Response of MUTZ-3 dendritic cells to the different components of the Haemophilus influenzae type B conjugate vaccine: towards an in vitro assay for vaccine immunogenicity

Abstract

Potency testing is mandatory for vaccine registration and batch release. Due to various limitations to in vivo potency testing, there is need for relevant in vitro alternatives. These alternative tests should preferably comprise cells from the target (human) species. The whole suite of immune responses to vaccination that occur in vivo in humans cannot be tested in vitro using a single cell type. Even so, dendritic cells (DC) form an important candidate cell type since they are pivotal in inducing and orchestrating immune responses. Cell lines are preferred over ex vivo cells for reasons of safety, accessibility, and reproducibility. In this first feasibility study we used the human cell line MUTZ-3, because it most closely resembles ex vivo human DC, and compared its response to monocyte-derived DC (moDC). Haemophilus influenzae type B (HiB) vaccine was chosen because its components exert different effects in vivo: while the HiB antigen, polyribosyl ribitol phosphate (PRP) fails to induce sufficient protection in children below 2 years of age, conjugation of this polysaccharide antigen to outer membrane protein (OMP) of Neisseria meningitides, results in sufficient protection. Effects of PRP, OMP, conjugated PRP-OMP, and adjuvanted vaccine (PedVax HiB), on cytokine production and surface marker expression were established. PRP induced no effects on cytokine production and the effect on surface marker expression was limited to a minor decrease in CD209 (DC-SIGN). In both MUTZ-3 and moDC, OMP induced the strongest response both in cytokine production and surface marker expression. Compared to OMP alone conjugated PRP-OMP generally induced a weaker response in cytokine production and surface marker expression. The effects of PedVax HiB were comparable to conjugated PRP-OMP. While moDC showed a larger dynamic range than MUTZ-3 DC, these cells also showed considerable variability between donors, with MUTZ-3 DC showing a consistent response between the replicate assays. In our view, this makes MUTZ-3 DC the cells of choice. In conclusion, our results demonstrate that the MUTZ-3 DC assay allows discrimination between compounds with different immunogenicity. The potential of this cell line as (part of) an in vitro immunogenicity assay should be further explored.