Lenalidomide Acts As a Positive Immunomodulator through Modulating the Functions of Human Plasmacytoid Dendritic Cells

Background: Lenalidomide (LEN), is a core anti-multiple myeloma (MM) drug (so-called Immunomodulatory Drugs; IMiD). LEN has been reported to enhance function and proliferation of effector immune cells such as T cells and NK cells. In addition, LEN treatment leads to relatively low rate onset of herpes zoster viral infection compared to treatment of bortezomib as an alternative therapeutic tool for MM. However, cellular and molecular mechanisms underlying its immunomodulatory effects still remain largely unclear. Although there is evidence indicating the immunomodulatory effects of LEN on mouse conventional DCs, there are no reports showing its effects on human DC subsets. Human plasmacytoid DCs (pDCs) dedicate a large proportion of their transcription machinery to making type I interferons (IFNs) and are the major source of IFN-α in the blood (Ito T. Blood 2006; 107: 2423), which have the potential to enhance immune effectors such as T cells, B cells, monocytes, and NK cells. Thus, pDCs play a central role in antiviral immune response in innate host defense. Therefore, we focused on the effects of LEN on the functions of human pDCs.

Methods: Using cell sorting, flow cytometry, microarray, Bio-Plex Multiplex assay, and ELISA methods, functions were analyzed in blood human BDCA4⁺ pDCs from healthy adult volunteers. This study was approved by the Institutional Review Board of Kansai Medical University.

Results: We found that 3 to 300 nM of bortezomib killed pDCs but 0.1 to 3 µM of LEN (covering clinical in vivo plasma concentration range for both agents) did not affect pDC survival and their CD86 expression in response to CpG2216. Bortezomib inhibited dose-dependently pDC-derived IFN-α but 0.1 to 3 µM of LEN sustained IFN-α level in the pDC culture when stimulated with optimal concentration of CpG2216 (3 µM). Of note, in stimulation with low concentrated CpG2216 (0.1 µM), 1 µM of LEN enhanced pDC-derived IFN-α production (184 % of control culture; p=0.027). These results indicate that the clinical concentration of LEN at least sustained and potentially enhanced IFN-α production from pDCs in response to weak stimulation. To seek the chemokine production by pDCs enhanced by the LEN treatment, we used gene microarray analysis and found transcript expressions of CXCL2, CXCL8, CXCL9, CXCL10, CXCL11 and CCL19 were upregulated in LEN-treated pDCs. CXCL2 potentially attracts CTLs and NK cells, CXCL8, CXCL9, CXCL10, and CXCL11 do effector memory T cells, and CCL19 does naïve T and B cells (Piqueras B. Blood 2006; 107: 2613). By Bio-Plex Multiplex assay in the supernatants of pDCs in response to CpG in the presence or absence of 1 µM LEN, we confirmed at protein levels that these chemokines were upregulated (CXCL2; 167 % of control culture, CXCL8; 140 % of cont., CXCL9; 181 % of cont., CXCL10; 160 % of cont., CXCL11; 265 % of cont., and CCL19; 279 % of cont.). In addition, we found LEN upregulated expression of GITR-ligand on pDCs, which has been reported to promote NK cell activity in pDC-NK cell interaction.

Conclusion: LEN enhances production of the pDC-derived chemokines, which allows attraction of several types of immune effectors, and in turn the sustained pDC-derived endogenous type I IFNs and the upregulated GITR-ligand expression may potentially contribute to efficient activation of the attracted immune cells. These data suggest LEN functions as a positive immunomodulator through elaborately modulating pDC functions. Thus, our findings provide a plausible explanation for an advantage of its use for anti-viral defense against herpes and unveiled a part mechanism of IMiD function of LEN in the treatment for MM.