In Vivo Syngeneic Tumor Models with Acquired Resistance to Anti–PD-1/PD-L1 Therapies

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ABSTRACT

Antibodies targeting PD-1 and PD-L1 have produced durable responses in a subset of patients with cancer. However, a majority of these patients will ultimately relapse due to acquired resistance. To explore the underlying mechanisms of this secondary resistance, we developed five syngeneic murine tumor variants with acquired resistance to anti-PD-1 and/or PD-L1 antibodies in vivo. Resistant in vivo models were obtained by serial treatment/reimplantation cycles of the MC38 colorectal, MB49 and MBT2 bladder, and RENCA kidney and TyrNras melanoma models. Tumor immune infiltrates were characterized for wild type and resistant tumors using spectral cytometry and their molecular alterations analyzed using RNA sequencing analyses. Alterations in the tumor immune microenvironment were strongly heterogeneous among resistant models, involving select lymphoid and/or myeloid subpopulations. Molecular alterations in resistant models included previously identified pathways as well as novel candidate genes found to be deregulated in several resistant models. Among these, Serpinf1, coding for pigment epithelial-derived factor (PEDF) was further explored in the MC38 and the MBT2 models. Overexpression of Serpinf1 induced resistance to anti-PD-1 antibodies in the MC38 model, whereas knockdown of Serpinf1 sensitized this model as well as the primarily resistant MBT2 model. Serpinf1 overexpression was associated with increased production of free fatty acids and reduced activation of CD8þ cells, while orlistat, a compound that reduces the production of free fatty acids, reversed resistance to anti-PD-1 therapy. Our results suggest that a panel of syngeneic resistant models constitutes a useful tool to model the heterogeneity of resistance mechanisms encountered in the clinic.  

Introduction

Immune checkpoint inhibitors (ICI) directed against programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) have shown impressive clinical efficacy in a wide range of cancer types. Several mAbs have been approved by the FDA for the treatment of patients with various indications including melanoma, non–small cell lung cancer (NSCLC), bladder cancer, and renal cell carcinoma (1–4). mAbs targeting PD-1 and PD-L1 allow the restoration of T-cell antitumor functions (5). However, a large proportion of patients demonstrates de novo resistance to these therapies or relapse after a primary response. Mechanisms of resistance to ICIs remain poorly understood. Mutations inducing b-catenin activation have been linked to primary resistance to anti-PD-L1 and anti-CTLA-4 treatment, correlating with T-cell evasion in patients with melanoma (6). Mutations in b2 microglobulin causing inefficient antigen presentation by HLA class. Denis CIR-21-0802