Single cell tracking by time-lapse MRI: Imaging the patrolling of non-classical monocytes to characterize their role in cancer

• Applicant: Privatdozent Dr. Max Masthoff
• Subject Area: Radiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549903517

The complex interplay of tumor and immune cells within the tumor microenvironment (TME) responsible for progression and metastasis is increasingly understood using tools from molecular (imaging) research and cell biology, which has led to the new age of immunotherapy in cancer treatment. However, the role of each cell type or subset of immune cells has not yet been fully understood. That especially holds true for so-called non-classical “patrolling” monocytes (pMO), a distinct subset of monocytes showing a specific immunophenotype to be differentiated from “classical” inflammatory monocytes, that exhibit a characteristic intravascular motion pattern, called patrolling. While initial studies have shown an anti-tumoral role of these non-classical monocytes within the TME, their intravascular motion towards the primary tumor site as well as their prevalence and importance during tumor progression or immunotherapy is unknown. Recently, we have developed a non-invasive, dynamic single-cell imaging technique, called time-lapse MRI, that allows to detect and follow intravascular monocytes with velocities similar to patrolling behavior within the murine brain. We have shown, that the number of the detected intravascular cells is altered during inflammation, cancer progression and therapy. However, it is unknown which distinct monocyte subset is observed by time-lapse MRI and how modulation of that cell population and its intravascular motion pattern is correlated with cancer progress and its TME. In this project, we therefore aim to 1) specify the monocyte subset and the intravascular motion behavior observed by time-lapse MRI in health (i.e. so-called steady-state) and 2) utilize time-lapse MRI to resolve the role of pMO during tumor progression and therapy. To address aim 1, we will on the one hand modify the pMO population (wildtype, pMO deficient and GFP expressing pMO mice) and on the other hand modify the intravascular motion of pMO by either blocking or stimulating patrolling, whilst performing time-lapse MRI, intravital microscopy and ex vivo validation. Second, we will also perform similar modifications to pMO and their patrolling behavior during tumor progression in a murine glioblastoma model analyzing their impact on tumor growth, TME formation and composition, and efficacy of tumor therapy. Altogether, the proposed project will (i) establish a new method for non-invasive dynamic imaging of intravascular monocytes, perspectively applicable to other cell types, as well as (ii) unfold the role of non-classical monocytes and their patrolling behavior in tumor progression and TME formation, thereby striving towards potential new therapeutic strategies.

• DFG Programme: Research Grants