-stage vaccine
To understand what it is, you need to quickly review how ours works immune system and in particular the one that is defined adaptive immunity. The cells that produce the antibodies are the B lymphocytes. At any given moment, a large number of these immune cells are roaming around our body, in a state which is referred to as virginor “naïve”. That is, it is about B lymphocytes that hunt for viruses and bacteria that are recognized by their receptors, but which have not yet gone against the maturation process with which the affinity of the antibodies they produce towards the invading microorganism is maximized. For this to happen, it is necessary that they meet the enemy, and then undergo mutations that make their bond with each other more and more specific. the antigen against which they are directed.
Every B lymphocyte produces a different kind of antibodywith a different effectiveness, and directed against a antigen different. In case of HIVmany of these antibodies recognize only one single strain of the virus and therefore, even if they prove to be effective, they would not be useful for protecting against the risk of infection, given the high genetic variability of HIV. A small subset of antibodies, called antibodies neutralizing to wide spectrum or Broadly neutralizing antibodiesis instead able to recognize and neutralize almost all strains of HIV, because it targets some portions of the virus that tend to have very low variability.
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