TReatment for ImmUne Mediated PathopHysiology

Inclusion Criteria: 1. Patient with liver injury of ≤ 6 weeks duration resulting in an international normalization ratio (INR) of ≥ 1.5 or \< 2.0 (not corrected by vitamin K) with evidence of hepatic encephalopathy (HE), INR of ≥ 1.5 or \< 2.0 for at least 7 days duration without evidence of HE or INR ≥ 2.0 without evidence of HE. 2. Age is greater than or equal to 1 year and less than 18 years of age. 3. Patient or their legally authorized representative(s) (LAR) must consent (and assent, if applicable) to be in the study and must have signed and dated an approved informed consent form which conforms to federal and institutional guidelines. 4. Females of reproductive potential should not plan on conceiving children during the study and must agree to use a medically accepted form of contraception. Exclusion Criteria: 1. Evidence of active infection with Hepatitis A, B, C, E or evidence of acute herpes simplex virus (HSV) or adenovirus infection 2. Travel within the past 3 months to an area highly endemic for Hepatitis E 3. Diagnosis of hemophagocytic lymphohistiocytosis (HLH) Note: Patients with a history of consanguinity and/or central nervous system (CNS) dysfunction that is exaggerated compared to the degree of liver dysfunction (as judged by the site investigator) will not be enrolled until results of rapid genetic testing are available. Turn-around time for genetic testing results is estimated to be 72-96 hours. 4. Aplastic anemia as defined by standardized criteria \[1\] diagnosed prior to enrollment 5. Diagnosis of autoimmune Hepatitis (AIH) 6. Diagnosis of acute Wilson disease 7. Diagnosis of inborn error of metabolism Note: Suspicion of metabolic disease is not an exclusion for entry into the Trial. 8. Diagnosis of acute drug or toxin-induced liver injury 9. History of recreational drug use within the past 4 weeks 10. Therapy with an immunosuppressive agent, including chemotherapy, biological therapies or an experimental drug or device within the past 6 weeks 11. Liver injury due to ischemia 12. Liver dysfunction diagnosed more than 6 weeks prior to screening 13. History of allergy to horse dander 14. Sepsis 15. Imminent risk of death as judged by the clinical site investigator, including but not limited to; signs of cerebral herniation at the time of enrollment and presence of intractable arterial hypotension 16. Solid organ or stem cell transplant recipient 17. Pregnant or breast-feeding at the time of proposed study entry 18. Clinical AIDS or HIV positive 19. History of any form of malignant neoplasm and/or tumors treated within five years prior to study entry (other than non-melanoma skin cancer or in situ cervical cancer) or where there is current evidence of recurrent or metastatic disease 20. Received a live-virus vaccine within 4 weeks of study entry 21. Patients with positive respiratory secretion testing for respiratory viral infection including SARS-CoV-2, influenza and respiratory syncytial virus only if they also have declining respiratory function 22. Psychiatric or addictive disorders that would preclude obtaining informed consent/assent 23. Patient is unwilling or unable to adhere with study requirements and procedures 24. Currently receiving other experimental therapies