Dr. Henrich hoped that the new blood cells from the new marrow would find and kill all the old ones, which were both cancerous and infected with H.I.V., and that the antiretroviral drugs would protect the new blood cells against H.I.V.

When no virus could be found in the men for months, they stopped taking the drugs.

In July, Dr. Henrich announced that one man had been off the drugs for seven weeks and the other for 15, and that no virus had been found. (It normally returns within a month or so.)

At that time, he and other researchers referred to the men as being in remission, not cured. But Dr. Henrich warned that the virus “could come back in a week, or in six months.”

On Friday, he said it had returned in one man in August and in the other man last month.