I regularly see posts or comments on social media claiming mRNA vaccines are not vaccines but gene therapy.

Here’s why this is not so.

A vaccine is a biological preparation that primes the immune system to recognise and fight a specific pathogen. This typically involves introducing a weakened or inactive form of the pathogen, or a component of it, into the body. In response, the immune system produces antibodies and T cells that can recognise and fight the pathogen if it encounters it in the future.

mRNA vaccines use a different delivery method from vaccines using older technology. The end result is the same. The immune system responds to the challenge from the vaccine by producing a comprehensive defence against the real pathogen. This includes antibodies: Y-shaped proteins that bind to specific antigens on the surface of pathogens which either neutralise the pathogen directly or mark it for destruction by other immune cells; and T cells. There are two main types of T cells, helper T cells which coordinate the immune response by activating other immune cells, and cytotoxic T cells, which directly attack and kill infected or abnormal cells.

mRNA vaccines are vaccines. They are a biological preparation designed to stimulate the immune system to develop a protective response against a specific pathogen.

OK, but aren’t they really gene therapy?

mRNA vaccines and gene therapy differ significantly in their purpose and mechanism:

The purpose of mRNA vaccines is to trigger an immune response against a specific pathogen. mRNA is not and cannot be integrated into the host’s DNA. It does its job and is quickly broken down. As with many vaccines, depending on the pathogen, the immune response may be temporary and need to be refreshed periodically.

The purpose of gene therapy is to treat or cure genetic disorders by introducing a correct and functional copy of a defective gene. Gene therapy delivers the functional gene into the host’s cells. This gene is integrated into the host’s DNA, providing a long-term solution to a genetic defect.

The key difference is that mRNA vaccines aim to trigger an immune response against a pathogen, a response which may be temporary, while gene therapy aims to correct genetic defects by making a permanent change to host DNA.

mRNA vaccines do not and cannot integrate into the host’s DNA, while gene therapy involves integrating the therapeutic gene into the host’s genome.

While both mRNA vaccines and gene therapy involve genetic material, their goals, mechanisms, and outcomes are distinct. mRNA vaccines are a valuable tool for preventing infectious diseases, while gene therapy holds promise for treating genetic disorders.

But why can’t mRNA get into the cell nucleus and change DNA?

To understand this we need to know a little about gene expression and the differences between DNA and mRNA.

You can imagine DNA as a long, twisted ladder. The sides of the ladder are made up of alternating sugar and phosphate molecules, while the rungs are composed of pairs of nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

Genes are specific segments of DNA that code for particular proteins. These proteins are the building blocks of our bodies, performing various functions like transporting oxygen, providing structure, and regulating metabolism.

When a gene is expressed, that is, read and translated into proteins, the DNA sequence is first transcribed into RNA, another nucleic acid similar to DNA but in a single strand rather than a helix, and with uracil (U) replacing thymine (T).

The RNA molecule travels to the ribosomes, cellular structures responsible for protein synthesis. Ribosomes read the RNA sequence in groups of three nucleotides called codons. Each codon is a code giving instructions for building a specific amino acid. As the ribosome reads the RNA sequence, it assembles a chain of amino acids based on the genetic code. This chain folds into a protein with a specific structure and function.

mRNA plays a crucial role in gene expression, but it is not capable of altering the host’s DNA. There are three main reasons for this:

Cellular Compartmentalisation: The nucleus, which contains the DNA, is a separate compartment within a cell, surrounded by a double membrane called the nuclear envelope. This barrier prevents most molecules, including mRNA fragments, from entering the nucleus.

mRNA Function: mRNA’s primary function is to carry information from the DNA in the nucleus to the ribosomes in the cytoplasm, where proteins are synthesized. It is not designed to enter the nucleus and interact with DNA.

DNA Replication and Transcription: The process of DNA replication and transcription, which involves copying the DNA sequence to produce new DNA, is highly regulated and involves specialized enzymes and proteins. Because mRNA is constructed differently from DNA, mRNA cannot insert itself into or alter the double helix structure of DNA.

mRNA vaccines are an efficient way of provoking an immune response to a pathogen. They are not and cannot act as gene therapy.