Ruxolitinib treatment permits lower cumulative glucocorticoid dosing in children with secondary hemophagocytic lymphohistiocytosis

Hemophagocytic syndrome is also known as hemophagocytic lymphohistiocytosis (HLH). This rare life-threatening syndrome is characterized by excessive proliferation and activation of lymphocytes caused by cytokine storms and severe systemic inflammatory responses. According to the accepted doctrine, the pathogenesis of HLH is closely associated with the “cytokine storm” [1]. Depending on the etiology, there are two forms of HLH: primary autosomal recessive inheritance, also known as familial hemophagocytic lymphohistiocytosis, and secondary HLH, which develops because of strong immune activation. Primary HLH is mostly caused by genetic defects leading to immune system dysfunction. Infection, connective tissue disease, and malignancy are considered common causes of secondary HLH [2‐4]. Epstein-Barr virus (EBV), a DNA virus and member of the Herpesviridae family, has been consistently associated with HLH [5‐15].

HLH in children is a rare disease with a high fatality rate. Studies have shown that most cytokines related to HLH are activated through activation of the Janus Kinase (JAK)/signal transducer and activator of transcription signaling pathway, which not only regulates the biological activity of cytokines, but also affects the differentiation of primary T cells into T helper (TH) cell families, TH1, TH2, TH17, and regulatory T cells [16].

The above clinical and laboratory findings are related to the pathophysiology of HLH. High interleukin levels cause fever. Elevated ferritin > 10,000 μg/L has been demonstrated to be 90% sensitive and 96% specific for HLH [17‐20]. Activation of lymphocytes can result in high concentrations of soluble IL-2 receptor [21].

Most clinicians still adopt the HLH-04 protocol recommended by the Histiocyte Society for the treatment of HLH [22]. Conventional treatment options typically include three phases of induction therapy, maintenance therapy, and/or hematopoietic stem cell transplantation. The drugs for HLH include dexamethasone, cyclosporine A, and etoposide. However, a multi-center study in 2016 revealed no significant benefit from cyclosporine and intrathecal injections, and macrophage activation syndrome secondary to connective tissue disease is not always treated with the HLH-04 regimen. The five-year survival rate for secondary HLH in adults worldwide is approximately 54% and the survival rate reported in China is even lower, ranging from 31.7–56.1% [23, 24]. Hence, less toxic, more effective, and better targeted immunosuppressive treatments in HLH are urgently needed.

In recent years, JAK inhibitors have been the focus of research on new small molecule targeted therapies and can be used for the treatment of inflammatory diseases such as hematological diseases, tumors, rheumatoid arthritis, ulcerative colitis, and other autoimmune diseases [25]. Ruxolitinib is a Janus-associated kinase 1/2 (JAK1/2) inhibitor that impedes downstream signaling pathways of cytokines such as interferon-γ, IL-2, and IL-6 to reduce inflammatory responses triggered by these cytokines, which play important roles in HLH.

Treatment of children with secondary HLH is an off-label use for ruxolitinib because it is only used for myelofibrosis [26], polycythemia [27], and graft-versus-host disease (GVHD) [28‐30]. But ruxolitinib was found to control inflammatory storms and prolong survival in secondary HLH model mice; this treatment was also effective in 10 cases of HLH [31‐35], including one child from the USA [33].

Herein, we present 11 cases of children treated with ruxolitinib. We compared the effects of ruxolitinib administration in children with HLH to the effects of conventional therapy in a control group of children with HLH; both groups were followed up for 2–2.5 years.

In this study, we found that administration of ruxolitinib to children with HLH was effective for controlling their body temperature, improving inflammatory indices (ferritin, IL-2R), and ameliorating symptoms of CNS involvement. Combining glucocorticoids and antiviral agents resulted in the resolution of viral infection and reduction in the dose of glucocorticoids.

