Background/Purpose: Hemophagocytic lymphohistiocytosis (HLH) is an often fatal disorder of infancy resulting from homozygous mutations in proteins involved in cytolysis (e.g. MUNC13-4, RAB27a, Perforin 1, Syntaxin11, STXBP2). HLH treatment is an etoposide based aggressive chemotherapy, and associated mortality remains problematic. Secondary forms of HLH, or macrophage activation syndrome (MAS), frequently result beyond infancy from rheumatologic, infectious, and oncologic conditions. MAS is typically treated with immunosuppression, including high dose Corticosteroids, Cyclosporine, and, recently, the IL-1 receptor antagonist, Anakinra (CCA). Of late, mutations in HLH associated cytolytic pathway genes have been identified in children with MAS. The importance of these mutations in the pathophysiology of MAS, and the appropriate treatment for MAS in these settings remains unclear. 

Methods: Chart review was performed for a teen with MAS successfully treated with CCA. Cytolytic activity of a natural killer (NK) cell line was assessed following over-expression of a RAB27a mutant protein identified in this girl. Lentiviral expression vectors were generated with the RAB27a mutation, and a wild-type RAB27a sequence control, sequenced for authenticity, and introduced into the NK-92 human NK cell line by transduction. Transduced NK cells were analyzed for transgene expression by co-expression of green fluorescence protein, and tested for their ability to lyse calcein violet loaded K562 NK target cells at varying effector to target cell ratios.

Results: An 18-year-old girl presented with 2 weeks of fever (>102^oF) and abdominal pain. Exam revealed a febrile, semi-coherent female with hepatosplenomegaly. Extensive infectious, oncologic, and rheumatic diseases work-ups were negative. Laboratory findings revealed pancytopenia; severe hepatitis; coagulopathy; elevated ferritin, triglycerides, soluble CD25, and soluble CD163; increased CD163 staining of bone marrow; markedly decreased NK cell function; ESR of 10 mm/hr. Sequencing of HLH genes revealed a single copy RAB27a mutation (259 G>A, A87P) known to be associated with type II Griscelli syndrome/HLH. She met 8 of 8 HLH criteria and was treated for MAS with CCA. She markedly and rapidly clinically improved. Her ferritin fell from 8,446 to 201 ng/ml (<115), and her AST fell from 4,639 U/L to 176 U/L, within 4 days of CCA. Lentiviral transduction of wild-type RAB27a into the NK-92 cell line had no effect on cytolysis of K562 target cells in vitro, whereas over-expression of the 259 G>A patient mutation decreased cytolytic activity by ~50%.

Conclusion: The distinction between HLH and MAS is becoming blurred as mutations in HLH genes are identified in patients with MAS. Perhaps later age of onset reflects heterozygous versus homozygous defects in cytolytic pathway proteins. Our data suggests single gene copy mutations can partially disrupt cytolytic activity through a dominant negative effect. Important treatment differences exist between protocols for HLH and MAS, and our patient’s response to CCA immunosuppression suggests HLH associated genetic mutations presenting later in life may be responsive to less aggressive/toxic (non-chemotherapeutic) immunosuppression.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/rapid-and-effective-response-to-immunosuppression-in-treating-macrophage-activation-syndrome-associated-with-a-heterozygous-dominant-negative-mutation-in-rab27a-leading-to-decreased-cytolytic-activity/