Inhaled TLR9 Agonist Renders Lung Tumors Permissive to PD-1 Blockade by Promoting Optimal CD4+ and CD8+ T-cell Interplay

Abstract

Currently approved inhibitors of the PD-1/PD-L1 pathway represent a major advance for the treatment of lung cancers, yet they are ineffective in a majority of patients due to lack of preexisting T-cell reactivity. Here, we show that a TLR9 agonist delivered by inhalation is able to prime T-cell responses against poorly immunogenic lung tumors and to complement the effects of PD-1 blockade. Inhaled TLR9 agonist causes profound remodeling in tumor-bearing lungs, leading to the formation of tertiary lymphoid structures adjacent to the tumors, CD8 T-cell infiltration into the tumors, dendritic cell expansion, and antibody production. Inhalation of TLR9 agonist also increased the pool of functional PD-1T-bet effector CD8 T cells in tumor-bearing lungs. Effector CD8 T cells generated by inhaled TLR9 agonist treatment were licensed by PD-1 blockade to become highly functional CTLs, leading to a durable rejection of both lung tumors and tumor lesions outside the lungs. CD4 T cells activated in response to inhaled TLR9 play a critical role in this process by controlling the proliferation, preventing exhaustion, and guiding the differentiation of optimally functional CTLs. This study characterizes a strategy to apply localized TLR9 stimulation to a tumor type not accessible for direct injection, a strategy that may expand the therapeutic potential of PD-1 blockade in non-small cell lung cancer. These findings demonstrate that local delivery of a toll-like receptor 9 agonist can change the immune content of an entire organ and enhance the efficacy of immune checkpoint inhibition. http://cancerres.aacrjournals.org/content/canres/78/17/4943/F1.large.jpg .

Low-dose metronomic cyclophosphamide complements the actions of an intratumoral C-class CpG TLR9 agonist to potentiate innate immunity and drive potent T cell-mediated anti-tumor responses

“…Combination treatment significantly improved the survival of mice bearing CT26 tumors in the lung compared with mice receiving monotherapy treatments ( Figure 3D). A similar result was observed in a 4T1 lung metastasis model [6], in which the combination of systemic low-dose CY plus inhaled SD-101 conferred increased survival in 4T1 tumor-bearing mice ( Supplementary Figure 2A, 2B).…”

“…in mouse tumor models that employing the innate immune system to prime a T cell response, in combination with checkpoint blockade, results in deep and durable antitumor efficacy [5,6]. In cancer patients with unresectable or metastatic melanoma who have not had previous anti-PD-1 therapy, the combination of intratumoral SD-101 and systemic pembrolizumab produced a 71-78% objective response rate, higher than expected with pembrolizumab monotherapy.…”

“…SD-101 (10 µg) was delivered to the lung intranasally (i.n.) as previously described [6], twice weekly, and low-dose CY (16 mg/ kg body weight) was given orally, five doses weekly. Combination treatment significantly improved the survival of mice bearing CT26 tumors in the lung compared with mice receiving monotherapy treatments ( Figure 3D).…”

“…To establish CT26 pulmonary metastasis, CT26 intravenous lung metastasis models were used [6]. In the CT26 i.v.…”

<p>Toll-Like Receptor 9 Agonists in Cancer</p>

“…TLR9 agonists have demonstrated potent synergy with anti-PD-1 and/or anti-CTLA-4 ICI in multiple models including melanoma, 153,155 lung cancer, 156 HPV positive oropharyngeal cancer, 157 head and neck squamous cell carcinoma, 158 breast cancer, 153 colorectal cancer, 153 and lymphoma. 159 Using two separate melanoma models of diametric immunogenicity, Reilley et al demonstrated the importance of intra-tumoral therapy and TME-centric immune activation in mediating responses to TLR9 agonist and anti-PD-1/anti-CTLA-4 ICI.…”