Immune-checkpoint blockade transforms outcomes for some patients and fails others, and tumor mutational burden alone doesn't explain the gap. Tertiary lymphoid structures (TLSs) — organized immune aggregates that assemble inside tumors — have emerged among the strongest predictors of who responds. This review maps how TLSs are defined, detected, and graded across cancer types; why their maturity and location govern prognosis and immunotherapy response; and the preclinical strategies now being tested to build TLSs in tumors that lack them.
Published in Med (Cell Press), this comprehensive review was led by Florent Peyraud — an Institut Bergonié oncologist who completed his PhD at Explicyte under Prof. Antoine Italiano — with senior authorship from Alban Bessede and Antoine Italiano. Explicyte’s translational team co-authored the work and contributed original digital-pathology and multiplex-immunofluorescence imaging of TLSs at different maturation stages (Figures 1 and 2), drawing on the standardized mature-TLS scoring methodology the group developed and validated across thousands of tumor samples.
The review organizes TLSs into three stages — early/immature aggregates, primary follicle-like, and fully mature secondary follicle-like structures with germinal centers. It anchors this on a standardized pathology algorithm validated on 357 samples (211 carcinomas, 146 sarcomas), which defines a TLS as an aggregate of more than 50 admixed B and T cells on HES-stained slides and grades maturity by a visible germinal center on HES or a CD23+ follicular dendritic cell network by IHC.
Using HES plus CD20 and CD23 IHC on serial sections, Explicyte screened 1,295 tumor samples spanning 33 histotypes and found mature TLSs in 35.7% (427/1,295), with the lowest prevalence in soft-tissue sarcoma and the highest in colorectal, head and neck, and pancreatic tumors (Figure 2). Applied in routine pathology, the same approach identified mature TLSs in 33.5% of 1,383 cases — 36.2% of carcinomas, 24.8% of sarcomas, and 25.0% of neuroendocrine tumors.
Across NSCLC, STS, HNSCC, RCC, urothelial, and colorectal cancers treated with anti-PD1/PD-L1, mature TLSs — but not immature ones — correlated with higher response rates and longer PFS and OS, independently of PD-L1 expression and CD8+ T-cell infiltration. In the TLS-selected PEMBROSARC sarcoma cohort, pembrolizumab produced a 30% objective response rate and 40% six-month non-progression, versus 2.4% and 4.9% in an unselected cohort.
The review details AI tools that read TLSs directly from H&E/HES whole-slide images. One detection model was trained on 2,959 manually annotated TLSs from 212 sarcoma patients, generalized to other cancer types, and correlated TLS presence with improved overall survival; a pan-cancer classifier reached 90% sensitivity at 68% specificity, pointing toward standardized, tissue-sparing screening.
The therapeutic section synthesizes preclinical strategies to build or mature TLSs — CXCL13, CCL21, and LIGHT delivery, STING/CD40/TLR9 agonists, radiotherapy, chemotherapy, and antiangiogenic-plus-PD-L1 combinations. Early clinical translation is underway: a histology-agnostic phase 2 trial of avelumab plus regorafenib in mature-TLS-positive tumors showed durable responses even in typically immunotherapy-resistant settings such as MSS colorectal, biliary tract, and thyroid cancers, with 11 TLS-guided trials tracked in the review.
For drug developers, TLSs offer a biomarker that predicts immunotherapy benefit where TMB and PD-L1 fall short — and a therapeutic target in their own right.
Mature TLSs predict checkpoint-inhibitor benefit independently of PD-L1 and CD8+ T-cell infiltration, making them a candidate stratifier for trials in tumors where existing biomarkers underperform. For combination-regimen developers, TLS-inducing agents — from CXCL13 and LIGHT to STING and TLR9 agonists — offer a route to convert cold tumors into responsive ones. Both hinge on reliable, standardized TLS detection and scoring, which is where validated grading algorithms and digital pathology become decisive.
