They were once seen as lowly cellular garbage trucks. But now, microscopic substances found in the blood called exosomes may help us understand how cancer cripples the immune system and goes on its destructive rampage throughout the body.
UCI Health scientists, along with researchers around the country, are studying the role these bubble-like sacs play in the development of cancer with the aim of devising better treatments and diagnostic tools to catch tumors at their earliest and most treatable stages.
The role of exosomes
Nearly all cells, including cancer cells, release exosomes into the blood. Early studies of these tiny structures suggested they served cellular housekeeping functions, such as clearing out unneeded proteins and other cellular debris when cells turned over and divided.
But scientists now know that these sacs carry with them bits of proteins, DNA and RNA from their originating cells. When they enter the bloodstream, they travel to distant locations in the body and spread their cargo at these remote sites.
Even more recent research indicates exosomes may dampen immune function, creating an environment that supports cancer and helps it spread.
“Over the past several years, we’ve come to recognize that exosomes are not just benign bags of cellular garbage,” says oncologist Dr. Edward Nelson, chief of the Division of Hematology/Oncology at the UCI School of Medicine.
“Investigators are now looking at exosomes as a possible window into the presence of tumors or cancer. What we do know is that when people have large tumors, they have more exosomes floating in their blood.”
Study links exosome spikes to tumor growth
To better understand the relationship between exosomes and tumor development, Nelson and his colleagues at the UCI Health Chao Family Comprehensive Cancer Center launched a study last year of 20 patients with different types of cancer, including lung, liver, ovarian, pancreatic, breast and colon. View the clinical trial ›
Patients undergoing treatment were tracked for six months to see if there was a correlation between the level of exosomes in the blood and whether the treatment was working, or if exosome concentrations might be an early indication that the tumor was not responding to treatment.
“If we know that a spike in exosomes means that the tumor is starting to grow, it will help us monitor treatment more closely,” says Nelson, who is working with Aethlon Medical Inc., a San Diego-based biotech company, and expects to have study results before the end of the year.
How immune system gets suppressed
This research may also shed light on how exosomes released from cancer cells hamper the immune system’s ability to limit the growth of tumors.
Exosomes seem to facilitate the conversion of T-cells — the immune system cells that fight disease — into cells that shut off the immune response, says Nelson. “These exosomes seem to be part of the pathways that drive this immune-suppressive environment.”
The ultimate aim of these studies is to uncover new strategies for targeting cancer.
“This research is especially attractive to me as a tumor immunologist because we’re always looking for ways to make the immune system fight cancer better,” says Nelson. “If you have a mechanism by which you could deplete the exosomes, you have the potential to manipulate and decrease the immune-suppressive environment. This looks promising.”