Blood cellular profile of patient K108E prior to and post stem cell transplant. Hematologic profiles were obtained by standard automated measurements (neutrophils, platelets, hemoglobin), and immune cell populations (total T lymphocytes, CD4⁺ T cells, CD8⁺ T cells, natural killer [NK] cells, B lymphocytes, monocytes) were established by fluorescence-activated cell sorter using cell-specific markers. (The degree of monocytopenia was inconsistently evident from machine differential counts beyond the patient’s initial presentation; those derived from flow cytometric evaluation are shown.) The patient was treated as hemophagocytic lymphohistiocytosis using a modified version of the HLH-2004 protocol (blue triangle) with resulting decline in neutrophil, B, and NK cell counts, accompanied by clinical stabilization. The patient then moved rapidly into conditioned hematopoietic stem cell transplant (red triangle; 9 months of age).