Marie Meeths

Spectrum of clinical presentations in familial hemophagocytic lymphohistiocytosis type 5 patients with mutations in STXBP2

Hemophagocytic lymphohistiocytosis (HLH) is an often-fatal hyperinflammatory syndrome characterized by fever, hepatosplenomegaly, cytopenia, and in some cases hemophagocytosis. Here, we describe the mutation analysis, clinical presentation, and functional analysis of natural killer (NK) cells in patients with mutations in STXBP2 encoding Munc18-2, recently associated with familial HLH type 5. The disease severity among 11 persons studied here was highly variable and, accordingly, age at diagnosis ranged from 2 months to 17 years. Remarkably, in addition to typical manifestations of familial HLH (FHL), the clinical findings included colitis, bleeding disorders, and hypogammaglobulinemia in approximately one-third of the patients. Laboratory analysis revealed impairment of NK-cell degranulation and cytotoxic capacity. Interleukin-2 stimulation of lymphocytes in vitro rescued the NK cell-associated functional defects. In conclusion, familial HLH type 5 is associated with a spectrum of clinical symptoms, which may be a reflection of impaired expression and function of Munc18-2 also in cells other than cytotoxic lymphocytes. Mutations in STXBP2 should thus also be considered in patients with clinical manifestations other than those typically associated with HLH.

Different NK cell–activating receptors preferentially recruit Rab27a or Munc13-4 to perforin-containing granules for cytotoxicity

The autosomal recessive immunodeficiencies Griscelli syndrome type 2 (GS2) and familial hemophagocytic lymphohistiocytosis type 3 (FHL3) are associated with loss-of-function mutations in RAB27A (encoding Rab27a) and UNC13D (encoding Munc13-4). Munc13-4 deficiency abrogates NK-cell release of perforin-containing lytic granules induced by signals for natural and antibody-dependent cellular cytotoxicity. We demonstrate here that these signals fail to induce degranulation in resting NK cells from Rab27a-deficient patients. In resting NK cells from healthy subjects, endogenous Rab27a and Munc13-4 do not colocalize extensively with perforin. However, phorbol 12-myristate 13-acetate and ionomycin stimulation or conjugation to susceptible target cells induced myosin-dependent colocalization of Rab27a and Munc13-4 with perforin. Unexpectedly, individual engagement of receptors leukocyte functional antigen-1, NKG2D, or 2B4 induced colocalization of Rab27a, but not Munc13-4, with perforin. Conversely, engagement of antibody-dependent cellular cytotoxicity receptor CD16 induced colocalization of Munc13-4, but not Rab27a, with perforin. Furthermore, colocalization of Munc13-4 with perforin was Rab27a-dependent. In conclusion, Rab27a or Munc13-4 recruitment to lytic granules is preferentially regulated by different receptor signals, demonstrating that individual target cell ligands regulate discrete molecular events for lytic granule maturation. The data suggest Rab27a facilitates degranulation at an early step yet highlight a reciprocal relationship between Munc13-4 and Rab27a for degranulation.

Comparison of primary human cytotoxic T-cell and natural killer cell responses reveal similar molecular requirements for lytic granule exocytosis but differences in cytokine production.

Cytotoxic lymphocytes, encompassing cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, kill pathogen-infected, neoplastic, or certain hematopoietic cells through the release of perforin-containing lytic granules. In the present study, we first performed probability-state modeling of differentiation and lytic granule markers on CD8(+) T cells to enable the comparison of bona fide CTLs with NK cells. Analysis identified CD57(bright) expression as a reliable phenotype of granule marker-containing CTLs. We then compared CD3(+)CD8(+)CD57(bright) CTLs with NK cells. Healthy adult peripheral blood CD3(+)CD8(+)CD57(bright) CTLs expressed more granzyme B but less perforin than CD3(-)CD56(dim) NK cells. On stimulation, such CTLs degranulated more readily than other T-cell subsets, but had a propensity to degranulate that was similar to NK cells. Remarkably, the CTLs produced cytokines more rapidly and with greater frequency than NK cells. In patients with biallelic mutations in UNC13D, STX11, or STXBP2 associated with familial hemophagocytic lymphohistiocytosis, CTL and NK cell degranulation were similarly impaired. Therefore, cytotoxic lymphocyte subsets have similar requirements for Munc13-4, syntaxin-11, and Munc18-2 in lytic granule exocytosis. The present results provide a detailed comparison of human CD3(+)CD8(+)CD57(bright) CTLs and NK cells and suggest that analysis of CD57(bright) CTL function may prove useful in the diagnosis of primary immunodeficiencies including familial hemophagocytic lymphohistiocytosis.

Clinical presentation of Griscelli syndrome type 2 and spectrum of RAB27A mutations.

Griscelli syndrome type 2 (GS2) is an autosomal‐recessive immunodeficiency caused by mutations in RAB27A, clinically characterized by partial albinism and haemophagocytic lymphohistocytosis (HLH). We evaluated the frequency of RAB27A mutations in 21 unrelated patients with haemophagocytic syndromes without mutations in familial HLH (FHL) causing genes or an established diagnosis of GS2. In addition, we report three patients with known GS2. Moreover, neurological involvement and RAB27A mutations in previously published patients with genetically verified GS2 are reviewed.

