Poster CC6 - The Role of Lymphoid cells in Muscle Regeneration in the Presence of ECM Derived Biomaterials in Murine Volumetric Muscle Loss

Introduction: The implantation of medical devices and biomaterials can cause disturbances in the delicate balance between immune tolerance and activation. Previous research has shown that implanting decellularized extracellular matrix (ECM) based biomaterials leads to the preferential recruitment of XCR1+ CD103+ cDC1s to the trauma site after volumetric muscle loss (VML) correlating with variations in XCL1 protein and gene expression. Understanding T and natural killer (NK) cell interactions within the ECM environment holds promise for enhancing regenerative therapeutics.

Materials and

Methods: Surgical bilateral 3-4 mm defects were created in the quadricep muscle groups of C57BL/6 mice. ECM is implanted in the surgical site to promote a pro-regenerative environment, an injury (untreated) control, as well as a polyethylene (PE) is used to induce a profibrotic response. NK cells were depleted with an initial dose of 200ug of anti-NK1.1 antibody or isotype control 2 days prior to surgery via an intraperitoneal (IP) injection. An additional 100ug was injected during the day of surgery as well as every 3 days until completion of the study. 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 live immune cells, when compared to control injury and PE there was a significant increase of NK cells in the ECM group (Fig 1C). In addition, we saw persistent presence of NK cells in the muscle 42 days post injury. In addition, we were able to successfully deplete NK cells in the site of trauma and in the blood 7 days post injury (Fig 1D & E).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 site of injury, the persistence of NK cells 42 days post injury, could potentially be contributing to the outcomes of integration into host tissue.

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