Multiple myeloma (MM) remains incurable by the present therapeutic modalities, leading to the idea to develop various forms of immunotherapy. γδT cells are important effectors in the first-line defense against infections and tumors, and play a critical role in host defense and tumor surveillance. Aminobisphosphonates can effectively expand human γδT cells in combination with IL-2. Because expanded γδT cells have been demonstrated to exert potent anti-MM effects in vitro, γδT cell-based immunotherapy has attracted considerable attention as a novel treatment against MM. However, the clinical efficacy of γδT cell-based immunotherapy has been limited in patients with MM. We previously demonstrated that bone marrow stromal cells (BMSCs) blunt γδT cell activity and thus protect MM cells. To improve the therapeutic efficacy of γδT cells in vivo, therefore, we need to develop a maneuver to restore the anti-MM activity of γδT cells in the bone marrow microenvironment in which MM cells reside. Lenalidomide (LEN), a novel immunomodulatory anti-MM agent, shows pivotal anti-MM activity by targeting immune cells as well as MM cells and their surrounding cells in the bone marrow microenvironment. The present study was undertaken to further clarify the role of the bone marrow microenvironment in MM in the cytotoxic activity of γδT cells against MM cells and to determine whether LEN is able to modulate γδT cell activity and restore its anti-MM effects in the bone marrow. When γδT cells expanded with zoledronic acid (Zol) and IL-2 were cocultured with peripheral blood mononuclear cells (PBMC)-derived OCs or MM cell lines, γδT cells almost completely destroyed both types of cells, suggesting the susceptibility of OCs as well as MM cells to γδT cells. However, the cytotoxic activity of γδT cells against MM cells was markedly attenuated in the presence of BMSCs but not OCs. γδT cells expanded with Zol and IL-2 up-regulated their surface expression of LFA-1, CD26, and the molecules associated with NK or cytotoxic T cell activation including NKG2D and DNAX accessory molecule-1 (DNAM-1; CD226). Among these molecules, stromal cells markedly down-regulated DNAM-1 expression along with a decrease in interferon-γ production by γδT cells. DNAM-1 is regarded as an essential factor in NK cell-mediated cytotoxicity against various cancers. MM cells constitutively expressed DNAM-1 ligands, poliovirus receptor (CD155) and nectin-2; treatment with a blocking antibody against DNAM-1 substantially reduced the cytotoxic activity of γδT cells against MM cells, suggesting a critical role of DNAM-1 in the anti-MM effects of γδT cells. Interestingly, when γδT cells were cocultured with BMSCs in the presence of clinically relevant doses of LEN (1 microM) and Zol (0.1-1 microM), the suppression of interferon-γ production and DNAM-1 expression of γδT cells by BMSCs were substantially reduced. Moreover, such γδT cells exerted potent anti-MM effects, suggesting antagonism of the suppressive effects of BMSCs on γδT cell activity and its anti-MM effects. LEN (0.1-10 microM) and Zol (0.1-5 microM) in combination were able to substantially expand γδT cells from PBMCs in the absence of IL-2. These expanded γδT cells expressed the activation markers LFA-1, CD26, NKG2D and DNAM-1 at levels similar to those in γδT cells expanded by Zol and IL-2. However, LEN alone did not show any significant effects on γδT cell expansion and activation, suggesting a costimulatory role of LEN on Zol-primed γδT cells. These results collectively suggest that MM cells evade attack by γδT cells in the bone marrow through attenuation of γδT cell activity by BMSCs, and that LEN and Zol in combination may restore γδT cell activity and its anti-MM effects to improve the efficacy of γδT cell-based immunotherapy against MM.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.