Tool to control cellular activity could advance biology and medicine

A cell’s ability to react to its surroundings is one of its fundamental roles. Therefore, it makes sense that one of the objectives of scientists is to manipulate that process so that cells react to their desires.

Cell receptors, which act as ignition slots on a cell and need keys such as particular hormones, medications, or antigens to initiate particular cellular activities, provide one path toward this goal.

Thanks to synthetic receptors, most notably the chimeric antigen receptors used in CAR-T cell cancer therapy, people already have some control over this series of events. However, the range of keys that current synthetic receptors can accept and the activities they can initiate are restricted.

Researchers from Stanford have now created a new synthetic receptor that can accept a wider variety of inputs and generate a more varied set of outputs, as described in the study that was published in the journal Nature.

This invention, known as “Programmable Antigen-gated G protein-coupled Engineered Receptors” (PAGER), is based on G protein-coupled receptors. These receptors are a group of more than 800 proteins found in the human body that activate G-proteins, which are molecular switches inside cells that regulate a variety of essential processes.

The researchers illustrated PAGER's adaptability by effectively regulating neuronal activity, inducing immunological responses, and administering treatments in laboratory experiments.

I think PAGER has potential for impact, both in the G protein-coupled receptor biology field and in synthetic circuits or cell-based therapies. When you put technology out there, it is always exciting to see all the creative ways that people use and transform the technology in ways that you never even imagined. There is so much more that is possible.”

Alice Ting, Professor and Study Senior Author, School of Medicine and Biology, Stanford University

Holding the Keys

Although G-protein-coupled receptors can trigger a variety of cellular processes, scientists had previously shunned them for programmable applications due to the difficulty of customizing their “keys,” which required steering the receptors' evolution for years to produce a single desired option.

G-protein coupled receptors, normally, can be activated by specific small molecules that bind in a pocket in the receptor. Essentially, what we did is fuse something that blocks that pocket, and it only opens up when it binds something you have chosen.”

Nicholas Kalogriopoulos, Postdoctoral Fellow and Study Co-Lead Author, Stanford University

In other words, the researchers strengthened the ignition by adding a layer of protection in the form of a nanobody and peptide antagonist. The nanobody and peptide antagonist only permit key insertion under particular circumstances, much like a car owner debating whether to lend their vehicle to a friend.

In addition to restricting access to the receptor, this setup allows the access criteria to be changed by changing the “owner”, because of its modularity and the widespread influence of G-proteins, PAGER may allow for an astonishing range of cell responses.

It All Works

The researchers collaborated with Ivan Soltesz, the James R. Doty Professor in Neurosurgery and Neurosciences at Stanford Medicine, and Yulong Li, the Boya Professor at Peking University, who both are Co-authors of the paper, to test PAGER.

The very collaborative environment of Stanford expedited the study. I think it really led to the success of the experiment and the project.”

Reika Tei, Postdoctoral Fellow and Study Co-Lead Author, Stanford University

In laboratory tests, the researchers employed PAGER to modify T-cell migration, modify the inflammatory state of macrophages (a type of immune cell), change neuronal activity in cell culture and a section of a mouse brain, and release therapeutic antibodies in response to tumor antigens.

Ting said, “We did not expect all four applications to work right away, but they did, which made me feel really good about the technology. We did not have any application where we tried it and it did not work which is not a promise to everyone that it will work for them but it was robust.”

PAGER's next steps include investigating various uses, streamlining its architecture, and improving its capacity for autonomous operation, such as delivering medications automatically in response to receptor binding. Even though PAGER is still in its infancy, the researchers are optimistic about its potential, particularly as other labs start using it for experiments.

Kalogriopoulos said, “We have made PAGER easily programmable, and we would love to apply it to all sorts of places, but we do not have the expertise for that. We need people who actually study the biology of a specific disease or cellular function because they know the proper inputs and outputs. So I’m really excited for people to take it and start using it.”