In the poorest parts of Africa, where HIV/AIDS runs rampant and medical facilities are in short supply, many patients never know their T-cell count–an indicator of the health of the immune system that helps doctors decide when to start medication and assess how well the medicine is working. A group of scientists at Harvard Medical School aim to change that. They are developing a T-cell counter the size of a business card that is inexpensive and easy to use. The device will soon be tested in Rwanda.
T cells are a type of white blood cell that mediate the immune system’s response to viral invaders. These cells are attacked by the immunodeficiency virus, so the number of healthy T cells in the blood serves as a key index of the severity of HIV infection and is used to monitor the effectiveness of medication.
“This kind of device could have a dramatic effect on the practice of HIV medicine,” says Bill Rodriguez, an infectious-disease expert at Massachusetts General Hospital and Harvard Medical School, in Boston, who is collaborating on the project. “It’s almost impossible to manage the disease,” he says, without having an accurate T-cell count for the patient. “The person can look reasonably well clinically even when the immune system is wiped out. Then one opportunistic infection can take over and have a devastating effect.”
Unfortunately, people in many parts of Africa, particularly rural areas, do not have access to flow-cytometry machines, the laser-based machines typically used to count T cells. And getting results from the urban centers that do have these machines can take weeks.
Watch a video of cells captured on the microchip in real time.
A handheld device that can deliver results in real time could have a profound impact on HIV treatment in these countries. So Rodriguez and his collaborator, Mehmet Toner, a bioengineer at Harvard Medical School and the Harvard MIT Division of Health Sciences and Technology, developed a small chip lined with a tiny channel 4 millimeters wide and 50 micrometers tall. The channel is spotted with molecules that bind to a protein known as CD4 that’s found on the T cells. As blood flows through the channel, these molecules effectively grab the target T cells. The number of captured cells can then be counted using a simple light microscope.
In a study of HIV-positive patients published this month in the Journal of AcquiredImmune DeficiencySyndromes, researchers found that the microfluidics device delivered T-cell counts that were closely correlated to those collected with standard flow cytometry. Rodriguez plans to test the device in Rwanda in the next few months and later in other areas with high HIV rates, such as some parts of South America and Asia. (He says that the device is unlikely to play a major role in the United States and other wealthy nations, where doctors typically use additional tests to monitor patients’ viral status.)
The device, which uses whole blood, is easier than standard methods for nonskilled medical staff to use because it does not require samples to be processed prior to testing. Several companies have already expressed interest in licensing and commercializing the technology.
Still, Toner and his collaborators are working on further improvements, including a new version of the chip that can be read without a microscope. They have just developed a way to count cells electrically by bursting them open while still in the chamber to release the charged particles within. Tiny electrodes in the chip then measure the resulting electrical change, which is proportional to the number of cells. “Ultimately, we need a self-contained system, like the glucose-monitoring devices you can buy at the drugstore,” says Toner.
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