Abstract: Background Mutations in the perforin 1 (PRF1) gene account for up to 58% of familial hemophagocytic lymphohistiocytosis syndromes. The resulting defects in effector cell cytotoxicity lead to hypercytokinemia and hyperactivation with inflammation in various organs. Objective We sought to determine whether autologous gene-corrected T cells can restore cytotoxic function, reduce disease activity, and prevent hemophagocytic lymphohistiocytosis (HLH) symptoms in in vivo models. Methods We developed a gammaretroviral vector to transduce murine CD8 T cells in the Prf−/− mouse model. To verify functional correction of Prf−/− CD8 T cells in vivo, we used a lymphocytic choriomeningitis virus (LCMV) epitope-transfected murine lung carcinoma cell tumor model. Furthermore, we challenged gene-corrected and uncorrected mice with LCMV. One patient sample was transduced with a PRF1-encoding lentiviral vector to study restoration of cytotoxicity in human cells. Results We demonstrated efficient engraftment and functional reconstitution of cytotoxicity after intravenous administration of gene-corrected Prf−/− CD8 T cells into Prf−/− mice. In the tumor model infusion of Prf−/− gene-corrected CD8 T cells eliminated the tumor as efficiently as transplantation of wild-type CD8 T cells. Similarly, mice reconstituted with gene-corrected Prf−/− CD8 T cells displayed complete protection from the HLH phenotype after infection with LCMV. Patients' cells showed correction of cytotoxicity in human CD8 T cells after transduction. Conclusion These data demonstrate the potential application of T-cell gene therapy in reconstituting cytotoxic function and protection against HLH in the setting of perforin deficiency

Abstract: Most hereditary forms of hemophagocytic lymphohistiocytosis (HLH) are caused by defects of cytotoxicity, including the vesicle trafficking disorder Griscelli syndrome type 2 (GS2, RAB27A deficiency). Deficiency of the mitogen-activated protein kinase activating death domain protein (MADD) results in a protean syndrome with neurological and endocrinological involvement. MADD acts as a guanine nucleotide exchange factor for small guanosine triphosphatases, including RAB27A. A homozygous splice site mutation in MADD was identified in a female infant with syndromic features, secretory diarrhea, and features of HLH. Aberrant splicing caused by this mutation leads to an in-frame deletion of 30 base pairs and favors other aberrant variants. Patient natural killer (NK) cells and cytotoxic T cells showed a severe degranulation defect leading to absent perforin-mediated cytotoxicity. Platelets displayed defective adenosine triphosphate secretion, similar to that in GS2. To prove causality, we introduced a CRISPR/Cas9-based MADD knockout in the NK cell line NK-92mi. MADD-deficient NK-92mi cells showed a degranulation defect and impaired cytotoxicity similar to that of the patient. The defect of cytotoxicity was confirmed in another patient with MADD deficiency. In conclusion, RAB27A-interacting MADD is involved in vesicle release by cytotoxic cells and platelets. MADD deficiency causes a degranulation defect and represents a novel disease predisposing to an HLH phenotype

Abstract: Hemophagocytic lymphohistiocytosis (HLH) is a rare immunological disease, which can be mistaken for sepsis easily. Among the infectious causes that may trigger secondary HLH, tuberculosis (TBC), a rather rare pathogen nowadays, is typical. To our knowledge, this is the first case report of an infant suffering from TBC-associated HLH-induced acute respiratory failure who was treated successfully using extracorporeal membrane oxygenation. An 8-month-old boy with fever (over the last 8 wk) and pancytopenia was transferred to our institution with acute respiratory failure and for extracorporeal membrane oxygenation therapy. Bone marrow biopsy revealed hemophagocytosis. Immunological work-up for familial HLH was negative. In a desperate search for the cause of secondary HLH, an interferon-gamma release assay for TBC returned positive. However, microscopy for acid-fast bacteria as well as polymerase chain reaction for TBC were initially negative. Despite this, the child was treated with tuberculostatic therapy. TBC was finally confirmed. The child remained on extracorporeal membrane oxygenation for 28 d. Further work-up showed typical lesions of disseminated TBC. The mother was identified as the source of TBC. The boy presents with mild sequelae (fine motor skills). In infants with suspected septicemia, TBC should be considered as differential diagnosis even if the results are initially negative

Abstract: Introduction: Inborn errors of immunity (IEI) are characterized by a dysfunction of the immune system leading to increased susceptibility to infections, impaired immune regulation and cancer. We present a unique consanguineous family with a history of Hodgkin lymphoma, impaired EBV control and a late onset hemophagocytic lymphohistiocytosis (HLH). Methods and results: Overall, family members presented with variable impairment of NK cell and cytotoxic T cell degranulation and cytotoxicity. Exome sequencing identified homozygous variants in RAB27A, FBP1 (Fructose-1,6-bisphosphatase 1) and ACAD9 (Acyl-CoA dehydrogenase family member 9). Variants in RAB27A lead to Griscelli syndrome type 2, hypopigmentation and HLH predisposition. Discussion: Lymphoma is frequently seen in patients with hypomorphic mutations of genes predisposing to HLH. We hypothesize that the variants in FBP1 and ACAD9 might aggravate the clinical and immune phenotype, influence serial killing and lytic granule polarization by CD8 T cells. Understanding of the interplay between the multiple variants identified by whole exome sequencing (WES) is essential for correct interpretation of the immune phenotype and important for critical treatment decisions