Twenty-five years ago, we reported that agonist anti-CD137 monoclonal antibodies eradicated transplanted mouse tumors because of enhanced CD8+ T-cell antitumor immunity. Mouse models indicated that anti-CD137 agonist antibodies synergized with various other therapies. In the clinic, the agonist antibody urelumab showed evidence for single-agent activity against melanoma and non-Hodgkin lymphoma but caused severe liver inflammation in a fraction of the patients. CD137's signaling domain is included in approved chimeric antigen receptors conferring persistence and efficacy. A new wave of CD137 agonists targeting tumors, mainly based on bispecific constructs, are in early-phase trials and are showing promising safety and clinical activity.
Significance:
CD137 (4-1BB) is a costimulatory receptor of T and natural killer lymphocytes whose activity can be exploited in cancer immunotherapy strategies as discovered 25 years ago. Following initial attempts that met unacceptable toxicity, new waves of constructs acting agonistically on CD137 are being developed in patients, offering signs of clinical and pharmacodynamic activity with tolerable safety profiles.
Interleukin-12-based local gene therapy of cancer constitutes an active area of clinical research using plasmids, mRNAs and viral vectors. To improve antitumor effects, we have experimentally tested the combination of mRNA constructs encoding interleukin-12 (IL-12) and interleukin-18 (IL-18). Moreover, we have used a form of IL-18 (DR-18) which has preserved bioactivity but does not bind to the IL-18BP decoy receptor. Both cytokines dramatically synergize to induce IFNγ release from mouse splenocytes, and, if systemically co-transferred to the liver, they mediate lethal toxicity. However, if given intratumorally to B16OVA tumor-bearing mice, the combination attains efficacy against the directly treated tumor and moderate tumor-delaying activity on distant uninjected lesions. Co-treatment was conducive to the presence of more activated CD8+ T cells in the treated and non-injected tumors. In keeping with these findings, the efficacy of treatment was contingent on the integrity of CD8+ T cells and cDC1 dendritic cells in the treated mice. Furthermore, efficacy of IL-12 plus DR-18 local mRNA co-injection against distant concomitant tumors could be enhanced upon combination with anti-PD-1 mAb systemic treatment, thus defining a feasible synergistic immunotherapy strategy.
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