Abstract
Multiple sclerosis (MS) is a chronic neurodegenerative disease driven by infiltration of activated innate immune cells into the central nervous system (CNS). Current imaging approaches for diagnosing and monitoring disease progression rely on structural lesions and cannot directly assess innate immune activity. Here, we describe a dendrimer positron emission tomography (PET) tracer, 18F-flurimedrimer (18F-FMD), for non-invasive, longitudinal tracking of activated myeloid cells. In an experimental autoimmune encephalomyelitis (EAE) murine model, 18F-FMD specifically detects myeloid activation at presymptomatic and symptomatic stages, with PET signal correlating with disease severity. Moreover, 18F-FMD sensitively captures therapeutic response to fingolimod (FTY72…
Abstract
Multiple sclerosis (MS) is a chronic neurodegenerative disease driven by infiltration of activated innate immune cells into the central nervous system (CNS). Current imaging approaches for diagnosing and monitoring disease progression rely on structural lesions and cannot directly assess innate immune activity. Here, we describe a dendrimer positron emission tomography (PET) tracer, 18F-flurimedrimer (18F-FMD), for non-invasive, longitudinal tracking of activated myeloid cells. In an experimental autoimmune encephalomyelitis (EAE) murine model, 18F-FMD specifically detects myeloid activation at presymptomatic and symptomatic stages, with PET signal correlating with disease severity. Moreover, 18F-FMD sensitively captures therapeutic response to fingolimod (FTY720) and a CSF1R dendranib (H74DS3M8), both of which suppress immune cell activation and attenuate disease severity. These findings highlight the potential of 18F-FMD PET for specific, real-time monitoring of innate immune responses, and the applicability of the dendrimer in clinical settings for monitoring therapeutic efficacy, advancing the development of personalized, myeloid-targeted strategies for MS.
Data availability
All data are included in the Supplementary Information or available from the authors, as are unique reagents used in this Article. The raw numbers for charts and graphs are available in the Source Data file whenever possible. The raw PET imaging and flow cytometry data generated in this study have been deposited in the Figshare database under https://doi.org/10.6084/m9.figshare.30644609. Source data are provided with this paper.
References
National Multiple Sclerosis Society. Number of people with MS | Atlas of MS. https://atlasofms.org/map/global/epidemiology/number-of-people-with-ms. 1.
Loma, I. & Heyman, R. Multiple sclerosis: pathogenesis and treatment. Curr. Neuropharmacol. 9, 409–416 (2011).
Attfield, K. E., Jensen, L. T., Kaufmann, M., Friese, M. A. & Fugger, L. The immunology of multiple sclerosis. Nat. Rev. Immunol. 22, 734–750 (2022).
Mishra, M. K. & Yong, V. W. Myeloid cells—targets of medication in multiple sclerosis. Nat. Rev. Neurol. 12, 539–551 (2016).
Hernández-Pedro, N. Y., Espinosa-Ramirez, G., de la Cruz, V. P., Pineda, B. & Sotelo, J. Initial Immunopathogenesis of Multiple Sclerosis: innate Immune Response. Clin. Dev. Immunol. 2013, 413465 (2013).
Lucchinetti, C. et al. Heterogeneity of multiple sclerosis lesions: implications for the pathogenesis of demyelination. Ann. Neurol. 47, 707–717 (2000).
Prineas, J. W. et al. Immunopathology of secondary-progressive multiple sclerosis. Ann. Neurol. 50, 646–657 (2001).
Wingerchuk, D. M., Lucchinetti, C. F. & Noseworthy, J. H. Multiple sclerosis: current pathophysiological concepts. Lab. Investig. 81, 263–281 (2001).
Ajami, B., Bennett, J. L., Krieger, C., McNagny, K. M. & Rossi, F. M. V. Infiltrating monocytes trigger EAE progression, but do not contribute to the resident microglia pool. Nat. Neurosci. 14, 1142–1149 (2011).
Greter, M. et al. Dendritic cells permit immune invasion of the CNS in an animal model of multiple sclerosis. Nat. Med. 11, 328–334 (2005).
Bailey, S. L., Schreiner, B., McMahon, E. J. & Miller, S. D. CNS myeloid DCs presenting endogenous myelin peptides ‘preferentially’ polarize CD4+ TH-17 cells in relapsing EAE. Nat. Immunol. 8, 172–180 (2007).
