OM-197-MP-AC adjuvant properties: the in vitro maturation of normal and leukemic dendritic cells in a serum-free culture model

Dendritic cells (DC) play a pivotal role in linking innate and adaptive immunity. Only mature DC are able to initiate adaptive immune responses by sensitising naive antigen-specific T cells. For clinical immunotherapeutic applications, safe and efficient clinical grade maturation factors of DC are required. Here, we investigated the impact of OM-197-MP-AC (OM-197), a synthetic lipid A analogue pseudo-dipeptide derived from amino acids linked to three fatty acid chains, on the maturation of human monocyte-derived-DC (Mo-DC) and leukemia-derived DC generated in serum-free conditions. After culture with clinical grade GM-CSF and IL-13, OM-197 at 20 microg/ml efficiently induced CD83+ Mo-DC. In comparison to immature Mo-DC that were derived by culture with GM-CSF and IL-13 only, CD40, CD80, CD86, HLA-ABC and HLA-DR molecules were up-regulated upon OM-197 or LPS treatment similarly. In MLR, OM-197-matured Mo-DC were found to be as potent stimulators as LPS-matured Mo-DC for CD4+ T cell proliferation. No significant difference in IFN-gamma quantification was shown between naive CD4+ T cells stimulated by LPS- or OM-197-Mo-DC suggesting that OM-197-Mo-DC can drive naive T cells towards a Th1 response profile that was mainly independent of IL-12 secretion. Similarly, CD8+ T cells could be efficiently polarized into IFN-gamma-secreting-cells by OM-197-Mo-DC, and activated polyclonal pp65-cytomegalovirus-specific CD8+ T lymphocytes. Finally, myeloid leukemic blasts were able to differentiate in vitro into mature functional DC-like cells upon OM-197 treatment in our culture model. Overall, the in vitro effects of clinical grade adjuvant OM-197, showed that it represents a potent inducer of both normal and leukemic-DC maturation, and is likely a good candidate for adjuvant immunotherapy in DC-based vaccines.