Humanized mice, patient samples: TIM-3 may flag severe bone infections

When a Staphylococcus aureus (S. aureus) infection settles around an artificial joint, the next decision can range from antibiotics to implant removal or amputation. At University of Rochester Medicine, researchers found high levels of TIM-3, a T-cell protein, in chronic bone infections studied in humanized mice and patient samples; high TIM-3 in patient serum was associated with poor clinical outcomes.

The stakes are large even when the initial infection is rare. Surgeons perform approximately 2 million joint replacements worldwide each year, while infections after elective orthopedic surgery occur in 1–5% of cases. When infection returns or persists, relapse rates can reach up to 30%, with costs of up to $150,000 per patient. Early detection could help doctors decide how aggressively to intervene before S. aureus spreads through bone.

The findings point to T cells that have become dysfunctional during persistent infection. The researchers say constant stimulation by the bacteria leaves T cells dysfunctional and pushes them to express checkpoint proteins, which act like brakes on their ability to fight infection. The pattern resembles T-cell exhaustion seen in cancer and viral infections, but has been less understood in S. aureus bone disease.

Concretely, the proposed application is a blood-based risk signal. Muthukrishnan says serum immune checkpoint protein levels could predict patient outcomes with 90% accuracy, potentially helping orthopedic surgeons choose between conservative and aggressive care. Drugs that block these checkpoints have already been shown to boost T-cell performance in cancer patients, so the team suggests they could eventually be used alongside antibiotics rather than replacing them.

That remains a lab-stage result, not a new standard of care. The study does not describe a clinical test of checkpoint drugs for bone infection, and the serum test is still an aim of the research program. Katya McDonald, a Ph.D. candidate, and Motoo Saito, a postdoctoral associate, were co-first authors of the study published in Communications Medicine; whether releasing the TIM-3 brake improves outcomes in patients still requires testing.