Journal of Clinical Oncology, 2004 ASCO Annual Meeting Proceedings (Post-Meeting Edition).
Vol 22, No 14S (July 15 Supplement), 2004: 2552
© 2004 American Society of Clinical Oncology

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Abstract

Induction of myeloma cell apoptosis by polyclonal rabbit anti-thymocyte globulin (rATG)

University of Rochester, Rochester, NY

2552

Background: Myelomatous plasma cells have a variable surface phenotype which depends on the stage of differentiation arrest. Polyclonal anti-thymocyte globululin (rATG) is generally thought of as an anti-T cell lineage reagent, although it has potent activity against many cell surface antigens expressed on B cells. We describe the use of rATG to induce in vitro apoptosis of CD19+ plasmablasts, CD138+ cell lines and freshly isolated myeloma cells. Methods: We tested the ability of rATG (Thymoglobulin; Sangstat), anti-CD20 (rituximab), and anti-CD52 (Campath-1H) to induce apoptosis in human plasmablasts, myeloma cell lines (RPMI 8226, NCI-H929, U266) and freshly isolated myeloma cells from bone marrow aspirates of 5 untreated patients isolated by CD138 magnetic bead affinity columns. Surface marker phenotyping was performed for all cells. Cells were incubated with rATG (0.01 - 1000 mcg/ml), anti-CD20 (0.01–10 mcg/ml) anti-CD52 (0.01–100 mcg/ml), and pooled rabbit immunoglobulin in media containing heat inactivated sera. Apoptosis was assessed at 18 hours post-exposure by annexin-V plus TOPRO-3 staining, nuclear fragmentation, caspase 3/8/9 staining, mitochondiral membrane potential, and sub-diploid DNA quantitation. Results: All myeloma cells and cell lines were phenotyped by FACS and found to express surface at least 3 antigens known to have reactivity with rATG (MHC class I, CD80, CD38, CD40, CD45). No myeloma cells, cell lines, or pre-plasmablasts expressed significant expression of the target antigens for rituximab (CD20) or campath-1H (CD52). Compared with controls, rATG at 100 mcg/ml induced significant apoptosis of naive B cells (94±11%, p<0.001), CD40L stimulated plasmablasts (99±12%, p<0.001), all myeloma cell lines (93±7%, p<0.001), and myeloma cell isolates (91±24%, p<0.001). Neither CD40L stimulated pre-plasmablasts, myeloma cells or cell lines had apoptotic levels statistically different from controls. Conclusions: These results indicate that rATG, but not campath-1H or rituximab, is an active agent against multiple myeloma tumor cells. Further testing in a rigorous clinical trial to determine in vivo efficacy is warranted.

Author Disclosure

Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Sangstat

Abstract presentation from the 2004 ASCO Annual Meeting