Randomized Stepped Wedge Study of Emapalumab in APECED Enteritis

* INCLUSION CRITERIA: 1. Participant must be able to understand and provide informed consent. 2. Aged \>= 2 to \<= 75 years. 3. Currently co-enrolled on NIH protocol 11-I-0187, "The Natural History and Pathogenesis of Human Fungal Infections." 4. Patients with APECED (genetic or clinical diagnosis) and enteritis (with APECED ES \> 50 at screening). 5. Duration of enteritis greater than 6 months. 6. Is naive or unresponsive to other treatments for enteritis. 7. Willingness to use acyclovir or valacyclovir prophylaxis for the prevention of herpes viral reactivation. 8. Willingness to use entecavir prophylaxis against hepatitis B virus reactivation, if applicable. 9. Vaccinations should be up to date in agreement with current Centers for Disease Control and Prevention immunization guidelines prior to start of emapalumab. 10. Proficient in written English. 11. Participants who can get pregnant or impregnate their partner must agree to use at least one highly effective method of contraception when engaging in sexual activities that can result in pregnancy, starting at screening until 12 weeks after the last dose. Highly effective contraceptive measures include: * Stable use of combined (estrogen- and progestogen-containing) hormonal contraception (oral, intravaginal, transdermal) or progestogen-only hormonal contraception (oral, injectable, implantable) starting 1 month prior to screening. * Intrauterine device (IUD); intrauterine hormone-releasing system. * Two barrier methods (e.g., condom with spermicide, diaphragm with spermicide, or cervical cap and spermicide). Internal and external condoms may not be used together. * Bilateral tubal ligation. Periodic abstinence (calendar, symptothermal, and post-ovulation methods), withdrawal (coitus interruptus), spermicides only, and lactational amenorrhea method are not acceptable methods of contraception. EXCLUSION CRITERIA: 1. Known history of hypersensitivity to emapalumab. 2. History of active intestinal disease other than enteritis such as inflammatory bowel disease. 3. Current or recent use of any investigational drug (within 3 months or 5 half-lives, whichever is longer, prior to screening). 4. Scheduled to participate in another clinical study involving an investigational drug during the course of this study. 5. History of alcohol or drug abuse within 6 months prior to screening. 6. Presence of one or more of the following clinically significant laboratory abnormalities: 1. Serum ALT \>= 3 times upper limit of normal (ULN). 2. Serum total bilirubin \>= 2 times ULN. 3. Serum creatinine \>= 2 times ULN. 7. Planned or anticipated major surgical procedure during the study. 8. Plans to receive any live or live attenuated vaccines within 1 month of the anticipated first dose of emapalumab. 9. Known or suspected immunodeficiency disorder besides APECED. 10. History of untreated invasive opportunistic infections (e.g., tuberculosis, non-tuberculous mycobacterial infections, histoplasmosis, listeriosis, coccidioidomycosis, pneumocystis pneumonia, aspergillosis) despite infection resolution or otherwise recurrent infections of abnormal frequency or prolonged infections suggesting an immune-compromised status as judged by the investigator. 11. Untreated latent tuberculosis infection. 12. Infection with HIV. 13. Untreated infection with hepatitis B or C. 14. History of serious bacterial infection within the last 3 months prior to screening, unless treated and resolved with antibiotics, or any chronic bacterial infection (e.g., chronic pyelonephritis, osteomyelitis). 15. Current pregnancy or breastfeeding. 16. Past or current medical problems or findings from physical examination, EKG, or laboratory testing that are not listed above, which, in the opinion of the investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or that may impact the quality or interpretation of the data obtained from the study.