A common discussion point surrounding COVID-19 vaccines involves whether they constitute gene therapy. This article clarifies the scientific distinctions between these two medical interventions. Understanding their unique mechanisms helps address misconceptions about how these vaccines protect against disease.
What is Gene Therapy?
Gene therapy is a medical technique designed to treat or prevent disease by modifying an individual’s genes. This approach involves introducing new genetic material into cells, replacing a disease-causing gene with a healthy copy, inactivating a malfunctioning gene, or adding a new gene to provide a beneficial function. The primary goal is to make lasting changes to a person’s DNA, which serves as the body’s genetic “cookbook” providing instructions for all cellular processes.
Vectors, often modified viruses like adeno-associated viruses, are commonly used to deliver these functional genes into target cells. Once delivered, the genetic material aims to integrate into the host cell’s DNA, leading to a sustained therapeutic effect.
How mRNA and Viral Vector COVID-19 Vaccines Function
COVID-19 vaccines utilize distinct mechanisms to prepare the immune system. mRNA vaccines, such as those from Pfizer-BioNTech and Moderna, deliver genetic instructions in the form of messenger RNA (mRNA) to human cells. This mRNA contains the blueprint for producing a harmless piece of the SARS-CoV-2 virus’s spike protein, which is found on the virus’s outer surface.
After injection, the lipid nanoparticles encapsulating the mRNA fuse with cells, releasing the mRNA into the cytoplasm. Ribosomes within the cell then read these instructions to produce the spike protein. The produced spike proteins are displayed on the cell surface, prompting the immune system to recognize them as foreign and generate antibodies and T-cells, without the mRNA ever entering the cell’s nucleus where DNA is stored.
Viral vector vaccines, like those developed by Johnson & Johnson and AstraZeneca, use a modified, harmless virus as a “vector” to deliver genetic instructions. This vector, often an adenovirus, is engineered so it cannot replicate or cause illness in humans. The vector carries DNA instructions for the spike protein into the recipient’s cells, typically entering the nucleus.
Once inside the cell, the DNA instructions are transcribed into mRNA, which then directs the cell’s machinery to produce the spike protein. Similar to mRNA vaccines, the produced spike proteins are presented to the immune system, triggering a protective response against the actual virus. The viral vector itself is cleared by the body and does not integrate its genetic material into the host’s DNA as part of its intended mechanism.
Key Differences from Traditional Gene Therapy
A fundamental distinction lies in the target and permanence of the genetic material. Traditional gene therapy aims to make lasting changes to a person’s DNA, often integrating new genetic material into the host genome for long-term therapeutic effects.
In contrast, COVID-19 vaccines deliver temporary genetic instructions for protein production, not to alter the host’s genome. mRNA vaccines deliver their instructions to the cytoplasm, and the mRNA molecules do not enter the cell’s nucleus where DNA is stored.
While viral vector vaccines deliver DNA into the cell’s nucleus, their genetic material typically does not integrate into the host DNA. The purpose of these vaccines is to teach the immune system to recognize a pathogen by producing a transient protein, rather than to correct a genetic defect or introduce permanent genetic changes.
The Body’s Processing of Vaccine Components
After the mRNA or viral vector components deliver their instructions, the body naturally processes and eliminates them. The mRNA molecules from vaccines are inherently fragile and are quickly degraded by cellular enzymes within a few days after they have served their purpose of instructing protein production. These broken-down components are then either recycled by the cell or eliminated from the body as metabolic waste.
Modified viral vectors used in vaccines are also cleared by the immune system. These vectors are designed to be replication-deficient, meaning they cannot multiply within the host cells. Once the spike protein instructions are delivered, the viral vector is recognized and cleared, preventing its indefinite persistence in the body.
The spike proteins produced by the cells in response to the vaccine are transient; they are identified, attacked, and destroyed by the immune system within a few weeks, as they are recognized as foreign.