Therefore, anti-2M mAb may impact a larger and heterogeneous 2M-expressing cancer patient populace. Previous research has shown that BMSCs in MM MC 70 HCl BM play a crucial role in MM drug resistance43. to improve MM patient outcome. Keywords:2-microglubulin, monoclonal antibody, antibody-dependent cell-mediated cytotoxicity, complement-dependent cytotoxicity, multiple myeloma == Introduction == Multiple myeloma (MM) is usually a clonal plasma cell neoplasm that utilizes the bone marrow (BM) microenvironment for survival and proliferation1-3. Current myeloma therapies such as hematopoietic cell transplantation and combinatorial chemotherapies are rarely curative and relapse is usually common. This implies that therapy-resistant myeloma-initiating cells exist and that new therapeutics must be developed to target and eradicate these chemoresistant myeloma cells. Lenalidomide is usually a potent novel thalidomide analog which has demonstrated remarkable clinical activity in the treatment of MM4. The strong evidence-based clinical success of lenalidomide in MM patients has led to its approval by US-FDA under the trade name of Revlimid capsules by Celgene Corporation. However, adverse effects and drug resistance have been observed in MM patients, which are great challenges for the extended application of lenalidomide5. Targeted immunotherapy with monoclonal antibodies (mAbs) is an effective and safe method for the treatment of cancers. However, there is still no mAb-based cancer therapy approved to treat patients with MM. Early clinical trials of mAbs targeting CD20 and CD38 have conveyed only very limited benefit to the treatment of MM6-8. In recent years, efforts have been made to identify potential therapeutic mAbs by defining option or novel MM target antigens, i.e., CD409,10, IL6R11, HM1.2412,13, CD7414, CD4715, TRAIL-R116, CS117, as well as to conjugate mAbs with classic or novel drugs to specifically kill MM cells, i.e., CD56-maytansinoid (DM1)18, CD138-DM1/DM419. Development of mAbs with improved cytotoxicity, targeting new and known myeloma-associated antigens, continues to be an active research area. MC 70 HCl 2-microglubulin (2M) is usually a part of the major histocompatibility complex (MHC) class I molecule around the cell surface of nucleated cells20. We have recently exhibited that human 2M is usually a potential target for MM treatment21. Our previous studies showed that anti-2M mAbs have strong direct apoptotic effects on myeloma and other hematological malignancies with less toxicity on normal tissues and cells in vitro and in mouse models21,22, suggesting that anti-2M mAbs might be a novel therapeutic agent for MM. Furthermore, others have reported similar results by using anti-MHC class-1 single-chain Fv diabody or anti-2M antibodies to induce apoptosis in human myeloma23, renal cell carcinoma24, and prostate Mouse monoclonal to BLK cancer25. Natural killer (NK) cell-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) is usually a critical mechanism for many approved therapeutic mAbs26-28. FcRIIIa, a member of the leukocyte receptor family FcRs, is known to be a major triggering receptor of ADCC in NK cells. FcRIIIa polymorphism status of NK cells from cancer patients plays a key role MC 70 HCl in the clinical outcome of patients receiving rituximab27, trastuzumab29, or cetuximab28. Complement-dependent MC 70 HCl cytotoxicity (CDC) is usually a cytolytic cascade mechanism by which complement proteins present in serum are activated by antigen-specific antibodies. CDC is usually triggered by the binding of C1q, a subunit of C1, to the CH2 domain name of a cell-bound IgG antibody, leading to the formation of the membrane attack complex (MAC) and ultimately lysis of target cells30. Human IgG1 and IgG3 efficiently mediate effector function activities, while IgG2 and IgG4 are generally ineffective31,32. In this study, we evaluated anti-2M mAb-mediated MC 70 HCl ADCC and CDC activities against established human MM cell lines and primary MM cells from patients. The ADCC and CDC activities of anti-2M mAbs were more against tumor cells, and BM microenvironment could not safeguard MM cells from anti-2M mAb-mediated ADCC and CDC activities. Lenalidomide enhanced in vitro and in vivo anti-2M mAb-mediated ADCC activities. == Materials and Methods == == Cell lines and primary cells == Human myeloma cell line ARP-1 and CAG were established at the University of Arkansas for Medical Sciences from BM aspirates of patients with MM33. MM.1S was kindly provided by Dr. Steven Rosen of Northwestern University (Chicago, IL). U266 WT and U266/R10R were generously provided by Dr. Robert Z. Orlowski of MD Anderson Cancer.