Exposure to exogenous DNA can modify the sensitivity of the Fas apoptotic pathway

Danger, death and DNA vaccines

DNA vaccines, although successful in many animal models of various diseases, remain insufficiently immunogenic in humans. Among the countless approaches to improve them is the stimulation of the innate immune system by promoting the apoptotic death of the transfected host cells, which is the focus of this review.

Can tolerogenic dendritic cells help to modulate allo-immune responses in the setting of hematopoietic cell transplantation?

Recent evidence suggests that recipient as well as donor dendritic cell (DC) subsets are implicated in hematopoietic engraftment, graft-vs.-host disease occurrence, immune reconstitution and graft-vs.-leukemia effects observed after allogeneic hematopoietic cell transplantation. Although further data are needed to better understand the precise role of different DC subsets, strategies based on their manipulation to obtain tolerogenic DC can be envisaged. Here, we propose that DC blocked in an immature stage, using immunosuppressive agents, or lymphoid DC can be adequate candidates to control the alloreactive conflict post-allograft.

Polybrene and interleukin-4: two opposing factors for retroviral transduction of bone-marrow-derived dendritic cells

BACKGROUND

Gene transfer using retroviral transduction offers the advantage of long-term transgene expression in developing strategies that use dendritic cells (DCs) for immunotherapy. The goal of this study was to infect DCs in an immature state in order to take advantage of their proliferating and tolerogenic potential.

METHODS

Immature DCs were generated from murine bone marrow (BM) using either GM-CSF alone or GM-CSF plus IL-4. The cells were transduced directly with retroviral supernatants or by co-culture with the GP + E-86 retroviral packaging cell line in the presence of two different cationic polymers: polybrene and protamine sulfate. Phenotypic and functional characterization of the transduced cells were then performed.

RESULTS

Our results show a low efficiency of retroviral infection of DCs in the presence of polybrene. This cationic polymer was found to be directly cytotoxic to murine DCs and thus favored the growth of contaminating macrophages. This effect was not observed using protamine sulfate. Furthermore, stimulation by IL-4 early in the culture increased DC differentiation, proliferation and transduction. However, we found that DCs generated in GM-CSF plus IL-4 presented a more mature phenotype with an enhanced allogeneic stimulating activity. Finally, we showed that DCs themselves down-regulated transgene expression in the co-cultured packaging cell line in a promoter-dependent manner.

CONCLUSIONS

We have defined optimal conditions to generate and transduce murine BM-derived DCs. This included: the use of protamine sulfate during exposure to retroviral infectious supernatant and the addition of IL-4 at an early stage of the culture. Nevertheless, this cytokine also induced DC maturation. These findings have potential implications in experimental gene therapy.

Cell-based therapy approaches using dying cells: from tumour immunotherapy to transplantation tolerance induction

Cell-based therapies are promising approaches to treat uncontrolled pathologies, such as tumours. Apoptotic tumour cells have recently been proposed as a source of tumour-associated antigens to stimulate an efficient immune response. However, a complex relationship exists between apoptosis and the immune system. In this review, the different factors that may influence immune responses against apoptotic cells are detailed and discussed in the light of recent publications. These factors include the nature of the phagocytes and the receptors involved in apoptotic cell uptake, as well as the environment in which cells are dying. A possible distinction between apoptosis and necrosis by immune system sentinels adds a further level of complexity. The potential use of the immunomodulatory properties associated with apoptosis to favour engraftment and induce tolerance in transplantation is then discussed. In conclusion, this review will suggest appropriate conditions to efficiently and safely use apoptotic cells as a new cell therapy product.