Heparanase promotes tumor infiltration and antitumor activity of CAR-redirected T-lymphocytes

Adoptive transfer of chimeric antigen receptor (CAR)-redirected T lymphocytes (CAR-T cells) has had less striking effects in solid tumors(1–3) than in lymphoid malignancies(4, 5). Although active tumor-mediated immunosuppression may play a role in limiting efficacy(6), functional changes in T lymphocytes following their ex vivo manipulation may also account for cultured CAR-T cells’ reduced ability to penetrate stroma-rich solid tumors. We therefore studied the capacity of human in vitro-cultured CAR-T cells to degrade components of the extracellular matrix (ECM). In contrast to freshly isolated T lymphocytes, we found that in vitro-cultured T lymphocytes lack expression of the enzyme heparanase (HPSE) that degrades heparan sulphate proteoglycans, which are main components of ECM. We found that HPSE mRNA is down regulated in in vitro-expanded T cells, which may be a consequence of p53 binding to the HPSE gene promoter. We therefore engineered CAR-T cells to express HPSE and showed improved capacity to degrade ECM, which promoted tumor T-cell infiltration and antitumor activity. Employing this strategy may enhance the activity of CAR-T cells in individuals with stroma-rich solid tumors.