The DNA in our cells contains genes and elements that regulate them.  Together, this DNA directs our cells to function properly.  But a large proportion of our DNA does not have a known function.  Sometimes this DNA is called “junk” DNA.  If this junk DNA becomes active, it can cause damage to the cells.  Over millions of years of evolution, cells have developed ways to prevent this DNA from becoming active.  In diseases like Alzheimer's Disease (AD), the abnormal tau protein that is formed causes cells to lose some of this ability, allowing the junk DNA to become active.  A class of DNA elements called LINE-1 can act like retroviruses when they become active.  This LINE-1 DNA makes an enzyme called a reverse transcriptase, which enables it to make copies of itself.  The cell recognizes these copies as foreign, as if they were from a virus.  This in turn leads to an innate immune response, which initiates a cascade of reactions including inflammation, damage to the functional DNA, and death of the cells.  TPN-101 is designed to block the LINE-1 reverse transcriptase. Since that enzyme is similar to the reverse transcriptase that retroviruses like HIV use to copy their DNA, TPN-101 is similar to drugs that block the HIV reverse transcriptase, but it is more potent than those drugs at blocking the LINE-1 reverse transcriptase.  By blocking this enzyme, we hope to stop the inflammation and loss of brain cells that results from the abnormally activated immune system.  By doing so, we hope to slow down the progression of the clinical symptoms of AD.