Evaluate the Safety, Tolerability, PK and PD of SAD of Intravenously Adminsterted ALTB-268 in Healthy Participants

Inclusion Criteria: 1. Male or female, non-smoker (no use of tobacco or nicotine products within 3 months prior to screening), ≥18 and ≤55 years of age, with body mass index (BMI) \>18.5 and \<32.0 kg/m2 and body weight ≥50.0 kg for males and ≥45.0 kg for females. 2. Healthy as defined by: 1. the absence of clinically significant illness and surgery within 4 weeks prior to dosing. 2. the absence of clinically significant history of neurological, endocrine, cardiovascular, respiratory, hematological, immunological, psychiatric, gastrointestinal, renal, hepatic, and metabolic diseases. 3. Female participants of non-childbearing potential must be: 1. post-menopausal (spontaneous amenorrhea for at least 12 consecutive months prior to dosing) with confirmation by documented follicle- stimulating hormone (FSH) levels ≥40 mIU/mL; or 2. surgically sterile (bilateral oophorectomy, bilateral salpingectomy, hysterectomy, or bilateral tubal ligation) at least 3 months prior to dosing. 4. Able to understand the study procedures, agree to comply with all study visits, procedures, and restrictions, agree to comply with the prescribed dosage regimens and communicate to study personnel about AEs and concomitant medication use, and provide signed informed consent to participate in the study. Exclusion Criteria: 1. Any clinically significant abnormal finding at physical examination at screening and/or Day -1. 2. Clinically significant abnormal laboratory test results at screening and/or Day -1; or positive serology test results for hepatitis B surface antigen (HBsAg), hepatitis C virus (HCV) antibody, or human immunodeficiency virus (HIV) antigen and antibody, or QuantiFERON®-TB test at screening. 3. Any history of suicidal ideation as evidenced by answering "yes" to questions 4 or 5 on the suicidal ideation portion of the C-SSRS completed at screening, or any history of suicide attempts. 4. Any history of clinical depression. 5. C-SSRS score at Day -1 (baseline) above Type 1 ideation. 6. PHQ-8 total score ≥5 at screening and/or Day -1 (baseline).