Ifergan, I. & Miller, S. D. Potential for targeting myeloid cells in controlling CNS inflammation. Front. Immunol. 11, 571897 (2020).
Confavreux, C. & Vukusic, S. The clinical course of multiple sclerosis. in Handbook of Clinical Neurology Vol. 122, 343–369 (Elsevier, 2014). 1.
Montalban, X. et al. Ocrelizumab versus placebo in primary progressive multiple sclerosis. N. Engl. J. Med. 376, 209–220 (2017).
Fischer, S., Proschmann, U., Akgün, K. & Ziemssen, T. Lymphocyte counts and multiple sclerosis therapeutics: between mechanisms of action and treatment-limiting side effects. Cells 10, 3177 (2021).
McDonald, W. I. et al. Recommended diagnostic criteria for multiple sclerosis: guidelines from the international panel on the diagnosis of multiple sclerosis. Ann. Neurol. 50, 121–127 (2001).
Luus, C., Hanani, R., Reynolds, A. & Kassiou, M. The development of PET radioligands for imaging the translocator protein (18 kDa): what have we learned? J. Label. Compd. Radiopharm. 53, 501–510 (2010).
Chen, M.-K. & Guilarte, T. R. Translocator protein 18 kDa (TSPO): molecular sensor of brain injury and repair. Pharmacol. Ther. 118, 1–17 (2008).
Airas, L., Rissanen, E. & Rinne, J. O. Imaging neuroinflammation in multiple sclerosis using TSPO-PET. Clin. Transl. Imaging 3, 461–473 (2015).
Polvinen, E., Matilainen, M., Nylund, M., Sucksdorff, M. & Airas, L. M. TSPO-detectable chronic active lesions predict disease progression in multiple sclerosis. Neurol. Neuroimmunol. Neuroinflammation 10, e200133 (2023).
Owen, D. R. et al. An 18-kDa Translocator Protein (TSPO) polymorphism explains differences in binding affinity of the PET radioligand PBR28. J. Cereb. Blood Flow. Metab. 32, 1–5 (2012).
Nutma, E. et al. Activated microglia do not increase 18 kDa translocator protein (TSPO) expression in the multiple sclerosis brain. Glia 69, 2447–2458 (2021).
Jain, P. et al. Neuroinflammation PET imaging: current opinion and future directions. J. Nucl. Med. 61, 1107–1112 (2020).
Wu, C., Li, F., Niu, G. & Chen, X. PET imaging of inflammation biomarkers. Theranostics 3, 448–466 (2013).
Carlson, M. L. et al. Development and initial assessment of [18F]OP-801: a novel hydroxyl dendrimer PET tracer for preclinical imaging of innate immune activation in the whole body and brain. Mol. Imaging Biol. 25, 1063–1072 (2023).
Jackson, I. M. et al. Clinical radiosynthesis and translation of [18F]OP-801: a novel radiotracer for imaging reactive microglia and macrophages. ACS Chem. Neurosci. 14, 2416–2424 (2023).
Sharma, A. et al. Dense hydroxyl polyethylene glycol dendrimer targets activated glia in multiple CNS disorders. Sci. Adv. 6, eaay8514 (2020).
Kambhampati, S. P. et al. Systemic and intravitreal delivery of dendrimers to activated microglia/macrophage in ischemia/reperfusion mouse retina. Investig. Ophthalmol. Vis. Sci. 56, 4413–4424 (2015).
Kambhampati, S. P. et al. Systemic dendrimer nanotherapies for targeted suppression of choroidal inflammation and neovascularization in age-related macular degeneration. J. Control. Release 335, 527–540 (2021).
Henningfield, C. M. et al. Selective targeting and modulation of plaque associated microglia via systemic hydroxyl dendrimer administration in an Alzheimer’s disease mouse model. Alzheimers Res. Ther. 16, 101 (2024).
Nance, E. et al. Dendrimer-mediated delivery of N-acetyl cysteine to microglia in a mouse model of Rett syndrome. J. Neuroinflammation 14, 252 (2017).
Arteaga Cabeza, O. et al. Neuroprotective effects of a dendrimer-based glutamate carboxypeptidase inhibitor on superoxide dismutase transgenic mice after neonatal hypoxic-ischemic brain injury. Neurobiol. Dis. 148, 105201 (2021).
Niño, D. F. et al. Cognitive impairments induced by necrotizing enterocolitis can be prevented by inhibiting microglial activation in mouse brain. Sci. Transl. Med. 10, eaan0237 (2018).
