A First in Human Study of the Safety, Tolerability, and the Physiologically Based Pharmacokinetics of XFB19 in Healthy Adult Volunteers.

Inclusion Criteria: 1. Must have given written informed consent before any study-related activities are carried out and must be able to understand the full nature and purpose of the study, including possible risks and adverse effects. 2. Adult males and females, 18 to 55 years of age (inclusive) at screening. 3. Body mass index ≥ 18.0 and ≤ 35.0 kg/m2 with a body weight ≥ 45 kg at screening. 4. Be non-smokers (including tobacco, e-cigarettes, and marijuana) for at least 1 month prior to first investigational drug administration. 5. Medically healthy without clinically significant abnormalities (in the opinion of the Investigator) at the Screening Visit and prior to dosing including: 1. Physical examination without any clinically significant findings 2. Systolic blood pressure in the range of 90 to 160 mmHg (inclusive) and diastolic blood pressure in the range of 50 to 95 mmHg (inclusive) after 5 minutes rest in supine position 3. Heart rate (HR) in the range of 40 to 100 bpm (inclusive) after 5 minutes rest in supine position 4. Body temperature (tympanic or oral) in the range of 35.5°C to 37.7°C (inclusive) 5. No clinically significant findings in serum chemistry, hematology, coagulation, and urinalysis tests 6. Triplicate 12-lead ECGs (taken after the volunteer has been supine for at least 5 minutes) with QT intervals corrected using Fridericia's method (QTcF) ≤ 450 msec for males and ≤ 470 msec for females and no clinically significant abnormalities 6. Female volunteers must: 1. Be of nonchildbearing potential, i.e., surgically sterilised (hysterectomy, bilateral salpingectomy, bilateral tubal ligation, bilateral oophorectomy at least 6 weeks before screening) or postmenopausal (defined as no menses for 12 months without an alternative medical cause and a follicle-stimulating hormone \[FSH\] level \> 40 IU/L at the Screening Visit) OR 2. If of childbearing potential, must agree not to donate ova, not to attempt to become pregnant, and, if engaging in sexual intercourse with a male partner, must agree to use an acceptable method of contraception from the time of signing the participant informed consent form (PICF) until at least 30 days after the last dose of the study drug 7. Male volunteers must agree not to donate sperm, and, if engaging in sexual intercourse with a female partner who could become pregnant, must agree to use an acceptable method of contraception from the time of signing the consent form until at least 30 days after the last dose of study drug. 8. Have suitable venous access for blood sampling. 9. Be willing and able to comply with all study assessments and adhere to the protocol schedule and restrictions. Exclusion Criteria: 1. History or presence of any clinically significant (as determined by the PI) cardiovascular, pulmonary, hepatic, renal, hematological, gastrointestinal, endocrine, immunologic, dermatologic, or neurological disease, including any acute illness or major surgery, within the past 3 months. 2. Current infection that requires systemically absorbed antibiotic, antifungal, antiparasitic, or antiviral medications. 3. Any history of malignant disease in the last 5 years (excluding surgically resected skin squamous cell or basal cell carcinoma). 4. Presence of clinically relevant immunosuppression from, but not limited to, immunodeficiency conditions such as common variable hypogammaglobulinemia. 5. Use of or plans to use systemic immunosuppressive (e.g., corticosteroids, methotrexate, azathioprine, cyclosporine) or immunomodulating medications (e.g., interferon) during the study or within 3 months prior to the first study drug administration. 6. History of risk factors for torsade de pointes (including a family history of long QT syndrome or sudden cardiac death) or a known arrythmia. 7. Liver function test (LFT) results \> 1.5 times the upper limit of normal (ULN) for gamma glutamyl transferase (GGT), bilirubin (total, conjugated, and unconjugated), alkaline phosphatase (ALP), aspartate aminotransferase (AST), or alanine aminotransferase (ALT). Volunteers with bilirubin, ALP and/or ALT/AST above the limits specified may be included, at the discretion of the Investigator, if the levels are unaccompanied by clinical signs. 8. Positive test results for human immunodeficiency virus (HIV-1 or HIV-2) antibodies, hepatitis C virus (HCV) antibodies, or hepatitis B surface antigen (HBsAg) at the Screening Visit. Patients with HCV antibodies, or HBsAg could be included if the viral load for HCV or hepatitis B are negative. 9. Positive test result for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via polymerase chain reaction or commercially validated antigen test, per site's standard clinical procedure. 10. Presence of sequelae of gastrointestinal, liver, kidney, or other conditions known to interfere with the absorption, distribution, metabolism, or excretion of drugs. 11. Estimated creatinine clearance (CrCl) \< 60 mL/min using the Cockcroft-Gault formula or serum creatinine more than 1.5 x ULN. 12. History of substance abuse or alcohol abuse (defined as more than 10 standard drinks per week or regularly consuming more than 4 standard drinks per day where 1 standard drink is 10 g of pure alcohol and equivalent to 285 mL beer \[4.9% Alc./Vol\], 100 mL wine \[12% Alc./Vol\], or 30 mL spirit \[40% Alc./Vol\]) within 12 months prior to the Screening Visit. 13. Positive drugs of abuse or alcohol breath test results at the Screening Visit or at CRU check in (Day -1) (repeat tests allowed if false positive suspected). Non-habitual use and agreement to refrain from using any THC/CBD products during the study is allowed. 14. Use of any prescription or over the counter (OTC) medication (including herbal products, diet aids, and hormone supplements) within 10 days or 5 half-lives of the medication (whichever is longer) prior to the first study drug administration, excepting use of contraceptives and occasional use of acetaminophen (up to 1 g every 8 hours or 3 g per day maximum). 15. Demonstrated clinically significant (required intervention, e.g., emergency room visit, epinephrine administration) allergic reactions (e.g., food, drug, or atopic reactions, asthmatic episodes) which, in the opinion of the Investigator, would interfere with the volunteer's ability to participate in the study. 16. Known hypersensitivity to any of the study drug ingredients. 17. Use of any vaccinations within 10 days prior to first study drug administration. 18. For women of childbearing potential, a positive serum pregnancy test at the Screening Visit or a positive urine pregnancy test (with confirmatory positive serum pregnancy test) at CRU check-in (Day -1). 19. Currently breastfeeding. 20. Donation of blood or plasma or loss of whole blood of more than 500 mL within 30 days prior to first study drug administration or receipt of a blood transfusion within 2 months prior to first study drug administration. 21. Participation in another clinical study of an investigational drug within 30 days or 5 half-lives of the investigational agent (whichever is longer) prior to the first study drug administration. 22. Any other condition or prior therapy that in the opinion of the Investigator would make the volunteer unsuitable for this study, including inability to cooperate fully with the requirements of the study protocol or likelihood of noncompliance with any study requirements.