We have previously demonstrated in human and mouse systems

that ex vivo transduction of DC precursors with LVs for production of granulocyte macrophage colony stimulating factor (GM-CSF), interleukin-4 (IL-4) and tumor antigens induced self-differentiation of potent anti-cancer therapeutic DC vaccines (“self-differentiated myeloid derived antigen presenting cell reactive against tumors – SmartDCs”) [5] and [6]. Recently, we have developed a 28-h method compatible with good manufacturing practices (GMP) for production of cryopreserved SmartDCs in sufficient amounts for clinical cancer immunotherapy studies [7]. Another explored use of iDCs is to accelerate the immune regeneration of patients receiving CD34+ hematopoietic SCT by ameliorating the homeostatic reconstitution and enhancing antigen presentation in lymphopenic SCR7 recipients. After HSCT, patients show slow DC recovery, requiring approximately 60 days in order to reach pre-transplant levels [8]. We

have recently established a proof-of-concept animal model using NOD/Rag1(−/−)/IL-2rγ(−/−) (NRG) immune deficient mice which lack T, B and NK cells and can be repopulated with cells from the human peripheral blood [9]. We showed that human SmartDCs expressing the HCMV pp65 (65 kDa lower matrix phosphoprotein) antigen dramatically enhanced the engraftment, in vivo expansion and functionality of autologous human T cells reactive against pp65 in NRG mice [10]. Quantitative pp65 selleck kinase inhibitor CTL responses produced in the mice could be directly measured by tetramer assay and ELISPOT. We observed a significantly faster expansion of human CD4+ and CD8+ T cells in the spleen and peripheral blood and a massive recruitment of lymphocytes to the SmartDC/pp65 injection site [10]. Thus, this model confirmed our hypothesis that preconditioning

the host with iDCs producing homeostatic (mediated through expression of human cytokines) and antigen-specific (mediated through expression of pp65) stimuli accelerated human T cell responses in a lymphopenic host. A major limitation in the use of LVs for vaccine development is their intrinsic potential to integrate in the genome of the infected cells which, at least theoretically, could below cause insertional mutagenesis or “genotoxicity” [11] and [12]. Lentiviral gene transfer into hematopoietic stem cells with lentiviral vectors has recently reached the clinics for gene therapy replacement and was shown to be safe [13]. On the other hand, the use of LVs for immunization approaches is also an expanding field [6], but so far only pre-clinical, since following a risk/benefit calculation, integrating viruses are usually perceived as non-safe for vaccine development. It is known that non-integrated lentiviral DNA can support transcription, and, for growth-arrested cells, “episomal” LV can produce steady high-level transgene expression [14], [15], [16] and [17].