Antiretroviral therapy (ART) is highly effective at suppressing HIV to undetectable levels in the blood. However, small levels of latent virus remain in the body, and stopping treatment allows the infection to resurface. Researchers discovered which tissues SIV, the nonhuman monkey form of HIV, reemerges in first, only seven days after ART is discontinued.
Researchers from Texas Biomedical Research Institute (Texas Biomed) used genetic sequencing techniques on the nonhuman primate version of the virus to determine that lymph nodes in the abdomen are the leading source of rebound infection after the first week of discontinuing antiretroviral treatment.
The study regarding simian immunodeficiency virus (SIV) was reported in the journal Science Translational Medicine. SIV is very closely related to HIV and is commonly used as a proxy to study HIV in animal models.
There are more than 800 lymph nodes throughout the body. Knowing which types of lymph nodes to target can lead to more tailored therapies or treatments and hopefully prevent HIV from spreading and prolong HIV remission.
Dr. Ling
“Lymphoid tissues are known to be large reservoirs of latent HIV,” adds Texas Biomed Professor Binhua “Julie” Ling, MD, PhD, the senior paper author. “However, there has been no definite proof that they are the cause of the initial viral rebound; it is only a theory. Now, we have evidence that SIV, and maybe HIV, is lurking in specific types of lymph nodes and spleen tissues and is among the first to resurface in blood when medication is discontinued.”
Antiretroviral therapy (ART) is highly effective at suppressing HIV to undetectable levels in the blood. However, minute levels of latent virus are found throughout the body, including the brain, lung, gut, spleen, lymph nodes, and other organs. When treatment is stopped, it opens the door for the virus to rebound.
“If we can identify the starting point of the virus rebound, we can work on developing treatments that target those tissues and stop the virus from spreading in the first place,” Dr. Ling says.
Dr. Ling and her team used several advanced genetic tools and sequencing techniques to track the virus. They teamed up with Brandon Keele, PhD, at the AIDS and Cancer Virus Program at Fredrick National Laboratory, who generated barcoded viruses. More than 9,000 individual viruses in the stock have unique genetic barcodes, “like when you go to Walmart and each item has its unique barcode to scan,” Dr. Ling explains.
Those barcoded viruses were given to seven nonhuman primates. After infection was established, the primates began receiving antiretroviral therapy. After four to six months on ART, the animals had either very small amounts or no detectable virus circulating in blood, much like people living with HIV who are on ART. When treatment was stopped after more than a year of ART, researchers were able to assess the very earliest stages of viral rebound.
Thanks to the barcoded viruses, they could identify in which tissues the virus had replicated the fastest and spread the furthest just seven days after treatment was stopped. They matched the barcodes most prevalent in blood plasma to the barcodes detected in specific tissues. Notably, the standard test did not detect any virus in blood at the seven-day mark — the amounts present were too low to be detected — but more sensitive deep sequencing did.
The researchers discovered three major contributors: mesenteric lymph nodes, which are found in the tissue connecting the intestines to the abdominal wall; the spleen, a lymphatic system organ that filters blood; and inguinal lymph nodes, which are located in the groin.
Additional investigations revealed that CD4 T cells, a kind of immune cell prevalent in the mesenteric lymph nodes and spleen, had higher levels of intact virus and replication activity, which linked to higher rates of barcoded viruses from those locations in blood plasma. Qingsheng Li, PhD, from the University of Nebraska-Lincoln, confirmed this with a unique technology.
Surprisingly, some animals showed no signs of viral return, indicating that they had better virus control in the first week after medication was discontinued than others. Through single-cell sequencing and transcriptomic analyses, the team identified a few genes of interest that contribute to dysregulation of normal cell function and may play a role in the differences between animals that recovered quickly and those that continued to suppress viral activity. The researchers want to understand more about these genes and how they may alter human immune responses.
The researchers acknowledge that the study size of seven animals is small and that tissue sample size was also limited. Nonetheless, the results point to key organs to explore specific, targeted therapies.
“There are more than 800 lymph nodes throughout the body,” says Dr. Ling. “Knowing which types of lymph nodes to target can lead to more tailored therapies or treatments and hopefully prevent HIV from spreading and prolong HIV remission.”
