(633c) Microneedle-Based Immune Monitoring Platform Samples Cells and Interstitial Fluid from Tissue in Situ

Current protocols for immune system monitoring involve collecting cells from blood or cerebrospinal fluid, or via invasive sampling and biopsies. However, since major populations of immune cells reside within tissues, these invasively-obtained body fluid samples are, at best, indirect indicators of the status of the immune system. Further, these methods are difficult to incorporate into long-term, repetitive, longitudinal immune monitoring. On the other hand, direct interrogation of the immune system, as currently employed by simple delayed-type hypersensitivity tests (e.g., Mantoux tuberculin test), does not provide information about the phenotype and functional characteristics of responding immune cells. We report here a technology that addresses these challenges simultaneously, with the synergistic goals of providing enhanced diagnostic methods for sampling and analyzing the function of the immune system, and providing a greater insight into the status of the immune system than state of the art assays. We have fabricated alginate-coated, cell-sampling microneedles capable of sampling cells and interstitial fluid and permitting the quantification of constituents like IgG. Cell recruitment was enhanced by incorporating chemoattractants in the alginate coating within 8 hours of application to mouse ears and dorsal flank. Cells obtained from retrieved microneedle arrays could be subjected to phenotype analysis and stained for surface markers. We employed a subcutaneous alginate gel injection model to determine the optimal time of sampling and the chemoattractant dosing, Alginate gels injected subcutaneously into the dorsal flanks of mice showed enhanced infiltration of CD4+ T cells under the influence of inflammatory chemoattractants and showed increasing infiltration of cells with time, over 48 hours. Microneedle arrays retrieved at different points of time, under the influence of different chemoattractants and antigens, are currently being analyzed to further understand the temporal characteristics of immune cell recruitment towards sites of inflammation. This work allows ex vivo analysis of cells retrieved directly from the local tissue environment and enables the investigation of antigen-specific cell interrogation for diagnostic purposes as well as answering spatio-temporal questions related to immunology in local tissue environments.