The tumor vasculature an attractive CAR T cell target in solid tumors

T cells armed with a chimeric antigen receptor, CAR T cells, have shown extraordinary activity against certain B lymphocyte malignancies, when targeted towards the CD19 B cell surface marker. These results have led to the regulatory approval of two CAR T cell approaches. Translation of this result to the solid tumor setting has been problematic until now. A number of differences between liquid and solid tumors are likely to cause this discrepancy. The main ones of these are undoubtedly the uncomplicated availability of the target cell within the blood compartment and the abundant expression of the target molecule on the cancerous cells in the case of hematological malignancies. Targets expressed by solid tumor cells are hard to engage due to the non-adhesive and abnormal vasculature, while conditions in the tumor microenvironment can be extremely immunosuppressive. Targets in the tumor vasculature are readily reachable by CAR T cells and reside outside the immunosuppressive tumor microenvironment. It is therefore hypothesized that targeting CAR T cells towards the tumor vasculature of solid tumors may share the excellent effects of CAR T cell therapy with that against hematological malignancies. A few reports have shown promising results. Suggestions are provided for further improvement.