A Long Term Study to Demonstrate the Safety and Efficacy of Tildrakizumab in Subjects With Psoriatic Arthritis and Ankylosing Spondylitis or Non-Radiographic Axial Spondyloarthritis.

Inclusion Criteria:

1. Subject has provided written informed consent for this long-term extension study.

2. Subjects with psoriatic arthritis (PsA) and ankylosing spondylitis (AS) or
non-radiographic axial spondyloarthritis (nr-axSpA) who met the inclusion criteria of
the parent studies and completed the parent study treatment period (e.g., up to Week
48 for the parent Phase 2 studies, with the return for the end of treatment (EoT)
assessment at Week 52).

3. PsA subjects who achieved a 20% reduction from Baseline in ACR20 response criteria at
Week 52, and AS or nr-axSpA subjects who achieved ASAS40 response criteria at Week 52,
AND the subject has received sufficient clinical benefit, in the opinion of the
Investigator, to support continued treatment with tildrakizumab. These criteria using
response criteria at Week 52 will apply to all subjects, including those subjects who
enter the study from the wash-out phase of their parent study (after Week 52) due to
the timing of study site activation of the long-term extension study.

4. No concomitant use of both leflunomide and methotrexate, No history of active
tuberculosis (TB) or symptoms of TB.

Exclusion Criteria:

1. New onset during the parent study of arthritic conditions other than the subject's
original condition.

2. Female subjects of childbearing potential who do not agree to abstain from
heterosexual activity or practice a dual method of contraception, for example, a
combination of the following: (1) oral contraceptive, depo-progesterone, or
intrauterine device; and (2) a barrier method (condom or diaphragm). Male subjects
with female partners of childbearing potential who are not using birth control as
described above must use a barrier method of contraception (e.g., condom) if not
surgically sterile (i.e., vasectomy). Contraceptive methods must be practised upon
entering the study and through 16 weeks after the last dose of IMP. If a subject
discontinues prematurely, the contraceptive method must be practised for 16 weeks
following final administration of IMP.

3. Female is pregnant or breastfeeding, or planning to become pregnant or initiate
breastfeeding while enrolled in the study or up to 16 weeks after the last dose of
IMP.

4. Subject has previously been enrolled in this long-term extension study.

5. Any condition that in the opinion of the Investigator represents an obstacle for study
conduct and/or represents a potential unacceptable risk for the subject.

6. Subject has an active infection or history of infections as follows:

- a serious infection, defined as requiring hospitalization or intravenous
anti-infectives within 8 weeks prior to the first IMP dose of the extension
study, with the last dose having been received within 7 days of start of the
extension study,

- recurrent or chronic infections, e.g., chronic pyelonephritis, chronic
osteomyelitis, bronchiectasis, or other active infection that, in the opinion of
the Investigator, might cause this extension study to be detrimental to the
subject.

7. Major chronic inflammatory or connective tissue disease other than PsA or AS/nr axSpA
(e.g., rheumatoid arthritis, systemic lupus erythematosus, Lyme disease, and gout).

8. Known diagnosis of fibromyalgia, regional pain syndromes or active uveitis/symptomatic
inflammatory bowel disease requiring therapy (AS/nr-axSpA subjects),

9. Subject has any concurrent medical condition or uncontrolled, clinically significant
systemic disease (e.g., renal failure, heart failure, hypertension, liver disease,
diabetes, or anaemia) that, in the opinion of the Investigator, could cause continued
treatment to be detrimental to the subject.

10. Subject has a known history of infection with hepatitis B, hepatitis C, or human
immunodeficiency virus during the parent study.

11. Subject had a myocardial infarction, unstable angina pectoris, or ischemic stroke
within the past 6 months prior to the first IMP dose for this extension study.

12. Subject has any active malignancy, including evidence of cutaneous basal or squamous
cell carcinoma or melanoma.

13. Subject has a history of malignancy EXCEPT treated and considered cured cutaneous
basal or squamous cell carcinoma, in situ cervical carcinoma, OR in situ breast ductal
carcinoma.

14. Subjects with a history of alcohol or drug abuse during the parent study.

15. Significant risk of suicidality at the Baseline assessment of this extension study
based on the Investigator's judgment or, if appropriate, as indicated by a response of
"yes" since the last visit to question 4 or 5 in the suicidal section, or any response
in the behavioral section of the Columbia-Suicide Severity Rating Scale (C SSRS).

16. Subject has a need for use of a live vaccine within 10 weeks of final anticipated dose
of IMP for the long-term extension study.

17. Concomitant use of prohibited medications or use of commercially available or
investigational biologic therapies (other than tildrakizumab) for psoriasis, PsA,
and/or AS/nr axSpA.

General:

18. Subjects who have been placed in an institution on official or judicial orders.

19. Subjects who are related to or dependent on the Investigator, Sponsor, or study site
such that a conflict of interest may arise.