Reduced Natural Killer Function Accompanies MDS Disease Progression and Is Restored by Lenalidomide (CC5013, Revlimid®) Via a Mechanism Divergent from Interleukin-2 (IL-2).

Background: Patients with myelodysplastic syndromes (MDS) display several abnormalities of T cell and NK cellular immunity. Tumor lysis by NK cells occurs through orchestrated control by inhibitory NK receptors (NKRs) and activating NKRs. Lenalidomide is an immunomodulatory (IMiD) drug structurally related to thalidomide, which has proven clinical efficacy for the treatment of low-risk MDS (

Methods: MDS patients were categorized according to WHO category, age, sex, IPSS, and cytogenetics. Peripheral blood cells (PBMCs) were isolated from patients and normal donors and NK receptor expression determined in paired healthy and patient PBMCs by 3-color flow cytometry. NK receptor expression was analyzed for CD158a (KIR2DL1, KIR2DS1), CD158b (KIR2DL2, KIR2DL3, KIR2DL3), KIR3DL1, KIR2DS4, NKG2A, NKG2D, NKp30, NKp44, and NKp46. Cytotoxicity assays were performed using 5-hour ⁵¹Cr-release assays.

Results: Forty-eight MDS patients and 37 normal donors were analyzed, demonstrating that NK cytolytic function was reduced in the patient population (19% ± 21 S.D. vs. 44% ± 21) (p<0.001). Reduced NK function in MDS was significantly associated with higher IPSS (p=0.01), abnormal karyotype (p=0.05), presence of excess blasts (p=0.01), and age-adjusted bone marrow hypercellularity (p=0.04). MDS patients had reduced display of the activating receptor NKp30, accompanied by NKG2D (an activating C lectin-like (NKG2)-family receptor) downregulation that closely correlated with impaired NK function (p=0.001). NK-mediated cytotoxicity and NKR expression were examined after treatment with lenalidomide 5μM for 72 hours or IL-2 in normal donors and MDS patients. Lenalidomide augmented NK lytic function in normal donors (vehicle, 42% ± 15 vs. lenalidomide, 71% ± 17; P≤0.01 by t test) and in 10 out of 17 (59%) of the MDS patients (vehicle, 25% ± 25 vs. lenalidomide 42% ± 33). IL-2 increased NK cytolytic function in all MDS patients (vehicle, 16% ± 16 vs. lenalidomide, 47% ± 33) and the percentage of NK cells expressing CD69 was increased from both MDS patients and normal controls. Similarly, the percentage of NK cells expressing NKp30, NKG2D, NKp44 but not NKp46 was significantly enhanced by IL-2 culture. In contrast, lenalidomide treatment failed to induce NKR expression in MDS patients and normal controls.

Conclusions: These findings suggest that impairment of NK cytolytic function in MDS derives in part from reduced display of the activating NK receptors such as NKG2D, which accompanies disease progression. Lenalidomide augments NK function in some patients; however, the mechanisms of functional augmentation by IL-2 and lenalidomide are divergent. Evasion of NK immunosurveillance may be an important factor associated with MDS disease progression.