409P - Tertiary lymphoid structures are scarce but associated with BCR clonal expansion, B cell activity and checkpoint inhibitor response in advanced osteosarcoma

Background

Tertiary lymphoid structures (TLS) have been associated with tumor response to checkpoint inhibitors (ICIs) in soft tissue sarcoma as well as several epithelial cancers. However, its role in bone sarcoma has not been thoroughly investigated to date.

Methods

We retrospectively evaluated the presence of TLS by histology examination in 75 osteosarcoma specimens, including 29 primary lesions and 46 recurrent lesions. There were 48 males and 27 females, with a median age of 16(range 7∼57) yo. RNA-seq was performed to interrogate the immune cell infiltration, B-cell receptor (BCR) repertoire as well B cell activity-related pathways. The therapeutic response of ICIs in relation to TLS was also investigated in 31 patients with advanced osteosarcoma.

Results

We observed the presence of tumor-associated TLS in 13(17.3%), TLS outside the tumor in 16 (21.3%), absence of TLS in 32 (42.7%) samples and not evaluable in 14 (18.7%) samples. Surprisingly, the mPFS following ICI was 5.5 months in patients with tumor-associated TLS, yet tremendously shorter in patients with TLS outside tumor (2.0 months) or without TLS (3.0 months). Additionally, we found the majority of tumor-associated TLS were located peri-tumor (11) rather than intra-tumor (2), indicating a potential suppressive microenvironment of TLS formation. There was no association of age, gender, lymph node status, and metastasis burden with the presence of TLS. However, metastatic lesions and tumors pretreated with gemcitabine-docetaxel were more likely to be TLS-present. Interestingly, the presence TLS was significantly associated with T cell activation and NK cell activity in the tumor microenvironment. Higher clonality, but not diversity or richness, of BCR repertoire found in TLS-present tumors suggested the role of BCR clonal expansion in antitumor activity. Furthermore, we observed an upregulation of numerous targetable checkpoint molecules associated with TLS-present tumors, such as TIM3, VISTA, PD-L1, PD-1, LAG3, IDO, CTLA4, CD40, etc.

Conclusions

Our report suggested the presence of TLS as a potential biomarker and the induction of TLS as an appealing strategy to boost ICI immunotherapy in osteosarcoma.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Ruijin Hospital.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.