Abstract 3849: Exosomes in polycythemia vera: "mini platelets" with oncogenic and thrombogenic potential
Authors: Uziel Orit , Shacham-Abulafia Adi , Spectre Galia , Ziv Ester , Geiger Karyn Revital , Sarsor Zinab , Ron Neria , Beery Einat , Raanani Pia , Revel-Vilk Shoshana , Naamad Mira , Rozovski Uri 
Published: June 2022

Abstract
Polycythemia vera (PV) is a classical "myeloproliferative neoplasm" characterized by clonal proliferation of myeloid progenitor cells caused by their acquisition of a mutation in the JAK2 gene. Its common complications are thrombosis and second primary malignancies. Secreted from virtually all cell types, exosomes are extracellular vesicles that carry bioactive cargo derived from their cells of origin. When engulfed, their cargo may alter the phenotype of the recipient cells. For example, neoplastic exosomes modulate the cellular makeup of bystander cells. Therefore, since mutated JAK2 is present in virtually all PV-patients, we hypothesize that PV-derived exosomes (hereafter PV-exo) carry the mutated JAK2 oncogene and are taken up by non-clonal cells, thus contributing to the thrombotic manifestations and oncogenic potential of patients with PV. We isolated and characterized exosomes from PV-patients and from the Human erythroleukemia (HEL) cell line (hereafter HEL-exo). We exposed normal cells implicated in thrombosis and skin cells to these exosomes and examined the cells' phenotypic changes and activation after exposure. Using Sanger sequencing we discovered that both PV-exo and HEL-exo, like their parental cells, carry the mutated JAK2 transcripts, allowing clonal cells to export oncogenes to distant, non-clonal sites. Our preliminary findings suggest that these exosomes promote pro-coagulant and malignant phenotypes in multiple ways. Thrombin generation assay pointed to a significantly higher generation of thrombin in the presence of PV-exo than those derived from healthy donors. Similarly, flow cytometry analysis revealed that PV-exo increased the expression of platelet activation markers. Moreover, Trans Endothelial Electrical Resistance (TEER) assay results suggest that HEL-exo induces endothelial dysfunction. Furthermore, using the Sulforhodamine B assay, we found that exposure to HEL-exo increased the proliferation of normal keratinocytes. In summary, we developed the concept of exosomes as “mini metastasis” that might promote disease manifestations either directly or indirectly. Since unlike solid tumors, hematological malignancies do not metastasize, exosomes derived from neoplastic hematological cells may fulfill this function. Such exosomes may spread oncogenes (e.g., mutated JAK2), damage non-clonal tissues (e.g., endothelial dysfunction) or act as a miniature reflection of their cells of origin (e.g., exosomes as mini platelets) in a parallel way to "real" metastasis; this concept may affect treatment related decisions. For example, by reducing clonal burden, early treatment even in “low risk” patients may prevent exosomal spread and exosomal-dependent damage to distant tissues. The results of our study highlight PV-exo as promoters of PV-complications, thrombosis and malignant transformation.
Citation Format: Orit Uziel, Adi Shacham-Abulafia, Galia Spectre, Ester Ziv, Karyn Revital Geiger, Zinab Sarsor, Neria Ron, Einat Beery, Pia Raanani, Shoshana Revel-Vilk, Mira Naamad, Uri Rozovski. Exosomes in polycythemia vera: "mini platelets" with oncogenic and thrombogenic potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3849.