In Vivo Evaluation of Immunomodulating Effects of Lenalidomide (L) on Tumor Cell Microenvironment as a Possible Underlying Mechanism of the Antitumor Effects Observed in Patients (pts) with Chronic Lymphocytic Leukemia (CLL).

Introduction: L is a more potent analogue of thalidomide with antitumor activity reported in MDS and multiple myeloma. Clinical anti-leukemic activity of L is reported for the first time by our group in pts with CLL. The underlying mechanism of its antitumor activity remains undetermined. We investigated the effect of L on the tumor microenvironment and studied the modulation of soluble cytokines and immune cells (T and NK cells) in pts receiving L.

Patients and Methods: CLL pts enrolled on the clinical study with L were eligible. Pre and post (day 7) samples were obtained for evaluation of changes in serum cytokine and immune cell environment. Malignant cells were also obtained to investigate the in vitro antitumor activity of L prior to initiating treatment on clinical trial.

Results: With Anexin V staining for evaluation of apoptosis induction, in vitro testing of pts samples (n=10) showed only a modest increase in apoptosis at 200mg of L - levels clinically not achievable. Yet same pts treated with L on clinical study showed significant antitumor response, suggesting the mechanism to be possibly related to modulation of the tumor microenvironment. In evaluation of the tumor cytokine microenvironment (n= 10) we noted significant L induced increase in IL-10 (n=6), IL-8 (n=8), IP-10 (n=10), IL-8 (n=8), TNF-alpha (n=4) and decrease in PDGF (n=5) and RANTES (n=5). While evaluation of the immune cell repertoire we observed an absolute increase in T-cell as well as NK-cell after treatment with L.

Conclusion: Our in vitro evaluation does not suggest a direct apoptotic effect of L on the malignant CLL cells and thus support the hypothesis that the anti-leukemic effect noted in the clinical trial (reported separately) is most likely from in vivo modulation of the tumor microenvironment as is demonstrated from changes in the cytokine milieu and the cellular immune response. Collectively these changes may be responsible for the immune modulating properties of L and the resultant anti-CLL activity in pts.