Tag Archives: CD4

Stem cells edited to produce an HIV-resistant immune system


A team of haematologists has engineered a particular white blood cell to be HIV resistant after hacking the genome of induced pluripotent stem cells (iPSCs).

The technique has been published in the Proceedings of the National Academy of Sciences and was devised by Yuet Wai Kan of the University of California, former President of the American Society of Haematology, and his peers.

The white blood cell the team had ideally wanted to engineer was CD+4 T, a cell that is responsible for sending signals to other cells in the immune system, and one that is heavily targeted by the HIV virus. When testing for the progress of HIV in a patient, doctors will take a CD4 cell count in a cubic millimetre of blood, with between 500 and 1,500 cells/mm3 being within the normal range. If it drops below around 250, it means HIV has taken hold — the virus ravages these cells and uses them as an entry point.

HIV gains entry by attaching itself to a receptor protein on the CD+4 T cell surface known as CCR5. If this protein could be altered, it could potentially stop HIV entering the immune system, however. A very small number of the population have this alteration naturally and are partially resistant to HIV as a result — they have two copies of a mutation that prevents HIV from hooking on to CCR5 and thus the T cell.

In the past, researchers attempted to replicate the resistance by simply transplanting stem cells from those with the mutation to an individual suffering from HIV. The rarity of this working has been demonstrated by the fact that just one individual, Timothy Ray Brown (AKA the Berlin patient), has been publicly linked to the treatment and known to be HIV free today. The Californian team hoped to go right to the core of the problem instead, and artificially replicate the protective CCR5 mutation.

Kan has been working for years on a precise process for cutting and sewing back together genetic information. His focus throughout much of his career has been sickle cell anaemia, and in recent years this has translated to researching mutations and how these can be removed at the iPSC stage, as they are differentiated into hematopoietic cells. He writes on his university web page: “The future goal to treatment is to take skin cells from patients, differentiate them into iPS cells, correct the mutations by homologous recombination, and differentiate into the hematopoietic cells and re-infuse them into the patients. Since the cells originate from the patients, there would not be immuno-rejection.” No biggie.

This concept has now effectively been translated to the study of HIV and the CD+4 T cell.

Kan and his team used a system known as CRISPR-Cas9 to edit the genes of the iPSCs. It uses Cas9, a protein derived from bacteria, to introduce a double strand break somewhere at the genome, where part of the virus is then incorporated into the genome to act as a warning signal to other cells. An MIT team has already used the technique to correct a human disease-related mutation in mice.

When Kan and his team used the technique they ended up creating HIV resistant white blood cells, but they were not CD+4 T-cells. They are now speculating that rather than aiming to generate this particular white blood cell with inbuilt resistance, future research instead look at creating HIV resistant stem cells that will become all types of white blood cells in the body.

Of course, with this kind of therapy the risk is different and unexpected mutations could occur. In an ideal world, doctors will not want to be giving constant cell transplants, but generating an entirely new type of HIV resistant cells throughout the body carries its own risks and will need stringent evaluation if it comes at all close to being proven.

Speaking to Wired.co.uk, Louis Picker of the Vaccine and Gene Therapy Institute at Oregon Health and Science University seemed cautiously hopeful: “This is an old idea, with an extensive literature, that is being updated in this paper with the use of the new CRISPR technology, which makes it much much easier to modify human genes.

“Given that the so-called Berlin patient was apparently functionally cured by getting a bone marrow transplant from a (rare) CCR5-null mutant donor, the approach would indeed be promising from a scientific standpoint. Keeping in mind that bone marrow transplant is not likely to be an option for treating the vast majority of HIV positive subjects on effective anti-retroviral therapy. CRISPR technology is no question a break-through, but whether this application will have wide impact is difficult to predict at this time.”

The California also used another technique to make the alterations to the genes. This resulted in resistance in CD+4 T-cells, with levels of the virus being reduced. However, further T-cell transplants were shown to be needed to maintain this. This result in itself is quite astounding, but not the cure Kan is working for.

