Construction of a recombinant adenovirus vector encoding Fas ligand with a CRE/Loxp inducible system

Alloantigen specific deletion of primary human T cells by Fas ligand (CD95L)-transduced monocyte-derived killer-dendritic cells

Numerous studies have been performed in vitro and in various animal models to modulate the interaction of dendritic cells (DC) and T cells by Fas (CD95/Apo-1) signalling to delete activated T cells via induction of activation-induced cell death (AICD). Previously, we could demonstrate that Fas ligand (FasL/CD95L)-expressing 'killer-antigen-presenting cells' can be generated from human monocyte-derived mature DC (mDC) using adenoviral gene transfer. To evaluate whether these FasL-expressing mDC (mDC-FasL) could eliminate alloreactive primary human T cells in vitro, co-culture experiments were performed. Proliferation of human T cells was markedly reduced in primary co-cultures with allogeneic mDC-FasL, whereas a strong proliferative T-cell response could be observed in co-cultures with enhanced green fluorescent protein-transduced mDC. Inhibition of T-cell proliferation was related to the transduction efficiency, and the numbers of mDC-FasL present in co-cultures. In addition, proliferation of pre-activated alloreactive CD4(+) and CD8(+) T cells could be almost completely inhibited in secondary co-cultures using mDC-FasL as stimulatory cells, which was the result of induction of apoptosis in the majority of preactivated T cells. The specific deletion of alloreactive T cells by mDC-FasL was confirmed by an unaffected proliferative response of surviving T cells towards allogeneic 'third-party' peripheral blood mononuclear cells in a third stimulation, or upon unspecific stimulation with anti-CD3/CD28 beads. The results of this study demonstrate that allospecifically activated T cells are efficiently eliminated by mDC-FasL, supporting further investigations to apply FasL-expressing 'killer-DC' as a novel strategy for the treatment of allograft rejection.

Elimination of activated but not resting primary human CD4 and CD8 T cells by Fas ligand (FasL/CD95L)-expressing Killer-dendritic cells

Dendritic cells (DC) genetically engineered to express high levels of Fas ligand (FasL/CD95L) have been demonstrated to delete T cells in an antigen specific manner in several different animal models in vivo. However, the immunomodulatory capacity of primary human FasL-expressing Killer-DC has not been determined. Therefore, human Killer-DC were generated from mature monocyte-derived DC using the inducible CRE/LoxP adenoviral vector system, and the immunoregulatory capacity of these cells was analyzed in cocultures with primary human T cells in vitro. Combined transductions of DC by AdloxPFasL and AxCANCre resulted in FasL expression in > 70% of DC without affecting the mature phenotype. Proliferation of activated primary human T cells was inhibited up to 80% in cocultures with FasL-expressing DC but not EGFP-transduced DC, which was due to induction of apoptosis in activated but not resting CD4+ and CD8+ T cells. Apoptosis induced by Killer-DC could be blocked by an anti-FasL-antibody in a dose dependent fashion. The present results demonstrate that FasL-expressing Killer-DC eliminate activated but not resting primary human CD4+ and CD8+ T cells by induction of Fas-mediated apoptosis supporting the concept to apply Killer-DC as a novel strategy for the treatment of T cell-dependent autoimmune disease and allograft rejection in humans.

The JAM-assay: optimized conditions to determine death-receptor-mediated apoptosis

Apoptosis induced by interaction of members of the TNF-/TNF-receptor superfamily has been considered as a major mechanism of cell-mediated cytotoxicity. For functional analysis, the 51Cr release assay has been widely used, which requires loss of membrane integrity in the apoptotic target cell. However, loss of membrane integrity is a late event during apoptosis and therefore only late apoptotic cells will be detected by this method. In contrast, the JAM-assay first described by Polly Matzinger has been demonstrated to be more sensitive than the 51Cr release assay, since this method is dependent on DNA-fragmentation which precedes loss of membrane integrity in most apoptotic cells. The JAM-assay is easier to perform, less expansive, and safer than the current standard (51)Cr release assay. Therefore, this article will focus on optimized conditions of the JAM-assay to detect and quantitate Fas (CD95/Apo-1)-induced apoptosis as an example of death-receptor-mediated cytotoxicity.

Mature but not immature Fas ligand (CD95L)-transduced human monocyte-derived dendritic cells are protected from Fas-mediated apoptosis and can be used as killer APC

