Thymulin decline with age may restore anticancer immunity in older patients

Thymulin, a peptide produced by the thymus, acts as a systemic brake on inflammation by suppressing pro-inflammatory myeloid cells through NF-κB pathway inhibition, yet its production collapses as the thymus atrophies into fat tissue around age 50 in most individuals. An international team found that aged mice and humans show dramatically elevated frequencies of pro-inflammatory myeloid cells with markedly higher IL-1α, IL-1β, IL-6, and TNF-α production, enriched within breast tumor microenvironments and directly associated with accelerated tumor progression. Using heterochronic parabiosis and bone marrow chimeras, they demonstrated that thymulin—abundant in young circulation—suppresses this inflammatory activation in aged myeloid cells. The core finding: thymulin not only restrains chronic inflammation but enhances antitumor T-cell immunity, improves tumor control, and critically sensitizes tumors to anti-PD-L1 immunotherapy in an age-dependent manner. For the longevity-minded reader, this reveals a concrete therapeutic pathway: thymulin replacement as a strategy to reverse immune decline specifically in treatment-resistant cancers in older patients.