Optimization of a dendritic cell-based assay for the in vitro priming of naïve human CD4+ T cells.

Methods to prime human CD4(+) T cells in vitro would be of significant value for the pre-clinical evaluation of vaccine candidates and other immunotherapeutics. However, to date, there is no reliable method for the induction of primary human T cell responses in the laboratory. Here, we optimized a culture strategy incorporating highly purified lymphocytes and dendritic cells, in the absence of any exogenous growth factors, for the in vitro sensitization of naïve CD4(+) T cells against a variety of protein antigens. This fully autologous approach, which was superior to the more traditional PBMC assay for supporting the induction of primary human T helper cell responses in culture, elicited effector cells capable of producing a variety of Th cytokines, including IFNgamma, TNFalpha, IL-2, IL-5, IL-17 and IL-21, and memory cells that could be restimulated multiple times with a specific antigen. Through simple modifications to this culture method, we evaluated the role of dendritic cell maturation state and regulatory T cells on the sensitization of naïve T helper cells, which highlights its utility for addressing basic questions of human immunobiology. Finally, using the formulated yellow fever vaccine, YF-VAX (R), we provide a proof-of-concept demonstration of the utility of the system for evaluating the T cell immunogenicity of vaccine candidates in a pre-clinical setting.

In vitro antibody response to tetanus in the MIMIC system is a representative measure of vaccine immunogenicity.

In response to the recurrent failure of animal vaccine protection studies to accurately predict human trial results, we have developed a fully human modular immune in vitroconstruct (MIMIC) to serve as a preliminary screen for efficacy testing of potential vaccine formulations. To validate the potential of this approach, we monitored the in vitro-generated tetanus (TT)-specific antibody levels in a cohort of donors before and after receiving tetanus vaccination. Purified CD4_T cell and B cell populations were combined with autologous tetanus vaccine-pulsed dendritic cells to generate specific antibody. Enumeration of TT-specific IgG antibody-secreting cells by ELISPOT displayed a significant increase in the magnitude of this population after vaccination. The relative magnitudes of the in vitro-generated TT-specific antibody response before and after vaccination largely recapitulated the TT-specific IgG serum titer profiles measured in the same individuals. These findings provide evidence that the MIMIC system can be a rapid and representative in vitro method for measuring vaccine immunogenicity via induction of the memory B cell response.