The impact of neoadjuvant therapy on the formation of tertiary lymphatic structures and the distinct prognosis in prostate cancer.

411 Background: This study aims to investigate the characteristics and prognostic predictive efficiency of tertiary lymphoid structures (TLS) in prostate cancer (PCA). We also perform experiments to explore the effects of neoadjuvant hormone therapy (NHT) on TLS formation and immune infiltration in PCA. Methods: We retrospectively collected paraffin-embedded tumor tissue samples from 27 patients who didn`t receive NHT and underwent radical prostatectomy for PCa, and these patients were categorized as Cohort 1. We Additionally retrospectively collected 28 PCa tumor samples, from 14 NHT treated and 14 NHT naive patients, which are categorized as Cohort 2. We prospectively collected prostate biopsy tissue samples, as well as corresponding radical prostatectomy tumor specimens, from 21 patients who all received NHT and are categorized as Cohort 3. We performed HE staining and Multiplex immunohistochemical (mIHC) staining for ki67, panCK, CD21, CD4, CD8, and CD20 to evaluate TLS characteristics and immune infiltration level in different cohorts. We enrolled two GEO cohorts to evaluate the difference of TLS signature between NHT treated PCA and NHT-Naive PCA patients, and between pre-NHT and post-NHT tumor paired samples. We developed an immunocompetent orthotopic prostate cancer mouse model based on CRISPR-Cas9 gene editing technology. In in vivo experiments, we utilized flow cytometry to investigate the difference of CD4 and CD8 immune cell infiltration level in tumor tissues of mice treated or not with androgen deprivation treatment. Results: We found most of the NHT-naive PCa tissues were TLS positive (93%), and the majority of TLSs are located within the tumor region. Patients with positive mature TLSs, SFL-TLSs and higher intra-tumor TLSs density had significantly longer PFS duration. Compared with that in patients received no NHT, TLSs maturity grade and density were higher in NHT treated patients. A matched analysis using biopsy and paired post-NHT tumor samples revealed that NHT significantly increased the positive detection rate of tertiary lymphoid structures (TLSs) within the tumor, the maturity grade of TLSs, and the level of CD8+ T cell infiltration within the TLSs. Transcriptome analysis revealed elevated TLSs signature expression and CD8+ T cell infiltration in NHT treated tumor samples. In vivo experiments also show elevated CD3+ and CD8+ T cells infiltration level after NHT treatment. Conclusions: This study comprehensively characterizes TLSs in PCa and highlights the heterogeneity among patients. Our clinical cohort data, transcriptome sequencing analysis, and in-vivo experiment data confirm that neoadjuvant hormone therapy promotes immune cell infiltration, as well as the formation and maturation of TLSs within PCa tissues. Combining endocrine therapy with immunotherapy is a potential treatment approach for promoting prostate cancer prognosis.