Hereditary pulmonary alveolar proteinosis (herPAP) is a rare lung disease caused by mutations in the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor genes, resulting in disturbed alveolar macrophage differentiation, massive alveolar proteinosis, and life-threatening respiratory insufficiency. So far, the only effective treatment for herPAP is repetitive whole-lung lavage, a merely symptomatic and highly invasive procedure. We introduce pulmonary transplantation of macrophage progenitors as effective and long-lasting therapy for herPAP. In a murine disease model, intrapulmonary transplanted macrophage progenitors displayed selective, long-term pulmonary engraftment and differentiation into functional alveolar macrophages. A single transplantation ameliorated the herPAP phenotype for at least 9 months, resulting in significantly reduced alveolar proteinosis, normalized lung densities in chest computed tomography, and improved lung function. A significant and sustained disease resolution was also observed in a second, humanized herPAP model after intrapulmonary transplantation of human macrophage progenitors. The therapeutic effect was mediated by long-lived, lung-resident macrophages, which displayed functional and phenotypical characteristics of primary human alveolar macrophages. Our findings present the concept of organotopic transplantation of macrophage progenitors as an effective and long-lasting therapy of herPAP and may also serve as a proof of principle for other diseases, expanding current stem cell-based strategies toward potent concepts using the transplantation of differentiated cells.

CMV can infect dendritic cells (DCs), and direct Ag presentation could, therefore, lead to the priming of CMV-specific CD8+ T cells. However, CMV-encoded immune evasins severely impair Ag presentation in the MHC class I pathway; thus, it is widely assumed that cross-presentation drives the priming of antiviral T cells. We assessed the contribution of direct versus cross priming in mouse CMV (MCMV) infection using recombinant viruses. DCs infected with an MCMV strain encoding the gB498 epitope from HSV-1 were unable to stimulate in vitro naive gB498-specific CD8+ T cells from TCR transgenic mice. Infection of C57BL/6 mice with this recombinant virus led, however, to the generation of abundant numbers of gB498-specific T cells in vivo. Of the DC subsets isolated from infected mice, only CD8α+ DCs were able to stimulate naive T cells, suggesting that this DC subset cross-presents MCMV-encoded Ag in vivo. Upon infection of mice with MCMV mutants encoding Ag that can either be well or hardly cross-presented, mainly CD8+ T cells specific for cross-presented epitopes were generated. Moreover, even in the absence of immune evasion genes interfering with MHC class I–mediated Ag presentation, priming of T cells to Ag that can only be presented directly was not observed. We conclude that the host uses mainly DCs capable of cross-presentation to induce the CMV-specific CD8+ T cell response during primary, acute infection and discuss the implications for the development of a CMV vaccine.

Development of lentiviral vectors (LVs) in the field of immunotherapy and immune regeneration will strongly rely on biosafety of the gene transfer. We demonstrated previously the feasibility of ex vivo genetic programming of mouse bone marrow precursors with LVs encoding granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4), which induced autonomous differentiation of long-lived dendritic cells (DCs), referred to as self-differentiated myeloid-derived antigen-presenting-cells reactive against tumors (SMART-DCs). Here, LV biosafety was enhanced by using a DC-restricted and physiological promoter, the major histocompatibility complex (MHC) II promoter, and including co-expression of the herpes simplex virus-thymidine kinase (sr39HSV-TK) conditional suicide gene. Tricistronic vectors co-expressing sr39HSV-TK, GM-CSF and IL-4 transcriptionally regulated by the MHCII promoter or the ubiquitous cytomegalovirus (CMV) promoter were compared. Despite the different gene transfer effects, such as the kinetics, levels of transgene expression and persistency of integrated vector copies, both vectors induced highly viable SMART-DCs, which persisted for at least 70 days in vivo and could be ablated with the pro-drug Ganciclovir (GCV). SMART-DCs co-expressing the tyrosine-related protein 2 melanoma antigen administered subcutaneously generated antigen-specific, anti-melanoma protective and therapeutic responses in the mouse B16 melanoma model. GCV administration after immunotherapy did not abrogate DC vaccination efficacy. This demonstrates proof-of-principle of genetically programmed DCs that can be ablated pharmacologically.

The property of DC to generate effective CTL responses is influenced by TLR signaling. TLR ligands contain molecular signatures associated with pathogens, have an impact on the antigen processing and presentation by DC, and are being exploited as potential adjuvants. We hypothesized that the TLR2/6 heterodimer agonist S-[2,3-bispalmitoyiloxy-(2R)-propyl]-R-cysteinyl-amido-monomethoxyl polyethylene glycol (BPP), a synthetic derivative of the Mycoplasma macrophage activating lipopeptide-2, is a potent adjuvant for cross-priming against cellular antigens. Systemic administration of BPP-induced maturation of CD8a 1 DC and CD8aÀ DC in the spleen and resulted in enhanced cross-presentation of intravenously co-administered antigen in mice. In addition, administration of BPP and cell-associated OVA generated an effective CTL response against OVA in vivo in a CD4 1 T helper celldependent manner, but independent of IFN-a. Delivering antigenic peptides directly linked to BPP led to superior CTL immunity as compared to giving antigens and adjuvants admixed. In contrast to other TLR ligands, such as CpG, systemic activation of DC with BPP did not result in shut-down of antigen presentation by splenic DC subsets, although cross-priming against subsequently encountered antigens was reduced. Together, our data provide evidence that BPP is a potent stimulus to generate CTL via cross-priming.