Story via Wired

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HIV Treatment at 500 CD4 Level Would Put Half of Patients in Need of ART Within a Year of Seroconversion

Raising the CD4 cell threshold for the initiation of antiretroviral therapy to 500 cells/mm3 would mean that almost 50% of patients would need to start HIV treatment within a year of their infection with HIV, investigators from an international study of seroconverters report in the October 15th edition of Clinical Infectious Diseases.

A threshold of 350 cells/mm3 would result in approximately a third of patients starting therapy within a year of infection with the virus.

Large numbers of patients with HIV are diagnosed late and the investigators comment: “Our findings provide strong support for public health campaigns to encourage early HIV infection diagnosis and testing.”

US HIV treatment guidelines now recommend that patients should start antiretroviral therapy when their CD4 cell count falls below 500 cells/mm3. European guidelines endorse treatment at a CD4 threshold of 350 cells/mm3, as do World Health Organization (WHO) guidelines for middle- and low-income countries.

The earlier initiation of HIV therapy appears to have several advantages. For instance, the results of observational studies suggest that it reduces the risk of both HIV-related and non-HIV-related illnesses. Moreover, prompt therapy may also have public health benefits, significantly reducing the risk of onward HIV transmission.

But raising the CD4 cell threshold for the initiation of therapy will have cost implications for health systems, many of which are already struggling. An accurate understanding of the length of time between infection with HIV and a fall in CD4 cell count low enough to merit therapy is needed to assist planning.

Investigators from the CASCADE (Using Concerted Action on AIDS and Death In Europe) study analysed the medical records of 18,495 individuals with a known date of HIV seroconversion to predict the amount of time between infection with the virus and a fall in CD4 cell count to below 500, 350 and 200 cells/mm3. They also calculated the proportion of patients who would reach these CD4 cell count thresholds one, two and five years after infection with HIV.

Most of the patients (78%) were men and were infected with HIV through sex with another man (55%). Median age at the time of serconversion was 30 years.

The median length of follow-up was 3.74 years.

According to the investigators’ calculations, median CD4 cell counts one, two and five years after infection with HIV were 510 cells/mm3, 460 cells/mm3 and 315 cells/mm3, respectively.

If guidelines recommended HIV therapy at a CD4 cell count of 500 cells/mm3, then 48% of individuals would need to start treatment within a year of seroconversion. This compared to 26% of patients if the threshold was 350 cells/mm3 and 9% of individuals if the level was 200 cells/mm3.

The estimated median times between seroconversion and a drop in CD4 cell count to below 500, 350 and 200 cells/mm3 were 1.19, 4.19 and 7.93 years respectively.

However, CD4 cell loss differed according to individual patient characteristics. Older age was associated with a lower CD4 cell count at the time of seroconversion and faster loss of CD4 cells during follow-up (p < 0.001). In addition, individuals infected with HIV via injecting drug use or heterosexual contact had a steeper CD4 cell count decrease than gay men (p < 0.001).

The investigators calculated the time between seroconversion and a fall in CD4 cell count to the study thresholds for three groups of patients.

For heterosexual women aged 25 to 30, the median times between seroconversion and a fall in CD4 cell count below 500, 350 and 200 cells/mm3 were 10.71, 5.66 and 1.63 years respectively.

The times for gay men aged 30 to 35 years were 0.95, 3.94 and 7.67 years, and 0.04, 4.08 and 9.15 years for heterosexual men in the same age group.

“These data signify a substantial increase in the number of individuals who require treatment within the first 5 years after becoming infected following the recent changes in [US and WHO] guidelines,” write the authors. “These estimates…will be essential to health care planners estimating the additional costs of increasing the CD4 cell count threshold for cART (combination antiretroviral therapy) initiation.”

The investigations add: “Our data urgently call for a campaign to encourage early HIV testing to ensure that infected individuals receive a diagnosis of HIV infection and access care well before they reach the CD4 cell count threshold at which treatment is indicated.”

Original Article by Michael Carter at NAM

The following video features an excellent 3D animation which explains the HIV replication process very clearly.  Available from Dr Rufus Rajadurai YouTube page

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