The researchers found that when the mRNA vaccine enters the human liver cells, it triggers the cell's DNA, which is inside the nucleus, to increase the production of the LINE-1 gene expression to make mRNA.

The mRNA then leaves the nucleus and enters the cell's cytoplasm, where it translates into LINE-1 protein. A segment of the protein called the open reading frame-1, or ORF-1, then goes back into the nucleus, where it attaches to the vaccine's mRNA and reverse transcribes into spike DNA.

Reverse transcription is when DNA is made from RNA, whereas the normal transcription process involves a portion of the DNA serving as a template to make an mRNA molecule inside the nucleus.

"In this study we present evidence that COVID-19 mRNA vaccine BNT162b2 is able to enter the human liver cell line Huh7 in vitro," the researchers wrote in the study, published in Current Issues of Molecular Biology. "BNT162b2 mRNA is reverse transcribed intracellularly into DNA as fast as 6 [hours] after BNT162b2 exposure."