Abstract 1493: Therapeutic efficacy and tolerability of combined immune checkpoint blockade in metastatic melanoma patients is influenced by the gut microbiome
Authors: Gopalakrishnan Vancheswaran , Andrews Miles , Chen Wei-Shen , Spencer Christine , Vence Luis , Reuben Alexandre , Cooper Zachary A. , Prieto Peter A. , Tetzlaff Michael T. , Khan MA Abdul Wadud , Lazar Alexander , Hudgens Courtney W. , Haydu Lauren E. , Tawbi Hussein A. , Hwu Patrick , Hwu Wen-Jen , Amaria Rodabe N. , Burton Elizabeth M. , Woodman Scottt E. , Diab Adi , Patel Sapna P. , Glitza Isabella C. , Zhang Jianhua , Petrosino Joseph , Jenq Robert R. , Davies Michael A. , Gershenwald Jeffrey E. , Sharma Padmanee , Allison James P. , Futreal Andrew , Wargo Jennifer A. 
Published: August 2019

Abstract
Background: The gut microbiome is increasingly being recognized as a strong modulator of anti-PD1 based cancer immunotherapy. Compelling evidence demonstrates differential bacterial enrichment and diversity in responders (R) versus non-responders (NR), mediated by profound influences on systemic and anti-tumor immune infiltrates. However, this has not been studied in the setting of treatment with combined immune checkpoint blockade (CICB), which is associated with superior response rates, but higher rates of potentially debilitating toxicities.
Methods: We assembled a cohort of patients with metastatic melanoma receiving CICB (n=54). All patients were classified as R (n=31, CR + PR) or NR (n=23, SD + PD) based on RECIST v1.1, and as having grade 3 or higher (T; n=29), or less than grade 3 (NT; n=25) immune related adverse event(s) by NCI CTCAE 4.0 criteria. Baseline stool samples were characterized by 16S rRNA sequencing. Correlative analyses of peripheral immune cell populations by flow cytometry (n=12) and circulating T cell repertoire by TCR-sequencing (n=12) were done on matched pre-treatment blood samples.
Results: The overall gut microbial landscape in these patients was varied with high abundance of Bacteroidales and Clostridiales. Ordination of beta-diversity distances revealed a lack of clustering by subtype of primary tumor (uveal, mucosal, cutaneous) consistent with no significant effect of the tumor histology. While no apparent response or toxicity associations were evident based on diversity, notable compositional differences were appreciated. Comparison of relative abundances by LEfSe (LDA&gt;2, p&lt;0.05), and pairwise Mann-Whitney tests revealed an enrichment of Bacteroides stercoris (p=0.03), and Parabacteroides distasonis (p=0.04) in R, and Lactobacillales (p=0.005) in NR. Consistent with our prior findings, the median relative abundance of the order Clostridiales was again higher in R (0.34) versus NR (0.26). On the other hand, Bacteroides intestinalis (p=0.01) and Anaerotignum lactatifermentans (p=0.006) were enriched in T and NT, respectively. Importantly, correlative analyses with circulating immune cell subsets revealed distinct associations by differential bacterial enrichment (including positive correlations between overall CD8+ T-cell abundance and R-taxa), and a clustering effect by high or low T-cell repertoire entropy.
Conclusion: These findings build on our prior work and support the notion of a close link between the gut microbiome and therapeutic outcomes to checkpoint blockade therapy. Extensive studies are underway in both matched human biospecimens and in pre-clinical models to further understand mechanisms of interactions with immune markers, and to establish causality. Taken together, these data support a critical role for the gut microbiome as both a predictive tool and therapeutic target.
Citation Format: Vancheswaran Gopalakrishnan, Miles Andrews, Wei-Shen Chen, Christine Spencer, Luis Vence, Alexandre Reuben, Zachary A. Cooper, Peter A. Prieto, Michael T. Tetzlaff, MA Abdul Wadud Khan, Alexander Lazar, Courtney W. Hudgens, Lauren E. Haydu, Hussein A. Tawbi, Patrick Hwu, Wen-Jen Hwu, Rodabe N. Amaria, Elizabeth M. Burton, Scottt E. Woodman, Adi Diab, Sapna P. Patel, Isabella C. Glitza, Jianhua Zhang, Joseph Petrosino, Robert R. Jenq, Michael A. Davies, Jeffrey E. Gershenwald, Padmanee Sharma, James P. Allison, Andrew Futreal, Jennifer A. Wargo. Therapeutic efficacy and tolerability of combined immune checkpoint blockade in metastatic melanoma patients is influenced by the gut microbiome [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1493.