- Category: Search for a Cure
- Published on Wednesday, 03 July 2013 00:00
- Written by Keith Alcorn
Two people with HIV who received stem cell transplants to treat lymphoma are now controlling HIV replication without antiretroviral medication in the early weeks of treatment interruption, following the discovery that both had experienced loss of detectable HIV DNA, researchers from Boston reported Wednesday at the 7th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention (IAS 2013) in Kuala Lumpur.
Although the treatment patterns of the 2 patients bear some similarities to the Berlin Patient, who experienced a "functional cure" of HIV infection after aggressive chemotherapy, immunosuppressive treatment, and a bone marrow transplant from a donor with genetic resistance to HIV, the Boston patients also differ in several respects, which could provide important clues about how remission from active HIV infection could be achieved in other people with long-standing HIV infection.
The findings were reported by Timothy Henrich of Brigham and Women’s Hospital in Boston, who has led the team conducting extensive tests on the patients. The analysis involves a small group of patients with HIV who were evaluated after allogeneic hematopoietic stem cell transplants for lymphoma at hospitals in Boston (transfer of stem cells that will replace all blood cells, derived from genetically matched donors). Although 3 patients were originally evaluated, 1 died of recurrent Hodgkin lymphoma 6 months after the transplant.
Both surviving patients had been receiving prolonged antiretroviral therapy (ART) and received stem cell transplants with a reduced-intensity conditioning regimen of chemotherapy designed to eradicate the cancer and eliminate existing bone marrow cells. The conditioning regimen did not include radiotherapy and it did not eliminate the residual lymphocyte population. In contrast, the Berlin Patient received a much more aggressive regimen which eliminated existing bone marrow cells.
The current transplants also differed from the Berlin Patient because they did not come from donors with genetic resistance to HIV infection (CCR5-delta-32 mutation), so the cells were susceptible to HIV infection.
Measurements of HIV DNA showed that around 200 days after transplantation HIV DNA levels had declined below 50 log copies per million peripheral blood mononuclear cells (PBMCs) in one patient, while HIV DNA fell below this level around 280 days after transplant in the other patient. In both cases HIV DNA levels have continued to decline after this point. They have now been followed after transplantation for 21 months (Patient A) and 42 (Patient B).
More sensitive HIV DNA testing using larger samples of blood obtained by leukapheresis, and rectal tissue biopsy showed that HIV DNA was below the limit of detection in both patients. Patient A provided a sample of 25 million PBMCs, and testing with a limit of detection of 0.07 copies per million PBMCs failed to detect HIV DNA. Patient B provided a sample of 50 million PBMCs, and testing with a limit of detection of 0.01 international units per million PBMCs similarly failed to detect HIV DNA.
Viral co-culture from CD4 lymphocytes failed to detect HIV in either patient. A rectal biopsy from Patient B failed to detect HIV DNA in rectal cells that would be expected to provide a reservoir for HIV (limit of detection 2 copies per million cells).
After establishing that HIV DNA could not be detected, the researchers conducted extensive discussions with the patients and healthcare providers over a 6-month period about the acceptability of an experimental or analytic treatment interruption in order to test viral control off antiretroviral medication.
Both patients consented after review of the study protocol by an internal review board. The patients are now being intensively monitored with weekly viral load (HIV RNA) tests and bi-weekly testing of HIV DNA in PBMCs, and after 6-8 weeks the patients gave large volumes of blood for more sensitive analysis of HIV DNA. Leukapheresis will be repeated every 3 months.
To date, Patient A has been off treatment for 7 weeks and Patient B for 15 weeks. Neither patient has yet shown any evidence of viral replication by RNA testing or any evidence of HIV DNA in PBMCs. Week 6 testing of larger blood samples from Patient B has similarly failed to detect HIV. Neither transplant recipient showed any evidence of HIV-specific immune responses.
Henrich told reporters that the research group believes the substantial reduction in the viral reservoir to be a consequence of a post-transplant graft-versus-host reaction.
"This graft-versus-host effect clears out the residual host cells," he said. "For 6 to 9 months after the reduced intensity conditioning transplant we see a mingling of the donor and host cells, and what happens over time is that the donor cells clear out the host cells."
"The peripheral blood lymphocytes that it clears out are a major reservoir for HIV," he continued. "What we think is happening is that there is a non-specific clearing by the donor cells which recognize the host cells as being just a little bit different."
Testing carried out around 200 days after the transplants showed that in both patients, host cells had been almost entirely replaced by donor-derived PBMCs; only 0.00041%-0.00081% of PBMCs were still host-derived in one patient, and the distribution was almost identical in the other patient.
Donor cells seem to be protected "by the fact that we kept them on antiretroviral therapy during and after transplantation while the residual reservoir was decaying and the new donor cells were taking over," said Henrich.
The researchers are careful not to describe their findings as a functional cure. Dan Kuritzkes of Brigham and Women’s Hospital and Harvard Medical School, also a member of the research group, commented that previous studies of structured treatment interruption showed that the majority of patients experienced viral rebound within 2 to 4 weeks, virtually everyone was viremic by week 8, and most reached a plateau in viral rebound by weeks 12-16. "In each study, 1 or 2 patients tend to lag behind the others, so that’s why we’re being careful," he said.
Researchers do not rule out the re-emergence of virus replication even after a year, which is why intensive sampling will continue for the foreseeable future.
"This is not a practical strategy that we can do for most people with HIV," Henrich told reporters. "Stem cell transplantation is dangerous. There can be up to 20% mortality associated with stem cell transfer in the first year after transplantation."
The chief value of the study will be in what it tells researchers about the reductions in HIV DNA that might need to be achieved in order to control HIV off treatment, Henrich concluded.
"How low do we need to go -- what level of reduction of the reservoir do you need in order to achieve a lasting impact?" he asked. "We hope our study will shed light on this important question."
T Henrich, E Hanhauser, M Sirignano, D Kuritzkes, et al. In depth investigation of peripheral and gut HIV-1 reservoirs, HIV-specific cellular immunity, and host microchimerism following allogeneic hematopoetic stem cell transplantation. 7th International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention. Kuala Lumpur, June 30-July 3, 2013. Abstract WELBA05.