I was on the Keytruda Immunotherapy trial a little over a year ago. The only side effect I can recall was a rash. (not bad) Unfortunately I could not finish the trial as I developed a new cancerous lesion. After they discovered the lesion, they opened up my profile and found that I was actually on the drug and not the placebo. I am not HPV + but for those who were diagnosed as HPV +, the research is showing those patients are showing better outcomes than those of us who are not. I would not hesitate to try the immunotherapy again if they offered a new drug.
Good luck!