Production and Properties of Large Numbers of Dendritic Cells from Human Blood

Abstract

Dendritic cells (DC) form a system of antigen presenting cells that are specialized to stimulate resting T cells and to initiate T-dependent immune responses (“nature’s adjuvant”) [for review see ¹]. Despite the difficulties in purifying this trace (< 1% at most sites) cell population a good deal is known about how DC sensitize T cells both in tissue culture and whole animal models. The limited numbers of DC hindered, however, molecular studies and the use of these cells for adoptive immunotherapy. In 1992 we described a simple method to grow large numbers of DC from murine blood² or bone marrow³. In this liquid culture system GM-CSF induced MHC class II-negative progenitor cells to develop proliferating cellular aggregates, and from these, many typical DC were then released. These DC exhibited a characteristic morphology, mobility, phenotype, and strong T cell stimulatory capacity. Importantly, DC grown in such cultures have been shown to process antigen, to home to the T-dependent regions, and to sensitize mice in vivo thus illustrating their potential as immunogens ^2,4 . In the human system GM-CSF + TNFβ was then shown to induce the formation of substantial numbers of DC from CD34+ cord blood progenitor cells^5,6. Putative DC (as judged from morphology and phenotype, functional assays were not performed) yet only in small numbers could also be generated from CD34+ human bone marrow progenitors, again in the presence of GM-CSF + TNFa⁷. Neither neonatal blood nor bone marrow are, however, an ideal source of DC for potential clinical applications (e.g. immunotherapy). Peripheral blood would be a most suitable source, yet the enrichment of substantial numbers of CD34+ cells is impractical due to their low incidence (< 0.1% of mononuclear cells as opposed to 1–4 % in bone marrow⁸).