Evaluating the Pharmacokinetics, Pharmacodynamics, and Safety of Efgartigimod Administered Intravenously in Children With Generalized Myasthenia Gravis
Evaluating the Pharmacokinetics, Pharmacodynamics, and Safety of Efgartigimod Administered Intravenously in Children With Generalized Myasthenia Gravis
The purpose of this trial is to investigate the PK, PD, safety, and activity of efgartigimod
 IV in children from 2 to less than 18 years of age with gMG.

 Trial details include:

 -  The maximum trial duration for each individual participant will be approximately 28
 weeks

 -  The treatment duration will be 8 weeks for the dose-confirmatory part (Part A) and 18
 weeks for the treatment response-confirmatory part (Part B)
Inclusion Criteria:

 1. Ability of the participant and/or his/her legally authorized representative to
 understand the requirements of the trial and provide written informed consent/assent,
 if applicable (including consent/assent for the use and disclosure of research-related
 health information), willingness and ability to comply with the trial protocol
 procedures (including attending the required trial visits).

 2. Male or female participants between 2 to less than 18 years of age at the time of
 providing informed consent/assent. Age groups are enrolled in a staggered fashion
 respectively: 6 participants in the 12 to less than 18 years of age group followed by
 6 participants in the 2 to less than 12 years of age group at the time of providing
 informed consent/assent.

 3. Diagnosed with Generalized Myasthenia Gravis (gMG) with confirmed documentation

 4. Meeting the clinical criteria as defined by the Myasthenia Gravis Foundation of
 America (MGFA) class II, III, and IVa.

 5. Eligible participants should have an unsatisfactory response (efficacy and/or safety)
 to immunosuppressants, steroids or acetylcholinesterase (AChE) inhibitors and should
 be on stable concomitant Generalized Myasthenia Gravis (gMG) therapy of adequate
 duration before screening.

 6. Positive serologic test for acetylcholine receptor (anti-AChR) antibodies at screening
 (for younger participants (<15kg) historical values can be used).

 7. Contraceptive use should be consistent with local regulations regarding the methods of
 contraception for those participating in clinical trials.

 1. Male participants: Male participants must agree to not donate sperm from the time
 the informed consent form was signed until the end of the trial.

 2. Female participants: Female adolescents of childbearing potential must have a
 negative serum pregnancy test at screening and a negative urine pregnancy test at
 baseline before investigational medicinal product (IMP) can be administered.

 Exclusion Criteria:

 1. Participants with Myasthenia Gravis Foundation of America (MGFA) class I, IVb, and V.

 2. Female adolescents of childbearing potential (FAOCBP): Pregnancy or lactation, or the
 participant intends to become pregnant during the trial or within 90 days after the
 last dose of investigational medicinal product (IMP).

 3. Has any of the following medical conditions:

 1. Clinically significant uncontrolled active or chronic bacterial, viral, or fungal
 infection at screening.

 2. Any other known autoimmune disease that, in the opinion of the investigator,
 would interfere with an accurate assessment of clinical symptoms of myasthenia
 gravis or put the participant at undue risk.

 3. History of malignancy unless deemed cured by adequate treatment with no evidence
 of recurrence for ≥3 years before the first administration of the investigational
 medicinal product (IMP). Participants with the following cancers can be included
 at any time:

 -  Adequately treated basal cell or squamous cell skin cancer

 -  Carcinoma in situ of the cervix

 -  Carcinoma in situ of the breast

 -  Incidental histological findings of prostate cancer (TNM Classification of
 Malignant Tumors stage T1a or T1b)

 4. Clinical evidence of other significant serious diseases, or have had a recent
 major surgery, or who have any other condition that, in the opinion of the
 investigator, could confound the results of the trial or put the participant at
 undue risk

 4. Worsening muscle weakness secondary to concurrent infections or medications
 (aminoglycosides, fluoro-quinolones, beta-blockers, etc).

 5. A documented lack of clinical response to plasma exchange (PLEX).

 6. Received a live or live-attenuated vaccine fewer than 28 days before screening.
 Receiving an inactivated, subunit, polysaccharide, or conjugate vaccine any time
 before screening is not exclusionary.

 7. Received a thymectomy <3 months before screening or 1 is planned to be performed
 during the trial period.

 8. The following results from these diagnostic assessments will be considered
 exclusionary:

 1. Positive serum test at screening for an active viral infection with any of the
 following conditions:

 -  Hepatitis B virus (HBV) that is indicative of an acute or chronic infection

 -  Hepatitis C virus (HCV) based on HCV antibody assay

 -  Human immunodeficiency virus (HIV) associated with a CD4 count <200
 cells/mm3 with an acquired immunodeficiency syndrome (AIDS)-defining
 condition, such as: Cytomegalovirus retinitis with loss of vision,
 Pneumocystis jiroveci pneumonia, chronic intestinal cryptosporidiosis,
 HIV-related encephalopathy, Mycobacterium tuberculosis (pulmonary or
 extrapulmonary), or invasive cervical cancer

 2. Positive nasopharyngeal swab polymerase chain reaction (PCR) test for severe
 acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

 9. Using the following prior or concomitant therapies:

 1. Use of an investigational product within 3 months or 5 half-lives (whichever is
 longer) before the first dose of the investigational medicinal product (IMP).

 2. Use of any monoclonal antibody within the 6 months before the first dose of the
 investigational medicinal product (IMP).

 3. Use of intravenous immunoglobulin (IVIg), administered subcutaneously or
 intramuscularly, or Plasma exchange (PLEX) within 4 weeks before screening.

 10. Total immunoglobulin G (IgG) levels <6 g/L at screening.

 11. A known hypersensitivity reaction to efgartigimod or any of its excipients.