Several in vitro and animal studies have been performed to modulate the interaction of APCs and T cells by Fas (CD95/Apo-1) signaling to delete activated T cells in an Ag-specific manner. However, due to the difficulties in vector generation and low transduction frequencies, similar studies with primary human APC are still lacking. To evaluate whether Fas ligand (FasL/CD95L) expressing killer APC could be generated from primary human APC, monocyte-derived dendritic cells (DC) were transduced using the inducible Cre/Loxp adenovirus vector system. Combined transduction of DC by AdLoxpFasL and AxCANCre, but not single transduction with these vectors, resulted in dose- and time-dependent expression of FasL in >70% of mature DC (mDC), whereas <20% of immature DC (iDC) expressed FasL. In addition, transduction by AdLoxpFasL and AxCANCre induced apoptosis in >80% of iDC, whereas FasL-expressing mDC were protected from FasL/Fas (CD95/Apo-1)-mediated apoptosis despite coexpression of Fas. FasL-expressing mDC eliminated Fas(+) Jurkat T cells as well as activated primary T cells by apoptosis, whereas nonactivated primary T cells were not deleted. Induction of apoptosis in Fas(+) target cells required expression of FasL in DC and cell-to-cell contact between effector and target cell, and was not dependent on soluble FasL. Induction of apoptosis in Fas(+) target cells required expression of FasL in DC, cell-to-cell contact between effector and target cell, and was not dependent on soluble FasL. The present results demonstrate that FasL-expressing killer APC can be generated from human monocyte-derived mDC using adenoviral gene transfer. Our results support the strategy to use killer APCs as immunomodulatory cells for the treatment of autoimmune disease and allograft rejection.

BXD recombinant inbred mice represent a novel T cell-mediated immune response tumor model

To develop a better animal model for studying the effects of the host environment in neoplasia, we injected various genetically well-characterized H-2(d) RI strains of BXD mice with syngeneic breast cancer cells (TS/A) and monitored the growth of tumors over time. There was a marked difference in the growth of the implanted breast cancer cells among the 14 BXD RI strains, with 4 patterns of tumor development being observed: in type I, the implanted tumor cells grew rapidly in the first 2 weeks, necrosis of the tumors was observed and metastases to the intestinal lymph nodes and pancreas was observed, causing death; in type II, the implanted tumor cells grew slowly and attained a size after day 50 that required killing the animal, with tumor necrosis being rare and metastases absent; in type III, the implanted tumor cells grew initially but underwent a slow decline after 4 weeks; and in type IV, the implanted tumor cells failed to develop. Apoptosis of the implanted tumor cells was responsible for the regression of tumor nodules. The T-cell immune response minimized tumor development in types III and IV since T-cell depletion of the BXD RI mice resulted in aggressively growing tumors in these strains.

Promoter strength in adenovirus transducing vectors: down-regulation of the adenovirus E1A promoter in 293 cells facilitates vector construction

Most adenovirus transducing vectors have the cytomegalovirus major immediate-early (CMV) or the Rous sarcoma virus long terminal repeat (RSV) promoter driving expression of the transgene. Both of these promoters are highly active in transfection and transduction assays in 293 cells, in which transducing vectors are constructed and grown, and in HeLa cells. The CMV promoter exhibits rapid activation while the RSV promoter exhibits a lag prior to the onset of viral DNA replication in transduction assays. While the use of very strong promoters facilitates expression of the transgene, high-level expression of certain gene products hinders virus construction and growth. For such genes, the use of the adenovirus type 5 E1A promoter offers advantages. The E1A promoter exhibits modest activity in HeLa cells after transfection or transduction, but very little activity in 293 cells, suggesting that the E1A promoter would permit construction and growth of vectors encoding deleterious gene products that could not be constructed with the CMV and RSV promoters. This idea was tested through attempts to construct viruses encoding the immunoglobulin loop 6 and transmembrane regions of the prostaglandin F2alpha receptor regulatory protein (FPRP), a product that inhibits adenovirus vector construction for reasons that are not clear. Only the E1A promoter permitted construction and growth of the transducing vector encoding the fragment of FPRP.

A novel system for mitigation of ectopic transgene expression induced by adenoviral vectors

Adenoviral (Ad) vectors are good candidates for gene therapy in view of their high in vivo gene delivery efficiency. However, greater control over the tissue distribution of transgene expression is required to avoid potentially deleterious effects in non-target organs. In this regard, the liver is particularly at risk due to the high natural tropism of Ad for this organ, where dose limiting toxicity has been seen due to toxic transgene expression. We hypothesized that the cre/loxP system could be utilized to reduce unintended transgene expression at this site. This concept was tested using an Ad vector (AdLCLLL) carrying a reporter gene cassette in which the promoter and luciferase gene were flanked by LoxP sequences. Co-administration of this vector with a second vector carrying the cre recombinase gene in vitro and in vivo resulted in specific down-regulation of transgene expression. This novel approach thus has the potential to improve the safety of gene therapy strategies that rely upon the delivery of genes which may be hepatotoxic.

An enhanced system for construction of adenoviral vectors by the two-plasmid rescue method

The two-plasmid rescue method of constructing Ad vectors, which relies on either homologous or Cre-mediated recombination between two plasmids cotransfected into 293 or 293Cre4 cells, respectively, offers advantages over other approaches because of its simplicity. We have improved the efficiency of vector construction by both homologous and Cre-mediated recombination by replacing the single ITR in the shuttle plasmid with a head-to-head ITR junction. We have also expanded the versatility of this method by incorporating a Cre expression cassette into the plasmids to permit high-efficiency Cre-mediated vector rescue using 293 cells, abrogating the need for Cre-expressing cell lines. This new system retains the simplicity of the original but results in an approximately 100-fold increase in the number of recombinant viruses produced, all of which contain the foreign DNA insert, and allows high-efficiency Cre-mediated vector isolation using any E1-complementing cell line.