CyTOF
Finding HIV’s ‘Sweet Spot’
Posted on by Lawrence Tabak, D.D.S., Ph.D.
Each year, about 30,000 people in the United States contract the human immunodeficiency virus (HIV), the cause of AIDS [1]. Thankfully, most can control their HIV infections with antiretroviral therapy and will lead productive, high-quality lives. Many will even reach a point where they have no detectable levels of virus circulating in their blood. However, all must still worry that the undetectable latent virus hidden in their systems could one day reactivate and lead to a range of serious health complications.
Now, an NIH-funded team has found that patterns of sugars at the surface of our own human immune cells affect their vulnerability to HIV infection. These data suggest it may be possible to find the infected immune cells harboring the last vestiges of virus by reading the sugar profiles on their surfaces. If so, it would move us a step closer to eliminating latent HIV infection and ultimately finding a cure for this horrible virus.
These fascinating new findings come from a team led by Nadia Roan, Gladstone Institutes, San Francisco and Mohamed Abdel-Mohsen, The Wistar Institute, Philadelphia, PA. Among its many areas of study, the Roan lab is interested in why HIV favors infecting specific subsets of a special type of immune cell called memory CD4 T cells. These cells come in different varieties. They also play important roles in the immune system’s ability to recall past infections and launch a rapid response to an emerging repeat infection.
For years, her team and others have tried to understand the interplay between HIV and human immune cells primarily by studying the proteins present at the cell surface. But living cells and their proteins also are coated in sugars and, the presence or absence of these carbohydrates is essential to their biochemistry.
In the new study, published in the journal eLife, the researchers included for the first time the patterns of these sugars in their study of cell surface proteins [2]. They, like many labs, hadn’t done so previously for technical reasons: it’s much easier to track these proteins than sugars.
To overcome this technical hurdle, Roan’s team turned to an approach that it uses for quantifying levels of proteins on the surface of single cells. The method, called CyTOF, uses metal-studded antibodies that stick to proteins, uniquely marking precise patterns of selected proteins, in this case, on individual HIV-infected cells.
In collaboration with Abdel-Mohsen, a glycobiology expert, they adapted this method for cell surface sugars. They did it by adding molecules called lectins, which stick to sugar molecules with specific shapes and compositions.
With this innovation, Roan and team report that they learned to characterize and quantify levels of 34 different proteins on the cell surface simultaneously with five types of sugars. Their next questions were: Could those patterns of cell-surface sugars help them differentiate between different types of immune cells? If so, might those patterns help to define a cell’s susceptibility to HIV?
The answer appears to be yes to both questions. Their studies revealed tremendous diversity in the patterns of sugars at the cells surfaces. Those patterns varied depending on a cell’s tissue of origin—in this case, from blood, tonsil, or the reproductive tract. The patterns also varied depending on the immune cell type—memory CD4 T cells versus other T cells or antibody-producing B cells.
Those sugar and protein profiles offered important clues as to which cells HIV prefers to infect. More specifically, compared to uninfected memory CD4 T cells, the infected ones had higher surface levels of two sugars, known as fucose [3] and sialic acid [4]. What’s more, during HIV infection, levels of both sugars increased.
Scientists already knew that HIV changes the proteins that the infected memory CD4 T cell puts on its surface, a process known as viral remodeling. Now it appears that something similar happens with sugars, too. The new findings suggest the virus increases levels of sialic acid at the cell surface in ways that may help the virus to survive. That’s especially intriguing because sialic acid also is associated with a cell’s ability to avoid detection by the immune system.
The Roan and Abdel-Mohsen labs now plan to team up again to apply their new method to study latent infection. They want to find sugar-based patterns that define those lingering infected cells and see if it’s possible to target them and eliminate the lingering HIV.
What’s also cool is this study indicates that by performing single-cell analyses and sorting cells based on their sugar and protein profiles, it may be possible to discover distinct new classes of immune and other cells that have eluded earlier studies. As was the case with HIV, this broader protein-sugar profile could hold the key to gaining deeper insights into disease processes throughout the body.
References:
[1] Diagnoses of HIV infection in the United States and dependent areas, 2020. HIV Surveillance Report, May 2020; 33; Centers for Disease Control and Prevention.
[2] Single-cell glycomics analysis by CyTOF-Lec reveals glycan features defining cells differentially susceptible to HIV. Ma T, McGregor M, Giron L, Xie G, George AF, Abdel-Mohsen M, Roan NR.eLife 2022 July 5;11:e78870
[3] Biological functions of fucose in mammals. Schneider M, Al-Shareffi E, Haltiwanger RS. Glycobiology. 2016 Jun;26(6):543.
[4] Sialic acids and other nonulosonic acids. Lewis AL, Chen X, Schnaar RL, Varki A. In Essentials of Glycobiology [Internet]. 4th edition. Cold Spring Harbor (NY): Cold Spring Harbor Laboratory Press; 2022.
Links:
HIV/AIDS (National Institute of Allergy and Infectious Diseases/NIH)
Roan Lab (University of California, San Francisco)
Mohamed Abdel-Mohsen (The Wistar Institute, Philadelphia, PA)
NIH Support: National Institute of Allergy and Infectious Diseases; National Institute of Diabetes and Digestive and Kidney Diseases; National Institute on Aging; National Institute of Neurological Disorders and Stroke
Creative Minds: Exploring the Role of Immunity in Hypertension
Posted on by Dr. Francis Collins
Meena Madhur / Credit: John Russell
If Meena Madhur is correct, people with hypertension will one day pay as much attention to their immune cell profiles as their blood pressure readings. A physician-researcher at Vanderbilt University School of Medicine, Nashville, Madhur is one of a growing number of scientists who thinks the immune system contributes to—or perhaps even triggers—hypertension, which increases the risk of stroke, heart disease, kidney disease, and other serious health problems.
About one of every three adult Americans currently have hypertension, yet a surprising number don’t know they have it and less than half have their high blood pressure under control—leading many health experts to refer to the condition as a “silent killer”[1,2]. For many folks, blood pressure control can be achieved through lifestyle changes, such as losing weight, exercising, limiting salt intake, and taking blood pressure medicines prescribed by their health-care provider. Unfortunately, such measures don’t work for everyone, and some people continue to suffer damage to their kidneys and blood vessels from poorly controlled hypertension.
Madhur wants to know whether the immune system might be playing a role, and whether this might hold some clues for developing new, more targeted ways of treating high blood pressure. To get such answers, this practicing cardiologist will use her 2016 NIH Director’s New Innovator Award to conduct sophisticated, single-cell analyses of the immune systems of people with and without hypertension. Her goal is to produce the most comprehensive catalog to date of which human immune cells might be involved in hypertension.
