Data from 4-1BB Agonism Averts TIL Exhaustion and Licenses PD-1 Blockade in Glioblastoma and Other Intracranial Cancers

Abstract

<div>AbstractPurpose:<p>The success of checkpoint blockade against glioblastoma (GBM) has been disappointing. Anti–PD-1 strategies may be hampered by severe T-cell exhaustion. We sought to develop a strategy that might license new efficacy for checkpoint blockade in GBM.</p>Experimental Design:<p>We characterized 4-1BB expression in tumor-infiltrating lymphocytes (TIL) from human GBM. We implanted murine tumor models including glioma (CT2A), melanoma (B16), breast (E0771), and lung carcinomas intracranially and subcutaneously, characterized 4-1BB expression, and tested checkpoint blockade strategies <i>in vivo</i>.</p>Results:<p>Our data reveal that 4-1BB is frequently present on nonexhausted CD8<sup>+</sup> TILs in human and murine GBM. In murine gliomas, 4-1BB agonism and PD-1 blockade demonstrate a synergistic survival benefit in a CD8<sup>+</sup> T-cell–dependent manner. The combination decreases TIL exhaustion and improves TIL functionality. This strategy proves most successful against intracranial CT2A gliomas. Efficacy in all instances correlates with the levels of 4-1BB expression on CD8<sup>+</sup> TILs, rather than with histology or with intracranial versus subcutaneous tumor location. Proffering 4-1BB expression to T cells licenses combination 4-1BB agonism and PD-1 blockade in models where TIL 4-1BB levels had previously been low and the treatment ineffective.</p>Conclusions:<p>Although poor T-cell activation and severe T-cell exhaustion appear to be limiting factors for checkpoint blockade in GBM, 4-1BB agonism obviates these limitations and produces long-term survival when combined with anti–PD-1 therapy. Furthermore, this combination therapy is limited by TIL 4-1BB expression, but not by the intracranial compartment, and therefore may be particularly well-suited to GBM.</p></div>