Cellular Composition and Contribution of Tertiary Lymphoid Structures to Tumor Immune Infiltration and Modulation by Radiation Therapy

Abstract

Immune-based anti-cancer strategies combined with radiation therapy (RT) are actively being investigated but many questions remain, such as the ideal treatment scheme and whether a potent immune response can be generated both locally and systemically. In this context, tumor-associated tertiary lymphoid structures (TLS) have become a subject of research. While TLS are present in several types of cancer with strong similarities, they are especially relevant in medullary breast carcinoma (MBC). This suggests that MBC patients are ideally suited for investigating this question and may benefit from adapted therapeutic options. As RT is a corner-stone of MBC treatment, investigating interactions between RT and TLS composition is also clinically relevant. We thus first characterized the lymphoid structures associated with MBC in a patient case report and demonstrated that they closely resemble the TLS observed in a genetical mouse model. In this model, we quantitatively and qualitatively investigated the cellular composition of the tumor-associated TLS. Finally, we investigated TLS regulation after hypo-fractionated RT and showed that RT induced their acute and transient depletion, followed by a restoration phase. This study is the first work to bring a comprehensive and timely characterization of tumor-associated TLS in basal conditions and after RT. It highlights cellular targets (i.e., Tregs) that could be selectively modulated in subsequent studies to optimize anti-tumor immune response. The study of TLS modulation is worth further investigation in the context of RT and personalized medicine.

Emerging Opportunities of Radiotherapy Combined With Immunotherapy in the Era of Breast Cancer Heterogeneity

“…In a meta-analysis, CD3 + , CD8 + and the ratio of CD8 + /FOXP3 + TILs presented the most significant positive effect on survival (hazard ratio (HR): 0.59 (confidence interval (CI) 0.43–0.78; HR:0.71 (CI:0.62–0.82 and HR:0.48, CI:0.34–0.68, respectively) (55). The relevance of local lymphoid structures to support immune activation in response to RT has also been recently suggested by our group in medullary BC (56), a type of BC infiltrated with tertiary lymphoid structures (TLS). We showed acute and transient TLS depletion after hypo-fractionated RT, followed by a restoration phase and identified possible cellular targets (i.e., Tregs) that could be selectively modulated in subsequent studies to optimize anti-tumor immune response (56).…”

“…The relevance of local lymphoid structures to support immune activation in response to RT has also been recently suggested by our group in medullary BC (56), a type of BC infiltrated with tertiary lymphoid structures (TLS). We showed acute and transient TLS depletion after hypo-fractionated RT, followed by a restoration phase and identified possible cellular targets (i.e., Tregs) that could be selectively modulated in subsequent studies to optimize anti-tumor immune response (56).…”

Tertiary lymphoid structures in the era of cancer immunotherapy

“…The effect of cancer therapies on TLSs and the resulting potential impact on patient clinical outcome have begun to be explored. In the Kras LSL−G12D/+ Trp53 −/− (KP) genetically engineered mouse model of lung cancer, hypo-fractionated radiotherapy induces an early reduction in TLS densities followed by their restoration within 2 weeks 119 . Two independent studies of human NSCLC reported that TLSs present in lesions regressing after neoadjuvant anti-PD1 therapy 30 or chemotherapy 120 were associated with longer disease-free survival and overall survival 120 .…”

Radiotherapy in the Era of Immunotherapy With a Focus on Non-Small-Cell Lung Cancer: Time to Revisit Ancient Dogmas?

“…The reduction of the irradiated tissue volume would lead to the theoretical sparing of tumor-associated lymphocytes from the peri-tumoral TME, which can be rich in immune cells and can contain tertiary lymphoid structures ( 54 ). This sparing strategy could lead to a pro-immunogenic effect by sparing effector TILs which could otherwise be depleted following irradiation ( 54 ). It could also avoid the enhancement of proliferation and suppressive function of intra-tumoral T-reg, which has been shown following stereotactic irradiation ( 55 ).…”