AI Scans of a Neglected Chest Organ Predict Longevity and Immunotherapy Response, Two Nature Papers Find

Researchers at Mass General Brigham have published two studies in the same issue of Nature arguing that the thymus, an organ long considered biologically retired after puberty, continues to shape immune competence, disease risk, and survival well into adulthood.

The work centers on a deep-learning model trained on CT imaging. According to a press release reviewed by the Harvard Gazette, the AI framework was trained on more than 5,500 CT images to quantify size, shape, and the degree of fatty replacement inside the thymus, producing a composite "thymic health" score. That is the methodological detail worth sitting with: this is not a blood draw or a biopsy. It is a readout derived from scans many patients already receive.

In the first study, the team applied the scoring tool to data from more than 25,000 adults enrolled in a lung cancer screening trial and more than 2,500 participants from the Framingham Heart Study. As reported in the Mass General Brigham press release, individuals with higher thymic health scores had roughly a 50% lower risk of death from any cause, a 63% lower risk of cardiovascular death, and a 36% lower risk of developing lung cancer compared with those with the poorest scores. The associations held after adjusting for age and other covariates, though the observational design means confounding cannot be ruled out. Thymic health is almost certainly correlated with a cluster of upstream health behaviors and metabolic states, not all of which can be modeled out.

The second study addressed a question with direct clinical stakes: does thymic function predict who responds to immune checkpoint inhibitors? According to Inside Precision Medicine's coverage of the Nature papers, the team analyzed CT scans and outcomes from a pan-cancer cohort of 3,476 patients receiving checkpoint inhibitors. Patients with stronger thymic health had about a 37% lower risk of cancer progression and a 44% lower risk of death, even after accounting for patient, tumor, and treatment variables. The researchers also validated the thymic health score against T cell receptor diversity data from the prospective TRACERx lung cancer cohort, which provides a plausible mechanistic link: a healthier thymus produces a broader T cell repertoire, and a broader repertoire likely gives checkpoint blockade more targets to work with.

Hugo Aerts, director of the Artificial Intelligence in Medicine Program at Mass General Brigham and corresponding author on both papers, told the Harvard Gazette that "the thymus has been overlooked for decades and may be a missing piece in explaining why people age differently, and why cancer treatments fail in some patients."

The prior literature on this question was genuinely sparse. As the Mass General Brigham press release notes, previous research linking T cell diversity to immune aging relied largely on small, blood-based analyses. The new datasets are several orders of magnitude larger, and crucially they use imaging that is already embedded in standard clinical workflows. That is the practical upside. The caution is that an association between a CT-derived score and downstream outcomes is not the same as a demonstrated causal pathway or an actionable intervention. The team is now examining, per the press release, whether incidental radiation to the thymus during lung cancer treatment affects patient outcomes, which would be a cleaner test of directionality.

Neither paper has yet been replicated by an independent group, and the deep-learning model has not been externally validated on imaging data from outside the original training distribution. Those are standard next steps before a scoring tool moves into prospective clinical use. What the two studies do establish, with unusual statistical power, is that the chest organ most physicians stopped measuring decades ago may be worth a second look.

Sources cited:
- Harvard Gazette (https://news.harvard.edu/gazette/story/2026/03/thymus-may-be-critical-to-adult-health/)
- Mass General Brigham press release (https://www.massgeneralbrigham.org/en/about/newsroom/press-releases/thymus-critical-to-longevity-and-cancer-treatment)
- Inside Precision Medicine (https://www.insideprecisionmedicine.com/topics/oncology/thymic-health-may-predict-response-to-cancer-immunotherapy/)
- ScienceDaily (June 1, 2026 dispatch) (https://www.sciencedaily.com/releases/2026/06/260601025352.htm)