Multiple myeloma (MM) still remains incurable even with the implementation of novel therapeutic modalities, leading to the idea to develop various forms of immunotherapies. In this regard, γδ T cells bearing Vγ9Vδ2 TCR expanded from peripheral blood mononuclear cells (PBMCs) have attracted attention as potent effectors available in a novel immunotherapy against MM. Human Vγ9Vδ2 γδ T cells can be expanded ex vivo by aminobisphosphonates in combination with IL-2, and effectively target and impair MM cells. However, MM cells appear to protect themselves from external insults by immune cells in a unique bone marrow microenvironment created by the accumulation of mesenchymal stem cells/bone marrow stromal cells (BMSCs) with defective osteoblastic differentiation and acid-producing osteoclasts. To improve the therapeutic efficacy of γδ T cells, therefore, we need to develop a maneuver to effectively enhance the expansion and activity of γδ T cells while disrupting the MM cell-bone marrow interaction. Lenalidomide (Len), a novel immunomodulatory anti-MM agent, shows pivotal anti-MM activity by targeting immune cells as well as the interaction of MM cells and their surrounding cells in the bone marrow. The present study was undertaken to explore the efficacy of Len in combination with zoledronic acid (Zol) or a precursor of isopentenyl pyrophosphate (IPP) (E)-4 hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), a microbial antigen for Vγ9Vδ2 TCR, on the induction and expansion of Th1-like γδ T cells with enhanced cytotoxic activity against MM cells in the skewed bone marrow microenvironment in MM. When combined with Zol (1μM), clinically relevant doses of Len (around 1 μM) substantially expanded γδ T cells from PBMCs to the levels similar to IL-2 (100 U/ml). Len was able to expand γδ T cells more robustly in combination with HMB-PP (1 μM) than Zol from PBMCs from the majority of normal donors. However, Len alone did not show any significant effects on γδ T cell expansion and activation, suggesting a costimulatory role of Len on Zol or HMB-PP-primed γδ T cells. The surface expression of LFA-1, and the cytotoxicity-associated molecules NKG2D, DNAX accessory molecule-1 (DNAM-1; CD226) and TRAIL were up-regulated in the expanded γδ T cells. Although functional diversity has been demonstrated in γδ T cells expanded by various stimuli, Len in combination with either Zol or HMB-PP enhanced intracellular IFN-γ along with the surface NKG2D but not Foxp3 in γδ T cells at higher levels than IL-2, suggesting robust induction of Th1-like γδ T cells by Len. Importantly, γδ T cells expanded with the combinatory treatments with Len and Zol or HMB-PP exerted potent cytotoxic activity against MM cells but not normal cells surrounding MM cells in bone marrow samples from patients with MM. Such treatments with Len was able to maintain the cytotoxic activity of the γδ T cells against MM cells in acidic conditions with lactic acid, and restored their anti-MM activity blunted in the presence of BMSCs. Interestingly, the expanded γδ T cells markedly suppressed the colony formation in semi-solid methylcellulose assays of RPMI8226 and KMS-11 cells [81±1 (mean ± SD) vs. 0±0 and 40±1 vs. 16±4 colonies/dish, respectively, p<0.01], and decreased in size their side populations, suggesting targeting a drug-resistant clonogenic MM cells. These results collectively demonstrate that Len and HMB-PP as well as Zol are an effective combination for ex vivo expansion of Th1-like γδ T cells with potent anti-MM activity, and suggest that Len in combination with Zol may maintain their in vivo anti-MM activity in the bone marrow where MM cells reside. The present results warrant further study on Len-based immunotherapy with γδ T cells.
No relevant conflicts of interest to declare.
Asterisk with author names denotes non-ASH members.