Mishra, M. K. et al. Dendrimer brain uptake and targeted therapy for brain injury in a large animal model of hypothermic circulatory arrest. ACS Nano 8, 2134–2147 (2014).
Carlson, M. L. et al. Development and initial assessment of [18F]OP-801: a novel hydroxyl dendrimer PET tracer for imaging maladaptive inflammation in the whole body and brain. Mol. Imaging Biol. 25, 1063–1072 (2023).
Voskuhl, R. R. & MacKenzie-Graham, A. Chronic experimental autoimmune encephalomyelitis is an excellent model to study neuroaxonal degeneration in multiple sclerosis. Front. Mol. Neurosci. 15, 1024058 (2022). 1.
Hamilton, A. M. et al. Central nervous system targeted autoimmunity causes regional atrophy: a 9.4T MRI study of the EAE mouse model of Multiple Sclerosis. Sci. Rep. 9, 8488 (2019).
McCarthy, D. P., Richards, M. H. & Miller, S. D. Mouse models of multiple sclerosis: experimental autoimmune encephalomyelitis and Theiler’s virus-induced demyelinating disease. Methods Mol. Biol. Clifton NJ 900, 381–401 (2012).
Barthelmes, J. et al. Induction of experimental autoimmune encephalomyelitis in mice and evaluation of the disease-dependent distribution of immune cells in various tissues. J. Vis. Exp. 53933. https://doi.org/10.3791/53933 (2016). 1.
Dagkonaki, A. et al. Mannan-MOG35-55 reverses experimental autoimmune encephalomyelitis, inducing a peripheral type 2 myeloid response, reducing CNS inflammation, and preserving axons in spinal cord lesions. Front. Immunol. 11, 575451 (2020).
Pyka-Fosciak, G., Stasiolek, M. & Litwin, J. A. Immunohistochemical analysis of spinal cord components in mouse model of experimental autoimmune encephalomyelitis. Folia Histochem. Cytobiol. 56, 151–158 (2018).
Nissen, J. C., Thompson, K. K., West, B. L. & Tsirka, S. E. Csf1R inhibition attenuates experimental autoimmune encephalomyelitis and promotes recovery. Exp. Neurol. 307, 24–36 (2018).
Hagan, N. et al. CSF1R signaling is a regulator of pathogenesis in progressive MS. Cell Death Dis. 11, 904 (2020).
Liaw, K. et al. Dendrimer size effects on the selective brain tumor targeting in orthotopic tumor models upon systemic administration. Bioeng. Transl. Med. 5, e10160 (2020).
Zhang, F. et al. Uniform brain tumor distribution and tumor associated macrophage targeting of systemically administered dendrimers. Biomaterials 52, 507–516 (2015).
Lesniak, W. G. et al. Biodistribution of fluorescently labeled PAMAM dendrimers in neonatal rabbits: effect of neuroinflammation. Mol. Pharm. 10, 4560–4571 (2013).
Wang, X.-S. et al. Idazoxan reduces blood–brain barrier damage during experimental autoimmune encephalomyelitis in mouse. Eur. J. Pharmacol. 736, 70–76 (2014).
Wolburg, H., Wolburg-Buchholz, K. & Engelhardt, B. Involvement of Tight junctions during transendothelial migration of mononuclear cells in experimental autoimmune encephalomyelitis. in Neuroinflammation in Stroke (eds Dirnagl, U. & Elger, B.) 17–38. https://doi.org/10.1007/978-3-662-05426-0_2 (Springer Berlin Heidelberg, 2004). 1.
Gandhi, R., Laroni, A. & Weiner, H. L. Role of the innate immune system in the pathogenesis of multiple sclerosis. J. Neuroimmunol. 221, 7–14 (2010).
Bittner, S., Afzali, A. M., Wiendl, H. & Meuth, S. G. Myelin oligodendrocyte glycoprotein (MOG35-55) induced experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice. J. Vis. Exp. 51275. https://doi.org/10.3791/51275 (2014). 1.
Thomas, T. P. et al. Cationic poly(amidoamine) dendrimer induces lysosomal apoptotic pathway at therapeutically relevant concentrations. Biomacromolecules 10, 3207–3214 (2009).
Alnasser, Y. et al. Preferential and increased uptake of hydroxyl-terminated PAMAM dendrimers by activated microglia in rabbit brain mixed glial culture. Mol. J. Synth. Chem. Nat. Prod. Chem. 23, 1025 (2018).
