Background
Despite the success of adoptive cell therapy in hematological malignancies, the clinical experience with solid tumors has not been encouraging. The extracellular matrix (ECM) surrounding the tumor presents a significant physical barrier, restricting entry of adoptively transferred cells into the tumor microenvironment (TME). Although T cells expressing the ECM degrading heparanase, have shown preclinical promise, every studied cancer exhibits elevated heparanase expression, resulting in: (1) increased tumor growth and metastasis in preclinical models, and (2) contributing to poor patient survival. Thus, alternate enzymes with anti-tumor properties that can remodel the ECM need to be developed to improve the efficacy of T/NK cell therapies. The matrix metalloprotease 8 (MMP8) is a potent anti-tumor enzyme, unlike other MMPs and heparanase that have pro-tumor and metastatic properties. In this study, we sought to test whether T/NK cells MMP8, will promote infiltration of T cells into the tumor and facilitate reprogramming of the TME, leading to tumor regression.
Methods
We manufactured healthy donor derived: (1) T cells, (2) NK cells, and (3) CD19 or Her2-specific CAR T cells with (MMP8-CAR T cells) and without MMP8 overexpression. We used a panel of in vitro assays including RT-PCR, Western Blotting and collagen degradation to test the activity of the MMP8 from engineered T/NK cells. We used transwell assays with Matrigel to investigate the ability of T/NK cells to kill tumor cells embedded in the matrix. We performed xenotransplant models in NSG mice to test the antitumor potential of MMP8-CAR T cells.
Results
We demonstrated that manufactured T/NK cells lack the ability to degrade components of the ECM matrix. Recombinant expression of MMP8 endowed T/NK cells the ability to efficiently degrade ECM components promoting their migration across Matrigel in transwell assays without altering their phenotype or proliferation. One key advantage of matrix degradation is the promotion of infiltration of multiple immune cells. Using MMP8 T cells, that are unable to directly kill tumor cells, we showed that by degrading the ECM, they facilitate migration and antitumor activity of NK cells. We tested the in vivo efficacy of the MMP8-CAR T cells or MMP8-NK cells in NSG mice engrafted with SKOV3 tumors and show that MMP8 secreting cells reject the tumor and showed prolonged survival for >100 days unlike the transient response of parental CAR T cells.
Conclusions
MMP8 expressing T/NK cells present a generic method to promote the infiltration of immune cells and unleash their full anti-tumor potential.
Ethics Approval
The NSG mouse studies were performed under the study protocol (PROTO201700010), as approved by the Institutional Animal Care and Use Committee in University of Houston.