Cellular and transcriptional impacts of Janus kinase and/or IFN-gamma inhibition in a mouse model of primary hemophagocytic lymphohistiocytosis

Clinical Characteristics and Treatment of Familial Hemophagocytic Lymphohistiocytosis

Familial hemophagocytic lymphohistiocytosis (fHLH) comprises a group of autosomal recessive disorders characterized by germline loss-of-function variants that negatively impact lymphocyte cytotoxicity. These disorders exhibit variable clinical presentations, most often in association with severe hyperinflammation. fHLH is diagnosed through clinical and laboratory assessments as well as genetic testing and immunologic assays. In the absence of therapy to control the hyperactive immune system, fHLH is generally fatal. Treatment has historically taken the form of cytotoxic chemotherapy and/or immunosuppressive therapy, although targeted inhibitors of inflammatory cytokines and their downstream signaling are increasingly being utilized. Definitive treatment requires allogeneic hematopoietic cell transplantation.

CXCL9 and IL-18: potential biomarkers for efficacy evaluation in refractory hemophagocytic lymphohistiocytosis treated with RED (ruxolitinib, emapalumab and dexamethasone)

Hemophagocytic lymphohistiocytosis (HLH) is a severe inflammatory disorder characterized by excessive cytokine release. More than 30% of HLH cases are refractory to frontline therapy. Unfortunately, there is no universally accepted second-line regimen, and about 30% of patients fail to respond to current salvage treatments. Moreover, evidence guiding alternative therapies and the optimal timing for switching to new treatments in refractory patients is limited. This study retrospectively analyzed the efficacy and safety of the RED regimen (ruxolitinib, emapalumab, and dexamethasone) in 15 refractory HLH patients who had failed at least two previous salvage therapies. Overall, eight (53.3%) patients achieved partial remission, and four of those eight proceeded to hematopoietic stem cell transplantation (HSCT). Notably, pre-RED levels of C-X-C motif chemokine 9 (CXCL9) and interleukin-18 (IL-18) were significantly higher in patients who later responded to RED, suggesting that these biomarkers may predict a better response. We also observed that, for eight partial-remission patients, hemoglobin, fibrinogen, aspartate aminotransferase, calcium, and CXCL9 levels tracked well with early therapeutic responses (one to two weeks). No grade 3 or higher adverse effects were linked to the RED regimen. This comprehensive investigation of the RED approach in HLH, although small in sample size, supports the possibility that RED can serve as an effective and relatively safe salvage therapy for refractory HLH.

Pathogenicity of tick-derived lymphocytic choriomeningitis virus in BALB/c mice

BACKGROUND

Lymphocytic choriomeningitis virus (LCMV) is a zoonotic pathogen primarily transmitted by rodents. Recently, LCMV has been detected in ticks from northeastern China; however, the pathogenicity of this virus in murine models remains to be elucidated.

RESULTS

Here, we examined the tick-derived LCMV strain JX14 by inoculating BALB/c mice with 3.5 × 105 pfu of virus. The mice infected with LCMV displayed clinical manifestations including unkempt fur, anorexia, depression, and oliguria, which subsequently resolved by 10 days post infection (dpi) leading to survival of the infection. During the early phase of infection, low viral titers were detected in throat and anal swabs. The excreted virions demonstrated proliferation in Vero cells and were capable of inducing infection in mock-infected mice. Viral RNA was detected in the blood and organs, with detectable levels persisting for up to six months specifically in the heart. A total of 16 amino acid substitutions were identified in the L, Z, and GPC proteins between the original JX14 strain and the strain obtained after six months of infection in BALB/c mice. Pathological lesions were identified in most organs within 5 dpi except for the kidneys and testicles. Interferon gamma (IFN-γ) level was significantly elevated during the early stage of infection and returned to baseline levels within 10 days.

CONCLUSIONS

This study furnishes significant insights into the pathogenic traits of the tick-derived LCMV strain JX14, thereby potentially providing a valuable in vivo research model for examining the immunological responses elicited by chronic viral infections.

Hemophagocytic lymphohistiocytosis: current treatment advances, emerging targeted therapy and underlying mechanisms

Hemophagocytic lymphohistiocytosis (HLH) is a rapidly progressing, life-threatening syndrome characterized by excessive immune activation, often presenting as a complex cytokine storm. This hyperactive immune response can lead to multi-organ failure and systemic damage, resulting in an extremely short survival period if left untreated. Over the past decades, although HLH has garnered increasing attention from researchers, there have been few advancements in its treatment. The cytokine storm plays a crucial role in the treatment of HLH. Investigating the detailed mechanisms behind cytokine storms offers insights into targeted therapeutic approaches, potentially aiding in early intervention and improving the clinical outcome of HLH patients. To date, there is only one targeted therapy, emapalumab targeting interferon-γ, that has gained approval for primary HLH. This review aims to summarize the current treatment advances, emerging targeted therapeutics and underlying mechanisms of HLH, highlighting its newly discovered targets potentially involved in cytokine storms, which are expected to drive the development of novel treatments and offer fresh perspectives for future studies. Besides, multi-targeted combination therapy may be essential for disease control, but further trials are required to determine the optimal treatment mode for HLH.

Differential effects of itacitinib, fedratinib, and ruxolitinib in mouse models of hemophagocytic lymphohistiocytosis

ABSTRACT

Hemophagocytic lymphohistiocytosis (HLH) comprises a severe hyperinflammatory phenotype driven by the overproduction of cytokines, many of which signal via the JAK/STAT pathway. Indeed, the JAK1/2 inhibitor ruxolitinib has demonstrated efficacy in preclinical studies and early-phase clinical trials in HLH. Nevertheless, concerns remain for ruxolitinib-induced cytopenias, which are postulated to result from the blockade of JAK2-dependent hematopoietic growth factors. To explore the therapeutic effects of selective JAK inhibition in mouse models of HLH, we carried out studies incorporating the JAK1 inhibitor itacitinib, JAK2 inhibitor fedratinib, and JAK1/2 inhibitor ruxolitinib. All 3 drugs were well-tolerated and at the doses tested, they suppressed interferon-gamma (IFN-γ)-induced STAT1 phosphorylation in vitro and in vivo. Itacitinib, but not fedratinib, significantly improved survival and clinical scores in CpG-induced secondary HLH. Conversely, in primary HLH, in which perforin-deficient (Prf1-/-) mice are infected with lymphocytic choriomeningitis virus (LCMV), itacitinib, and fedratinib performed suboptimally. Ruxolitinib demonstrated excellent clinical efficacy in both HLH models. RNA-sequencing of splenocytes from LCMV-infected Prf1-/- mice revealed that itacitinib targeted inflammatory and metabolic pathway genes in CD8 T cells, whereas fedratinib targeted genes regulating cell proliferation and metabolism. In monocytes, neither drug conferred major transcriptional impacts. Consistent with its superior clinical effects, ruxolitinib exerted the greatest transcriptional changes in CD8 T cells and monocytes, targeting more genes across several biologic pathways, most notably JAK-dependent proinflammatory signaling. We conclude that JAK1 inhibition is sufficient to curtail CpG-induced disease, but combined inhibition of JAK1 and JAK2 is needed to best control LCMV-induced immunopathology.