A Study to Investigate Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of AZD5492 in Adult Participants With Systemic Lupus Erythematosus or Idiopathic Inflammatory Myopathies.

Inclusion Criteria:

1. Participant must be 18 to 70 years of age inclusive, at the time of signing theinformed consent.

2. Diagnosis of SLE:

3. Diagnosis of SLE according to the 2019 EULAR/ACR classification criteria forSLE

4. Positive for one or more of: anti-nuclear antibodies (titre ≥ 1:80), anti-dsDNAor anti-Sm at screening.

5. Active, moderate-severe disease at screening, defined as clinical SLEDAI-2K ≥

7. Intolerance or inadequate response to ≥ 3 available SOC treatments, used for atleast 3 months each, for which at least one must be a biologic SoC orcyclophosphamide.

8. Diagnosis of IIM:

9. Must have "probable" or "definite" diagnosis of PM or DM (excluding IBM andcancer associated myositis) according to the 2017 EULAR/ACR classificationcriteria for adult myositis.

10. Positive for ≥ 1 disease-specific autoantibody at screening.

11. MMT-8 score of ≤ 142/150 and/or CDASI-A > 6

12. Fulfill at least one of the following criteria of active disease at screening:

(i) One or more muscle enzyme elevation (CK, AST, ALT, aldolase, LDH) ≥ 1.3 × ULN (ii) If criterion 3(d)(i) is not met, then at least one of the following criteriamust be met:

1. Report from MRI performed within 3 months prior to screening with evidence ofmuscle inflammation

2. Report from muscle biopsy performed within 3 months prior to screening thatdemonstrates active inflammation

3. Report from electromyography performed within 3 months prior to screening thatexhibits irritable myopathic pattern.

(e) Intolerance or inadequate response to corticosteroids and ≥2 other SoCtreatments, used for at least 3 months each, for which at least one must be abiologic SoC, immunoglobulin or cyclophosphamide.

4. For participants receiving any of the following therapies at screening:

5. Oral prednisone (or equivalent): Daily dose ≤ 20 mg/day and must be stable for ≥ 1 week prior to Day 1.

6. Immunosuppressive treatment: for ≥ 3 months prior to Day 1 and at a stable dosefor ≥ 4 weeks prior to Day 1.

Exclusion Criteria:

1. Any complications of the disease under study which are judged by the investigator tobe life or organ threatening or to require treatments which are not permitted in theprotocol, including but not limited to:

2. Active severe SLE-driven renal disease.

3. History of, or current diagnosis of, catastrophic or severe APS (for examplediagnosis of an arterial or central/pulmonary venous clot) within 1 year priorto signing the ICF.

4. Rapidly progressive and/or severe ILD or ILD that requires oxygensupplementation/therapy (of any type).

5. Inclusion Body Myositis or cancer associated myositis.

6. Active severe, unstable or history of neuropsychiatric SLE

7. IIM: Pulmonary function tests at screening (or within one month of screening,provided participant confirms no change in respiratory symptoms in the interim)which meet any of the following criteria:

8. FVC ≤60% of predicted

9. DLCO ≤70% of predicted

10. Deterioration in either FVC or DLCO at screening compared to pulmonary functiontests performed ≥3 months previously.

11. Significant history of or at risk of severe infections.

12. Participants with HIV infection

13. Participants with active EBV or CMV.

14. Participants with evidence of chronic or active hepatitis B defined as HBsAgpositive or HBcAB positive

15. Participants with evidence of chronic or active hepatitis C

16. Participants with positive COVID-19 PCR.

17. Known history of a primary immunodeficiency, splenectomy, or any underlyingcondition that predisposes the participant to infection.

18. Significant CNS pathology.

19. Receipt of B-cell-depleting therapy including CD19 or CD20 directed monoclonalantibodies (including but not limited to, ocrelizumab, ofatumumab, obinutuzumab, orrituximab) <3 months prior to Day 1.