In a quiet lab in La Jolla, a molecule called SAR'877 is reawakening immune cells that had all but given up their fight against cancer. At Scripps Research, Professor John Teijaro and his team are pioneering a bispecific drug that doesn’t just boost the immune system—it guides the boost exactly where it’s needed, reviving exhausted T cells without unleashing the dangerous inflammation that has derailed similar therapies. For patients who’ve run out of options, this precision could be transformative.
Cancer immunotherapies like checkpoint inhibitors and cytokines have changed outcomes for many, but their limitations are stark: some patients don’t respond, others relapse, and powerful side effects like systemic inflammation can force treatment to stop. SAR'877 aims to overcome both hurdles by combining two functions in one molecule. One end targets PD-1, releasing the brakes on T cells, while the other delivers a weakened form of interleukin-15 (IL-15) directly to those same cells. Because the cytokine is tethered and weakened, it acts locally—stimulating only the T cells already primed to fight, not the entire immune system.
In mouse models of chronic viral infection—a gold standard in immunology developed decades ago in the lab of Scripps’ Michael Oldstone—SAR'877 outperformed both standalone PD-1 inhibitors and untargeted IL-15, clearing viruses from blood and kidneys more effectively than any combination of existing treatments. Even more surprising was the role of CD4+ helper T cells. Long overlooked in cancer immunotherapy, these cells surged in activity under SAR'877. When researchers removed them, the drug’s benefits vanished—revealing a hidden linchpin in the immune response.
The results in cancer models were just as striking. Across 12 different tumor types, SAR'877 shrank tumors in every case. In mice with liver or breast cancer, more than two-thirds saw their tumors completely eliminated. Now, a phase 1/2 clinical trial is underway, showing early promise in patients who no longer respond to conventional immunotherapies.
This isn’t just about stronger signals—it’s about smarter ones. By focusing stimulation on the immune cells already engaged in the fight, SAR'877 avoids the chaos of broad activation. And with IL-15’s reach carefully limited, the risk of life-threatening inflammation drops. As Teijaro puts it, “You can deliver the immune-stimulating signal to the cells that need it most.” That precision may be the key to unlocking durable responses in patients who’ve run out of hope—and out of treatments.