Albertazzi, L., Serresi, M., Albanese, A. & Beltram, F. Dendrimer internalization and intracellular trafficking in living cells. Mol. Pharm. 7, 680–688 (2010).
Sharma, A. et al. Targeting mitochondrial dysfunction and oxidative stress in activated microglia using dendrimer-based therapeutics. Theranostics 8, 5529–5547 (2018).
Zhang, F., Nance, E., Alnasser, Y., Kannan, R. & Kannan, S. Microglial migration and interactions with dendrimer nanoparticles are altered in the presence of neuroinflammation. J. Neuroinflammation 13, 65 (2016).
Goossens, J. Revised McDonald criteria allow earlier and more precise MS diagnosis. Medical Conferences https://conferences.medicom-publishers.com/specialisation/neurology/ectrims-2024/revised-mcdonald-criteria-allow-earlier-and-more-precise-ms-diagnosis-2/ (2024). 1.
Kitagawa, D. et al. Characterization of kinase inhibitors using different phosphorylation states of colony stimulating factor-1 receptor tyrosine kinase. J. Biochem. 151, 47–55 (2012).
Vermersch, P. et al. Masitinib treatment in patients with progressive multiple sclerosis: a randomized pilot study. BMC Neurol. 12, 36 (2012).
Ettcheto, M. et al. Masitinib for the treatment of Alzheimer’s disease. Neurodegener. Dis. Manag. 11, 263–276 (2021).
Webb, M. et al. Sphingosine 1-phosphate receptor agonists attenuate relapsing–remitting experimental autoimmune encephalitis in SJL mice. J. Neuroimmunol. 153, 108–121 (2004).
Di Dario, M. et al. Myeloid cells as target of fingolimod action in multiple sclerosis. Neurol. Neuroimmunol. Neuroinflammation 2, e157 (2015).
Chun, J. & Hartung, H.-P. Mechanism of action of oral fingolimod (FTY720) in multiple sclerosis. Clin. Neuropharmacol. 33, 91–101 (2010).
Vogel, D. Y. et al. Macrophages in inflammatory multiple sclerosis lesions have an intermediate activation status. J. Neuroinflammation 10, 809 (2013).
Leuti, A. et al. Macrophage plasticity and polarization are altered in the experimental model of multiple sclerosis. Biomolecules 11, 837 (2021).
Radandish, M., Khalilian, P. & Esmaeil, N. The role of distinct subsets of macrophages in the pathogenesis of MS and the impact of different therapeutic agents on these populations. Front. Immunol. 12, 667705 (2021).
Boven, L. A. et al. Myelin-laden macrophages are anti-inflammatory, consistent with foam cells in multiple sclerosis. Brain 129, 517–526 (2006).
Vankriekelsvenne, E. et al. Transmembrane protein 119 is neither a specific nor a reliable marker for microglia. Glia 70, 1170–1190 (2022).
Zrzavy, T. et al. Loss of ‘homeostatic’ microglia and patterns of their activation in active multiple sclerosis. Brain 140, 1900–1913 (2017).
van Wageningen, T. A. et al. Regulation of microglial TMEM119 and P2RY12 immunoreactivity in multiple sclerosis white and grey matter lesions is dependent on their inflammatory environment. Acta Neuropathol. Commun. 7, 206 (2019).
Fox, R. J. et al. Tolebrutinib in nonrelapsing secondary progressive multiple sclerosis. N. Engl. J. Med. 392, 1883–1892 (2025).
Rousset, O., Rahmim, A., Alavi, A. & Zaidi, H. Partial volume correction strategies in PET. PET Clin. 2, 235–249 (2007).
Van Der Weijden, C. W. J. et al. Myelin imaging of the spinal cord in animal models and patients with multiple sclerosis using [11C]MeDAS PET: a translational study. J. Nucl. Med. 66, 136–141 (2025).
Kuntner, C. & Stout, D. B. Quantitative preclinical PET imaging: opportunities and challenges. Front. Phys. 2, 12 (2014). 1.
Krishnamoorthy, G. & Wekerle, H. EAE: an immunologist’s magic eye. Eur. J. Immunol. 39, 2031–2035 (2009).
Moradi, F. et al. [18F]Flurimedrimer, a novel nanomedicine radiotracer, selectively targeting activated microglia in human brain. J. Nucl. Med. 66, 251092 (2025).
