Clarified that there needs to be a serious safety risk in order to have the participant discontinued. Updated exclusion criteria and schedule of activities to align with ARGX-113-1705. For participant safety, allowed vaccines to be administered according to common clinical practice and reduce the risk of confusing vaccination-related AEs (such as fever) with infusion-related AEs. Clarified that participants should not start treatment with a new standard of care. Clarified that in Quantitative Myasthenia Gravis evaluation, the rater can be a trained person instead of a physician. Updated criteria for AE of special interest and clarified that all SAEs will be followed up until resolution. Updated ethical conduct to align with protocol of ARGX-113-1704 The Netherlands-specific amendment version 1.1. upon request of the Ethics Committee of The Netherlands.

An additional 2 years (defined as part B) were added to the study to provide participants uninterrupted access to EFG until it was available either commercially or through another participant program. Redefined endpoint definitions. Changes in methodology and investigational plan. Endpoints were streamlined to reflect what would be summarized and labels added to clarify what would be analyzed in Part A and Part B of the trial. Corrected to reflect that changes from the treatment period baseline of the first cycle would be summarized (instead of changes from study entry baseline) as participants might start the study with an intertreatment period. Modified the endpoint definition and clarified tertiary endpoints. Given the long-time frame of the extension and the option of unscheduled visits being carried out at the request of the investigator, the more flexible option of working with a local laboratory was chosen over the central laboratory structure.

Updated benefit-risk assessment based on emerging data and consistency with investigator brochure version 9.0. Clarified that participants who completed >=1 cycle of treatment and >=1 year of ARGX-113-1705 and had started Part B were given the option to enroll in ARGX-113-2002 to receive EFG co-formulated with recombinant human hyaluronidase PH20 subcutaneously. Provided end of trial instructions. Exclusion criteria removed. Guidance on contraception was updated following results of nonclinical reproductive toxicity studies. Instructions were added to collect vaccination history. The ECG assessment was added to Part B to comply with the data safety monitoring board recommendation to monitor QT interval corrected by Fridericia abnormalities that could arise due to the accumulation of EFG. An additional change was made to allow for testing of participants who exhibited symptoms of Coronavirus disease-2019 (COVID-19) infection. Even in countries where COVID-19 safety measures were stopped according to local regulations, COVID-19 testing was continued and the results were sent to the sponsor for filing.