Chimeric Antigen Receptor T (CAR-T) cell therapy is a new type of cancer treatment that has shown great promise in treating blood cancers, such as B cell lymphomas and leukemias, and multiple myeloma. CAR-T cells are referred to as a “living drug”. They are made by collecting CD8+ T cells, a type of immune cell that has the potential to kill cancer cells, from the patient. In the laboratory, the collected T cells are engineered to produce a CAR molecule on their surface that recognizes a specific protein, or antigen, on the surface of the cancer cell. The CAR-T cells are then infused back into the patient and if all goes well, they will seek out and kill cancer cells that harbor the target antigen. Although CAR-T cell therapies can eradicate advanced disease and keep cancer at bay for many years, they lead to long-term survival in fewer than half of patients treated. Disease relapse after CAR-T cell therapy can occur due to lack of CAR-T cell persistence, or function or a combination of both.
During CAR-T cell manufacturing, the naïve T cells are treated with antibodies that bind to and stimulate CD3 and CD28 molecules on the T cell surface, which facilitates CAR gene transfer, increase CAR-T cell numbers, and promote their cancer-killing activity but may potentially compromise their long-term efficacy. In contrast, higher numbers of CD27+ T cells in the starting T cell population or the CAR-T cell product appear to have a more durable antitumor response. CD27 has long been associated with T cell memory for long-term protective immunity but the mechanism by which the CD27 molecules promote T cell memory was not previously known. “My PhD studies in Switzerland focused on trying to understand how the memory T cell state was programmed by CD27 costimulation, and identified TNIK (TRAF2- and NCK-interacting kinase) that acted downstream of CD27 to induce genes associated with memory differentiation” said Dr Carla Jaeger-Ruckstuhl, a postdoctoral fellow in Dr. Stan Riddell’s laboratory in the Translational Science and Therapeutics Division. In a recent publication in Immunity, Dr. Jaeger-Ruckstuhl dissected the role of CD27 in T cell memory. “The problem is that all naïve T cells express CD27 and the CD27-TNIK mechanism could not explain how T cells diversify both into effector cells needed to kill infected cells, and memory cells needed to respond to recurrent infection. When I joined the Riddell lab for postdoctoral training, I was motivated to resolve this question. Being able to generate memory T cells was also of translational importance since prior work from the Riddell lab had shown that central memory T cells engineered with CARs had the best long-term efficacy in cancer immunotherapy.”
To study the role of CD27 in T cell memory, Dr Jaeger-Ruckstuhl collaborated with Dr. Jim Olson’s lab at Seattle Children’s to generate a synthetic version of CD70, the natural ligand for CD27, to stimulate CD27 on naïve T cells. She found that CD27 stimulation by 70 at high doses antagonized CD28 signaling, transiently restrained proliferation and induced a metabolic, transcriptional, and epigenetic state that resembled memory T cells. “Carla’s perseverance and commitment to the project were critical for its success. She never wavered even when experiments provided what seemed to be confusing results,” said Dr. Riddell.
Since CD27 and T cell memory differentiation have been positively correlated with enhanced CAR-T efficacy, Dr Jaeger-Ruckstuhl examined if stimulating CD27 in place of CD28 during CAR-T cell manufacturing could enhance their therapeutic efficacy. CD3/CD27 or CD3/CD28 costimulated CAR-T cells were infused into mouse models of B cell lymphoma, lung cancer and breast cancer. In all cases, CD3/CD27 costimulated CAR-T cells displayed enhanced and more persistent antitumor activity.
“Our work raises many more questions that are the subject of ongoing and future work. The most immediate translational application would be to provide CD27 costimulation during manufacturing of CAR-T cells that target cancer cells,” said Dr Jaeger-Ruckstuhl. “An important finding in our study was that strong CD27 engagement recruited TRAF2 and SHP1 to an internalized complex and modulated Lck phosphorylation induced by CD3 and CD28 costimulation. T cell activation is complex and there are many cans that we were unable to open so far. It is likely that numerous other co-factors are being recruited to the CD27 receptor and we have only been able to study some of these co-factors and their downstream effects. Another translational direction would be to use this new knowledge to boost memory T cell function in vivo. This would require a better understanding of the determinants that regulate the induction of CD70, the CD27 ligand, on dendritic cells in lymphoid niches and what the consequences are on T cell migration, differentiation, and function,” concluded Dr Jaeger-Ruckstuhl.
The spotlighted research was funded by the National Institutes of Health.
Fred Hutch/University of Washington/Seattle Children's Cancer Consortium members Drs. Stanley Riddell, Scott Furlan, Lucas Sullivan, Steven Henikoff, Jay Sarthy, Raphael Gottardo and James Olson contributed to this work.
Jaeger-Ruckstuhl CA, Lo Y, Fulton E, Waltner OG, Shabaneh TB, Simon S, Murthuraman PV, Correnti CE, Newsom OJ, Engstrom IA, Kanaan SB, Bhise SS, Peralta JMC, Ruff R, Price JP, Stull SM, Stevens AR, Bugos G, Kluesner MG, Voillet V, Muhuthan V, Morrish F, Olson JM, Gottardo R, Sarthy JF, Henikoff S, Sullivan LB, Furlan SN, Riddell SR. 2024. Signaling via a CD27-TRAF2-SHP-1 axis during naive T cell activation promotes memory-associated gene regulatory networks. Immunity. 57(2):287-302