A study published in Nature Aging demonstrates that aging and biological sex significantly reshape how the immune system combats cancer, with clear consequences for immunotherapy success. Investigators at the Mass General Brigham Cancer Institute merged mouse-based experiments with human observations to pinpoint these differences, tracing them from the thymus, the organ responsible for T cell maturation, to the progressive shrinkage of lymph nodes over time.
Sex-based differences in immune aging
Lutz Menzel, Ph.D., the study’s lead author, and senior author Tim Padera, Ph.D., monitored immune changes in male and female mice throughout their lives. Their analysis revealed that middle-aged male mice experienced an earlier decline in naive CD8 T cells, the immune system’s primary responders to tumors, compared to females. This reduction aligned with smaller lymph nodes, limiting the number of T cells available to identify melanoma-specific antigens.
Human data reinforced these findings: biological males exhibited earlier thymic shrinkage and lower naive T cell counts, which corresponded with reduced tumor recognition capabilities. To test whether reversing these effects could strengthen immunity, the researchers temporarily reduced the suppressive influence of male sex hormones on the thymus in aging mice. This intervention restored naive T cell numbers, improved tumor detection, and enhanced responses to immune checkpoint inhibitors.
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The results indicate that sex hormones play a direct role in thymic function, which in turn governs how effectively the immune system adapts to cancer. This challenges the prevailing view that the thymus becomes irrelevant after childhood, instead demonstrating its ongoing importance for sustaining immune readiness.
Implications for cancer therapy
Immunotherapies, including checkpoint inhibitors, depend on a patient’s ability to produce new T cells capable of targeting tumors. The study’s findings suggest that older men, who face earlier thymic decline, could benefit from treatments designed to preserve or restore thymic output. For instance, strategies to counteract hormone-driven thymic suppression might help maintain naive T cell populations, potentially improving immunotherapy efficacy.
Reevaluating the thymus’s role
Separate research from the Scadden Lab and the Artificial Intelligence in Medicine (AIM) Program at Mass General Brigham has already questioned the assumption that the thymus becomes nonfunctional after puberty. This study builds on that work by showing that adult thymic activity directly influences the pool of naive T cells available for cancer defense. Without sustained thymic output, lymph nodes shrink, and the immune system’s ability to recognize new threats, including tumors, weakens.