PD42-03 HIGH LEVELS OF BASELINE IGG1, IGG3, AND IFN-G MAY BE ASSOCIATED WITH RESISTANCE TO BCG THERAPY FOR TREATMENT OF NMIBC Jorge Daza*, Yuanshuo Wang, Andrew Charap, Berengere Salome, Rachel Brody, Emilie Grasset, New York, NY; Giuliana Magri, Barcelona, Spain; Dominic LaRoche, Yong Lee, Tuscon, AZ; Rafael Cabal, Adam Farkas, Li Wang, Jun Zhu, Kristin Beaumont, Ketan Badani, Reza Mehrazin, Peter Wiklund, Robert Sebra, Matthew Galsky, Nina Bharwadj, Amir Horowitz, John Sfakianos, New York, NY INTRODUCTION AND OBJECTIVE: The mechanisms that contribute to protection from tumor recurrence after M.Bovis BCG are not fully elucidated. We aim to evaluate the role of Antibody Dependent Cell Cytotoxicity (ADCC) in BCG therapy for NMIBC. METHODS: Formalin-fixed and paraffin-embedded (FFPE) tissue sections before and after BCG therapy were used for bulk targeted gene expression analysis. Differential gene expression analysis was performed on targeted RNAseq data. Gene Set Enrichment Analysis (GSEA) was performed using the “Hallmark Gene Sets” from the Broad Intitute's Molecular Signatures Database (MSigDB) and customized assembled gene sets. Enzyme linked immunosorbent assay (ELISA) and OLink Proteomics Ò inflammation panel were used to profile IgG1/3, and Interferon Gamma (IFN-g), respectively on prospectively collected plasma from BCG-treated patients (N[14) at specific timepoints throughout the treatment. RESULTS: B cell markers and IFN-g signatures were the two most enriched pathways after BCG therapy in the GSEA (Fig. 1A). We also observed significantly increased gene expression of IgG1 and IgG3 after BCG therapy (Fig. 1B), which may induce ADCC reactivity via FcgRIIIA signaling. In non-recurrent cases, we observed an increase in plasma IgG1/3 concentration that preceded IFN-g hyperactivity after 1st and 3rd BCG doses (Fig. 2). In contrast, patients that recur after BCG therapy had higher levels of plasma IFN-g at baseline, which remained elevated throughout the induction phase unrelated to IgG1/3 concentrations (Fig. 2). While the median recurrence time was 3.9 months, the median follow-up for non- recurrent patients was 36.7 months. CONCLUSIONS: We observed increased expression of B cell- related genes and an IFN-g signature after BCG therapy. Moreover, we found that response to BCG may include activation of Immune cells through IgG1/IgG3-mediated ADCC reactivity. Future studies in larger patient cohorts should measure IFN-g during BCG therapy and consider a role for ADCC in mediating protection from tumor recurrence BCG therapy. Source of Funding: Self-funded PD42-04 TUMOR MICROBIOME ASSOCIATED WITH BCG RESPONSE IN NON-MUSCLE INVASIVE BLADDER CANCER Jacob Knorr*, Ava Adler, Jose Agudelo, Kyle Ericson, Prithvi Murthy, Rebecca Campbell, Petar Bajic, Nima Almassi, Christopher Weight, Georges-Pascal Haber, Aaron Miller, Byron Lee, Cleveland, OH INTRODUCTION AND OBJECTIVE: M. bovis Bacillus Calmette-Guerin (BCG) is the standard of care for high-risk non-muscle invasive bladder cancer. Despite well-established efficacy, no clinical marker has been identified to reliably predict durable response to BCG. A potential marker may be the local urinary microbiome, which has been closely tied to the host immune system and implicated in genitourinary disease. Our objective was to characterize the urinary microbiome in bladder tumors from BCG responders and non-responders. METHODS: We conducted microbiome analyses on formalin- fixed bladder tumor tissue from patients who subsequently received intravesical BCG therapy for bladder cancer. Patients were identified as BCG responders or non-responders, with BCG response defined as no disease two years from induction BCG. Paired tumor specimens were also included for non-responders who underwent cystectomy after BCG failure. DNA was extracted for 16S high-throughput sequencing (Illumina MiSeq). Sequence reads were assigned to genus-level amplicon sequence variants (ASVs) in DADA2 and analyzed in Phyloseq. Statistical tests included paired t-test and Permanova analysis. RESULTS: Species richness was not significantly different between BCG responders (n[14) and non-responders (n[12) (p[0.196). However, overall microbiome composition did differ significantly (p[0.011), with enrichment of Corynebacterium and Pseudomonas in responders vs. non-responders. In paired non- responder samples before BCG (n[12) and at cystectomy (n[9), there were no significant differences in species richness (p[0.489) or overall composition (p[0.107). However, the microbiome after BCG failure demonstrated differential enrichment in Acinetobacter, Lactobaccilus, Corynebacterium, Pseudomonas, and Staphylococcus. In targeted analysis, M. bovis was enriched in non-responder tumors after BCG failure. CONCLUSIONS: The bladder tumor microbiome may be asso- ciated with response to BCG therapy. Enrichment of Corynebacterium in responders is notable given taxonomic similarities with M. bovis. Enrich- ment in certain ASVs after BCG suggests this therapy alters the Vol. 206, No. 3S, Supplement, Sunday, September 12, 2021 THE JOURNAL OF UROLOGY Ò e725 Copyright © 2021 American Urological Association Education and Research, Inc. Unauthorized reproduction of this article is prohibited.