Hermans et al. found that administration of JAK inhibitors significantly inhibited the degranulation of mast cells and reduced the production of cytokines in an in vitro study of lymphocytes [39]. Ruxolitinib also reversibly improved the killing and degranulation of NK cells and ameliorated organ damage in HLH animal models [40, 41]. In 2016, Das et al. used lymphocytic choriomeningitis virus to infect perforin-deficient mice and construct a model of secondary HLH. A large dose of ruxolitinib (90 mg/kg) not only improved the disease symptoms and decreased cytokine levels in HLH model mice, but also increased the survival rates in mice [42, 43]. A small dose of ruxolitinib (1 mg/kg) also significantly improved long-term survival and clinical symptoms and promoted liver tissue regeneration [2]. Subsequently, a case of an 11-year-old child with refractory HLH who was treated with a combination of dexamethasone, etoposide, ruxolitinib (2.5 mg), and alemtuzumab was reported. Inflammatory factor levels rapidly decreased, organ function was restored, and no HLH relapse was observed even after etoposide treatment was discontinued [33]. Ruxolitinib was used as first-line treatment with dexamethasone in a 71-year-old patient with HLH. Administration of ruxolitinib (10 mg/dose, twice daily) was started on the 8th day of hospitalization; the patient’s condition and laboratory values improved on the 15th day of hospitalization [34]. A 38-year-old patient was treated with dexamethasone, immunoglobulin, etoposide, and rituximab; after administration of ruxolitinib (20 mg/dose, twice daily), there was an improvement in the patient’s phagocytic indicators such as serum ferritin, lactate dehydrogenase, and fibrinogen levels, but the patient eventually died of intracranial bleeding and multiple organ failure [35].

In this study, refractory cases of HLH were treated with ruxolitinib, resulting in the regulation of body temperature and inflammatory factors and improvement of CNS involvement. In addition, administration of ruxolitinib reduced the glucocorticoid dose, which is important for the normal growth and development of children.

Five cases (R1–R5) in group R had recurrent fever and showed no improvement in clinical features or inflammatory indicators such as IL-2R, ferritin, and C-reactive protein levels despite hormonal, immunosuppressive, and immunoglobulin therapies; hence, ruxolitinib was added to their treatment regimen. Their body temperature subsequently dropped rapidly and inflammatory indicators improved, demonstrating that ruxolitinib controlled the body temperature and inhibited the inflammatory response.

Two cases (R6, R7) with CNS involvement showed no improvement in neuropsychiatric symptoms after termination of the HLH-04 regimen, but gradually recovered with administration of ruxolitinib, suggesting a positive effect with CNS involvement. However, other studies have shown unsatisfactory therapeutic effects of ruxolitinib in patients with HLH combined with CNS involvement, attributing the lack of efficacy to its large molecular weight which prevents its penetration across the blood-brain barrier to act on the CNS [44]. This contradictory evidence warrants further study.

Four cases (R8–R11) were treated with ruxolitinib directly without using the HLH-04 regimen. One patient was diagnosed with HLH and HBV (published in the Journal of Pediatrics). As immunosuppressants and glucocorticoids may aggravate HBV infection, the child was treated with ruxolitinib combined with antiviral therapy using entecavir. All disease indicators improved significantly. During follow-up after more than 1 year, the body temperature of the child remained stable, and HBV-DNA was undetectable because of the treatment with antiviral drugs. This is the first study to use ruxolitinib alone to treat HLH. The other three children also had normal body temperature after treatment with ruxolitinib, and all indicators showed improvement.

Compared with group C, the dosage of glucocorticoids in R group children was apparently reduced throughout the treatment, suggesting that ruxolitinib can reduce the dosage of glucocorticoids or even replace glucocorticoid therapy, thereby reducing or avoiding glucocorticoid-related adverse reactions.

In children with co-infections, including EBV and HBV, there was no exacerbation of existing infections during ruxolitinib administration combined with antiviral therapy.

Possible side effects in children include oral ulcer, sweating, nausea, gastritis decreased appetite, thrombocytopenia, anemia, elevated liver enzymes and bilirubin, and hypertriglyceridemia. During the 2–2.5 years of follow-up, no children in group R had obvious adverse reactions. One patient developed fever again following discontinuation of ruxolitinib and had joint swelling and pain. That patient was diagnosed with juvenile idiopathic arthritis, and the patient’s condition improved after treatment with tocilizumab.

To date, there have been a few reports of individual cases being treated with ruxolitinib. In this study, we present 11 cases of children treated with ruxolitinib, demonstrating that ruxolitinib might be effective for treating HLH and is convenient to administer. It may be used as a first-line treatment for HLH with glucocorticoid reduction. Treatment with ruxolitinib also improved the symptoms of inflammatory factors and CNS involvement in refractory HLH. A limitation of this study was retrospective, and the sample size was small. In future, prospective studies with large sample cohort should be used to confirm the safety, optimal dosage, treatment duration, withdrawal criteria, long-term effects, and efficacy of ruxolitinib in HLH caused by different etiologies. The findings of this study indicate that ruxolitinib permits lower cumulative glucocorticoid dosing, partially replaces glucocorticoids and becomes a potential first-line drug for the treatment of HLH, which is important for the normal growth and development of children.