The DC activation marker CD83 binds to a CD4+ subpopulation of PBMC – options for immune therapy

Dendritic cells (DC) have been used in clinical trials for immune therapy of various malignancies. However, activation strategies for DC to date have been insufficient to mount a curative T cell response. We started to investigate the stimulatory DC maturation marker CD83, whose ligand is unknown. We cloned the extracellular domain of CD83 and expressed it in eukaryotic cells to obtain a physiologically glycosylated recombinant protein. As the affinity was too low for flow cytometric analyses, we designed a tetrameric CD83 complex and identified a CD4⁺ population of PBMC. Currently, we are optimising the expression to obtain larger amounts of CD83 for use in a glycan array in order to biochemically identify the ligand.

CD83 shares significant structural homology with sialic acid binding lectins (siglecs). Therefore, we used sambucus nigra lectin and maackia amurensis lectin II, which we conjugated with FITC, to analyse sialic acid density by flow cytometry. CD4+ T cells after incubation with OKT-3 and IL-2 and immature monocyte-derived DC express α2,6,-linked sialic acids at high levels. Both populations are known to induce immunological tolerance. After maturation of DC, α2,6-linked sialic acid density decreased significantly, whereas α2,3-sialic linked acid did not change. At present we investigate the functional relevance of α2,6-linked sialic acids for the tolerogenic status.