Washington, Dec 7 (IANS)

Two patients previously thought to be 'cured' of HIV after undergoing bone marrow transplants are now seeing the return of the virus in their blood, a US doctor has revealed.

Timothy Henrich, a physician-researcher at the Boston Brigham and Women's Hospital, believed the re-emergence of the virus demonstrates that HIV reservoirs, latent cells carrying the virus, "is deeper and more persistent" than scientists had realised.

"The return of detectable levels of HIV in our patients is disappointing, but scientifically significant," Henrich told Xinhua in a statement through e-mail.

"Through this research, we have discovered ...that our current standards of probing for HIV may not be sufficient to inform us if long-term HIV remission is possible if anti-retroviral therapy is stopped," he said.

The two HIV-positive patients, who do not want to be identified, received bone marrow transplants as part of treatment for Hodgkin' s lymphoma, a cancer of the blood, one in 2008, the other in 2010.

HIV became undetectable in both patients approximately eight months after transplant. This year, during spring, they agreed to cease anti-retroviral therapy to test whether the transplant had eliminated the virus from their bodies.

In July, the researchers announced that the two have shown no signs of HIV after they were off anti-retroviral therapy for 15 weeks and seven weeks, respectively.

But in August, the researchers detected HIV in one of the patients, who then resumed taking medication. The other opted to stay off the medicine but last month, after 32 weeks with no HIV detected, signs of the virus re-emerged and the patient also resumed anti-retroviral therapy.

According to researchers, the virus is now suppressing as expected and they are both currently in good health.