Desmoplastic stroma restricts T cell extravasation and mediates immune exclusion and immunosuppression in solid tumors

Zebin, Xiao, Leslie, Todd, Li, Huang, Estela, Noguera-Ortega, Zhen, Lu, Lili, Huang, Meghan, Kopp, Yue, Li, Nimisha, Pattada, Wenqun, Zhong, Wei, Guo, John, Scholler, Maria, Liousia, Charles Antoine, Assenmacher, Carl H., June, Steven M., Albelda, Ellen, Puré

Nature Communications |

The desmoplastic stroma in solid tumors presents a formidable challenge to immunotherapies that rely on endogenous or adoptively transferred T cells, however, the mechanisms are poorly understood. To define mechanisms involved, here we treat established desmoplastic pancreatic tumors with CAR T cells directed to fibroblast activation protein (FAP), an enzyme highly overexpressed on a subset of cancer-associated fibroblasts (CAFs). Depletion of FAP+ CAFs results in loss of the structural integrity of desmoplastic matrix. This renders these highly treatment-resistant cancers susceptible to subsequent treatment with a tumor antigen (mesothelin)-targeted CAR T cells and to anti-PD-1 antibody therapy. Mechanisms include overcoming stroma-dependent restriction of T cell extravasation and/or perivascular invasion, reversing immune exclusion, relieving T cell suppression, and altering the immune landscape by reducing myeloid cell accumulation and increasing endogenous CD8+ T cell and NK cell infiltration. These data provide strong rationale for combining tumor stroma- and malignant cell-targeted therapies to be tested in clinical trials.