Physician-researchers with City of Hope have developed a way to add features to T cells to help them overcome mechanisms of chimeric antigen receptor (CAR) T cell therapy resistance. Their new system is outlined in a paper published in Nature Biomedical Engineering.

CAR T cell therapy has revolutionised cancer care, providing a powerful option for some blood cancers. No treatment is perfect, however, and some patients develop resistance to CAR T cell therapies.

"Historically in the field, people have tried to overcome individual strategies that tumours use to evade immunotherapies. Engineering T cells to resist multiple strategies has been challenging due to the limited DNA packaging capacity of current vector systems," said Scott E. James, M.D., Ph.D., assistant clinical professor in City of Hope's Department of Hematology & Hematopoietic Cell Transplantation and lead author of the paper. "We developed a new method to facilitate encoding numerous features in T cells with the goal of overcoming multiple tumour escape mechanisms at the same time."

Current approved CAR T cell therapy takes immune cells from a patient's bloodstream and reprograms them to produce a CAR that recognises and binds to one specific protein, or antigen, found on cancer cells. Then, the engineered T cells are reintroduced into the patient's system, where they destroy the targeted tumour cells that they now bind to. However, problems can arise, including low expression of the targeted antigen that makes it hard for T cells to "see" it.

"The tumour essentially becomes invisible to the T cells," explained Dr. James. "One solution has been to go after multiple different antigens or molecules at the same time. Generally, most approaches have involved targeting two antigens, but we were able to target up to four using our new strategy in this project."

But it's not easy to just add multiple CARs into a T cell.

Dr James compares the problem to running out of storage capacity for your computer. By using a zip or flash drive—or in this case, an additional gene delivery system or vector—you double your storage capacity.

"There are limitations in how much genetic information that we can get into a cell, based on using a single-vector approach," he said. "By using two vectors, and selectively purifying cells that received both vectors, we can double the amount of space that is  available to encode novel cellular programs."

Working with collaborators at Memorial Sloan Kettering Cancer Center, Weill Cornell Medical College, the University of Pennsylvania and the National Institutes of Health, Dr. James and Marcel van den Brink, M.D., Ph.D., president of City of Hope Los Angeles and National Medical Center, and chief physician executive, engineered a system that uses a dual vector approach to double the genetic information capacity, allowing for the simultaneous targeting of multiple antigens.

It also allows for the use of switch receptors, which turn negative signals from a cancer cell to positive signals, to reduce T cell exhaustion, another mechanism of tumour escape. The approach has been tested with up to four antigens and three switch receptors, showing improved anti-tumour activity and T cells that proliferated more and lived longer. Named "zip-sorting" by the researchers, the system provides a powerful methodology to construct and compare novel cellular therapies.

"We built this platform so that researchers can now deliver double the amount of genetic information into a T cell," said Dr. James. "To demonstrate the utility of this system, we engineered T cells with multiple receptors to allow them to respond to multiple target molecules and resist immune suppression by tumour cells."

While the work so far has been conducted in experimental models, the hope is to optimise zip-sorting for investigating the method in human cells. For example, a team of researchers is working on a project to test large numbers of switch receptors to see which combinations work the best.

"Our proof-of-principle experiments demonstrate that T cells can be engineered to overcome multiple tumour resistance mechanisms simultaneously and this holds great promise for clinical translation," said Dr. van den Brink, senior author of the study.

In addition to using zip-sorting for adding CARs and switch receptors, the technique could have other applications, like potentially adding transcription factors, which may make T cells proliferate better, or safety switches that can deplete T cells if they become too active, Dr. James said.

"It was surprising that we could put as many features as we did into a T cell and still have it maintain activity in a tumour microenvironment that would be normally suppressive," said Dr James.

"We can now engineer cells that can avoid multiple immune evasion strategies, and this had previously been a significant challenge to engineer resistance to all these strategies at once, together, in the same cell. I look forward to seeing what else we might be able to add to further enhance the long-term efficacy of CAR T cell therapies."