Emmanuel Katsanis

Certain caspase-8 null cell lines demonstrate resistance to Fas-induced apoptosis, indicating that the Fas/FasL apoptotic pathway may be caspase-8-dependent. Some reports, however, have shown that Fas induces cell death independent of caspase-8. Here we provide evidence for an alternative, caspase-8-independent, Fas death domain-mediated apoptotic pathway. Murine 12B1-D1 cells express procaspase-3, -8, and -9, which were activated upon the dimerization of Fas death domain. Bid was cleaved and mitochondrial transmembrane potential was disrupted in this apoptotic process. All apoptotic events were completely blocked by the broad-spectrum caspase inhibitor Z-VAD-FMK, but not by other peptide caspase inhibitors. Cyclosporin A (CsA), which inhibits mitochondrial transition pore permeability, blocked neither pore permeability disruption nor caspase activation. However, CsA plus caspase-8 inhibitor blocked all apoptotic events of 12B1-D1 induced by Fas death domain dimerization. Our data therefore suggest that there is a novel, caspase-8-independent, Z-VAD-FMK-inhibitable, apoptotic pathway in 12B1-D1 cells that targets mitochondria directly.

DLI is traditionally used to provide graft-versus-leukemia (GvL) effects when given to patients relapsing post-hematopoietic cell transplantation (HCT). However, it is often associated with significant GvHD and has only modest efficacy against acute leukemias. Therefore, novel cellular therapies are needed to improve the outcome of high-risk or relapsed leukemia patients following HCT. Activated T helper-1 (aTh-1) lymphocytes are CD4(+)CD25(+)CD40L(+)CD62L(lo) effector memory cells that produce large amounts of IFN-γ and TNF-α. We demonstrate that post-transplant adoptive aTh-1 cell therapy enhances GvL with limited GvHD in an MHC-mismatched murine BMT model. aTh-1 infusions result in superior leukemia-free survival when compared with unstimulated splenocytes (SC), purified CD4(+) T-cells and T-cell-enriched SC. aTh-1 cells display cytotoxicity against A20 leukemia cells in vitro and persist in vivo for at least 2 months following adoptive transfer. Furthermore, in contrast to unstimulated SC, aTh-1 cell infusion is associated with only transient, mild suppression of donor-derived hematopoiesis. aTh-1 cell therapy is safe, effective and warrants further investigation as an alternative to DLI.

Because of significant medical advances in the past 50 years, the number of adult survivors of childhood/adolescent cancer has increased dramatically. Unfortunately, more than 60% of these survivors will have at least 1 long-term side effect from treatment. This growing population requires dedicated care by their primary physicians because they have specific risk factors depending on their initial cancer diagnosis and the treatment modalities they received. Internists and family physicians play an integral role in providing appropriate screening, treatment, and counseling to prevent morbidity and mortality in these patients.

T lymphocytes activated by dendritic cells (DC) which present tumor antigens play a key role in the antitumor immune response. However, in patients suffering from active cancer, DC are not efficient at initiating and supporting immune responses as they participate to T lymphocyte inhibition. DC in the tumor environment are functionally defective and exhibit a characteristic of immature phenotype, different to that of DC present in nonpathological conditions. The mechanistic bases underlying DC dysfunction in cancer responsible for the modulation of T-cell responses and tumor immune escape are still being investigated. Using two different mouse tumor models, we showed that tumor-infiltrating DC (TIDC) are constitutively immunosuppressive, exhibit a semimature phenotype, and impair responder T lymphocyte proliferation and activation by a mechanism involving CD39 ectoenzyme.

We have previously reported on the anti-tumoral potential of a chaperone-rich cell lysate (CRCL) vaccine. Immunization with CRCL generated from tumors elicits specific T and NK cell-dependent immune responses leading to protective immunity in numerous mouse tumor models. CRCL provides both a source of tumor antigens and danger signals leading to dendritic cell activation. In humans, tumor-derived CRCL induces dendritic cell activation and CRCL-loaded dendritic cells promote the generation of cytotoxic T lymphocytes in vitro. The current study was designed to identify the signaling events and modifications triggered by CRCL in antigen presenting cells. Our results indicate that tumor-derived CRCL not only promotes the activation of dendritic cells, but also significantly fosters the function of macrophages that thus appear as major targets of this vaccine. Activation of both cell types is associated with the induction of the MAP kinase pathway, the phosphorylation of STAT1, STAT5 and AKT and with transcription factor NF-kappaB activation in vitro and in vivo. These results thus provide important insights into the mechanisms by which CRCL-based vaccines exert their adjuvant effects on antigen presenting cells.