Ashvattha Therapeutics, Inc. A Phase 1/2 Study to Evaluate Safety, PK and Biodistribution of an Imaging Agent, 18F-OP-801, After Intravenous Administration to Patients With ALS, Alzheimer’s Disease, Multiple Sclerosis, Parkinson’s Disease and Healthy Volunteers. https://clinicaltrials.gov/study/NCT05395624 (2024). 1.
James, M. L. et al. Imaging B cells in a mouse model of multiple sclerosis using 64 Cu-rituximab PET. J. Nucl. Med. 58, 1845–1851 (2017).
Cropper, H. C. et al. Longitudinal translocator protein-18 kDa–positron emission tomography imaging of peripheral and central myeloid cells in a mouse model of complex regional pain syndrome. Pain 160, 2136–2148 (2019).
Acknowledgements
We would like to thank Dr. Emily Becker for her assistance in preparing the manuscript. This work was supported by Ashvattha Therapeutics (to M.L.J.), NIH/NINDS (grant number: 1R21NS135513-01A1, to M.L.J.) and NSF GRFP (grant number: DGE-2146755, to R.C.K.).
Author information
Author notes
These authors contributed equally: Renesmee C. Kuo, Mackenzie L. Carlson.
Authors and Affiliations
Department of Electrical Engineering, Stanford University, Stanford, CA, USA
Renesmee C. Kuo 1.
Molecular Imaging Program at Stanford, Department of Radiology, Stanford University, Stanford, CA, USA
Renesmee C. Kuo, Samantha T. Reyes, Sydney C. Nagy, Mausam Kalita, Israt S. Alam, Noeen Malik, Isaac M. Jackson, Christopher J. Acosta, Irene N. Falk, E. Carmen Azevedo, Corinne Beinat & Michelle L. James 1.
Department of Neurology and Neurological Sciences, Stanford University, Stanford, CA, USA
Mackenzie L. Carlson & Michelle L. James 1.
Department of Medicine, Stanford University, Stanford, CA, USA
Yanrong Zhang & Lisa Nichols 1.
Ashvattha Therapeutics, Inc., Redwood City, CA, USA
Naze G. Avci, Madhuri Chattopadhyay, S. Sakura Minami & Jeffrey L. Cleland
Authors
- Renesmee C. Kuo
- Mackenzie L. Carlson
- Samantha T. Reyes
- Sydney C. Nagy
- Mausam Kalita
- Israt S. Alam
- Noeen Malik
- Isaac M. Jackson
- Christopher J. Acosta
- Irene N. Falk
- E. Carmen Azevedo
- Yanrong Zhang
- Lisa Nichols
- Corinne Beinat
- Naze G. Avci
- Madhuri Chattopadhyay
- S. Sakura Minami
- Jeffrey L. Cleland
- Michelle L. James
Contributions
R.C.K. and M.L.C. designed and implemented the study, led data acquisition and analysis, and wrote the manuscript and prepared all figures and tables. S.T.R., S.C.N., M.K., I.S.A., C.J.A., I.N.F., E.C.A., C.B., and M.C. helped with data acquisition. N.M. and I.M.J. synthesized the radiotracer. Y.Z. and L.N. at the Stanford Shared FACS Facility designed the flow cytometry panel and provided guidance on data analysis. N.G.A., S.S.M., and J.L.C. helped conceptualize and design the study and analysis. M.L.J. helped design the study and assisted with developing figures and interpreting data. All authors reviewed the manuscript.
Corresponding author
Correspondence to Michelle L. James.
Ethics declarations
Competing interests
N.G.A., M.C., S.S.M., and J.L.C. are employed by Ashvattha Therapeutics during the completion of this work. All other authors have declared no conflicts of interest.
Peer review
Peer review information
Nature Communications thanks the anonymous reviewers for their contribution to the peer review of this work. A peer review file is available.
Additional information
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
About this article
Cite this article
Kuo, R.C., Carlson, M.L., Reyes, S.T. et al. A radiolabeled dendrimer non-invasively identifies and tracks innate immune cell activation in a mouse model of experimental autoimmune encephalomyelitis. Nat Commun (2026). https://doi.org/10.1038/s41467-025-67907-x
Received: 24 January 2025
Accepted: 11 December 2025
Published: 30 January 2026
DOI: https://doi.org/10.1038/s41467-025-67907-x