A Phase 1, Randomized, Double Blinded, Placebo Controlled Study to Investigate the Safety, Tolerability, Pharmacokinetics, and Immunogenicity of Single and Multiple Ascending Doses of ARGX 119 in Healthy Participants

ARGX-119 is a new compound that may potentially be used for the treatment of
muscle control diseases such as congenital myasthenic syndrome. This type of
disease is caused by a defect in transmission of signals from nerve cells to
muscles. This can result in fluctuating muscle weakness of the arms/legs, eyes
or face and can be life threatening. Current treatments for muscle control
diseases are focused on treating the symptoms of the disease. ARGX-119 is being
developed to maintain and restore the signal transmission between nerve cells
and muscles and to possibly counteract the effects of the muscle control
diseases.

In this study we will investigate how safe the new compound ARGX-119 is and how
well it is tolerated when it is used by healthy subjects.

We also investigate how quickly and to what extent ARGX-119 is distributed and
eliminated from the body. In addition, we look at the effect of ARGX-119 on the
immune system. Furthermore, we will also look at the effect of specific markers
in the blood. This part of the study is mandatory.
We also look at the effect of the genetic information on the body*s response to
ARGX-119. This part of the study is not mandatory.
We compare the effects of ARGX-119 with the effects of a placebo.

ARGX-119 has not been administered to humans before. It has been extensively
tested in the laboratory and on animals.

In Part A In total the volunteer will visit the research center 11 times:
• once for the screening.
• once for stay in the research center. For the study it is necessary that the
volunteer stay in the research center for 1 period of 9 days (8 nights).
arrival Day -1 and departure on Day 8 of the study.
• eight times for short visits. After the stay in the research center there
will be 8 short visits to the research center. These short visits will take
place on Days 15, 22, 29, 36, 50, 64, 92 and 120.
• once for the follow-up visit. This follow-up visit will take place on Day 150.

In Part B in total the volunteer will visit the research center 13 times:
• once for the screening.
• three times for stays in the research center. For the study it is necessary
that the volunteer stay in the research center for 3 periods of 10, 3 and 9
days (9, 2 and 8 nights), respectively. Day 1 is the first day when you receive
the study compound. Departure of the research center on Days 9, 16 and 29 of
the study.
• eight times for short visits. After the stay in the research center there
will be 8 short visits to the research center. These short visits will take
place on Days 36, 43, 50, 57, 71, 99, 127 and 157.
• once for the follow-up visit. This follow-up visit will take place on Day
177.

Part A
The compound is given once on Day 1
in Groups 1 to 9 as an intravenous infusion for 1 hour: doses between 0.005
mg/kg and 15.0 mg/kg ARGX-119 or placebo
and in group 10 as an injection under the skin of 5.0 mg/kg ARGX-119 or placebo

Part B
The compound is given once weekly on four occasions: Day 1, 8, 15 and 22
as an intravenous infusion for 1 hour
Group 1: 0.3 mg/kg ARGX-119
Group 2: 0.9 mg/kg ARGX-119
Group 3: 2.5 mg/kg ARGX-119
Group 4: 5 mg/kg ARGX-119

Blood draw
Drawing blood may be painful or cause some bruising. The use of the indwelling
cannula can sometimes lead to inflammation, swelling, hardening of the vein,
blood clotting, and bleeding in the environment of the puncture site. In some
individuals, a blood draw can sometimes cause pallor, nausea, sweating, low
heart rate, or drop in blood pressure with dizziness or fainting.

In total, we will take about 212 mL in Part A and 282 mL in Part B of blood
from you from screening to follow-up. This amount does not cause any problems
in adults. To compare: a blood donation involves 500 mL of blood being taken
each time at once.

Heart tracing
To make a heart tracing, electrodes will be placed on the arms, chest and legs.
To monitor the electrical activity of the heart over a longer period,
electrodes will be placed on the chest and abdomen. Prolonged use of these
electrodes can cause skin irritation.

Coronavirus test
Samples for the coronavirus test will be taken from the back of your nose and
throat using swabs. Taking the samples only takes a few seconds, but can cause
discomfort and can give an unpleasant feeling. Taking a sample from the back of
the throat may cause the volunteer to gag. When the sample is taken from the
back of the nose, the volunteer may experience a stinging sensation and the
eyes may become watery.