C Heirman

Sirtuin 1 Promotes Th2 Responses and Airway Allergy by Repressing Peroxisome Proliferator-Activated Receptor-γ Activity in Dendritic Cells

Sirtuins are a unique class of NAD+-dependent deacetylases that regulate diverse biological functions such as aging, metabolism, and stress resistance. Recently, it has been shown that sirtuins may have anti-inflammatory activities by inhibiting proinflammatory transcription factors such as NF-κB. In contrast, we report in this study that pharmacological inhibition of sirtuins dampens adaptive Th2 responses and subsequent allergic inflammation by interfering with lung dendritic cell (DC) function in a mouse model of airway allergy. Using genetic engineering, we demonstrate that sirtuin 1 represses the activity of the nuclear receptor peroxisome proliferator-activated receptor-γ in DCs, thereby favoring their maturation toward a pro-Th2 phenotype. This study reveals a previously unappreciated function of sirtuin 1 in the regulation of DC function and Th2 responses, thus shedding new light on our current knowledge on the regulation of inflammatory processes by sirtuins.

Induction of antigen-specific CD8+ cytotoxic T cells by dendritic cells co-electroporated with a dsRNA analogue and tumor antigen mRNA.

The maturation state of dendritic cells (DCs) is an important determinant for the initiation and regulation of adaptive immune responses. In this study, we wanted to assess whether functional activation of human monocyte-derived DCs can be achieved by electroporation of an activation signal in the form of double-stranded (ds) RNA and whether simultaneous electroporation of the dsRNA with tumor antigen encoding mRNA can lead to the induction of a cytotoxic T-lymphocyte (CTL) response. Electroporation of immature DCs with poly(I:C12U), a dsRNA analogue, resulted in phenotypic as well as functional changes, indicative of DC maturation. Co-electroporation of DCs with both poly(I:C12U) and Melan-A/MART-1 encoding mRNA induced strong anti-Melan-A/MART-1 CD8+ T-cell responses in vitro. Higher numbers of Melan-A/MART-1-specific CTLs were consistently obtained with poly(I:C12U)-activated DCs compared to DCs matured in the presence of an inflammatory cytokine cocktail. These results indicate that DC co-electroporation with both dsRNA and tumor antigen encoding mRNA induces fully activated and antigen-loaded DCs that promote antigen-specific CTL responses and may provide the basis for future immunotherapeutic strategies.

Tumor-Reactive CD4+ T Cell Responses to the Melanoma-Associated Chondroitin Sulphate Proteoglycan in Melanoma Patients and Healthy Individuals in the Absence of Autoimmunity

To avoid immune escape by down-regulation or loss of Ag by the tumor cells, target Ags are needed, which are important for the malignant phenotype and survival of the tumor. We could identify a CD4+ T cell epitope derived from the human melanoma-associated chondroitin sulfate proteoglycan (MCSP) (also known as high m.w.-melanoma-associated Ag), which is strongly expressed on >90% of human melanoma lesions and is important for the motility and invasion of melanoma cells. However, MCSP is not strictly tumor specific, because it is also expressed in a variety of normal tissues. Therefore, self tolerance should prevent the induction of strong T cell responses against these Ags by vaccination strategies. In contrast, breaking self tolerance to this Ag by effectively manipulating the immune system might mediate antitumor responses, although it would bear the risk of autoimmunity. Surprisingly, we could readily isolate CD4+ Th cells from the blood of a healthy donor-recognizing peptide MCSP693–709 on HLA-DR11-expressing melanoma cells. Broad T cell reactivity against this Ag could be detected in the peripheral blood of both healthy donors and melanoma patients, without any apparent signs of autoimmune disease. In some patients, a decline of T cell reactivity was observed upon tumor progression. Our data indicate that CD4+ T cells are capable of recognizing a membrane glycoprotein that is important in melanoma cell function, and it may be possible that the sizable reactivity to this Ag in most normal individuals contributes to immune surveillance against cancer.

Kaposi's sarcoma‐associated herpesvirus (KSHV/HHV‐8) DNA sequences are absent in leukapheresis products and ex vivo expanded CD34+ cells from multiple myeloma patients

Recently it was reported that Kaposis sarcoma‐associated herpesvirus (KSHV/HHV‐8) infects bone marrow (BM) dendritic cells (DC) in multiple myeloma (MM) patients and therefore might play a role in MM development. Because of the use of myeloid growth factors like GM‐CSF and G‐CSF for the mobilization of peripheral blood progenitor cells (PBPC), the subsequent increase of DC precursors might imply a risk for KSHV contamination in PBPC grafts. Therefore, in this study leukapheresis products and ex vivo cultured CD34+ cell suspensions were analysed. KSHV DNA could not be amplified in any of them.

Identification of a melanoma-associated chondroitin sulfate proteoglycan (MCSP) peptide recognized by CD4 + T lymphocytes on human melanoma cells

The identification of tumor antigens recognized by cytolytic CD8+ T cells (CTLs) on human tumor cells has opened new avenues in cancer immunotherapy. There is consensus, that the induction of both, tumor-specific CTLs and CD4+ T helper cells is necessary for an optimal antitumor immunity. Unfortunately, only a few tumorspecific helper T cell epitopes have been described so far. We therefore have focused our research on the identification of melanoma antigens recognized by CD4+ T cells. One interesting candidate antigen is the human melanoma-associated chondroitin sulfate proteoglycan (MCSP), which is expressed on > 90% of human melanoma tissues and induces strong humoral responses in mice. In the present study, we describe the induction of MCSP-specific CD4+ T cell clones from the peripheral blood of a healthy human donor and the subsequent identification of the T cell epitope which is located in the core protein. The identified peptide was presented to the T helper cells by HLA-DR11 molecules, which are expressed by approximately 13% of Caucasians. The T cells directly recognized HLA-matched MCSP-expressing melanoma cells and produced high amounts of IFNgamma, a cytokine with important antitumoral effects. To the best of our knowledge, this is the first MCSP-derived T cell epitope described and it should be useful for melanoma immunotherapy. from Association for Immunotherapy of Cancer: Cancer Immunotherapy – 2nd Annual Meeting Mainz, Germany, 6–7 May 2004