Tumor matrix proteoglycan accumulation and processing alters T cell effector function and the response to immunotherapy in oligometastatic colorectal cancer

Versican (VCAN) is an immunoregulatory extracellular matrix proteoglycan that when cleaved by ADAMTS proteases releases an immunostimulatory fragment, versikine. Here, we confirm that VCAN accumulates within colorectal cancers (CRCs) and inhibits T cell trafficking/effector function. VCAN is heavily proteolyzed in a subset of CRCs (VCAN proteolytic predominant (VPP)), leading to enhanced T cell infiltration. This phenotype was found to be more common in oligometastatic CRCs. A phase 1b clinical trial examined the safety/efficacy of the sequential combination of stereotactic body radiotherapy and pembrolizumab in patients undergoing resection of their microsatellite stable oligometastatic CRCs. The primary endpoint was met with a 1-year recurrence free survival (RFS) of 60%. Of those enrolled, 40% of cancers had the VPP phenotype, which was associated with improved RFS and overall survival. The VPP phenotype was associated with improved circulating T cell effector function, which was enhanced with study treatment. Clinical trial information: NCT02837263. Overall design: PBMCs from trial participants were stored, prepared for sequencing, and then profiled using 10X Genomics fixed single-cell RNA sequencing according to the 10x genomics user guide CG000527 Rev E. Single cells were captured and barcoded using the 10X Chromium controller using its 3' or 10X Flex (probe- based) whole transcriptome kits. Gel Bead-In EMulsions (GEMs) were prepared, followed by cDNA amplification and size-based cleanup. Final libraries were sequenced using NovaSeq and NovaSeqX platforms to target at least 20k reads per cell.