Michael B. Jordan

How I treat hemophagocytic lymphohistiocytosis

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of pathologic immune activation, occurring as either a familial disorder or a sporadic condition, in association with a variety of triggers. This immune dysregulatory disorder is prominently associated with cytopenias and a unique combination of clinical signs and symptoms of extreme inflammation. Prompt initiation of immunochemotherapy is essential for survival, but timely diagnosis may be challenging because of the rarity of HLH, its variable presentation, and the time required to perform diagnostic testing. Therapy is complicated by dynamic clinical course, high risk of treatment-related morbidity, and disease recurrence. Here, we review the clinical manifestations and patterns of HLH and describe our approach to the diagnosis and therapy for this elusive and potentially lethal condition.

Homeostasis of alpha beta TCR+ T cells.

Cytokines contribute to T cell homeostasis at all stages of T cell existence. However, the particular cytokine involved varies as T cells progress from a naïve through an activated to a memory state. In many cases the important cytokines are members of the interleukin 2 subfamily of the short-chain type I cytokines. A case is made for the idea that the evolutionary divergence of the short-chain family allowed for concurrent divergence in leukocytes.

Hypomorphic mutations in PRF1, MUNC13-4, and STXBP2 are associated with adult-onset familial HLH

Familial hemophagocytic lymphohistiocytosis (HLH) is a rare primary immunodeficiency disorder characterized by defects in cell-mediated cytotoxicity that results in fever, hepatosplenomegaly, and cytopenias. Familial HLH is well recognized in children but rarely diagnosed in adults. We conducted a retrospective review of genetic and immunologic test results in patients who developed HLH in adulthood. Included in our study were 1531 patients with a clinical diagnosis of HLH; 175 patients were 18 years or older. Missense and splice-site sequence variants in PRF1, MUNC13-4, and STXBP2 were found in 25 (14%) of the adult patients. The A91V-PRF1 genotype was found in 12 of these patients (48%). The preponderance of hypomorphic mutations in familial HLH-causing genes correlates with the later-onset clinical symptoms and the more indolent course in adult patients. We conclude that late-onset familial HLH occurs more commonly than was suspected previously.

Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages

The histiocytoses are rare disorders characterized by the accumulation of macrophage, dendritic cell, or monocyte-derived cells in various tissues and organs of children and adults. More than 100 different subtypes have been described, with a wide range of clinical manifestations, presentations, and histologies. Since the first classification in 1987, a number of new findings regarding the cellular origins, molecular pathology, and clinical features of histiocytic disorders have been identified. We propose herein a revision of the classification of histiocytoses based on histology, phenotype, molecular alterations, and clinical and imaging characteristics. This revised classification system consists of 5 groups of diseases: (1) Langerhans-related, (2) cutaneous and mucocutaneous, and (3) malignant histiocytoses as well as (4) Rosai-Dorfman disease and (5) hemophagocytic lymphohistiocytosis and macrophage activation syndrome. Herein, we provide guidelines and recommendations for diagnoses of these disorders.

Reduced-intensity conditioning significantly improves survival of patients with hemophagocytic lymphohistiocytosis undergoing allogeneic hematopoietic cell transplantation

Recent experience suggests that reduced-intensity conditioning (RIC) regimens can improve the outcomes of patients with hemophagocytic lymphohistiocytosis (HLH) undergoing allogeneic hematopoietic cell transplantation (HCT). However, studies directly comparing RIC to myeloablative conditioning (MAC) regimens are lacking. Forty patients with HLH underwent allogeneic HCT between 2003-2009 at Cincinnati Childrens Hospital. Fourteen patients received MAC consisting of busulfan, cyclophosphamide, and antithymocyte globulin plus or minus etoposide. Twenty-six patients received RIC consisting of fludarabine, melphalan, and alemtuzumab. All patients engrafted. Acute graft-versus-host disease grades II to III occurred in 14% of MAC patients and 8% of RIC patients (P = .3171). Posttransplantation mixed donor/recipient chimerism developed in 18% of MAC patients and 65% of RIC patients (P = .0110). The majority of patients with mixed chimerism received intervention with reduction of immune suppression plus or minus donor lymphocyte infusion or stem cell boost, which stabilized or increased donor contribution to hematopoiesis and prevented relapse of HLH in all but 1 patient. Grade II to III graft-versus-host disease occurred in 5 of 14 RIC patients after donor lymphocyte infusion. The overall estimated 3-year survival after HCT was 43% (confidence interval = ± 26%) for MAC patients and 92% (confidence interval = ± 11%) for RIC patients (P = .0001). We conclude that RIC significantly improves the outcome of patients with HLH undergoing allogeneic HCT.

