people whose CD4 T-cells were modified to make them resistant to HIV entry experienced
substantial CD4 cell gains and were able to maintain viral suppression after
interruption of antiretroviral therapy (ART), according to a late-breaker
presentation yesterday at the 53rd
Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) in
BioSciences in California has developed a technique that uses a zinc finger
nuclease to cut out the gene in CD4 cells that controls expression of the CCR5
co-receptor on the surface of cells. CCR5 is one of
the gateways most types of HIV use to enter cells.
People with a naturally occurring genetic mutation known as
CCR5-delta-32 – present in about 10% of Europeans – do not produce this
co-receptor. Individuals with two copies of the
mutation (one inherited from each parent) may be elite controllers who maintain
undetectable viral load without treatment, whilst those with one copy may have
lower than normal virus levels.
Researchers have attempted to replicate this natural
phenomenon as a potential strategy for curing HIV. The Berlin patient, who received stem cell transplants to
treat leukemia from a bone marrow donor with a double CCR5-delta-32 mutation, appears
to be free of HIV several years after stopping ART.
finger technique aims to produce the same effect by using 'molecular scissors'
to disrupt the normal CCR5-producing gene in chromosomes of T-cells (or
ultimately the hematopoietic stem cells that give rise to all immune cells). A
portion of CD4 cells are collected through apheresis, treated with the zinc
finger protein in a lab and the modified and multiplied cells – known as SB-728-T – are then returned to
have studied the technique in several small cohorts in phase I/II trials. As
previously reported, the procedure is generally well-tolerated and modified SB-728-T cells appear safe, with no notable safety concerns to date.
SB-728-T cells engrafted, multiplied and distributed themselves like
normal T-cells. As
previously reported, most participants experienced
substantial increases in CD4 cells – including some individuals who had not
previously achieved adequate immune recovery despite viral suppression on ART –
and gains have been maintained up to three years.
Another study presented as a poster at this year's ICAAC showed
reduction of the viral reservoir in participants in these earlier cohorts, as
indicated by a median 0.6 log decrease in HIV DNA in peripheral blood T-cells
at 12 months.
real test is whether the modified CD4 cells will be able to resist infection,
which can only be determined by doing a careful analytic treatment
interruption. Researchers at the University of Pennsylvania previously
described one SB-728-T recipient who was able to maintain viral suppression
during a 12-week treatment interruption, providing proof of concept.
Dale Ando, Sangamo's Chief Medical Officer, reported results from a cohort of seven
people who were CCR5-delta-32 heterozygous, meaning they carry one copy of the natural
mutation and one copy of the normal CCR5-producing gene. In theory, it should be
easier for gene therapy to produce T-cells completely lacking in CCR5 (known as
biallelic knockout) if nature has already done half the job.
study included five men and two women. All were white and ages ranged from 32
to 59 years. They had been HIV positive for two to 24 years. All were on stable
ART with undetectable viral load and current CD4 counts of least 500 cells/mm3
(range 561 to 800 cells/mm3), but nadir (lowest-ever) levels reached
as low as 88 cells/mm3. Viral set-points ranged from approximately
3600 to 245,000 copies/ml.
participant received a single SB-728-T infusion ranging from 9 to 20 billion
cells, with approximately 25% cell modification on average. Once infused, biallelic modification was achieved
in about 3% of peripheral blood CD4 cells, Ando said.
Eight weeks after the infusion, participants began a planned 16-week treatment
interruption. The interruption continued until CD4 count fell below 350
cells/mm3 or HIV RNA viral load rose above 100,000 copies/ml on
three consecutive weekly measurements. At the end of the planned interruption,
people who still had undetectable viral load could remain off treatment until
these thresholds were reached.
seen in earlier cohorts, circulating CD4 cells shot up from the baseline level
in the week after the infusion, with one person approaching 2500 cells/mm3.
CD4 counts then stabilised at closer to normal levels, that were sustained for up
to a year.
participants were classified as responders, meaning they re-suppressed viral load
after stopping treatment, experiencing at least a 1 log drop during treatment
interruption. The responders included both women in the study as well as the
youngest participant. Three people were classified non-responders. The final
participant was 12 weeks into an ongoing interruption and not further
the responders, one person had a jump in viral load after stopping ART which
was then suppressed to undetectable from week 11 to 19; treatment interruption
is ongoing. Another patient had transient undetectable viral load and also
remains off treatment. The third responder (10-503) completed a 20-week
treatment interruption with a 1 log decrease in viral load from her peak level while
non-responders resumed ART after their viral load rose and stayed above 100,000
copies/ml. The third had no change in viral load during a 16-week interruption.
responders had low viral set-points (3600 to 4800 copies/ml) compared with the non-responders
(50,000 to 245,000 copies/ml). Responders also had lower HIV DNA levels in
peripheral blood T-cells (maximum 122 copies/ml) than non-responders (maximum 931
copies/ml). Changes in viral load correlated with levels of double-knockout CD4
cells, with a higher proportion of biallelic modified cells predicting lower
is the first study to demonstrate that functional control of HIV by the immune
system may be possible by providing a population of CD4 T-cells made HIV
resistant by biallelic modification of CCR5 (SB-728-T)," the researchers
concluded. "The data demonstrate that the level of engrafted
CCR5-modified, HIV-protected CD4 T-cells and the magnitude of the HIV reservoir
are important factors in the functional control of HIV viremia during treatment
"The data presented today demonstrate that a single infusion of
SB-728-T can lead to profound suppression of viral load in the blood and sustained
functional control of the virus," Ando summarised in a press release
issued by Sangamo. "This is the first evidence that sustained functional
control of HIV in the absence of ART is possible."
findings support moving forward with a new cohort of people without the
CCR5-delta-32 mutation – like the vast majority of people with HIV – who will undergo
conditioning with the chemotherapy drug cyclophosphamide (Cytoxan)
to get rid of some
normal HIV-susceptible CD4 cells to make room for the new SB-728-T HIV-resistant
moderator Pablo Tebas, who studied the aforementioned University of
Pennsylvania patient, said these results are a "strong signal" that
this gene therapy approach is effective. He suggested that the increase in viral
load after stopping ART may be a necessary part of procedure, as resurgent
virus may kill off normal CD4 cells and therefore select for the modified