Children with Acute Severe Hepatitis of Undetermined Etiology Have a Systemic T Cell Activation and Interferon Gamma (Ifn-G) Activity Reminiscent of Hemophagocytic Histiocytosis: A Potential Role for T Cell and Ifn-G Directed Therapies

ABSTRACT

Background: Pediatric acute liver failure (PALF) cause is indeterminate in 30-50% of cases (iPALF). Children with acute severe hepatitis of unknown etiology (SH-u) may evolve to iPALF. Hemophagocytic Lymphohistiocytosis (HLH), a hyper-inflammatory state with marked T-cell activation (ACT) often involves the liver. SH-u evolving to iPALF could have hyperinflammatory immune signatures before fulfilling PALF criteria, and may overlap with HLH. We compared immune dysregulation signatures of SH-u, HLH, known PALF, and healthy controls (HC). Method(s) From 2019-2021, 15 patients (pts) hospitalized with SH-u and 7 pts with known PALF were prospectively enrolled. Age dependent standard diagnostic studies were performed. SH-u was defined as ALT>500, INR <2, and no hepatic encephalopathy. HLH enrollees met 2004 criteria. High dimension T-cell immunophenotyping, cytokine and chemokine profiling was done for SH-u, HLH (n=5), and HC (n=16) blood samples. T cell ACT was identified by co-expression of surface ACT markers HLA-DR and CD38. CD8 effector memory (EM) ACT of >9% identified pts with significant T cell ACT vs HC. Normally distributed data were compared by a two-tailed t-test or an ordinary One-Way Anova test with Turkey's multiple comparison test. Non-normally distributed data were compared by the Mann-Whitney test or KruskalWallis test with Dunn's multiple comparisons test. P values <0.05 were significant. Result(s) Pts ranged from 4days to 19years old. No age/sex differences existed between groups. One SH-u pt had a prior COVID infection. No pts met MIS-c criteria. Two SH-u pts ultimately met PALF criteria (INR>2). All pts with SH-u had higher CD8 EM T-cell ACT (mean +/- SEM = 43.7+/-6.3%;range 9.2 to 81.3%) than HC (2.9+/-0.5%) or PALF (4.0+/-0.9%);p<0.0001. T-cell ACT in SH-u was < HLH (90.3+/-2.7%;p<0.0001;Figure 1). T cell ACT was noted in the CD4 compartment, but CD8 compartment ACT was much > CD4. SH-u CD4/CD8 ratio was reduced compared to PALF pts. Though T cell ACT was greater in SH-u vs PALF, ferritin was lower in SH-u compared to PALF (1212+/-568 vs. 39517+/-32149;p<0.01) and very significantly < HLH (32415 +/-14845;p =0.002). Ferritin was <500 mg/L in 47% of SH-u pts. Despite overlapping T cell ACT with HLH, only 2 pts SH-u pts had cytopenia. IFN-gamma driven chemokines, CXCL9 and CXCL10, were elevated in SH-u, compared to HCs but similar to HLH pts. As a proof of concept, 2 patients with SH-u were treated with Emapalumab (an IFN-gamma blocking antibody) along with other immune modulators resulting in complete liver and immune function recovery. Conclusion(s) SH-u is associated with T-cell ACT. HLH and SH-u with T cell ACT have similarly increased IFN-gamma activity. Ferritin, however, may not be a reliable screening for SH-u patients with significant T cell ACT. If validated in larger studies of SH-u, the findings suggest a role for IFN-gamma blocking agents in a subgroup of SH-u prior to the development of PALF or possible bone marrow failure.