Phase 1 Study of ART5803 Safety and PK After IVIG in Healthy Participants

Inclusion Criteria:

1. The participant must be willing and able to provide written, signed informed consentafter the nature of the study has been explained and prior to any research-relatedprocedures.

2. The participant is a male or female, 18 to 65 years of age (inclusive) at the timeof informed consent, and has a body mass index (BMI) between 18 and 32 kg/m2 (inclusive) and a weight not exceeding 100 kg.

3. The participant is healthy, as determined by medical history, physical examinations,and the clinical Investigator's judgment.

4. The participant must be willing and able to comply with all study procedures.

5. Sexually active female participants of childbearing potential and male participantswith female partner(s) of childbearing potential must be willing to use a highlyeffective method of contraception while participating in the study. Thecontraceptive methods used for male and female participants must be documented inthe source documents.

6. Female participants of childbearing potential must have a negative pregnancy test atScreening and be willing to have additional pregnancy tests during the study.Females considered not of childbearing potential include those who are surgicallysterile (surgical bilateral oophorectomy, bilateral salpingectomy, or hysterectomy)confirmed by medical history or are post-menopausal (i.e., no menstrual bleeding formore than 12 months without an alternative medical cause and confirmation with morethan 1 follicle-stimulating hormone measurement of at least > 40 IU/L [or higher perlocal institutional guidelines]).Women of non-childbearing potential are notrequired to use any contraceptive method.

7. Male participants with female partners of childbearing potential must agree to usehighly effective methods of contraception, from study drug administration until atleast 90 days after the last study drug administration.

8. Male participants must agree not to donate sperm, and female participants must agreenot to donate eggs for the duration of the study and until at least 90 days afterthe last study drug administration.

9. Participants must agree not to donate blood for at least 3 months after theend-of-study (EOS) visit.

Exclusion Criteria:

1. The participant is pregnant or breastfeeding at Screening or planning to becomepregnant (self or partner) at any time during the study.

2. The participant has used an investigational product or medical device within 30 daysof Screening or for significant illness, such as cardiovascular, neurologic,pulmonary, hepatic, renal, metabolic, gastrointestinal, urologic, immunologic,endocrine, or psychiatric disease or disorder, or other abnormality, which mayinterfere with the evaluation or administration of the study drug, interpretation ofparticipant safety or study results, or would make participation in the study anunacceptable risk including any significant acute or chronic medical condition. TheInvestigator is responsible for assessing the clinical significance of findings fromhealth assessments and evaluations; however, consultation with the medical monitormay be warranted.

3. Has a concurrent disease or condition that, in the view of the PrincipalInvestigator, places the participant at high risk of poor treatment compliance or ofnot completing the study, or would interfere with study participation or wouldaffect safety. Participants with fully resolved childhood asthma with noreoccurrences or hospitalizations remain eligible for participation.

4. The participant is a regular smoker (cigarettes, e-cigarettes, and vaping included),defined as smoking daily. Participants who are non-daily smokers (up to ≤5cigarettes per week [or vaping or e-cigarette equivalent]) are permitted toparticipate in the study and must agree to refrain from smoking during thein-patient stays.

5. The participant has a contraindication to undergo LP, including internationalnormalized ratio (INR) >1.4 or other coagulopathy, platelet cell count of <120,000/µL, infection at the desired LP site, current use of anti-coagulantmedication except for low dose acetylsalicylic acid, degenerative arthritis, spinalscoliosis, back surgery, suspected increased intracranial pressure on history orneurologic examination, non-communicating hydrocephalus or intracranial mass, orprior history of spinal mass or trauma.

6. The participant has a severe drug allergic history or anaphylaxis to 2 or more foodproducts or medicines (including known sensitivity to acetaminophen/paracetamol,diphenhydramine or equivalent antihistamine, methylprednisolone or equivalentglucocorticoid, or lidocaine).

7. The participant has a known history of allergy or reaction to any component of theinvestigational agent formulation or IVIG or any of its components, or a history ofanaphylaxis or severe systemic reaction to blood products or following any biologictherapy.

8. The participant has a history of alcohol abuse or drug addiction in the past 12months.

9. The participant has undergone significant trauma or major surgery within 4 weeks ofScreening.

10. The participant has had a vaccination with live virus, attenuated live virus, or anylive viral components within 2 weeks prior to study drug administration or isplanning to receive these vaccines at any time during the study and up to 8 weeksfollowing the last study drug administration.

11. The participant has ANY of the following abnormalities in clinical laboratory testsat Screening, as assessed by the study-specific laboratory and confirmed by a singlerepeat if deemed necessary:

12. Serum creatinine level more than 1.25×upper limit of normal (ULN) or anestimated glomerular filtration rate value <80 mL/min/1.73 m2 calculated withthe Chronic Kidney Disease Epidemiology Collaboration formula and more thantrace protein in urine.

13. Total bilirubin, aspartate aminotransferase (AST) or alanine aminotransferase (ALT) values more than >2×ULN. Note: participants with a history of Gilbert'ssyndrome are excluded from participation in the study.

14. Hematological or coagulation values outside the normal reference range forlocal laboratory results unless regarded as not clinically significant.

15. Confirmed positive test for hepatitis B serology (hepatitis B surface antigenand core antibody) and/or hepatitis C polymerase chain reaction.

16. Values indicating a deficiency of immunoglobulin A (IgA) or anti-IgAantibodies.

17. The participant has a 12-lead ECG demonstrating an abnormal corrected QT interval byFridericia (QTcF) (>450 ms for males, >470 ms for females) or a QRS interval >120ms. If QTcF is abnormal (>450 ms for males, >470 ms for females) or a QRS interval >120 ms, the ECG should be repeated 2 more times, and the average of the 3 QTcF orQRS interval values (i.e., the initial reading plus 2 repeats for a total of 3readings, averaged) should be used to determine the participant's eligibility.

18. The participant has Investigator determined coronavirus disease of 2019 (COVID 19)within 4 weeks prior to Day 1, received the COVID-19 vaccine within 2 weeks prior tostudy drug administration, or plans to receive a COVID-19 vaccine within 9 weeksafter study drug administration. Regional and site COVID-19 testing policies shouldbe followed throughout the study.

19. The participant has a positive urine or blood result for drugs of abuse (defined asany illicit drug use) at Screening or Check-in (Day -1).

20. The participant has received any NMDAR modulator other than the study drug (e.g.,ketamine, memantine, dextromethorphan, amantadine, ifenprodil, phencyclidine [PCP],acamprosate, D-cycloserine) or IVIG from within 30 days or 5 half lives of the otherNMDAR modulator or IVIG (whichever is longer) of study drug administration until theend of the study.

21. The participant has a known history of primary immunodeficiency (congenital oracquired) or an underlying condition such as human immunodeficiency virus infection.

22. The participant has had a bacillus of Calmette and Guérin vaccine within 1 year ofenrollment.

23. The participant has a history of severe depression, bipolar disease, orschizophrenia.

24. The participant has a risk of suicide per the C-SSRS (a score of 4 or 5 on ideationor any suicidal behavior) or, according to the Investigator's clinical judgment, hasmade a suicide attempt in the previous 6 months, or has a history of deliberateself-harm in the past 6 months.