As the world continues to battle the coronavirus pandemic, scientists are looking towards gene therapy to find ways to develop vaccines for the Covid-19 virus. Gene therapy itself was developed based on how viruses work.

When a virus attacks a host, it introduces its genetic material into the host cell as part of its replication cycle. The genetic material serves as an instruction manual on how to produce more copies of the virus, hijacking the host body's normal production machinery to serve the needs of the virus. The host cells then produce additional copies of the virus, leading to more host cells being infected.

Like animals, humans have found a way to domesticate viruses as well, i.e., direct the virus's function to achieve favorable results, which is prominent in gene therapy. Such viruses which physically insert their genes into the host's genome could instead be used to carry "good" genes into a human cell. Scientists would first remove the genes in the virus that cause diseases, and replace those genes with genes encoding the desired effect.

All of this sounds quite sci-fi but it has been done numerous times in the past. Peter Kolchinsky, a virologist and a biotechnology investor, compiled how different viruses have been used for gene therapy in the past.

Kolchinsky tweeted, "SARS2 is a scary menace, but did you know that we've domesticated viruses? Like wolves vs dogs, we've tamed them, including some deadly ones, to perform many useful functions (and may help us stop SARS2)."

The human immunodeficiency virus (HIV) has killed millions of people. It works by disabling the host body's immune system until it can't defend the person against common, normally mild pathogens. Kolchinsky explained that HIV's special trick is to integrate its genome into that of the host body's cells.

This feature of HIV is used for gene therapy, as explained before, by replacing a chunk of the virus's genome with the hemoglobin gene to insert it into bone marrow stem cells of patients with sickle cell anemia, whose hemoglobin genes are malfunctioning.

Kolchinsky also tweeted, "Adenoviruses typically cause mild infections, including common colds. These, too, we are trying to use for gene therapies, particularly when we just want to temporarily make a protein in cells. One company is developing such an adenovirus gene therapy for heart disease to induce growth of new blood vessels when old ones are clogged. Another is using this virus to make oral vaccines that would otherwise require injection (eg flu vaccine pill). When we use a virus to deliver code for making something in cells, we call that a virus vector."

There is now a wealth of clinical experience with numerous vector types that include primarily vaccinia, measles, vesicular stomatitis virus (VSV), polio, reovirus, adenovirus, lentivirus, -retrovirus, adeno-associated virus (AAV) and herpes simplex virus (HSV).

However, as with all other procedures, viral vector-gene therapy has associated risks. Viruses can usually infect more than one type of cell, so, when viralvectorsare used to carrygenesinto the body, they might infect healthy cells as well as cancer cells.

Another danger is that the new gene might be inserted in the wrong location in the DNA, possibly causing harmful mutations to the DNA or even cancer. Moreover, when viruses are used to deliver DNA to cells inside the patient's body, there is a slight chance that this DNA could unintentionally be introduced into the patients reproductive cells. If this happens, it could produce changes that may be passed on if a patient has children after treatment.

One study to help find a vaccine for Covid-19 aims to use the principles behind gene therapy to get the vaccine ready. The researchers' method uses a harmless virus as a vector to bring DNA into the patient's cells. The DNA should then instruct the cells to make a coronavirus protein that would stimulate the immune system to fight off future infections.

While a mass-produced vaccine may still take a while, this study is one of at least 90 vaccine projects around the world trying to find a cure for Covid-19. However, some experts are worried that a vaccine may never be available. According to our previous report, Dr David Nabarro, a professor of global health at Imperial College London, who also serves as a special envoy to the WHO on Covid-19, said, "There are some viruses that we still do not have vaccines against."

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