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case_images: (A) Time course of B cell population in percent and rituximab administration in our patient. (B) Analysis of peripheral blood mononuclear cells obtained in March 2020 once B cells were detectable. 14% of the CD19+ B cells expressed the Breg markers CD24 and CD38 (Gate H), and 15% of CD19+ B cells produced IL-10 after stimulation with CpG and aCD40L. Gate F (mature/naive/transitional B cells), Gate G (memory B cells), Gate I (plasma-like cells). (C) Analysis of peripheral blood mononuclear cells obtained two weeks after application of rituximab in April 2020 demonstrating complete absence of CD19+ B cells.
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case_images: Since 2014, the GPA is well controlled with rituximab, an anti CD20 antibody, resulting in a complete depletion of B cells in peripheral blood and complete absence of clinical symptoms ( Figure 1 ). The last rituximab administration before the diagnosis of metastatic melanoma was in January 2019 ( Figure 1A ). Figure 1B ). For comparison: Zaimoku et al. showed a frequency of around 3% of CD24+ CD38+ B cells in a healthy control group, while two other studies reported a frequency of 4% and 7%, respectively in CD19+IL10+ cells in healthy control groups. After rituximab application in April 2020, no CD20 positive B cells were detectable anymore ( Figure 1C ).  Figure 3  demonstrates the timeline.
case_images: Multiplex Immunofluorescence staining and Immunohistochemistry of the primary melanoma (left) and a cutaneous metastases (right). B-cells are completely absent, and there is a peritumoral inflammatory infiltrate consisting primarily of CD4 and CD8 T-cells in the primary tumor and few CD8 T-cells and CD68 positive myeloid cells in the metastasis.
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case_images: Results showed that B cells were completely absent and there was a peritumoral inflammatory infiltrate consisting primarily of CD4+ and CD8+ T cells in the primary tumor, whereas we found no CD4+ T cells, but only a few CD8+ T cells and CD68+ myeloid cells in the metastasis ( Figure 2 ).
case_images: The medical timeline is demonstrated. Created with .
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case_images: After rituximab application in April 2020, no CD20 positive B cells were detectable anymore ( Figure 1C ).  Figure 3  demonstrates the timeline.