Identification and characterization of canine dendritic cells generated in vivo.

Emerging evidence suggests that host dendritic cells (DC) initiate and regulate graft-versus-host and graft-versus-tumor reactions after allogeneic hematopoietic cell transplantation (HCT). Even though decades of experimentation in the preclinical canine HCT model have substantially improved our understanding of the biology and safety of HCT in human patients, the in vivo phenotype of potent antigen-presenting cells in dogs is poorly defined. Therefore, peripheral blood leukocytes were obtained from dogs treated with recombinant human Flt3-ligand and phenotypically distinct cell populations, including putative DC, were purified by 4-color flow-cytometry and tested for their stimulatory potential in allogeneic mixed lymphocyte cultures (MLC). Cells characterized by surface expression of CD11c and HLA-DR, and absence of expression of CD14 and DM5, a marker of mature granulocytes, were found to be highly potent stimulators in allogeneic MLC. In contrast, all other immunophenotypically different cell populations tested had either weak or absent allostimulatory potential. Transmission electron microscopy of CD11c+/HLA-DR+/CD14-/DM5- cells revealed the morphology similar to that described for DC in humans and ex vivo-generated canine DC, including long cytoplasmic extensions, discrete lysosomes, and an abundant Golgi apparatus and endoplasmatic reticulum. In summary, CD11c+/HLA-DR+/CD14-/DM5- cells obtained from canine peripheral blood have functional and morphologic characteristics similar to those of human myeloid DC.