Genotype–phenotype study of familial haemophagocytic lymphohistiocytosis type 3

Background Mutations of UNC13D are causative for familial haemophagocytic lymphohistiocytosis type 3 (FHL3; OMIM 608898). Objective To carry out a genotype–phenotype study of patients with FHL3. Methods A consortium of three countries pooled data on presenting features and mutations from individual patients with biallelic UNC13D mutations in a common database. Results 84 patients with FHL3 (median age 4.1 months) were reported from Florence, Italy (n=54), Hamburg, Germany (n=18), Stockholm, Sweden (n=12). Their ethnic origin was Caucasian (n=57), Turkish (n=10), Asian (n=7), Hispanic (n=4), African (n=3) (not reported (n=3)). Thrombocytopenia was present in 94%, splenomegaly in 96%, fever in 89%. The central nervous system (CNS) was involved in 49/81 (60%) patients versus 36% in patients with FHL2 (p=0.001). A combination of fever, splenomegaly, thrombocytopenia and hyperferritinaemia was present in 71%. CD107a expression, NK activity and Munc 13-4 protein expression were absent or reduced in all but one of the evaluated patients. 54 different mutations were observed, including 15 new ones: 19 missense, 14 deletions or insertions, 12 nonsense, nine splice errors. None was specific for ethnic groups. Patients with two disruptive mutations were younger than patients with two missense mutations (p<0.001), but older than comparable patients with FHL2 (p=0.001). Conclusion UNC13D mutations are scattered over the gene. Ethnic-specific mutations were not identified. CNS involvement is more common than in FHL2; in patients with FHL3 and disruptive mutations, age at diagnosis is significantly higher than in FHL2. The combination of fever, splenomegaly, thrombocytopenia and hyperferritinaemia appears to be the most easily and frequently recognised clinical pattern and their association with defective granule release assay may herald FHL3.

Mice lacking asparaginyl endopeptidase develop disorders resembling hemophagocytic syndrome

Asparaginyl endopeptidase (AEP or legumain) is a lysosomal cysteine protease that cleaves protein substrates on the C-terminal side of asparagine. AEP plays a pivotal role in the endosome/lysosomal degradation system and is implicated in antigen processing. The processing of the lysosomal proteases cathepsins in kidney is completely defective in AEP-deficient mice with accumulation of macromolecules in the lysosomes, which is typically seen in lysosomal disorders. Here we show that mutant mice lacking AEP develop fever, cytopenia, hepatosplenomegaly, and hemophagocytosis, which are primary pathological manifestations of hemophagocytic syndrome/hemophagocytic lymphohistiocytosis (HLH). Moreover, AEP deficiency provokes extramedullary hematopoiesis in the spleen and abnormally enlarged histiocytes with ingested red blood cells (RBCs) in bone marrow. Interestingly, RBCs from AEP-null mice are defective in plasma membrane components. Further, AEP-null mice display lower natural killer cell activity, but none of the major cytokines is substantially abnormal. These results indicate that AEP might be a previously unrecognized component in HLH pathophysiology.

Treatment of the X‐linked lymphoproliferative, Griscelli and Chédiak–Higashi syndromes by HLH directed therapy

Griscelli syndrome type 2 (GS2), the X‐linked lymphoproliferative (XLP) and the Chédiak–Higashi (CHS) syndromes are diseases that all may develop hemophagocytic syndromes. We wanted to investigate whether the treatment protocols for hemophagocytic lymphohistiocytosis (HLH) can also be used for these syndromes.

Pathophysiology and spectrum of diseases caused by defects in lymphocyte cytotoxicity

In experimental settings, lymphocyte cytotoxicity has been recognized as a central mechanism for immune defense against infected and neoplastic cells. More recently, molecular determinants of lymphocyte cytotoxicity have been identified through studies of rare, inherited hyperinflammatory and lymphoproliferative syndromes that include hemophagocytic lymphohistiocytosis (HLH). These studies have unraveled a set of genes pivotal for the biogenesis and directed release of perforin-containing lysosomes that mediate target cell killing, in addition to other pathways including Fas that also contribute to induction of cell death. Furthermore, studies of such human primary immunodeficiencies have highlighted non-redundant roles of perforin for maintenance of immune homeostasis. Besides providing mechanistic insights to lymphocyte cytotoxicity, studies of individuals with rare hyperinflammatory diseases are highlighting the relevance of lymphocyte cytotoxicity to more common human diseases. It is increasingly recognized that mutations abrogating lymphocyte cytotoxicity not only cause HLH, but also are associated with susceptibility to cancer and autoimmune syndromes. In addition, patients may initially be present with neurological symptoms or severe infectious disease masquerading as variable immunodeficiency syndrome. Here, we highlight new knowledge regarding the molecular mechanisms regulating lymphocyte cytotoxicity and review how mutations in genes associated with HLH cause disease. We also discuss the wider implications of impairments in lymphocyte cytotoxicity for human disease predisposition.

Incidence and clinical presentation of primary hemophagocytic lymphohistiocytosis in Sweden

Primary hemophagocytic lymphohistiocytosis (HLH) represents a group of inherited hyperinflammatory immunodeficiencies, including familial HLH (FHL), Griscelli syndrome type 2 (GS2), and X‐linked lymphoproliferative syndrome (XLP). We previously reported an annual incidence of suspected primary HLH in Sweden 1971–1986 of 0.12 per 100,000 children. Here, we determined if the incidence had increased with concomitant awareness.

Transcriptional regulation of Munc13-4 expression in cytotoxic lymphocytes is disrupted by an intronic mutation associated with a primary immunodeficiency

A conserved regulatory element in intron 1 of UNC13D regulates Munc13-4 expression.