Intratumoral CpG-B Promotes Antitumoral Neutrophil, cDC, and T-cell Cooperation without Reprograming Tolerogenic pDC

Abstract

Cancer immunotherapies utilize distinct mechanisms to harness the power of the immune system to eradicate cancer cells. Therapeutic vaccines, aimed at inducing active immune responses against an existing cancer, are highly dependent on the immunological microenvironment, where many immune cell types display high levels of plasticity and, depending on the context, promote very different immunologic outcomes. Among them, plasmacytoid dendritic cells (pDC), known to be highly immunogenic upon inflammation, are maintained in a tolerogenic state by the tumor microenvironment. Here, we report that intratumoral (i.t.) injection of established solid tumors with CpG oligonucleotides-B (CpG-B) inhibits tumor growth. Interestingly, control of tumor growth was independent of tumor-associated pDC, which remained refractory to CpG-B stimulation and whose depletion did not alter the efficacy of the treatment. Instead, tumor growth inhibition subsequent to i.t. CpG-B injection depended on the recruitment of neutrophils into the milieu, resulting in the activation of conventional dendritic cells, subsequent increased antitumor T-cell priming in draining lymph nodes, and enhanced effector T-cell infiltration in the tumor microenvironment. These results reinforce the concept that i.t. delivery of TLR9 agonists alters the tumor microenvironment by improving the antitumor activity of both innate and adaptive immune cells. Intratumoral delivery of CpG-B disrupts the tolerogenic tumor microenvironment and inhibits tumor growth. .

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

“…Firstly, TLR9 agonists expand antigen-specific CD8+ T cells that upregulate PD-1 expression. 152,153 Secondly, TLR9 agonists in combination with anti-PD-1 ICI transform the TME, increasing CD8+ T cells, NK cells, DCs, and B cells even in PD-1 non- Figure 2 TLR and TLR9 cellular location and downstream signaling Notes: Created with BioRender.com. Abbreviations: AP-1, activator protein 1; IRF, interferon regulatory factor; IKK, IκB kinase; MAPK, mitogen activated protein kinase; MyD88, myeloid differentiation primary response 88; NFκB, nuclear factor kappa beta; SARM1, sterile α and TIR motif containing 1; TAK1, transforming growth factor-β-activated kinase-1; TLR, toll-like receptor; TRIF, TIR domain-containing adaptor-inducing IFN, beta; TRAF6, TNF receptor-associated factor 6 (TRAF6); TRAM, TRIF-related adaptor molecule; TIRAP/MAL, TIR-containing adaptor protein/MyD88-adaptor-like.…”

Warming up the tumor microenvironment in order to enhance immunogenicity

“…5 Using melanoma or thymoma tumors, we observed a significant reduction of the tumor growth following intratumoral CpG-B administration. However, we did not observe any tolerogenic-to-immunogenic conversion of TA-pDC phenotype after treatment, and the genetic depletion of pDCs did not affect the efficacy of the treatment.…”

“…Importantly, all these events are dependent on the primary recruitment of neutrophils after CpG-B administration, since both cDC activation and tumor-specific T cell priming are abrogated upon neutrophil depletion. 5 …”

In situ antitumor vaccination: Targeting the tumor microenvironment

“…Tumor‐induced dendritic cells (DCs) paralysis could be reversed by the combination of a CpG immunostimulatory sequence and a sialic acid mimetic Ac53FaxNeu5Ac (Bull et al, 2018). Intratumoral CpG‐B promoted antitumoral neutrophil, cDC, and T‐cell cooperation, thus disrupting the tolerogenic tumor microenvironment while suppressing tumor growth (Humbert, Guery, Brighouse, Lemeille, & Hugues, 2018). Intratumoral G100, the recently reported TLR4 agonist, induced local tumor regression and appeared to promote systemic immunity (Bhatia et al, 2019).…”