Opioid drugs such as morphine have been shown, in both human and animal models, to suppress many different types of immune cell activities, resulting in increased susceptibility to microbial infections and tumor development.
However not all opiate drugs seem to have a similar impact of the immune system. Buprenorphine is a potent semisynthetic opiate analgesic, with the property of a partial agonist at mu opioid receptor. The immunopharmacological properties of this opioid seem to differ from those of morphine and fentanyl.

When injected acutely in the experimental animal both peripherally or directly into the brain by intracerebroventricularly route, in contrast to morphine, that decreases most immune parameters considered, buprenorphine has no detrimental effect on immune function. Since the transdermal route of administration has been introduced in the clinic for buprenorphine and fentanyl, a comparison between the effects of a continuous s.c. infusion of equianalgesic doses of these two opioids was performed in mice. While fentanyl significantly reduced the immune parameters evaluated after 1 and 3 days of continuous infusion, buprenorphine did never affect the immune activity. By further increasing the duration of treatment, fentanyl-induced immunosuppression started to disappear, likely due to development of tolerance.
In conclusion we can affirm that buprenorphine at equianalgesic doses is more protective for immunity than other frequently used opioid drugs, such as morphine and fentanyl.