MDM2 is recognized as tumor associated antigen (TAA) in B-CLL by CD8+ autologous T lymphocytes

Proc Amer Assoc Cancer Res, Volume 46, 2005 5146 BACKGROUND: The human homolog of the murine double-minute 2 oncoprotein, MDM2, is an attractive candidate target for a general TAA. MDM2 was shown to be overexpressed in CLL cells compared to normal B lymphocytes on the protein level as well as on the mRNA level. Therefore MDM2 might serve as potential tumor associated antigen (TAA) in CLL enabling expansion of MDM2-specific T cells. Methods: Unpulsed native CLL cells and CD40 ligand (CD40L)-stimulated CLL cells as antigen presenting cells (APC) were used to expand autologous T cells from 12 patients. RESULTS: In 11/13 CLL samples expression of MDM2 by real-time RT-PCR was detectable in contrast to normal B lymphocytes. The number of T cells during four weeks of in vitro culture increased 2-fold with native CLL cells as APC and 3.5-fold with CD40L-stimulated CLL cells as APC. Up to 32.3% of CD8+ T cells recognized specifically an MDM2-derived peptide bound to HLA-A2-dimers after 4 weeks of in vitro culture. The expanded T cells were also able to secrete IFN-γ upon recognition of the antigen demonstrated by IFN-γ-ELISPOT assays. T cells not only recognized an HLA-A2 binding MDM2 peptide presented by TAP-deficient T2 cells, but also MDM2 overexpressing autologous CLL cells in an HLA-A2 restricted manner. Nor HLA-A2 negative CLL cells, neither non-malignant cells, i.e. PBMC from healthy donors or tonsilar B cells were specifically recognized. CONCLUSION: MDM2 was shown for the first time to be naturally processed and presented as TAA in primary CLL cells enabling the expansion of functional autologous tumor-specific T cells which might be applicable in clinical vaccination trials or as a tool for a CLL-specific immune monitoring in the context of vaccination approaches including CD40L-gene modified autologous leukemic cells.