Lenalidomide Effects on NK Function in Patients with Myelodysplastic Syndrome (MDS).

Abstract

Lenalidomide, which is a 4-amino-glutarimide analogue of thalidomide, has significant erythropoietic activity in patients with lower-risk MDS (List et al, NEJM , 351:26, 2004). Although its precise target of action in MDS is not known, lenalidomide modulates cellular response to varied stimuli including inhibition of angiogenic response and endotoxin induction of inflammatory cytokines and enhancement of antigen-induced immunologic response and erythropoietin receptor signaling. Clinical investigations in multiple myeloma indicate that the immunomodulatory effects of thalidomide and lenalidomide extends to the expansion of natural killer (NK) cells. We recently found that MDS patients have defective NK function, araising in part to reduced expression of activating NK receptors (NKRs) NKp30, CD244 (2B4), and NKG2D. To determine if lenalidomide may restore NK function in MDS, we investigated the effects of in vitro treatment with lenalidomide on NK function and phenotype. Lytic function was studied using peripheral blood mononuclear cells (PBMCs) as effector cells and the leukemia cell line, K562, as a target in standard 4-hr 51Cr-release assays at 12:1 and 25:1 effector:target (E:T) ratios. Among eight MDS patient's specimens evaluated, five patients had significant increase in tumor lysis after treatment with 1 μM lenalidomide for 72 hours (p ≤ 0.01, T-test). In similar experiments using PBMCs from normal donors, we found that NK lysis of K562 was 42% ± 15 (25:1 E:T ratio) pre-treatment which increased to 71% ± 17 (25:1 E:T ratio) after treatment, which was statistically significant (p ≤ 0.01, T-test). We also examined the in vitro effects of lenalidomide on lytic activity by the NK cell lines, NK92 and NKL, which was significantly increased after drug treatment. To discern the mechanisms of lenalidomide action in NK cell lines and normal NK cells, we evaluated NKR display by flow cytometry, and NKR function by antibody redirected cytotoxicity using the FcγR+ murine mastocytoma (P815) target cell line. Using NK92 and NKL cells, treatment with lenalidomide 1 μM for 72 hrs increased lysis by anti-NKG2D and anti-CD244 activating antibodies. We also found that NKG2D surface expression was increased on normal NK cells after lenalidomide treatment in vitro. These results suggest that some MDS patients may have improved NK function through the immunomodulatory effects of lenalidomide. The relationship between in vitro NK responsiveness to lenalidomide and in vivo hematological response warrants investigation in patients with MDS.