@barbie that's a short answer from a pain management doctor. Well, I did a quick search for you but I'm still not sure I get the point the doctor was trying to make with the text.

Mesenchymal stem cell exosomes: a two-edged sword in cancer therapy
-- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6488158/

The Mayo Clinic uses Nanoparticle Tracking Analysis to Study the Behavior of Exosomes and Microvesicles
-- https://www.exosome-rna.com/the-mayo-clinic-uses-nanoparticle-tracking-analysis-to-study-the-behavior-of-exosomes-and-microvesicles/