Lymphoid Tissue Equivalent Module Versus PBMC Assay

The MIMIC® System reproduces both T cell and B cell responses. The availability of an in vitro culture system that provides a reliable readout of antigen-induced antibody responses is crucial for understanding the immunobiology of human B cell activation and differentiation. Current methods for the study of recall human antibody responses in vitro rely, in large part, on techniques that were developed thirty or more years ago, such as PBMC assays. The generation of naïve B cell responses in vitro has been quite challenging; positive results have only been achieved with highly modified culture systems that include the use of exogenous factors during the assay to polyclonally stimulate B cell proliferation and antibody production. The development of the novel MIMIC® in vitro assay systems that supports the induction of primary human B cell responses in a physiologically relevant manner provides predictive insight into the biology of this lymphocyte population and serves as a valuable tool for assessing the immunogenicity of vaccines and other therapeutics prior to animal testing.

Charts comparing LTE to PBMC assays

The VaxDesign Campus is pursuing novel 2D and 3D assays to provide a more suitable environment for the induction of recall and naïve antigen-specific B cell and T cell responses in an in vitro system. We have established a relatively straightforward, standard well-format method for testing the response of human immune cells, including B cells, T cells, DCs, and FDCs. The LTE module provides a more reliable method for inducing robust T and B cell activity against naïve and recall antigens than is possible with total PBMC.

The results demonstrate a clear advantage of the LTE module over unfractionated PBMC in generating lymphocyte responses against the recall antigen, tetanus toxoid (TT). While there was an increase in the frequency of dividing T and B cells in cultures that received TT for 7 days, the number of true antigen-specific B cells, as assessed by ELISPOT assay, increased approximately 6-fold in the same assay wells. In contrast, the addition of antigen to total PBMC triggered little or no increase in the frequency of responding CD3+ T cells or CD19+ B cells, nor was there any increase in the number of antibody secreting B cells detected by ELISPOT.

We observe similar enhancements of Ag-specific T cell responses in the LTE module culture as compared to PBMCs for naïve antigens such as MSP-1 from malaria and rPA from bacillus anthracis as shown below. We have also added DCs to the PBMC culture, and still do not observe Ag-specific T cell responses.

Chart - Ag-specific responses

Chart - Donor responses