The "CAR pool" screens to identify the most effective cancer immunotherapy cells

The USCF researchers' new method analyzed the role
of different reconstructed T cells on cancer.
In recent years, genetically modified immune cells — equipped with molecular weapons to recognize and destroy tumor cells — have changed the outlook
for cancer treatment.
Now, researchers at the University of California, San Francisco, have developed a new method to compare large numbers of these CAR-T cells, each with slightly different molecular characteristics, to determine which is most effective and durable
for cancer.

In their study, published Nov.
9, 2022, in Science Translational Medicine, the team used a method known as a "CAR pool" to study CAR-T cells
with 40 different receptors.
This screening, which could be expanded to test hundreds or thousands of receptor combinations in the future, has already revealed new and surprising receptors that make these therapeutic cells more powerful
.

"CAR-T cells are absolutely transformative for many blood cancer patients," said
senior author Kole Roybal, Ph.
D.
, associate professor of microbiology and immunology at UCSF and member of the Gladstone-UCSF Institute for Genomic Immunology.
"This work is a stepping stone to designing these cells in smarter ways so that they work better, live longer and are effective
against more types of cancer.
"

Transformative treatments

T cells are white blood cells that express receptors on their surface and can recognize foreign substances
in the body.
When a matched molecule or particle enters a T cell receptor, the cell initiates an immune response to fend off the invader
.
This reaction destroys not only viruses and bacteria, but also cancer cells
.

When cancer patients receive CAR-T cell therapy, clinicians collect T cells
from the patient's blood or from a healthy donor.
They then altered these cells in the lab, adding DNA to induce immune cells to produce special, cancer-recognizing chimeric antigen receptors (CARs)
on their surfaces.
The modified cells are cultured and injected back into the patient
.
The new CARs help T cells specifically attack cancer cells
.
A variety of CAR-T cells have been approved for use in blood cancers, including lymphoma, leukemia, and multiple myeloma
.

"Our ability to take T cells out of the body, add new genetic programs for them, and put them back into the body as a living, programmable therapy has had a huge impact on the treatment of blood cancers," said Daniel Goodman, Ph.
D.
, a postdoctoral scholar at UCSF and co-first author
of the new study.
"However, this is just the beginning of engineering cells if we understand more fully how to manipulate their signaling and functional properties
.
"

Researchers have been working to get CAR-T cells to fight solid tumors
.
Even for many blood cancer patients, CAR-T cells work only temporarily, or not at
all.

One of the limiting factors in developing new CAR-T cell therapies is the high-throughput technology required to modify and test new receptors; There are hundreds of receptor fragments throughout the immune system, and they can be combined like Lego bricks into thousands of possible combinations
.

Simplify T cell detection

Roybal, Goodman and co-first author Camillia Azimi developed CAR-pools to rapidly test the effectiveness of
different CARs.
The screening works by generating a DNA library containing the genetic code of many immune receptors, introducing them into millions of cells that then compete in a test tube for skills
to survive, grow, recognize and destroy cancer.

"Our approach makes the process of testing new receptor-based therapies much faster," said
Azimi, who was a graduate student at the University of California, San Francisco at the time.
"Not only does this allow researchers to save time, but also to explore designs
they can't test individually.
"

For example, among the 40 CARs tested in the new study, there were not only classical T cell receptors, but also receptors borrowed from other types of related immune cells
.
For example, a B-cell receptor called BAFF-R is a major contender that makes T cells particularly effective against cancer
.

"If we hadn't used CAR-pooling, we would never have chosen to test BAFF-R
," Azimi said.

When BAFF-R-containing CAR-T cells were tested in mice with multiple myeloma, the mice survived longer and had a lower
chance of developing cancer compared to mice that received standard CAR-T cells.

A platform for future research

The research team plans to expand the use of CAR-pools to test more receptors
in reconstituted T cells.
Eventually, Roybal said, this approach could be used to develop different kinds of CAR-T cells that target different types of cancer; There may not be a one-size-fits-all answer
for different cancer types.

"We can certainly use CAR-pools to quickly find the best receptors
for a particular clinical setting," he said.
One set of receptors may be more beneficial for glioblastoma, but another set of receptors is most beneficial
for myeloma.
”

As researchers screen more and more immune receptors, they hope to reveal potential patterns
of how receptors innervate immune cell activity.
Ultimately, this could lead to more synthetic receptors that could treat not only cancer but also other diseases
.

"We want to understand how to make up the basic parts of these signaling domains and build the next generation of engineered cell therapies
," Goodman said.

The lab is also working to understand and improve aspects beyond the receptors of CAR-T cells to improve the effectiveness of
the treatment.

"There are many ways to modify these cells," Roybal said
.
"It's just part of the
puzzle.
"