TIM-3 Identified as Common Culprit and Predictive Biomarker in Severe Bone Infections
核心洞察
Researchers identified the T cell protein TIM-3 (搜索) as a common factor in the most severe Staphylococcus aureus (搜索) bone and joint infections, offering a potential biomarker for predicting patient outcomes.
Serum immune checkpoint protein levels predicted patient outcomes with 90 percent accuracy, and TIM-3 (搜索) was highly predictive of adverse disease outcomes (AUC = 0.89) in a pilot cohort.
T cells become exhausted during chronic S. aureus infection, expressing high levels of immune checkpoint proteins including TIM-3 (搜索) and LAG-3 (搜索), which act as brakes on the immune system.
Bone and joint infections cause significant health problems for patients and lead to millions of dollars in added health costs per year, yet clinicians lack reliable tools to predict which patients will develop severe or persistent disease. When standard-of-care antibiotics fall short, there are no immunotherapies available to help patients mount a stronger defense against infection. In a study published in Nature Communications Medicine, University of Rochester Medicine (搜索) researchers have pinpointed a T cell protein, TIM-3 (搜索), as a common component in the most severe bone infections—a discovery that identifies both a potential biomarker to inform care plans and a possible new treatment option using drugs already shown to boost T cell performance in cancer patients.
T Cell Exhaustion in Chronic Infection
Center for Musculoskeletal Research scientist Gowrishankar Muthukrishnan, PhD, studies the body's immune response to bone infections, which are most commonly caused by Staphylococcus aureus (搜索) (S. aureus) and can occur following surgery to repair bone or implant an artificial joint. Muthukrishnan and colleagues studied humanized mice and patient bone samples and found that in chronic S. aureus infection, T cells become dysfunctional and express high levels of immune checkpoint proteins, including TIM-3 (搜索). These proteins act like brakes that hold the immune system back. The researchers also found that high TIM-3 levels in patient serum were associated with poor clinical outcomes.
"T cells can be exhausted in cancer and viral infections, but our understanding of T cell exhaustion mechanisms during S. aureus infections has been limited," said Muthukrishnan, assistant professor of Orthopaedics and Microbiology and Immunology. "Our research shows that T cells respond similarly in bone infection but also experience exhaustion due to constant antigenic stimulation from bacteria, which prevents them from performing their intended immune functions effectively."
A Predictive Biomarker with 90 Percent Accuracy
The findings suggest that immune checkpoint proteins could help identify high-risk patients, and that blocking these proteins could represent a new treatment strategy—lifting the brakes on the immune system to better fight bone infections. "We've shown that serum immune checkpoint protein levels could predict patient outcomes with 90 percent accuracy, which could help orthopedic surgeons determine whether patients should receive aggressive or conservative treatment for joint infections," Muthukrishnan said. "A biomarker could signal the severity of infection and shed light on why some patients' bodies fight the infection successfully while others suffer devastating complications."
The study employed multi-omics approaches, including flow cytometry, single-cell RNA sequencing (scRNA-seq), and immunofluorescence, in a humanized NSG-SGM3 BLT mouse model and with human clinical samples to characterize the human T cell landscape in S. aureus osteomyelitis (搜索). The researchers found that human T cells are remarkably heterogeneous in gene expression and abundance. Notably, CD4 Th1/Th17 cells comprise a mixed population of activated, progenitor-exhausted, and terminally-exhausted states with increased expression of immune checkpoint proteins LAG-3 (搜索) and TIM-3 (搜索). These proteins are upregulated in the serum and bone marrow of patients with S. aureus prosthetic joint infection (搜索) (PJI). In a clinically informative pilot cohort, a multiparametric diagnostic integrating high serum immune checkpoint protein levels with low proinflammatory cytokine levels (IFN-γ, IL-2, TNF-α, IL-17) revealed that TIM-3 was highly predictive of adverse disease outcomes (AUC = 0.89).
Repurposing Cancer Immunotherapies
Katya McDonald, a PhD candidate, and Motoo Saito, a postdoctoral associate in the Muthukrishnan lab, are co-first authors of the study. McDonald highlighted the potential benefit of repurposing cancer treatments for bone infection; T cell drugs fight cancer by reprogramming or boosting the body's white blood cells' ability to find and kill tumor cells.
"These drugs have been effective in treating non-solid tumors," she said. "If we know TIM-3 (搜索) is on T cells in bone infection, we may be able to leverage these drugs to suppress it. While physicians will continue to use antibiotics, these cancer drugs could be used in conjunction to help boost the immune system response to the infection."
The Burden of Bone Infections
Orthopaedic surgeons perform approximately two million joint replacements worldwide each year. Infection of the implant and surrounding bone is a disastrous complication for patients; although the frequency of cases following elective orthopaedic surgery is low (1-5%), reinfection or relapse rates are very high (up to 30%) and cost up to $150,000 per patient. Early detection could stop S. aureus cells from multiplying and spreading, but without a diagnostic tool, physicians grapple with how aggressively to fight the infection once it is embedded in bone. Antibiotics may resolve S. aureus in some patients; others may need more aggressive approaches, including removal of the infected implant or amputation to protect the patient from a life-threatening infection. Approximately 13% of patients infected with S. aureus become septic and die from multiorgan failure. Some patients develop chronic S. aureus osteomyelitis (搜索), which can be extremely difficult to eradicate and may require repeated revision surgeries and prolonged antibiotic treatment.
Next Steps Toward Clinical Translation
Muthukrishnan has earned a $2.7 million grant from the NIH to study potential diagnostic and treatment options for implant-associated bone infection. As part of the project, his lab will assess patients based on their T cell exhaustion profiles and test immune checkpoint blockade drugs' effectiveness in reprogramming exhausted T cells in chronic infections. "There are more than 2,600 ongoing clinical trials for cancer drugs, but very limited research to date on their use for bacterial infection," Muthukrishnan said.
As part of the project, Muthukrishnan will collaborate with orthopedic surgeons to collect bone marrow samples during revision surgeries to analyze T cell exhaustion phenotypes. "We hypothesize that persistent S. aureus infections cause impairment of T cells and can be leveraged as a functional biomarker of S. aureus implant-associated osteomyelitis (搜索) disease outcome," Muthukrishnan said. Ultimately, he aims to develop a serum test to help determine whether patients should receive aggressive or conservative treatment, and whether FDA-approved checkpoint blockade drugs could become a standard of care for bone infections.