Vaccines use natural killer cells to stop omicrons, study says

The Covid vaccines were produced at a time during the pandemic before the emergence of the variants of the virus that cause concern, known as VOCs, for the acronym in English. Among them, the ômicron was responsible for the largest record of cases worldwide, on December 28, 2021.

In part, this increase in cases caused by the micron can be explained by the relaxation of measures to control the pandemic in several places and, also, by the ability of this strain to partially escape the protection given by vaccines, especially against infections.

But even world record cases have not been accompanied by proportionate increases in hospitalizations and deaths — this may be due to the cellular protection of the micron vaccines.

A study published last Tuesday (15) in the scientific journal Science Translational Medicine (from the same group as Science, one of the most prestigious journals), pointed out that the Pfizer, Moderna and Coronavac vaccines confer a type of cellular protection associated with killer cells. natural resources (NK). They are able to identify and attack cells infected by Sars-CoV-2.

Also according to the study, the same protection was observed against different variants, such as beta, delta and, most importantly, ômicron, which may explain how it causes a greater number of cases, but which, in general, are mild, without need for hospitalization.

In the research, which includes researchers from the Pontifical Catholic University of Chile, the Harvard School of Medicine and the Icahn School of Medicine at the Mount Sinai Institute in New York, blood samples from 38 participants were evaluated, of which 14 received two doses of the drug. vaccine from Pfizer, 13 from Coronavac and 11 were injected twice with the immunizer from Moderna.

In addition to cell protection activity, the researchers also analyzed IgG, IgM and IgA antibodies (immunoglobulins G, M and A, respectively; the first is associated with memory and appears after an infection, the other two are produced at the beginning infection or against an antigen). The samples were tested against the first form of the virus (D614G), and against alpha, beta, delta and omicron.

First, they observed a drop in antibodies that bind to the region called the RBD (receptor binding domain, the part of the virus that it uses to bind to and invade the host) against the micron. This occurred in all vaccines studied.

However, antibodies that bind to the virus’s spike protein (or spike, one of the proteins used by the virus to attach to cells) continued to be produced.

The antibodies that bind to natural killer cells through specific receptors known as Fc — and thus activate these cells to start a defense process in the body — are maintained in the three vaccines.

The activation of these cells is important to help attack cells infected by Sars-CoV-2, but without attacking healthy cells in the body, explains immunologist and associate professor at the Faculty of Medicine of Ribeirão Preto, University of São Paulo, Isabel Santos.

“One of the functions of the Fc interaction is to activate leukocytes [células de defesa] specialists known as natural killers [ou NK], which have substances that destroy cells infected by the virus. They function as a bridge between the antibody, the virus and the cells of the immune system,” he explains.

However, the researcher points out that this activation must be able to identify only cells affected by Sars-CoV-2.

“Before triggering this process, to avoid ‘friendly fire’ and focus only on infected cells, the Fc receptors need to be activated by antibodies produced against the spike. The insight of the study was to understand that these antibodies do not necessarily need to be specific against the region link domain [RBD]they can bind to several other regions of the viral protein and activate NKs,” he said.

In the article, the authors state that they observed a more pronounced drop in anti-RBD antibodies against the micron, probably associated with the accumulation of mutations in that region in the variant.

Despite the positive results, the study has some limitations, the authors point out.

Among them is the fact that they evaluated a relatively small number of samples (38) and that the protective response was only analyzed three weeks after the second dose – more recent research indicates that the protection, at least that measured by antibodies, of vaccines drops. after four to six months.

However, it is an important finding, especially at a time when many countries still have low vaccination coverage.

“Thus, it is urgent to understand how different vaccines confer immunity against the micron to direct efforts to increase global access to vaccines,” the study says.

“Further, defining the immunological mechanisms behind the attenuation of disease severity in the absence of a neutralization [total] of the virus can be the key to guide the development of pancoronavirus vaccines, effective against the different forms of the virus, and to design reinforcement campaigns”, he adds.