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Only a minority of patients derive long-term clinical benefit from anti-PD1/PD-L1 monoclonal antibodies. The presence of tertiary lymphoid structures (TLS) has been associated with improved survival in several tumor types. Here, using a large-scale retrospective analysis of three independent cohorts of cancer patients treated with anti-PD1/PD-L1 antibodies, we showed that the presence of mature TLS was associated with improved objective response rate, progression-free survival, and overall survival independently of PD-L1 expression status and CD8+ T-cell density. These results pave the way for using TLS detection to select patients who are more likely to benefit from immune checkpoint blockade., Competing Interests: DECLARATION OF INTERESTS LV, MB, SC, SLM, ML, IS, MT, GR, SP, MC, FC, CL, KB, MK, IG, CSF, VV, FC, WHF, and FLL: Nothing to disclose AB, JPG, and CR: Employees of Immusmol/Explicyte EO, AS: Employees of Astra Zeneca AI: Received research grants from Astra Zeneca, Bayer, BMS, Chugai, Merck, MSD, Pharmamar, Novartis, Roche, and received personal fees from Epizyme, Bayer, Lilly, Roche, and Springworks BB: Received grants from AstraZeneca , Pfizer , Eli Lilly , Onxeo , Bristol Myers Squibb , Inivata , Abbvie , Amgen , Blueprint Medicines , Celgene , GlaxoSmithKline , Ignyta , Ipsen , Merck KGaA , MSD Oncology , Nektar , PharmaMar , Sanofi , Spectrum Pharmaceuticals , Takeda , Tiziana Therapeutics , Cristal Therapeutics , Daiichi Sankyo , Janssen Oncology , OSE Immunotherapeutics , BeiGene , Boehringer Ingelheim , Genentech , SERVIER , Tolero Pharmaceuticals YL: Received grants and personal fees from Janssen, during the conduct of the study; personal fees and non-financial support from Astellas, grants and personal fees from Sanofi, personal fees and non-financial support from Roche, personal fees and non-financial support from AstraZeneca, grants, personal fees and non-financial support from MSD, personal fees and non-financial support from BMS, personal fees from Clovis , personal fees and non-financial support from Seattle Genetics, personal fees from Incyte, personal fees from Pfizer. AM: Received research grants from Mersu, Bristol-Myers Squibb, Boehringer Ingelheim, Transgene, MSD and received personal fees from Bristol-Myers Squibb, AstraZeneca, MedImmune, Oncovir, Merieux JCS: Has received consultancy fees from AstraZeneca, Astex, Clovis, GSK, GamaMabs, Lilly, MSD, Mission Therapeutics, Merus, Pfizer, Pharma Mar, Pierre Fabre, Roche/Genentech, Sanofi, Servier, Symphogen, and Takeda.

Background: LRRC15 is a member of the LRR (leucine-rich repeat) superfamily present on tumor-associated fibroblasts (CAFs) and stromal cells. The expression of LRRC15 is upregulated by the pro-inflammatory cytokine TGFβ. ABBV-085 is a monomethyl auristatin E (MMAE)-containing antibody-drug conjugate (ADC) designed to target LRRC15, and which has shown significant anti-tumor activity in several tumor models. This is the first focused examination of LRRC15 expression and ABBV-085 activity in soft-tissue sarcomas (STS)., Methods: We analyzed the LRRC15 expression profile by immunohistochemistry in 711 STS cases, covering a broad spectrum of STS histologies and sub-classifications. In vivo experiments were carried out by using LRRC15-positive and LRRC15-negative patient-derived xenograft (PDX) models of STS., Results: In contrast to patterns observed in epithelial tumors, LRRC15 was expressed not only by stromal cells but also by cancer cells in multiple subsets of STS with significant variations noted between histological subtypes. Overexpression of LRRC15 is positively correlated with grade and independently associated with adverse outcome. ABBV-085 has robust preclinical efficacy against LRRC15 positive STS patient-derived xenograft (PDX) models., Conclusion: We provide the first preclinical evidence that LRRC15 targeting with an antibody-drug conjugate is a promising strategy in LRRC15-positive STS. ABBV-085 is being evaluated in an ongoing clinical trial in STS and other malignancies.