Vaccine Takis / Rottapharm: how does it work and why is it different from others?

The clinical trial for the second Italian vaccine, developed by the Roman company Takis in collaboration with Rottapharm biotech, has started last week. The first volunteer vaccinated with COVID-eVax  is Luca Rivolti, a 21 year old man from Monza. COVID-eVax, is a DNA-based vaccine, different from all the others already authorized,. It is the very first vaccine of this type to reach clinical stage in Europe. Eighty volunteers will participate in the first phase of the experimentation between the San Gerardo hospital in Monza and the Pascale hospital in Naples. The aim is to test the safety of the vaccine and establish the dose and number of administrations.

Genetic vaccines against the pandemic

Takis was one of the first companies to understand the danger of the new coronavirus and to start the search for a vaccine. The company, specialized in the research of anticancer vaccines, immediately made available its skills and a technology – that of DNA-based genetic vaccines – with the potential to respond quickly to an epidemic that would soon become a worldwide emergency.

Genetic vaccines were the first to reach testing and then authorization from regulatory authorities, as they are the fastest to produce. Thanks to modern technologies, synthesis of genetic material in the laboratory takes little time and is also relatively inexpensive. The genetic sequence of the virus was disclosed in January 2020, a few weeks after the news of the first case of COVID-19. It was therefore possible to produce a synthetic version of it in the laboratory in record time. This is the starting point for a genetic vaccine, which does not need the whole virus.

The DNA vaccine

The Takis vaccine is therefore similar, but at the same time different, compared to the others already authorized. Let's start with the similarities: all vaccines have a common target: the Spike protein, which the coronavirus uses to infect human cells. These are, in fact, genetic vaccines: they do not contain the whole virus, but only a portion of its genetic material, which can be in the form of messenger RNA, encapsulated in fat particles (Pzifer, Moderna) or inside a viral vector harmless to the organism (Astra Zeneca, Reithera, Jhonson & Jhonson). Or, in Takis case, it can be based on DNA.

The COVID-eVax vaccine contains only a fragment of Sars-Cov-2 DNA that encodes a portion of the Spike protein responsible for binding to the ACE-2 receptor on human cells. The purpose of the vaccine, therefore, is to stimulate the production of antibodies that block the entry of the virus into cells, and of lymphocytes that destroy infected cells.

Why is it different from the others?

DNA is more stable than RNA: it can be stored at the normal temperature of a refrigerator or freezer, and in freeze-dried form even at room temperature, and can be transported without the need for maintaining  the cold chain. However, it is a larger molecule:  unlike RNA, which is made up of a single strand, DNA has two strands and the classic double helix structure. In other words, to enter cells it needs a procedure called "electroporation", which consists of administering a tiny electric shock that temporarily opens pores on the cell membrane, allowing DNA to enter.

The vaccine with the gun

Takis vaccine is not administered with the classic syringe, but with a tool similar to a gun. The gun contains the needle to inject the DNA, but also needles with the function of electrodes that transmit an electrical impulse of a few volts - comparable to those of a light bulb - at the injection site. The procedure takes a total of 35 milliseconds and is not painful for the patient, who typically only feels pressure on the arm and a small involuntary contraction of the muscle. It has no permanent effects: its function is only to open transient pores on the cell membrane, which close immediately after the cell's DNA enters. Side effects are likely similar to those of other vaccines, or perhaps even milder, since this type of vaccine does not contain an inactivated virus or excipients that can cause allergic reactions. However, there may be a small bruise at the injection site and pain in the arm.

The vaccine does not modify the human genome

The vaccine instructs the cell to synthesize a portion of the Spike protein, but does not modify the DNA of human cells. The fragment, in fact, is contained in a larger and circular DNA molecule, a plasmid. The plasmid is what in biology is called expression vector: it contains sequences that signal the beginning and the end of the gene to be expressed. The cellular enzymes responsible for reading the DNA recognize these sequences and start producing the corresponding protein. The plasmid, therefore, always remains separate from the human genome.

The theoretical possibility of integration exists, but it has a negligible frequency: in fact it has never been observed in preclinical and clinical evaluations of DNA-based products. Furthermore, plasmid DNA does not remain forever inside the cell, but is lost after a certain number of cell divisions. The probability that a DNA vaccine will integrate into the human genome, in short, is many orders of magnitude lower than the frequency of spontaneous mutations, which can emerge randomly, at any time in the human genome.

The mechanism of the vaccine

The muscle cells and immune cells residing at the injection site then begin to produce the Spike protein and present it on the surface, mimicking what would happen if there was really an infection in progress. But the vaccinated person is not infected and cannot infect anyone: the vaccine, in fact, cannot generate the whole virus. The Spike protein, on the other hand, is like a fingerprint, which teaches the immune system to recognize infected cells and above all stimulates it to produce antibodies capable of neutralizing Sars-Cov-2 infection.

The preclinical results

The preclinical data of the Takis vaccine were promising: the drug stimulated a good production of antibodies in animal models, which remain in blood circulation for months even after a single injection. Furthermore, the antibodies were able to neutralize the virus in vitro, which means that they prevent the infection of human cells. Some experiments have confirmed that the vaccine prevents the symptoms of the disease in animals that express the ACE-2 receptor, which allows the coronavirus to enter human cells.

The future of the fight against the pandemic

If the data is confirmed in humans in the phase I / II trial, first on 80 and then on 240 patients, the company will prepare for phase III, which could start in the autumn. It will also be crucial to monitor coronavirus variants that continue to emerge. Experiments are already underway to test the effectiveness of the vaccine on the main variants isolated to date: the English, South African and Brazilian ones. The Takis vaccine has one major advantage, however: it can be quickly updated based on emerging virus mutations by replacing only a few letters in its sequence,  a process that takes a few weeks at most.

The COVID-19 pandemic has accelerated the development of genetic vaccines and provided important proof of concept that this type of approach works. In fact, they represent effective tools for responding quickly to pandemics that could affect us in the future and for viruses with a high mutation rate.

Erika Salvatori