Phase 1, Randomised Double Blinded Placebo Controlled Study of ASLAN003

Inclusion Criteria: * The inclusion criteria for all subjects are as follows: * are capable of understanding and complying with the requirements of the study and have signed the informed consent form (ICF); * are able to communicate well with the Investigator, and understand and comply with the requirements of the study; * male subjects aged between 21 and 50 years, inclusive (Part A and Cohorts 5, 6 and 7 of Part B only); male subjects and female subjects of non childbearing potential aged ≥55 years (Cohort 8 of Part B only); * body mass index (BMI) in the range of 18 to 30 kg/m2, inclusive; * healthy, as determined by pre study medical history, physical examinations, vital sign measurements, electrocardiogram (ECG; 12 lead reporting RR, PR, QRS, corrected QT \[QTc\] and QT interval corrected for heart rate using Fridericia's formulas \[QTcF\]) recordings with no evidence of clinically relevant medical disorders based on the opinion of the Investigator; * whose out-of-normal range clinical laboratory test results are not clinically relevant and are acceptable to the Investigator; * male subjects must be willing to use barrier contraception during sexual intercourse, i.e. condoms, even if their partners are post-menopausal, surgically sterile or are using accepted contraceptive methods, from the first day of dose administrations until 3 months after the last dose administration; Exclusion Criteria: * The exclusion criteria for all subjects are as follows: * have participated in a study involving another investigational device or drug study within 90 days prior to randomisation in this study; * history of drug hypersensitivity reactions or hypersensitivity to drugs chemically related to the IP; * history or evidence of a clinically significant disorder, condition or disease (including, but not limited to, cardiopulmonary, oncologic, autoimmune, immunogenic, renal, metabolic, haematological or psychiatric), that, in the opinion of the Investigator, would pose a risk to subject safety or interfere with the study evaluation, procedures or completion; * existence of any surgical or medical condition which, in the judgement of the Investigator, may interfere with the absorption, distribution, metabolism or excretion of the IP; * clinically significant history or evidence of any active or suspected bacterial, viral, fungal or parasitic infection within the 30 days prior to randomisation (e.g. common cold, viral syndrome, flu-like symptoms, etc.); * active or recent history (within 30 days prior to randomisation) of acute viral infection of the skin (e.g. Herpes simplex, Molluscum contagiosum); * active or history of psoriasis, or a first-degree relative with active or history of psoriasis; * known history or evidence of active or latent tuberculosis infection (e.g. positive tuberculin skin test showing induration \>5 mm or positive tuberculin blood test) in absence of previous Bacillus Calmette Guerin vaccination, or recent exposure (within 6 months prior to randomisation in this study) to an individual with active tuberculosis or with intention to travel to a country with a high risk of tuberculosis during the study period (including the follow up period); * history of autoimmune disease including but not limited to lupus, rheumatoid arthritis, autoimmune thyroid disease and immune thrombocytopenia; * with QT or QTcF values higher than 450 ms at screening; * history of regular alcohol consumption (within 6 months prior to randomisation in this study), defined as: an average weekly intake of greater than 21 units or any average daily intake of greater than 3 units. One unit is equivalent to a half pint (220 mL) of beer or 1 (25 mL) measure of spirits or 1 glass (125 mL) of wine;