Background aims: Immunotherapy targeting MAGE-A3 in multiple myeloma (MM) could eradicate highly aggressive and proliferative clonal cell populations responsible for relapse. However, expression of many cancer-testis antigens, including MAGE-A3, can be heterogeneous, leading to the potential for tumor escape despite MAGE-A3-induced immunity. We hypothesized that a combination of the hypomethylating agent 5-azacitidine (5AC) and the histone deacetylase inhibitor (HDACi) MGCD0103 (MGC) could induce MAGE-A3 expression in MAGE-A3-negative MM, resulting in recognition and killing of MM cells by MAGE-A3-specific cytotoxic T lymphocytes (CTL).
Methods: Gene expression analyses of MAGE-A3 expression in primary MM patient samples at diagnosis and relapse were completed to identify populations that would benefit from MAGE-A3 immunotherapy. MM cell lines were treated with 5AC and MGC. Real-time polymerase chain reaction (PCR) and Western blotting were performed to assess MAGE-A3 RNA and protein levels, respectively. Chromium-release assays and interferon (IFN) secretion assays were employed to ascertain MAGE-A3 CTL specificity against treated targets.
Results: Gene expression analysis revealed that MAGE-A3 is expressed in MM patients at diagnosis (25%) and at relapse (49%). We observed de novo expression of MAGE-A3 RNA and protein in MAGE-A3-negative cell lines treated with 5AC. MGC treatment alone did not induce expression but sequential 5AC/MGC treatment led to enhanced expression and augmented recognition by MAGE-A3-specific CTL, as assessed by (51)Cr-release assays (P = 0.047) and enzyme-linked immunosorbent assay (ELISA) for IFN-γ secretion (P = 0.004).
Conclusions: MAGE-A3 is an attractive target for immunotherapy of MM and epigenetic modulation by 5AC, and MGC can induce MAGE-A3 expression and facilitate killing by MAGE-A3-specific CTL.