Inclusion Criteria:
1. Participants must be able and willing to provide informed consent.
2. Participants must be aged 18 to 55 years at the time of consent.
3. Participants must have a BMI within the range 18.5 to 29.9 kg/m2.
4. Participants must be in general good health.
5. All female participants of childbearing potential and all male participants who are able to father children and are sexually active and whose partners are at risk for pregnancy, must agree to use a highly effective method of contraception in combination with a condom from the time of signing the informed consent form through 94 days after the last IP administration.
Exclusion Criteria:
1. Have any condition that, in the investigator's opinion, might jeopardize the participant's safety or compliance with the protocol.
2. Have a history of any severe allergic reaction or anaphylaxis.
3. Have clinically significant abnormalities in clinical laboratory results, as judged by the Investigator, including estimated glomerular filtration rate (eGFR) \< 90 mL/min/1.73 m² (CKD-EPI 2021 formula).
4. Have participated in another interventional clinical trial and received an investigational drug within 28 days (or as determined by local requirements) or 5 half-lives prior to Day 1, whichever is longer, or are currently participating in another interventional clinical trial.
5. Have experienced major trauma or undergone major surgery within 3 months prior to Day 1.
6. Have a history of malignancy within 5 years before the screening visit, except for curatively treated carcinoma in situ of the cervix or non-metastatic squamous or basal cell carcinoma of the skin.
7. Have screening seated blood pressure ≥ 140 mm Hg (systolic) or ≥ 90 mm Hg (diastolic).
8. Have a screening 12-lead ECG with clinically relevant abnormalities that may affect the participant's safety or the interpretation of study results.
9. Have any of the following active or recent infections:
1. serious infection requiring hospitalization or parenteral antibiotics within 12 weeks prior to Day 1, serious bone/joint infection within 24 weeks, or history of infection of an artificial joint;
2. active herpes simplex or herpes zoster outbreak within 12 weeks prior to Day 1;
3. active infection requiring systemic antimicrobial treatment within 4 weeks prior to Day 1, or superficial skin infection requiring antibiotics within 1 week prior to Day 1;
4. active TB; or (e) immunocompromised status posing unacceptable risk per investigator judgment.
10. Have chronic hepatitis B, defined as positive hepatitis B surface antigen (HBsAg) or detectable hepatitis B virus (HBV) DNA at screening. Note: Participants who are hepatitis B core antibody (HBcAb) positive and HBV DNA undetectable may be eligible.
11. Have hepatitis C infection, defined as positive hepatitis C antibody (HCV Ab) with detectable HCV RNA. Participants with a history of hepatitis C treatment with undetectable HCV RNA at least 24 weeks after completion of treatment may be eligible.
12. Have a history of human immunodeficiency virus (HIV) infection or be positive for HIV at screening.
13. Have active or untreated syphilis infection, defined as a reactive Toluidine Red Unheated Serum Test (TRUST) or Treponema pallidum antibody (TP Ab) positive at screening.
14. Have known or suspected intolerance or hypersensitivity to any components of the formulation of ATH-097 and its excipients.
15. Have a history of drug abuse or addiction within 6 months of screening.
16. Have consumed more than 14 units of alcohol per week on average within 3 months prior to Day 1, or be unwilling to abstain completely from alcohol consumption from 7 days prior to Day 1 through discharge.
17. Be a current smoker defined as smoking more than 5 cigarettes (or equivalent nicotine-containing products) per week within the 6 months prior to Day 1, or have a positive urine cotinine test at Screening or Day -1.
18. Consume more than 5 cups of coffee, tea, or other caffeine-containing beverages per day on average within 3 months prior to Day 1, or be unwilling to abstain from all caffeine-containing products from 48 hours prior to Day 1 through discharge.
19. Have received live or attenuated vaccine(s) within 12 weeks prior to screening or plan to receive such vaccines during the study.
20. Have received biologic immunomodulatory agents within 3 months or 5 half-lives (whichever is longer) prior to dosing.
21. Have donated blood (excluding plasma donations) of approximately 1 pint (500 mL) or more within 30 days prior to Screening.
22. Have received a transfusion of blood or blood products within 30 days prior to Day 1 dosing.
23. If female, be nursing, lactating, pregnant, or planning to become pregnant within 94 days after the last dose of IP.
24. Have used any prescription or over-the-counter (OTC) medications, herbal preparations, dietary supplements, or vitamins that may affect the metabolism or pharmacokinetics of ATH-097 within 14 days or 5 half-lives (whichever is longer) prior to Day 1.
