Abstract 6164: Novel heparin nanoparticles targeting BDCA2 promote immune response
Authors: Greg Kirkpatrick, Caitlin Lemke-Miltner, Rui He, Sue Blackwell, Aliasger Salem, George J. Weiner
Journal: Cancer Research (2025)

Immune checkpoint inhibitors have revolutionized treatment of many types of cancer, but are not effective for all patients. One proposed mechanism of resistance is lack of local interferon production that results in an immunologically “cold” tumor. This barrier may be overcome by direct immune stimulation with TLR9 agonists. Early phase clinical studies in a variety of cancer types have demonstrated intratumoral injection of TLR9 agonists, as free drug or formulated into nanoparticles (NP), is safe and capable of inducing systemic tumor regression alone or in combination with immune checkpoint inhibitors. Plasmacytoid dendritic cells (pDCs) are potent producers of type I interferon such as interferon alpha (IFN⍺). They are key immune system regulators and play a central role in the response to TLR9 agonists. BDCA2 is a cell surface receptor expressed uniquely on pDCs. Signaling through BDCA2 is thought to decrease the immune response initiated by pDCs, particularly in response to TLR agonists. Heparin is a BDCA2 ligand and has been shown to inhibit the TLR9 agonist-driven IFN⍺ response. We developed a novel heparin-coated, polyamidoamine (PAMAM) NP containing a TLR9 agonist to investigate whether heparin-mediated targeting of these NP to pDCs via BDCA2 modulates the pDC response to TLR9. Control NP included those without surface heparin and those without TLR9 agonists. Fresh normal donor human peripheral blood mononuclear cells (PBMCs) were treated with NP for 20 hours. Supernatants were collected for IFN⍺ ELISA to determine whether a functional PBMC response, mediated in large part by pDCs, was stimulated by the NP. Flow cytometric evaluation was used to assess whether NP induced a phenotypic change in pDCs. Heparin-coated NP containing a TLR9 agonist was more effective than soluble TLR9 agonist at inducing IFN⍺production from PBMCs. Such NP also increased expression of PD-L1 on pDCs. Increased IFN⍺ production and PD-L1 expression were most pronounced with TLR9-containing particles that had a high heparin coating amount. Of note, a low heparin coating amount resulted in reduced IFN⍺ production and PD-L1 expression on pDCs. The published literature suggests BDCA2 signaling inhibits pDC activation induced by TLR9 agonists. In contrast, here we show that TLR9-containing NP coated with high concentrations of the BDCA2 ligand heparin actually enhances activation of pDCs. Biologically, this suggests signaling via BDCA2 may vary based on the concentration of ligand or how it is presented. Therapeutically, heparin-coated NP containing TLR9 agonists may represent a promising novel approach for stimulating a local immune response, with potential relevance in both cancer immunotherapy and vaccination. Additional studies are ongoing to confirm NP activity is mediated by BDCA2 and to optimize NP composition. This includes assessment of various NP structural components, concentrations and types of BDCA2 ligands, and various TLR agonists. Citation Format: Greg Kirkpatrick, Caitlin Lemke-Miltner, Rui He, Sue Blackwell, Aliasger Salem, George J. Weiner. Novel heparin nanoparticles targeting BDCA2 promote immune response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6164.