Study to Evaluate APVO210 in Healthy Subjects, Patients With Psoriasis, and Patients With Ulcerative Colitis

Inclusion Criteria: Main Inclusion Criteria: * Age 18 to 65 years old. * Body mass index (BMI) \> 18.5 kg/m2 and \< 30.0 kg/m2; minimum body weight of 50 kg. * Good health and no clinically significant findings on: * Physical examination * 12-lead ECG * Clinical laboratory tests (serum chemistry, haematology, coagulation, urine drug screen, and urinalysis (UA)) * Seated systolic blood pressure (BP) 90 to 140 mm Hg. * Seated diastolic BP 60 to 90 mm Hg. Psoriasis Patients (Expansion Cohort): Main Inclusion Criteria: * Clinical diagnosis of chronic plaque psoriasis with a disease duration of at least 6 months; patients with concurrent psoriatic arthritis may be enrolled. * Psoriasis Area and Severity Index (PASI) score ≥ 12 at baseline. * Psoriasis plaque BSA (Body surface area) ≥ 10% * PGA (Physician Global Assessment) ≥ 3. * Age 18 to 65 years old. * Body mass index \> 18.5 and \< 35.0 kg/m2; minimum body weight of 50 kg. Ulcerative Colitis Patients (Expansion Cohort): Main Inclusion Criteria: * Moderately to severely active ulcerative colitis as defined by: * Baseline Mayo Score of 6 to 12; and * Endoscopic sub-score ≥2 as read by central reader * Is intolerant, refractory, or only partially responsive to corticosteroids (not including budesonide), immunomodulators (azathioprine \[AZA\] or 6-mercaptopurine \[6-MP\], and methotrexate), or biologics. * Age 18 to 65 years old. * Body mass index \> 18.5 and \< 35.0 kg/m2; minimum body weight of 50 kg. Exclusion Criteria: Main Exclusion Criteria * Clinically significant manifestation of metabolic; hepatic; renal; haematological; pulmonary; cardiovascular; gastrointestinal; musculoskeletal; dermatological; urogenital; eye, ear, nose, and throat; psychiatric; or neurological disorders. * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \> 1.2 times the upper limit of normal (ULN) as defined by the laboratory. * Positive hepatitis panel (hepatitis B surface antigen \[HBsAg\] and anti-hepatitis C virus \[HCV\]) or positive human immunodeficiency virus (HIV) antibody. * Positive Quantiferon tuberculosis (TB) test at Screening Visit. * Receipt of live vaccine less than 1 month prior to Check in or plan to receive live vaccine during the study or up to 3 months following End of Treatment visit. * Infection in the 4 weeks prior to Check-in that required hospitalization or parenteral antibiotics. Psoriasis Patients (Expansion Cohort): Main Exclusion Criteria: * History of malignancy, diagnosed or known to be active or actively treated within the past 5 years, other than resected lesions of low malignant potential, such as basal cell skin cancers or low risk squamous cell carcinomas of the skin. * Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) \> 2 times the upper limit of normal (ULN) as defined by the laboratory. * Creatinine \> 1.5 times ULN as defined by the laboratory. * Positive hepatitis panel (hepatitis B surface antigen \[HBsAg\] and anti-hepatitis C virus \[HCV\]) or positive human immunodeficiency virus (HIV) antibody. * Positive Quantiferon tuberculosis (TB) test at Screening Visit. * Receipt of live vaccine less than 1 month prior to Check in or plan to receive live vaccine during the study or up to 3 months following End of Treatment visit. * Infection in the 4 weeks prior to Check-in that required hospitalization or parenteral antibiotics. * Use of a prescription medication that could have an effect on psoriasis (eg, lithium, systemic steroids, immunosuppressants) during the 14 days before Check-in; use of prescription medications for psoriasis is not permitted until after the Follow-up Visit. * Non plaque forms of psoriasis (eg, erythrodermic, guttate, or pustular). * Use of biologic agents (eg, adalimumab, etanercept, infliximab, ustekinumab, ixekizumab, secukinumab, guselkumab, tildrakizumab, brodalumab) or psoralen and ultraviolet A (PUVA) within 12 weeks prior to Check-in, ultraviolet B (UVB) phototherapy, use of tanning beds, or use of systemic medications such as methotrexate, cyclosporine A, acitretin, tofacitinib or apremilast within 4 weeks prior to Check-in, or topical anti-psoriasis medications (except emollients) within 2 weeks prior to Check-in. Ulcerative Colitis Patients (Expansion Cohort): Main Exclusion Criteria: * Ulcerative colitis requiring immediate surgical, endoscopic, or radiological intervention including massive haemorrhage, perforation and sepsis, suppurative complications, or toxic colon. * Stool positive for Clostridium difficile toxin, enteric pathogens, or ova and parasites. * Positive hepatitis panel (hepatitis B surface antigen \[HBsAg\] and anti hepatitis C virus \[HCV\]) or positive human immunodeficiency virus (HIV) antibody. * Positive Quantiferon tuberculosis (TB) test at Screening Visit. * Receipt of live vaccine less than 1 month prior to Check in or plan to receive live vaccine during the study or up to 3 months following End of Treatment visit. * Infection in the 4 weeks prior to Check-in that required hospitalization or parenteral antibiotics. * Use of biologic agents (eg, adalimumab, etanercept, infliximab, ustekinumab, ixekizumab, secukinumab, guselkumab, tildrakizumab, brodalumab) or psoralen and ultraviolet A (PUVA) within 12 weeks prior to Check-in, ultraviolet B (UVB) phototherapy, use of tanning beds, or use of systemic medications such as methotrexate, cyclosporine A, acitretin, tofacitinib or apremilast within 4 weeks prior to Check-in, or topical anti-psoriasis medications (except emollients) within 2 weeks prior to Check-in.