Nanoparticle size governs engagement with myeloid cells and hitchhiking to hematopoietic organs in myeloproliferative neoplasms

Nanoparticle design principles contribute to desirable in vivo performance, including prolonged circulation, desirable biodistribution profiles, and tuned interactions with the immune system. The importance of these variables, although well-established in solid tumors, remains elusive in the context of hematological malignancies. Here, we investigated the influence of liposome size on biodistribution and cellular uptake within hematopoietic compartments - bone marrow (BM) and spleen - in JAK2V617F myeloproliferative neoplasms (MPN). A milli-fluidic manufacturing platform combined with a Design-of-Experiments (DoE) approach was used to generate small, medium, and large liposomes. Liposome uptake was assessed ex vivo using blood samples from healthy donors and MPN patients, followed by in vivo biodistribution studies in a transgenic JAK2V617F MPN mouse model. Organ-level accumulation was quantified using hybrid fluorescence / computed tomography (FLT/CT) imaging, while cellular uptake was evaluated via flow cytometry. Whole-body imaging revealed that increasing liposome size enhanced delivery to both the spleen and BM, with larger liposomes exhibiting the highest accumulation in both organs. Cellular analysis corroborated the in vivo observations, demonstrating that large liposomes are taken up to a greater extent by monocytes and granulocytes, in both spleen and BM. At late time-points post-injection, the liposomal accumulation was twice as high in the BM in comparison to the spleen and peripheral blood, highlighting the progressively elevated accumulation and retention in the BM, as opposed to the elimination phase nanoparticles undergo in clearance organs and circulation at these time-points. Of note, among BM mature myeloid cells, neutrophils were associated with a higher nanoparticle uptake than monocytes, highlighting their capability to phagocytose material in circulation and hitchhike it to malignant or inflamed regions. These findings demonstrate that continuous flow manufacturing procedures can swiftly produce nanoparticles with desirable characteristics that are essential for tuning the biodistribution towards hematopoietic organs and myeloid immune cells. By providing mechanistic insights into nanoparticle behavior within hematopoietic compartments, this work advances our understanding of nanomedicine in vivo performance and highlights particle size as a critical quality attribute that can be optimized and controlled to improve targeted delivery to myeloid cells in the treatment of hematological malignancies.