New therapeutic target could boost CAR T-cell therapy success in solid tumors

Russell W. Jenkins, MD, PhD, a physician investigator in the Krantz Family Center for Cancer Research at the Mass General Cancer Center and an assistant professor of Medicine at Harvard Medical School, is senior author of a new study in Cancer Immunology Research, "TBK1 is Identified as a Therapeutic Strategy to Enhance CAR T-Cell Efficacy Using Patient-Derived Organotypic Tumor Spheroids".

The study was a collaboration with the late Soldano Ferrone, MD, PhD, and was carried across the finish line by his daughter Cristina Ferrone, MD, Moshe Sade-Feldman, PhD, and several other collaborators at Massachusetts General Hospital.

What question were you investigating with this study?

What factors contribute to treatment resistance in chimeric antigen receptor (CAR)-T cell therapy treatments for solid tumors?

While CAR-T therapy treatments have proven effective in patients with blood tumors, their effectiveness in solid tumors has been limited due to a variety of factors, including the tumor microenvironment.

We used a unique 3D microfluidic model of tumors to investigate the mechanisms of treatment resistance to CAR-T cells that were designed to target B7-H3, a common antigen in solid tumor cancers.

What was unique about your approach?

While there are several different 3D models of tumors are available, they are limited in their ability to faithfully reproduce key elements of the tumor microenvironment.

We used patient-derived organotypic tumor spheroids (PDOTS), microphysiologic 3D models that replicate key features of the tumor microenvironment, enabling the study of interactions between tumors and immune cells.

What did you find?

We found an increase in the expression of inhibitory receptors in the CAR T cells after their initial encounter with the target cells, which caused dysfunction and limited their efficacy.

By inhibiting the function of TBK1, a gene previously associated with immune evasion, we were able to restore CAR-T cell activity, prevent dysfunction and increase T cell proliferation.

We also found that inhibition or deletion of TBK1 made cancer cells more susceptible to immune cell targeting and destruction.

What are the clinical implications and next steps?

The findings suggest that targeting TBK1 could reduce treatment resistance and enhance CAR T efficacy in solid tumor cells that are expressing B7-H3.

The findings also demonstrate the feasibility and utility of using PDOTS to study interactions between tumors and immune cells.

How did you come to work with the ferrones?

Soldano Ferrone's lab was on the same floor as ours and his office was a few doors done from mine. We'd frequently bump into each other and chat while preparing a morning or afternoon coffee. Upon hearing about our PDOTS models, he said, "We should collaborate and test our CAR-T cells in your PDOTS models." 

As a newly minted PI, I was excited that such a senior investigator was interested in partnering but wasn't sure exactly where the science might lead us.

Initially, Soldano's group simply provided the CAR-T cells, and we tested them in a handful of PDOTS specimens. 

But when we started observing diminished sensitivity to CAR-T cells in our PDOTS models that otherwise "should" have been responsive, we knew we had something big. We iterated from that point on, and this project was co-led by Yi Sun, PhD, from my lab and Luke Maggs, PhD from the Ferrone Lab.

After Soldano's passing, we wanted to complete the project but needed continued support and supply of CAR-T cells. 

With the continued support of Cristina Ferrone, MD, (now at Cedars Sinai) and Xinhui Wang, MD, PhD, (MGH) to generate and supply the CAR-T cells, we were able to wrap up the project. 

What other resources or collaborations made this study possible?

All our studies using PDOTS require a robust tissue banking infrastructure to supply high quality patient tumor specimens. 

Without great partnerships and collaborations with Genevieve M. Boland, MD, PhD, and Sonia Cohen, MD, PhD, this work would not be possible.

In addition to the leadership and vision provided by Drs. Boland and Cohen, the day-to-day operations of collecting, banking, and distributing patient tumor specimens relies on a well-trained, skilled, and dedicated team, which is led by Tatyana Sharova and Aleigha Lawless.

Our team operates on the MGH Main Campus to take advantage of proximity to the clinics and operating rooms, and Izabela Panova (our floor lab manager on Jackson 9) makes sure everything continues to run smoothly. 

Moshe Sade-Feldman, PhD (also a KF-CCR PI and Asst. Prof. of Medicine) and his team were instrumental in performing the needed single-cell RNA sequencing studies to determine how the tumor microenvironment was changing both the tumor cells and the CAR T-cells in our PDOTS models.

Lastly, funding from the Massachusetts Life Sciences Center Research Infrastructure Grant to create the MGH Tumor Cartography Center enabled us to purchase a large portion of the instrumentation used in this study.