T cell burnout may have a fix: blocking MEK signaling

A major obstacle in cancer immunotherapy is T cell exhaustion: the immune system's fighters burn out just when they seem to be winning. Scientists at Memorial Sloan Kettering Cancer Center may have found a way to slow that burnout.

Reporting in the journal Immunity, the team led by physician-scientist Santosha Vardhana identified a signaling molecule called MEK as a key driver of exhaustion. The study, described by ScienceDaily, suggests that blocking MEK could extend the effectiveness of treatments such as checkpoint inhibitors.

"A tragic part of T cell exhaustion is that the immunotherapy seems to be working for patients, and then it fades," Vardhana said. "Many of them experience a brief wisp of promise only to have it taken away."

How MEK pushes T cells to burnout

The finding builds on earlier work from Vardhana's lab showing that metabolism plays a role. When T cells are repeatedly exposed to cancer proteins, their mitochondria become overburdened. The cells then ramp up production of cytotoxic proteins, but the effort comes at a cost.

"It turns out that the decision to make high levels of these proteins is regulated by MEK," Vardhana said.

If MEK becomes too active, it drives T cells into terminal exhaustion — a state where even powerful immunotherapy cannot revive them. Surprisingly, exhausted T cells are not sluggish. First author Tanmana Mitra, a student in the lab, said the cells were highly active, investing enormous energy into making proteins.

"That paradox made us ask where all that energy was going," Mitra said. "It changed how we think about T cell exhaustion — from a problem of too little energy to one of excessive energy demand."

A tradeoff: long persistence vs. short punch

In laboratory models, blocking MEK allowed T cells to persist longer in the harsh environment around a tumor. But the effect came with a compromise: cells produced fewer cancer-killing proteins at any given moment.

Vardhana described it as pacing yourself on a long road trip rather than driving at full speed until the tank is empty. The immune attack becomes less intense, but the cells survive longer.

The researchers caution that MEK inhibition won't fit every patient. For patients with small, quickly shrinking tumors or many tumor-fighting T cells, a short, powerful response may be preferable. For those with large tumors or few T cells, a slower, sustained attack might be more valuable.

Potential across multiple therapies

MEK inhibitors are already FDA-approved for other uses, which could speed testing in humans. Vardhana says the approach could improve several types of immunotherapy, including checkpoint inhibitors, CAR T cell therapy, tumor-infiltrating lymphocyte therapy, and bispecific antibodies.

The study also acknowledges that T cell exhaustion has a protective side. Andrea Schietinger, an MSK immunologist, previously found that exhaustion can act as a survival mechanism, keeping T cells from overstimulating and dying. Inhibiting MEK may shift that balance.

"Once we know the answer to what sets the balance between conservation of energy and strong cancer-fighting activity, the therapeutic possibilities really start to fan out," Vardhana said.

• cancer
• Immunity
• immunotherapy
• MEK
• Memorial Sloan Kettering
• Santosha Vardhana
• T cell exhaustion