Introduction

Immune checkpoint inhibitors (ICI), such as anti-PD1/PDL1 antibody, have been proved to be effective in advanced human bladder cancer. But we still don’t know why some patients respond to ICI but others not. In order to answer the question, preclinical mouse models mimicking the genetics of human bladder cancer are essential. We established two unique classes of novel mouse bladder cancer cell lines and examined if the syngeneic cell line tumors are applicable to immunological study of human bladder cancer.

Methods

We established BBN cell lines from N-Butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced mouse bladder cancer model and UPPL cell lines from Upk3a-CreERT2;Tp53 f/f; Pten f/f; Luciferase mouse model. Whole transcriptome profiling was performed on 12 BBN and 8 UPPL primary tumors. Unsupervised clustering and supervised clustering using BASE47, gene sets for identifying basal and luminal subtype, were performed. We treated the subcutaneous allografts of the established cell lines by anti-mouse Pdl1 antibody (10mg/kg, intraperitoneal injection, weekly) and analyzed the background of responders and non-responders with flow cytometry and T/B cell receptor (TCR/BCR) amplicon sequencing of tumor infiltrating lymphocytes.

Results

Finally 12 BBN cell lines and 8 UPPL cell lines were established. Unsupervised clustering of BBN and UPPL models demonstrated close clustering with human basal and luminal bladder cancers, respectively. More interestingly, BBN tumors had significant enrichment of immune related genes (Figure). We treated the allograft tumors of BBN963, BBN975 and UPPL1541 cell lines with anti-mouse Pdl1 antibody. Half of the BBN963-derived tumors responded to the treatment but BBN975 and UPPL1541-derived tumors not. Paradoxically BBN975 tumors, the non-responders, showed higher infiltration of CD3+ T cells.

Conclusions

We established mouse bladder cancer cell lines mimicking human basal and luminal bladder cancer. BBN963 could be used as mixed response model and BBN975 could be used as immune exhaustion model. We are now trying to elucidate the mechanism of differential response of the BBN and UPPL tumors to Pd1/Pdl1 blockade._x000D_

Funding

The Bladder Cancer Advocacy Network