Multiple cancers resistant to immune checkpoint blockade (i.e., anti-PD-1, PD-L1, and/or CTLA-4) demonstrate impaired APC activation. We therefore hypothesized that resistance to checkpoint blockade could be overcome with agents selected to enforce APC activation. Using the checkpoint-blockade resistant syngeneic B16 murine model, we screened such agents for their ability to overcome resistance to anti-PD-1 therapy. In the setting of PD-1 blockade, we found that intratumoral treatment with the TLR4 ligand monophosphoryl lipid A (MPL) and low-dose CD40 agonist monoclonal antibody (mAb) primes T cells which infiltrate and regress noninjected tumors at a distant site. Surprisingly, locally injected tumors were heavily infiltrated with neutrophils expressing costimulatory markers within 3 hours of treatment and then rapidly regressed. There was, however, persistence of activated dendritic cells and monocytes in the draining lymph node. Within 1 week, distant tumors were infiltrated with activated CD8 T cells, showed a marked increase in the T effector to T regulatory ratio, and began to regress. The regression of distant tumors was abolished in RAG1-deficient animals lacking lymphocytes. Treatment yielded no discernable toxicity, and cured animals fully resisted tumor re-implantation at 90 days, developing fur depigmentation at both the site of initial treatment, and the untreated tumor reimplantation site, but not elsewhere. Interestingly, systemic administration of MPL and CD40 was less effective than intratumoral treatment despite a 25-fold dose increase. In conclusion, low-dose intratumoral treatment with combined TLR4 and CD40 agonists induces anti-tumor T cells which in turn regress tumors at distant sites and provide durable immunity such that tumor re-implantation is resisted in a highly-specific manner. Given that this regimen relies on agents that are FDA-approved for other indications, or in clinical development, it is potentially translatable across a broad range of malignancies that are currently resistant to immunotherapy.
Citation Format: Danny N. Khalil, Luis Felipe Campesato, Yanyun Li, Taha Merghoub, Jedd D. Wolchok. Local intratumoral treatment with low-dose CD40 and TLR4 agonists overcomes resistance to PD-1 blockade to regress tumors systemically [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B059.
- ©2016 American Association for Cancer Research.