(H-319) Immunomodulation of T cells and NK cells by ECM derived biomaterials in murine volumetric muscle loss

Introduction:: The implantation of medical devices and biomaterial can result in an imbalance within the immune system. Our lab has previously shown that implanting decellularized extracellular matrix (ECM) based biomaterials results in preferential recruitment of XCR1⁺ CD103⁺ cDC1s to the trauma site after volumetric muscle loss (VML) correlating with differences in XCL1 protein and gene expression levels. Through the understanding of T and natural killer (NK) cells and their interaction within an ECM environment, it could advance regenerative therapeutics to assist in more favorable treatment outcomes.


Materials and Methods:: Bilateral 3-4 mm defects were surgically created in the quadricep muscle groups of C57BL/6 mice. Polyethylene (PE) was implanted into the injury site inducing a profibrotic response, ECM was used to promote a pro-regenerative environment, as well as an injury (untreated) control, and uninjured control mice. Differential cell recruitment and phenotypic differences in CD4 and CD8 T cells from draining (inguinal), distal (axillary and brachial, mandibular), and non-draining (mesenteric lymph nodes), as well as muscle and spleens were analyzed using multiparametric flow cytometry. Gene expression of Xcl1 was quantified through RT-PCR for lymphocytes sorted from muscle and in vitro simulation of NK cells.


Results, Conclusions, and Discussions:: After sorting from injured muscle tissue treated with ECM, RT-PCR of sorted immune cells found in VML injury, showed the predominate producers of the chemokine Xcl1 were NK cells (Fig 1a). When compared to the control media there was a 2-fold increase production of Xcl1 by the ECM + IL-4 group. The presence of low molecular weight hyaluronic acid (HA) +IL-4 resulted in a 1.79-fold increase of Xcl1 compared to the control (Fig 1b). As a fraction of total T cells, when compared to uninjured controls there was a significant increase in the CD4⁺ cells in the ECM group, and in contrast a significant increase of CD8⁺ T cells in mice with PE implants (Fig 1C). In addition, we saw differences in T cell activation in these regional and distal immune sites (Fig 1D)

Conclusion: The results indicated that there is a putative mechanism present where the ECM in conjunction with other damage associated molecular response (DAMPs) are interacting with the receptors of NK cells, inducing a regulatory response to the site of trauma through the recruitment of cross- presenting dendritic cells (XCR1+CD103+). When investigating the draining and non-draining lymph nodes and the spleen, it showed the systemic nature of the adaptive immune response to biomaterials to potentially contributing to the outcomes of integration into host tissue or an inflammatory foreign body response resulting in fibrosis.


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