Two patients in Boston whom doctors hoped they had cured of both H.I.V. and cancer through bone-marrow transplants have seen their H.I.V. return, researchers said Friday.

Although there was never an expectation that risky bone-marrow transplants would soon be a routine treatment for H.I.V., the news was frustrating to AIDS experts. Many had hoped that the “graft versus host” battle that virtually all such transplants set off could become a potent weapon, at least in a few high-risk cases.

In July, when the two cases were first discussed at an international AIDS conference, it was suggested that they might echo the case of Timothy Ray Brown, the famous “Berlin patient,” who has been free of H.I.V. since a 2008 bone-marrow transplant from a donor with a rare mutation that confers resistance to the virus. Some experts regard him as the first patient cured of H.I.V.

The resurgence of the virus in the two patients is “disappointing but scientifically significant,” Dr. Timothy J. Henrich, who oversees their care at Brigham and Women’s Hospital in Boston, said in a statement.