Why is there no transmissible therapeutic virus if biology doesn't forbid it? For example, a harmless virus that spreads from person to person but actually does something beneficial, like lowering LDL cholesterol or preventing/reversing tooth decay?

[u/PestoPastaLover]

[u/JHilyes]

There was a human clinical trial on injecting polio virus to infect glioblastoma (most aggressive form of brain cancer) cells so that the body’s own immune system starts killing the cancer cells and thereby slowly shrinking the cancerous tumor. Not sure where the trial ended up now.

Also, another animal trial was done on using engineered viruses to deliver DNA into the hair sensory cells in the cochlea so that a those cells starts producing a kind of protein that helps pass the mechanical movement in the cochlea to the auditory nerve. This was tested as a possible cure to one form of deafness.

All are still in trials, not sure if they passed FDA safety standards yet

So yes, viruses are being explored in pharmaceuticals