Simple Summary

Novel biomarkers that can identify melanoma patients responding to immune checkpoint inhibitor therapy are urgently needed. As high T-cell infiltration and low fibrotic activity are associated with response, we aimed to examine the serum biomarker potential of granzyme B degraded type IV collagen (C4G) products in combination with the fibrosis biomarker PRO-C3. We found that high C4G combined with low PRO-C3 has the potential to identify patients responding to immune checkpoint inhibitor therapy suggesting that these biomarkers may provide a non-invasive tool for patient selection and therapeutic decision-making in the future.

A T-cell permissive tumor microenvironment, characterized by the presence of activated T cells and low fibrotic activity is crucial for response to immune checkpoint inhibitors (ICIs). Granzyme B has been shown to promote T-cell migration through the basement membrane by the degradation of type IV collagen. In this study, we evaluated the biomarker potential of measuring granzyme B-mediated degradation of type IV collagen (C4G) in combination with a fibroblast activation biomarker (PRO-C3) non-invasively for identifying metastatic melanoma patients responding to the ICI ipilimumab. A monoclonal antibody was generated against C4G and used to develop a competitive electro-chemiluminescence immunoassay. C4G and PRO-C3 were measured in pretreatment serum from metastatic melanoma patients (n = 54). The C4G assay was found specific for a granzyme B-generated neo-epitope on type IV collagen. The objective response rate (ORR) was 2.6-fold higher (18% vs. 7%) in patients with high C4G levels (>25th percentile) vs. low levels (