Dendritic cell maturation stage determines susceptibility to the proteasome inhibitor bortezomib

The proteasome inhibitor bortezomib has been used successfully in the treatment of non-Hodgkin lymphomas in humans, and in the treatment of graft versus host disease (GVHD) and autoimmune diseases in animal models. The mechanism of growth inhibition and immunosuppression is only partly understood. Here, we have evaluated the differential effect of bortezomib on human monocyte derived immature and mature dendritic cells (DCs) as the maturation stage of DCs determines their function. We found bortezomib to induce apoptotic cell death in immature DCs and to a much lesser extent, in mature DCs. Furthermore, cytokine-induced maturation of immature DCs was inhibited by bortezomib, whereas already matured DCs remained unaffected as seen by phenotype and allostimulatory capacity. This corresponded to a decreased NF-kappaB activity in immature DCs, whereas NF-kappaB activity of mature DCs was not affected. In conclusion, our data expand on previous reports on the effects of proteasome inhibitors on human monocyte-derived DCs by demonstrating a differential effect of bortezomib on immature versus mature DCs. Our findings suggest a potential role of bortezomib in modulating immune responses in humans through inhibition of DC maturation

Quantitative analysis of EBV-specific CD4/CD8 T cell numbers, absolute CD4/CD8 T cell numbers and EBV load in solid organ transplant recipients with PLTD

Post transplant lymphoproliferative disease (PTLD) in solid organ transplant (SOT) recipients is assumed to be the result of impaired Epstein-Barr Virus (EBV)-specific cellular immunity. We analyzed the absolute CD4 and CD8 T cell counts as well as the EBV-specific CD4 and CD8 T cell responses in relation to EBV load in SOT recipients with PTLD. A prospective, single center study was initiated and 10 immunosuppressed patients with diagnosis of PTLD were analyzed and compared to 3 patients without PTLD (2 SOT recipients with EBV-reactivation, 1 patient with Infectious Mononucleosis) and 6 healthy EBV positive controls. EBV-specific CD8 T cells were enumerated using HLA class I tetramers and the IFN-gamma cytokine secretion assay. EBNA1-specific CD4 T cells were analyzed after protein stimulation and EBV load was quantified by real-time PCR. Absolute CD8 T cell counts were highly variable in all 19 cases analyzed. In contrast, the absolute EBV-specific CD8 T cell count was found to be low in 7/9 patients with PTLD (<5/mul whole blood). These frequencies were similar to absolute EBV-specific CD8 T cell numbers observed in healthy EBV positive donors, but much lower compared to patients with EBV reactivation but no PTLD. Absolute CD4 T cell counts were significantly lower in PTLD patients (mean: 336/mul+/-161 vs. controls 1008/mul+/-424, p=0.0001), with EBNA1-specific CD4 T cell responses being also low, but highly variable. Moreover, low absolute CD4 T cell counts (<230/mul) were associated with an elevated EBV load (>1000 copies/mug DNA). We conclude that SOT recipients with PTLD have an inadequate functional EBV-specific T cell response. Our data suggest that the frequency and function of circulating EBV-specific CD8 T cells are dependent on absolute CD4 T cell counts. Further studies are needed to verify if a low absolute CD4 T cell count presents a risk factor for the development of PTLD in SOT recipients