The Crosstalk Between Leptin Receptor Activation and iNKT Mediated Anti-Tumor Immunity in Multiple Myeloma

In recent years, researchers have showed a growing interest in the mechanistic relationship between bone marrow adipose tissue and adjacent tumors. However, the impact of bone marrow adipocytes on development of hematological malignancies, particularly multiple myeloma is unknown. With aging, bone marrow changes occur and fatty deposits can occupy up to 70% of the BM cavity. Interactions of bone marrow adipose tissue with bone cells and other immune cells, possibly suggest indirect ways in which bone marrow adipocytes may affect MM disease progression. Leptin, an adipokine released by adipocytes and crucial in energy homeostasis, displays immune modulatory properties but its role in anti-tumor immunity remains unclear. In this study we aimed to investigate the intriguing relationship between leptin receptor activation and invariant natural killer T (iNKT) cell mediated anti-tumor immunity in multiple myeloma. The murine immunocompetent 5T33MM model, mimicking the human disease closely, and human samples of newly diagnosed patients were used to investigate this research topic.

A marked increase in serum leptin levels and an upregulation of the leptin receptor expression on iNKT cells was observed in multiple myeloma, in both mice and newly diagnosed patients. In vitro functional analysis demonstrated a direct role for leptin in the downmodulation of the iNKT cell function and an indirect role by acting on the MM cells itself, potentiating the immunosuppressive effect on iNKT cells. We next evaluated the in vivo effects of blocking the leptin receptor together with activating iNKT cells with the prototypic glycolipid a-galactosylceramide (a-GalCer), in the 5T33 myeloma model. Remarkably, strong protection was seen in the combined regimen (a-GalCer and leptin receptor blockade), which was found to be linked to an amplified and sustained activation of iNKT cells, preventing them to become hypoactive. These findings suggest that leptin has a crucial immune suppressive role in myeloma development. Overall, our data reveal the leptin receptor axis as a novel target to treat multiple myeloma.