Liver myeloid-derived suppressor cells expand in response to liver metastases in mice and inhibit the anti-tumor efficacy of anti-CEA CAR-T

Abstract

Chimeric antigen receptor modified T cell (CAR-T) technology, a promising immunotherapeutic tool, has not been applied specifically to treat liver metastases (LM). While CAR-T delivery to LM can be optimized by regional intrahepatic infusion, we propose that liver CD11b+Gr-1+ myeloid-derived suppressor cells (L-MDSC) will inhibit the efficacy of CAR-T in the intrahepatic space. We studied anti-CEA CAR-T in a murine model of CEA+ LM and identified mechanisms through which L-MDSC expand and inhibit CAR-T function. We established CEA+ LM in mice and studied purified L-MDSC and responses to treatment with intrahepatic anti-CEA CAR-T infusions. L-MDSC expanded three-fold in response to LM and their expansion was dependent on GM-CSF, which was produced by tumor cells. L-MDSC utilized PD-L1 to suppress anti-tumor responses through engagement of PD-1 on CAR-T. GM-CSF, in cooperation with STAT3, promoted L-MDSC PD-L1 expression. CAR-T efficacy was rescued when mice received CAR-T in combination with MDSC depletion, GM-CSF neutralization to prevent MDSC expansion, or PD-L1 blockade. As L-MDSC suppressed anti-CEA CAR-T, infusion of anti-CEA CAR-T in tandem with agents targeting L-MDSC is a rational strategy for future clinical trials.

Mesothelin-Targeted CARs: Driving T Cells to Solid Tumors

“…Tumor cells and associated-stroma cells, including Tregs and myeloid-derived suppressor cells, overexpress inhibitory molecules, such as TGF-β, IDO, and PD-L1, which limiting CAR T-cell efficacy. (48, 55, 65, 67, 68) Although second-generation CARs are relatively efficient in the immunosuppressive microenvironment, as shown by us and other investigators,(83) costimulation alone is not sufficient. (66) To potentiate CAR T cells in an immunosuppressive environment, multiple approaches have been investigated, including antibody-based therapy and genetic approaches, such as engineering T cells, to express a dominant negative TGF-β receptor that restores T-cell effector functions in an immunocompetent mouse melanoma model.…”

“…However, the ideal costimulation domain may depend on context, as CAR function depends on multiple extraneous factors such as antigen density,(60, 61) CAR stoichiometry,(61) CAR affinity,(62–64) and the immunological features of the tumor microenvironment. (65–68)…”

“…Overexpression of PD-L1 by tumor cells has been shown to induce MSLN CAR T-cell exhaustion. (48, 65) The immunosuppressive effect of the PD-L1/PD-1 pathway can be reverted by the addition of PD-1/PD-L1–blocking antibody,(48) a PD1/CD28 converter(85, 86) or by the cointroduction of a PD-1 dominant negative receptor. Our results demonstrate that coexpression of a PD-1 dominant negative receptor together with a MSLN CAR potentiates long-term eradication of mesothelioma tumors.…”

Molecular Pathways: Targeting the Microenvironment of Liver Metastases

“…Analysis of an independent set of tumors by IHC validated these findings, showing that an increased lymphocytic infiltrate and increased expression of the TNFSF14/LIGHT protein were associated with improved overall and relapse-free survival. Another recent report, demonstrated that MDSC expand within the LME of CRCLM and can inhibit responses to CAR T cell therapy (74). These findings demonstrate that the immune cell infiltrate within the LME may be highly relevant to patient outcomes and manipulating these responses may be of therapeutic benefit.…”

Hurdles of CAR-T cell-based cancer immunotherapy directed against solid tumors

“…Preclinical data supports the hypothesis that the incorporation of co-stimulatory molecules, such as CD28, into CARs may help CAR-modified T cells to overcome the immunosuppressive tumor microenvironment mediated by Treg cells (Koehler et al, 2007;Lee et al, 2011;Loskog et al, 2006). Recently, a study by Burga et al showed that myeloid-derived suppressor cells expand in response to liver metastases and inhibit the anti-tumor efficacy of anti-CEA CAR-T cells; CAR-T cell efficacy was rescued when mice received CAR-T in combination with MDSC depletion (Burga et al, 2015). Tumor cells have been found to secrete high levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) in vivo implicated in MDSC recruitment, and GM-CSF neutralization may be an alternative approach to prevent MDSC expansion (Lesokhin et al, 2012;Schmidt et al, 2013).…”