THE TOLL-LIKE RECEPTOR 7/8 PATHWAY HAS PROGNOSTIC SIGNIFICANCE AND IS A THERAPEUTIC TARGET IN CNS LYMPHOMAS

Abstract

Introduction: The tumor microenvironment (TME) likely contributes to therapeutic resistance in CNS lymphomas (CNSL). Tumor-associated myeloid cells (TAMs), both macrophages and microglia, likely suppress the adaptive immune response and facilitate lymphoma progression via several mechanisms. Stimulation of TAMs via toll like receptors (TLRs) may potentiate an anti-tumor immune response.

Methods: We evaluated the phenotypes and prognostic significance of TAMs in clinical investigations and preclinical models and are investigating the pharmcodynamic impact of systemic and intratumoral injection of a TLR 7/8 agonist in a syngeneic A20 model of CNSL.

Results: Reductions in anti-tumor M1 TAMs in the TME, with transcriptional features of IFN-ϒ activation, are associated with tumor progression in patients with relapsed CNSL treated with rituximab, methotrexate and lenalidomide. IFN-ϒ knockout mice exhibit accelerated CNS lymphoma progression in tumor models and TAMs from IFN-ϒ wild-type mice exhibit a transcriptional phenotype consistent with TLR7/8 pathway activation. Higher TLR8 expression by TAMs correlated with longer PFS in a discovery set of PCNSL cases, and was associated with longer OS and high CD8 expression in a multicenter validation series. Expression of TLR8 by human macrophages, differentiated from PBMCs, is induced with IFN-ϒ, yielding M1 macrophages, but not by IL-4. These data demonstrate that TLR8 is a novel marker of M1 macrophages with prognostic significance, and suggest that pharmacologic agonists of the TLR7/8 pathway have potential to activate the anti-tumor potential of TAMs in CNS lymphomas. In collaboration with Gilead, we performed preclinical evaluations of a human TLR8 agonist, which activates mouse TLR7, via stereotactic injection of non-tumor bearing brains in BALB/c mice, demonstrating pharmacodynamic potency and safety. Intra-CNS injection of TLR7 agonist, but not vehicle, induced marked and diffuse perivascular accumulation of Iba1+ /iNOS+ M1 macrophages. We detected accumulation of CD8+ T cells adjacent to the injection site in brains exposed to the TLR7/8 agonist, but not vehicle. These results demonstrate that pharmacologic activation of the TLR7/8 pathway induces accumulation of Iba1+ M1 macrophages, and CD8+ T cells, and suggest that TLR7 activation promotes macrophage entry via the cerebral vasculature, without toxicity. In a syngeneic CNS lymphoma model, weekly systemic administration of TLR7 agonist delayed intracranial tumor progression. Targeted intra-CNS administrations of TLR7 agonist, without systemic administration, resulted in tumor regression and at least a trend toward longer OS.

Conclusions: These data suggest that pharmacologic activation of the TLR7/8 pathway, via systemic and/or intra-CNS delivery, is feasible and programs the myeloid TME to an anti-tumor phenotype, with significant translational therapeutic potential in monotherapy and combinatorial strategies in CNS lymphoma.

Research funding declaration: Supported by a grant from the Leukemia and Lymphoma Society

Keywords: aggressive B-cell non-Hodgkin lymphoma; immunotherapy; targeting the tumor microenvironment

No potential sources of conflict of interest.