Conventional type 1 dendritic cells, known as cDC1 cells, are immune cells that help initiate responses against intracellular pathogens and tumors. They are particularly important because they can cross-present cell-associated antigens to CD8-positive T cells. However, cDC1 cells are rare in vivo, making it difficult to obtain sufficient, uniform cell populations for mechanistic and preclinical studies.
Researchers at the National Cancer Institute, National Institutes of Health, have developed a bone marrow-derived culture system that produces large numbers of highly enriched CD103-positive cDC1 cells from mice. The study, published in Myeloid Cells , describes the system as induced cDC1, or iDC1, cultures.
Using a 23-day protocol with the cytokines FLT3L, low-dose GM-CSF, and Kit ligand, the researchers generated an estimated 1.5 billion CD103-positive cDC1 cells from the bone marrow of a single mouse. More than 95% of the final culture consisted of the target cells. The reported yield was at least 75 times higher than that achieved with previously available recombinant cytokine-based approaches.
The study evaluated the cultures beyond surface-marker measurements. Compared with other bone marrow-derived dendritic cell methods, iDC1 cultures contained fewer cDC2 cells, plasmacytoid dendritic cells, macrophages, and other non-target cells. Transcriptomic analyses and reference comparisons placed iDC1 cells closest to the cDC1 lineage and clearly distinct from macrophages.
The researchers also examined whether iDC1 cells retained key cDC1 functions. Following innate immune stimulation, the cells increased expression of co-stimulatory molecules and secreted IL-12p40 and several chemokines. In functional experiments, iDC1 cells cross-presented cell-associated antigen to CD8-positive T cells. In a mouse transfer experiment, iDC1 cells supported restoration of this response in two of four cDC1-deficient recipients, indicating in vivo activity while further research is needed to improve these responses.
Mechanistic experiments identified distinct roles for the culture factors. Kit ligand and GM-CSF acted together during the early phase of cDC1 generation. During later stages, GM-CSF supported cell proliferation and survival. The study also found that the +32 kb Irf8 enhancer, STAT5, and BRD4-associated regulatory programs contribute to efficient iDC1 generation.
The iDC1 system provides a reproducible source of relatively uniform cDC1 cells for studies of antigen processing, dendritic cell biology, vaccine research, tumor immunology, and other preclinical applications. The method was developed using mouse bone marrow cells. Further work is needed to determine whether comparable approaches can be established with human cells and whether they can support translational or clinical applications.
