Shrinking Lymph Nodes Explain Why Men Lose Cancer-Fighting T Cells Earlier

Why do men face nearly twice the cancer risk of women, with the gap widening sharply in middle age? A new study published in Nature Aging offers an unexpectedly anatomical answer: the lymph nodes of males contract earlier and more dramatically than those of females, draining away the naive CD8+ T cells that the immune system needs to recognize and attack tumors. The research, led by Lutz Menzel and Timothy Padera of Massachusetts General Hospital and Harvard Medical School, together with colleagues in Sweden, traces a chain of events that begins with the thymus, runs through a little-understood T cell lineage called virtual memory cells, and ends with compromised cancer surveillance in men during the very decades when cancer incidence climbs.

The starting point of the study was a striking clinical pattern. Data from the Surveillance, Epidemiology and End Results program show that men have higher overall cancer incidence, including melanoma, with the sex difference becoming apparent in middle age. When the researchers analyzed single-cell RNA sequencing data from human melanoma samples, they found that tumors from men contained a higher relative proportion of naive-like CD8+ T cells compared with antigen-experienced, cytotoxic or exhausted T cells. In other words, many of the T cells infiltrating male tumors appeared to be bystanders that had never been properly activated against the cancer. This suggested that the deficit was not inside the tumor itself but upstream, in the lymph nodes where T cell priming takes place.

Lymph nodes are the staging grounds of adaptive immunity. To mount an effective response against a tumor, rare naive T cells carrying the right T cell receptor must physically encounter antigen-presenting cells displaying tumor antigens. Because anticancer responses are inherently stochastic and driven by rare, functionally critical clones, the absolute number of naive T cells available in a draining lymph node directly determines the probability that a cancer-reactive clone will be found and activated. The team hypothesized that if male lymph nodes hold fewer naive CD8+ T cells, the odds of successful tumor antigen recognition fall accordingly.

To test this, the researchers turned to computed tomography scans from publicly available human imaging databases and performed three-dimensional volume segmentation of lymph nodes. The results were unambiguous: men had significantly smaller lymph nodes than women, along with larger spleens. In mice, lymph node size and cellularity declined with age in both sexes, but the decline occurred earlier and more markedly in males, producing a significant sex disparity by middle age. The effect was most pronounced in skin-draining lymph nodes, was independent of reproductive status and genetic background, and lymph node weight correlated strongly with cellularity, confirming that the shrinkage reflected a genuine loss of lymphocytes rather than structural remodeling alone.

The cellular culprit behind this attrition proved to be a process called antigen-agnostic differentiation into virtual memory T cells. Naive CD8+ T cells normally exit the naive pool either through genuine antigen activation or through a poorly understood pathway in which they convert into virtual memory cells without ever seeing a foreign pathogen. These virtual memory cells are shorter-lived, more prone to senescence, produce effector cytokines readily but lose proliferative capacity, and preferentially relocate from lymph nodes to the spleen, bone marrow and liver. Crucially, the propensity to undergo this conversion is stamped during thymic selection: clones with higher reactivity to self-peptides, marked by elevated CD5 expression, convert preferentially over time.

Here the sex bias emerged at a mechanistic level. Young adult male mice carried a higher frequency of CD5-high naive CD8+ T cells than females, and analysis of human single-cell datasets showed elevated CD5 expression among the most self-reactive CD8+ thymocytes and naive T cells in men. Although the frequency difference was modest, roughly 0.7 percent in women versus 1.1 percent in men, it operates on a compartment comprising more than 85 percent of all CD8+ T cells, creating a large absolute pool of highly self-reactive clones. The researchers built a simple mathematical model showing that this small initial difference drives cumulative divergence in virtual memory generation and naive T cell depletion over decades. Experiments with OT-I transgenic mice, whose T cells carry uniformly high self-reactivity, confirmed that strong self-reactivity alone is sufficient to accelerate virtual memory conversion and contract the naive pool.

