Efficacy and pharmacodynamic effect of anti-CD73 and anti-PD-L1 monoclonal antibodies in combination with cytotoxic therapy: observations from mouse tumor models

CD73 is a cell surface 5'nucleotidase (NT5E) and key node in the catabolic process generating immunosuppressive adenosine in cancer. Using a murine monoclonal antibody surrogate of Oleclumab, we investigated the effect of CD73 inhibition in concert with cytotoxic therapies (chemotherapies as well as fractionated radiotherapy) and PD-L1 blockade. Our results highlight improved survival in syngeneic tumor models of colorectal cancer (CT26 and MC38) and sarcoma (MCA205). This therapeutic outcome was in part driven by cytotoxic CD8 T-cells, as evidenced by the detrimental effect of CD8 depleting antibody treatment of MCA205 tumor bearing mice treated with anti-CD73, anti-PD-L1 and 5-Fluorouracil+Oxaliplatin (5FU+OHP). We hypothesize that the improved responses are tumor microenvironment (TME)-driven, as suggested by the lack of anti-CD73 enhanced cytopathic effects mediated by 5FU+OHP on cell lines in vitro. Pharmacodynamic analysis, using imaging mass cytometry and RNA-sequencing, revealed noteworthy changes in specific cell populations like cytotoxic T cells, B cells and NK cells in the CT26 TME. Transcriptomic analysis highlighted treatment-related modulation of gene profiles associated with an immune response, NK and T-cell activation, T cell receptor signaling and interferon (types 1 & 2) pathways. Inclusion of comparator groups representing the various components of the combination allowed deconvolution of contribution of the individual therapeutic elements; highlighting specific effects mediated by the anti-CD73 antibody with respect to immune-cell representation, chemotaxis and myeloid biology. These pre-clinical data reflect complementarity of adenosine blockade with cytotoxic therapy, and T-cell checkpoint inhibition, and provides new mechanistic insights in support of combination therapy.