Real & theorical symbiosis usage in bio/gene modifcation

When taken to the fantastical extreme, we've seen mutalism symbiosis in media take off in many ways since the 1940s sci-fi boom. Whether it be the idea of alien creatures from other worlds bonding with people(The Venom family of Symboties, Guyver Units and so on). Or plants, parasites and biomedical made creatures hybridized with humans to something more(Metal Gear's The End, Parasyte). But we also have rather real possibilities for symbiosis, as shown by microbiota, already available in the real world. For those unaware we have an ecosystem of things living within or on us that make our life generally easier and we are keeping them fed, sheltered and safe for lack of a better analogy. As my name and the title suggest, I believe deep down bio and gene modding can be improved if we push elements of symbiosis further, we'd just need to bio and gene mod other creatures as well as ourselves. Imagine if we could improve the proteins a medical leech(Hirudo Medicinalis) produces to increase better blood flow through out more of the body while still feeding it. Or taking any of the many elements of helminethic therapy (using what is normally considered parasitic creatures as helpers to tackle issues) and modifying their genetics to improve other things within us; namely to the point they become mutually beneficial to us and no longer a hazard.

Have you had thoughts of this? Do you know anyone actually trying to do this?  Ever catch a glimpse of someone possibly on to something and want to share? I've read a few topics on here that dip into on this subject and wanted to unify it with one topic and get people who have had it on their minds.