The purpose of this study is to assess the safety, tolerability, and efficacy of efgartigimod PH20 SC given by a prefilled syringe in participants with Antibody-Mediated Rejection (AMR) after kidney transplantation.

After a screening period of up to 6 weeks, eligible participants will be randomized in a 1:1:1 ratio. The study drug will be administered subcutaneously while patients remain on their standard background immunosuppression therapy (tacrolimus, mycophenolate mofetil, steroids) during the treatment period (48 weeks). At the end of the treatment period, the participants will enter an observational/follow-up period (approximately 24 weeks). The participants will be in the study for up to 78 weeks.

Inclusion Criteria:

• The participant is within the ages of 18 and 80 years old

• The participant had a kidney transplant (living or deceased donor) at least 6 months before the study

• The participant has received a diagnosis of active or chronic active antibody-mediated rejection (AMR) with detectable donor-specific antibodies at time of the study

• A participant may be allowed into the study if they receive the following medications:

  1. Received mycophenolate mofetil for at least 20 weeks before the study
  2. Has remained on a stable dose of mycophenolate mofetil and tacrolimus for at least 4 weeks before being allowed to participate in the study
  3. Has remained on tacrolimus doses between 5 to 10 ng/mL at least 4 weeks before being allowed to participate in the study
  4. Steroid dose was between 0 to 10 mg per day of prednisone (or dose equivalent) for at least 4 weeks before being allowed to participate in the study

Exclusion Criteria:

• Confirmed T-cell or mixed rejection at time of the study
• Recent change in immunosuppressive therapy agents
• Any other medical condition that, in the investigator's opinion, would interfere with the results of the study or put the participant at undue risk
• Pregnant or lactating state or intention to become pregnant during the study

The complete list of criteria can be found in the protocol