Patients with LRBA deficiency show CTLA4 loss and immune dysregulation responsive to abatacept therapy

Trafficking from bedside to bench Typically in translational research, a discovery in cell or molecular biology is later exploited to improve patient care. Occasionally, information flows in the opposite direction. Lo et al. found that patients with an autoimmune disorder caused by deficiency of a protein called LRBA responded dramatically to the drug abatacept (see the Perspective by Sansom). Abatacept contains a segment of a potent inhibitory immune receptor, CTLA4. Experiments prompted by this observation revealed the relationship between the two proteins: LRBA controls the intracellular trafficking and degradation of CTLA4. This information may further improve patient care, because other clinically approved drugs have the desired mechanism of action with potentially fewer side effects. Science, this issue p. 436; see also p. 377 A rare autoimmune disorder is caused by aberrant degradation of a potent inhibitory immune receptor. [Also see Perspective by Sansom] Mutations in the LRBA gene (encoding the lipopolysaccharide-responsive and beige-like anchor protein) cause a syndrome of autoimmunity, lymphoproliferation, and humoral immune deficiency. The biological role of LRBA in immunologic disease is unknown. We found that patients with LRBA deficiency manifested a dramatic and sustained improvement in response to abatacept, a CTLA4 (cytotoxic T lymphocyte antigen-4)–immunoglobulin fusion drug. Clinical responses and homology of LRBA to proteins controlling intracellular trafficking led us to hypothesize that it regulates CTLA4, a potent inhibitory immune receptor. We found that LRBA colocalized with CTLA4 in endosomal vesicles and that LRBA deficiency or knockdown increased CTLA4 turnover, which resulted in reduced levels of CTLA4 protein in FoxP3+ regulatory and activated conventional T cells. In LRBA-deficient cells, inhibition of lysosome degradation with chloroquine prevented CTLA4 loss. These findings elucidate a mechanism for CTLA4 trafficking and control of immune responses and suggest therapies for diseases involving the CTLA4 pathway.

XIAP deficiency: a unique primary immunodeficiency best classified as X-linked familial hemophagocytic lymphohistiocytosis and not as X-linked lymphoproliferative disease

X-linked inhibitor of apoptosis (XIAP) deficiency, caused by BIRC4 mutations, is described to cause X-linked lymphoproliferative disease (XLP) phenotypes. However, compared with XLP caused by SLAM-Associated Protein deficiency (SH2D1A mutation), XIAP deficiency was originally observed to be associated with a high incidence of hemophagocytic lymphohistiocytosis (HLH) and a lack of lymphoma, suggesting that classification of XIAP deficiency as a cause of XLP may not be entirely accurate. To further characterize XIAP deficiency, we reviewed our experience with 10 patients from 8 unrelated families with BIRC4 mutations. Nine of 10 patients developed HLH by 8 years of age. Most patients presented in infancy, and recurrent HLH was common. There were no cases of lymphoma. Lymphocyte defects thought to contribute to HLH development in SLAM-Associated Protein deficiency were not observed in XIAP deficiency. We conclude that XIAP deficiency is a unique primary immunodeficiency that is more appropriately classified as X-linked familial hemophagocytic lymphohistiocytosis.

Salvage therapy of refractory hemophagocytic lymphohistiocytosis with alemtuzumab

Hemophagocytic lymphohistiocytosis (HLH) is a life‐threatening hyperinflammatory syndrome that remains difficult to treat. Even with current standard HLH therapy, only approximately half of patients will experience complete resolution of disease, and early mortality remains a significant problem. Salvage therapies have been described only in limited case reports, and there are no large studies of second‐line therapies.

Hemophagocytosis causes a consumptive anemia of inflammation

IFN-γ stimulates blood-eating macrophages (hemophagocytes) by acting directly on macrophages to promote phagocytosis and uptake of blood cells.

Bim mediates apoptosis of CD127lo effector T cells and limits T cell memory

Following an acute T cell response, most activated effector cells die, while some survive and become memory cells. The pro‐apoptotic Bcl‐2 family member, Bcl‐2 interacting mediator of death (Bim) is critical for eliminating most effector T cells, while expression of CD127 (IL‐7Rα) has been proposed to mark effector cells destined to become memory cells. Here, we examined the effects of Bim on the death of effector T cells in relationship to CD127 expression and on development of T cell memory following lymphocytic choriomeningitis virus (LCMV) infection. We found that large numbers of CD127lo LCMV‐specific CD4+ and CD8+ T cells were lost in wild‐type mice, but were spared in Bim–/– mice. Further, while the numbers of CD127hi T cells declined only slightly during contraction of the response in wild‐type mice, they increased significantly in Bim–/– mice due to re‐expression of CD127 on CD127lo T cells that had avoided apoptosis. Functional memory T cells were significantly increased in Bim–/– mice; however, they underwent a slow attrition due to decreased proliferative renewal. Taken together, these data suggest that the absence of Bim‐mediated death of LCMV‐specific CD4+ and CD8+ T cells in vivo can increase T cell memory, but other homeostatic mechanisms control the long‐term maintenance of memory cells.