Peripheral Tissue Equivalent Module
The human immune system has two arms: (1) an innate response, which reacts within minutes through days and (2) an adaptive response, which reacts within one to two weeks.
The peripheral tissue equivalent (PTE) module is designed to simulate the innate immune response that occurs in the peripheral tissues of the body, such as the skin, lungs, and other mucosal tissues that may become exposed to pathogens in the environment. We can construct the PTE module manually or, more often, with an automated robotic platform. The automated process has advantages in throughput, reliability, and consistency. See Case Studies.
The PTE module can predict adjuvant and vaccine potency, toxicity, and other desired (and undesired) effects prior to the initiation of animal studies or clinical trials. In addition, because the PTE module replicates human inflammatory responses, many other applications are possible. For example, the PTE module has correctly predicted toxicity and immunostimulatory potential of a variety of biological and chemical compounds, with results that are consistent with the known biological activities of the agents in published reports.
The VaxDesign Campus of Sanofi Pasteur has developed different versions of the PTE module for subcutaneous or intramuscular exposure (Core PTE module) and for intravenous exposure (Vascular PTE module). We also have a transwell-based PTE module that does not incorporate an extracellular matrix material, but is an efficient method to generate important antigen-presenting cells known as dendritic cells. We have a mucosal tissue model (e.g., lung) under development.
The Core PTE module layers endothelial cells (HUVEC) over a collagen matrix. We have ensured that the endothelial cells are quiescient, or not subject to inflammation. We then place human immune cells (PBMCs) in nutrient solution onto the construct. Over a period of hours, certain types of immune cells known as monocytes primarily travel through the endothelial cell layer and into the collagen matrix. We then remove and replace the nutrient solution containing the remaining immune cells. The monocytes in the collagen matrix autonomously differentiate into antigen-presenting cells (APCs) over about a day. One type of APC, macrophages, stay in the collagen matrix. The other type of APC, dendritic cells, migrate back through the collagen and endothelial cell layer and into the nutrient solution. We then stimulate the dendritic cells with an antigen, vaccine, immunogen, or other product to generate an immune response. Unlike other methods, the entire process uses no exogenous factors to push the monocytes to differentiate. As a result, the dendritic cells are in different maturation states rather than synchronous maturation states, which more closely resembles what occurs in the body.
|Physiological aspect of PTE module||PTE (In Vitro)||In Vivo or Ex Vivo Human|
|Transendothelial migration of blood monocytes promotes differentiation|
|Monocyte differentiation into DCs and macrophages is autonomous and occurs within 1–3 days|
|Tissue-exit by crossing the endothelium in abluminal-to-luminal direction (into the lymphatics)|
|CD16+ subpopulation of blood monocytes (same as CX3CR1+ found in vivo) is preferentially recruited into tissues to become DCs|
|Increased extravasation of leukocytes when endothelium is activated Skin DCs are heterogeneous Increased maturation of DCs via activation by vaccines, adjuvants or pro- inflammatory cytokines|
The Vascular PTE module also uses an endothelial cell monolayer over a collagen matrix, but uses whole blood or fractions rather than PBMCs as the immune cell source. This approach increases the complexity of the PTE module by introducing an additional type of immune cell known as granulocytes as well as other immune factors that are present in whole blood. In some cases, granulocytes can cause hyperimmune responses that only the Vascular PTE module can simulate.
The transwell version of the PTE module enables the derivation of dendritic cells under physiologic conditions. This construct is important because dendritic cells are critical antigen presenting cells (APCs) that regulate the generation of adaptive immune responses. The transwell PTE module serves as a dendritic cell "factory" that is easier to use than the full three-dimensional PTE module.
The different types of PTE modules are useful depending on the nature of the study, either alone or in combination. For example, most vaccine studies would use the Core PTE module but immunotoxicity studies for an intravenous drug would use the Vascular PTE module (and possibly the Core PTE module as well). See MIMIC® Applications for more details on how the PTE module is used for different MIMIC® Applications.
We have demonstrated that the PTE module is more sensitive and accurate than standard PBMC assays. See Case Study.