Kirn has held academic positions at the University of California, San Francisco Medical School. The University of Oxford. And was chief medical resident at Harvard Medical School.
His published work on oncolytic adenoviruses includes Onyx-015 and has appeared in Nature.
He has co-authored over 100 publications in peer-reviewed journals.
He is co-Founder, co-Chairman and Chief Executive Officer of 4D Molecular Therapeutics (4DMT, which he founded with David Schaffer in 2013), a biotechnology working on adeno-associated virus gene therapy vectors. Prior to 4DMT, Kirn was Founder and Chief Executive Officer of Jennerex (2003-2013) and Vice President of Clinical Research at Onyx Pharmaceuticals (1994-2000).
