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CSAAS and MPIO-labelled cells
In: Publications written by: Prof. Dr. Igor M. Sauer
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As a result of the fruitful collaboration with the Institute for Analytical Sciences Berlin Nathanael Raschzok's paper on "Quantification of Cell Labelling with Micron-Sized Iron Oxide Particles Using Continuum Source Atomic Absorption Spectrometry" has been accepted by Tissue Engineering for publication. Co-authors are Nils Billecke, Nora N. Kammer, Mehmet H. Morgul, Michaela K. Adonopoulou, Igor M. Sauer, Stefan Florek, Helmut Becker-Ross, and Mao-Dong Huang.

Detection of cells after transplantation is necessary for quality control in regenerative medicine. Labelling with micron-sized iron oxide particles (MPIOs) enables non-invasive detection of single cells by magnetic resonance imaging. However, techniques for evaluation of the particle uptake are challenging. The aim of this study was to investigate continuum source atomic absorption spectrometry (CSAAS) for this purpose. Porcine liver cells were labelled with MPIOs and the iron concentration of the cell samples was investigated by a CSAAS spectrometer equipped with a Perkin-Elmer THGA graphite furnace. The weak iron line at 305.754 nm provides only about 1/600 sensitivity of the iron resonance line at 248.327 nm and was used for CSAAS measurements. Iron concentrations measured from labelled cells ranged from (5.8 ± 0.3) to (25.8 ± 0.9) pg Fe/cell, correlating to an uptake of (8.2 ± 0.5) to (25.7 ± 0.8) particles/cell. The results were verified by standardised morphometric evaluation. CSAAS enabled rapid quantification of particle load from small quantities of cells without extensive preparation steps. Thereby, CSAAS could be used for quality control in a clinical setting of cell transplantation.
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Our manuscript "Depletion of donor dendritic cells ameliorates immunogenicity of both skin and hind limb transplants" has been accepted for publication in Frontiers in Immunology, section Alloimmunity and Transplantation. Authors are Muhammad Imtiaz Ashraf, Joerg Mengwasser, Anja Reutzel-Selke, Dietrich Polenz, Kirsten Führer, Steffen Lippert, Peter Tang, Edward Michaelis, Rusan Catar, Johann Pratschke, Christian Witzel, Igor M. Sauer, Stefan G. Tullius, and Barbara Kern.

Acute cellular rejection remains a significant obstacle affecting successful outcomes of organ transplantation including vascularized composite tissue allografts (VCA). Donor antigen presenting cells (APC), particularly dendritic cells (DC), orchestrate early alloimmune responses by activating recipient effector T cells. Employing a targeted approach, we investigated the impact of donor-derived conventional DC (cDC) and APC on the immunogenicity of skin and skin-containing VCA grafts, using mouse models of skin and hind limb transplantation.
By post-transplantation day 6, skin grafts demonstrated severe rejections, characterized by predominance of recipient CD4 T cells. In contrast, hind limb grafts showed moderate rejection, primarily infiltrated by CD8 T cells. While donor depletion of cDC and APC reduced frequencies, maturation, and activation of DC in all analysed tissues of skin transplant recipients, reduction in DC activities was only observed in the spleen of hind limb recipients. Donor cDC and APC depletion did not impact all lymphocyte compartments but significantly affected CD8 T cells and activated CD4 T in lymph nodes of skin recipients. Moreover, both donor APC and cDC depletion attenuated the Th17 immune response, evident by significantly reduced Th17 (CD4+IL-17+) cells in the spleen of skin recipients and reduced levels of IL-17E and lymphotoxin-α in the serum samples of both skin and hind limb recipients. In conclusion, our findings underscore the highly immunogenic nature of skin component in VCA. The depletion of donor APC and cDC mitigates the immunogenicity of skin grafts while exerting minimal impact on VCA.

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