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.

An immunologic model for rapid vaccine assessment -- a clinical trial in a test tube.

While the duration and size of human clinical trials may be difficult to reduce, there are several parameters in pre-clinical vaccine development that may be possible to further optimise. By increasing the accuracy of the models used for pre-clinical vaccine testing, it should be possible to increase the probability that any particular vaccine candidate will be successful in human trials. In addition, an improved model will allow the collection of increasingly more-informative data in pre-clinical tests, thus aiding the rational design and formulation of candidates entered into clinical evaluation. An acceleration and increase in sophistication of pre-clinical vaccine development will thus require the advent of more physiologically-accurate models of the human immune system, coupled with substantial advances in the mechanistic understanding of vaccine efficacy, achieved by using this model. We believe the best viable option available is to use human cells and/or tissues in a functional in vitro model of human physiology. Not only will this more accurately model human diseases, it will also eliminate any ethical, moral and scientific issues involved with use of live humans and animals. An in vitro model, termed "MIMIC" (Modular IMmune In vitro Construct), was designed and developed to reflect the human immune system in a well-based format. The MIMIC System is a laboratory-based methodology that replicates the human immune system response. It is highly automated, and can be used to simulate a clinical trial for a diverse population, without putting human subjects at risk. The MIMIC System uses the circulating immune cells of individual donors to recapitulate each individual human immune response by maintaining the autonomy of the donor. Thus, an in vitro test system has been created that is functionally equivalent to the donor's own immune system and is designed to respond in a similar manner to the in vivo response.