The team then established causality in the opposite direction. They treated young adult female mice with interleukin-15 complexes, which act as a permissive signal lowering the self-reactivity threshold for virtual memory conversion. A four-week course of treatment transiently expanded the virtual memory compartment, and remarkably, seven months later these mice showed a lasting reduction in naive CD8+ T cells that mimicked the profile of age-matched untreated males. When tumors were implanted, the treated females had fewer activated CD8+ T cells in tumor-draining lymph nodes and reduced tumor control in middle age, despite showing no short-term impairment. Early-life skewing toward virtual memory cells, in other words, trades immediate immune readiness for long-term repertoire erosion.

The second half of the mechanism concerns the thymus. Because naive T cells were being lost faster in males, replenishment depended on continued thymic output, yet the thymus involutes earlier in men. Using the Swedish CArdioPulmonary bioImage Study cohort of more than a thousand middle-aged participants, the researchers showed that poor thymic health, graded by fatty replacement on CT scans, correlated significantly with lower numbers of circulating naive CD8+ T cells, and that recent thymic emigrants tracked with naive cell frequency. When the team surgically removed the thymus from young mice, the female advantage in lymph node cellularity and naive CD8+ T cell numbers vanished by middle age, and with it the sex differences in tumor-specific recognition and tumor suppression. Notably, naive CD4+ T cells remained relatively stable across ages, explaining why total T cell numbers can appear preserved even as the CD8+ compartment quietly collapses.

The therapeutic implications were the most striking part of the study. Because androgens suppress thymic function, the researchers tested sex steroid ablation in middle-aged male mice, using both surgical gonadectomy and the FDA-approved gonadotropin-releasing hormone antagonist degarelix. Both approaches increased thymic cellularity, restored recent thymic emigrant production, repopulated lymph nodes with naive CD8+ T cells, and raised the frequency of antigen-experienced and tumor-specific T cells in draining lymph nodes and tumors. Tumor growth dynamics equalized between the sexes, and preconditioning with degarelix enhanced the response to subsequent anti-PD-1 checkpoint blockade. In aged males the intervention was far less effective, underscoring a narrowing therapeutic window before stromal fibrosis and epithelial senescence irreversibly limit regeneration.

The study reframes immune aging as a sex-specific, anatomically localizable process rather than a diffuse decline. Effective cancer surveillance, the authors argue, depends not on the ratio of naive to memory cells but on the absolute number of unique naive clones physically present in draining lymph nodes at any moment, a quantity that men exhaust earlier through the twin pressures of self-reactivity-driven virtual memory conversion and androgen-accelerated thymic involution. The findings align with recent clinical evidence linking thymic atrophy to increased cancer risk and reduced immunotherapy responsiveness, and they suggest that short-term androgen blockade, already feasible in the clinic, deserves evaluation as a strategy to restore immune competence in middle-aged men, particularly before immunotherapy or in cancers where lymph node priming determines outcome.

Subject of Research: Sex-biased decline of naive CD8+ T cells and lymph node contraction during immune aging and its impact on cancer antigen recognition

Article Title: Lymph node contraction links sex-biased naive CD8+ T cell decline to compromised antigen recognition during middle age

Article References: Menzel, L., Zschummel, M., O’Melia, M. J., Sandstedt, M., Zhou, H., Lei, P.-J., Liu, L., Lee, H., Sen, D. R., Munn, L. L., Jonasson, L., & Padera, T. P. (2026). Lymph node contraction links sex-biased naive CD8+ T cell decline to compromised antigen recognition during middle age. Nature Aging. https://doi.org/10.1038/s43587-026-01238-4

Image Credits: AI Generated

DOI: 10.1038/s43587-026-01238-4

Keywords: immune aging, naive CD8+ T cells, lymph nodes, thymic involution, virtual memory T cells, sex differences, cancer immunotherapy, anti-PD-1, androgen ablation, tumor immunity, T cell receptor diversity, melanoma