Human-like mouse models for testing the efficacy and safety of anti-β ₂-microglobulin monoclonal antibodies to treat myeloma

Purpose: We showed recently that anti-β ₂-microglobulin (β ₂M) monoclonal antibodies (mAb) have remarkably strong apoptotic effects on myeloma cells in vitro and in SCID-hu mice. However, whether the mAbs will be therapeutic and safe in the treatment of myeloma patients, in whom every tissue expresses low densities of MHC class I molecules and elevated levels of soluble β ₂M are present, remains to be determined. Experimental Design: In this study, human-like myeloma mouse models (HLA-A2-transgenic NOD/SCID mice) were developed, which express mature and functional human MHC class I (HLA-A2and human β ₂M) on murine organs and present high levels of circulating human 2M derived from human myeloma cells. Myeloma-bearing mice were treated intraperitoneally with anti-β ₂M mAbs, and the distribution and effects of the mAbs on normal organs and established tumors were examined. Results: Our results show that anti-β ₂M mAbs were effective in suppressing myeloma growth in treated mice. The therapeutic efficacy of the mAbs in these mice are comparable with those observed in myeloma-bearing nontransgenic NOD/SCID mice in which no human MHC class I is expressed on murine organs. Furthermore, although the mAbs can be detected on different organs, no tissue damage or cell apoptosis was observed in the mice. Conclusion: Based on the antimyeloma efficacy and low toxicity in the mice, our study suggests that anti-β ₂M mAbs may be safe and the tissue-expressing and soluble β ₂Mmay not compromise their therapeutic effects in myeloma patients. This study provides further support for the future application of the mAbs as therapeutic agents for multiple myeloma.