| E.1 Medical condition or disease under investigation | 
| E.1.1 | Medical condition(s) being investigated  | 
| Primary Sjögren’s Syndrome  | 
 
 
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| E.1.1.1 | Medical condition in easily understood language  | 
| Primary Sjögren’s Syndrome  | 
 
 
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| E.1.1.2 | Therapeutic area  | Body processes [G] - Immune system processes [G12] | 
| MedDRA Classification | 
| E.1.2 Medical condition or disease under investigation | 
| E.1.2 | Version  | 21.0 | 
 
| E.1.2 | Level  | LLT | 
 
| E.1.2 | Classification code  | 10042846 | 
 
| E.1.2 | Term  | Syndrome Sjogren's | 
 
| E.1.2 | System Organ Class  | 100000004859 | 
 
 
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| E.1.3 | Condition being studied is a rare disease  |  No  | 
| E.2 Objective of the trial | 
| E.2.1 | Main objective of the trial  | 
| To evaluate the effect of efgartigimod IV compared to placebo on CRESS | 
 
 
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| E.2.2 | Secondary objectives of the trial  | 
• To evaluate the effect of efgartigimod IV compared to placebo on the histology of the parotid gland (selected sites only) • To evaluate the safety of efgartigimod IV compared to placebo in participants with pSS • To evaluate the effect of efgartigimod IV compared to placebo on clinical efficacy parameters  • To evaluate the effect of efgartigimod IV compared to placebo on STAR • To evaluate the PK of efgartigimod IV • To evaluate the PD of efgartigimod IV • To evaluate the immunogenicity of efgartigimod IV | 
 
 
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| E.2.3 | Trial contains a sub-study  |  No  | 
| E.3 | Principal inclusion criteria  | 
Participants are eligible to be included in the study only if all of the following criteria apply: - Is at least the legal age of consent for clinical trials when signing the informed consent form - Is capable of providing signed informed consent and complying with protocol requirements - Agrees to use contraceptive measures consistent with local regulations and measures described in the protocol - Meets the following criteria: ACR/EULAR 2016 pSS who met criteria ≤7 years before screening;   ESSDAI ≥5; Ro/SS-A positive; Residual salivary flow (UWSF rate >0 and/or SWSF rate >0.10) | 
 
 
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| E.4 | Principal exclusion criteria | 
Participants will be excluded from the study if any of the following criteria apply: - Known autoimmune disease or any medical condition that, in the investigator’s judgment, would interfere with an accurate assessment of clinical symptoms of pSS or puts the participant at undue risk - History of malignancy unless considered cured by adequate treatment with no evidence of recurrence for ≥3 years before the first administration of IMP. Adequately treated participants with the following cancers may be included at any time: Basal cell or squamous cell skin cancer; Carcinoma in situ of the cervix; Carcinoma in situ of the breast; Incidental histological finding of prostate cancer (TNM stage T1a or T1b) - Clinically significant uncontrolled active acute or chronic bacterial, viral, or fungal infection - Positive serum test at screening for an active infection with any of the following: HBV that is indicative of an acute or chronic infection, unless associated with a negative HBsAg or negative HBV DNA test; HCV based on HCV antibody assay unless a negative RNA test is available; HIV based on test results of a CD4 count of <200 cells/mm3 that are associated with an AIDS-defining condition, HIV based on test results of a CD4 count of >200 cells/mm3 not adequately treated with antiviral therapy - Clinically significant disease, recent major surgery (within 3 months of screening), or intention to have surgery during the study; or any other medical condition that, in the investigator’s opinion, would confound the results of the study or put the participant at undue risk - Immunoglobulin G (IgG) levels cannot be below a certain threshold ( 4g/L) - Positive covid test at study start - Some of the medications such as vaccines with live components or medicines that may be prescribed for Sjogren’s syndrome cannot be taken either shortly before or during this study - Current participation in another interventional clinical study or previously participation in an efgartigimod clinical study and treatment with ≥1 dose of IMP - Known hypersensitivity to IMP or 1 of its excipients - History (within 12 months of screening) of current alcohol, drug, or medication abuse as assessed by the investigator - Pregnant or lactating state or intention to become pregnant during the study - Secondary Sjögren’s syndrome overlap syndromes where another confirmed autoimmune rheumatic or systemic inflammatory condition is the primary diagnosis - Chinese traditional medicine with known immunomodulatory action A detailed list is provided in the protocol. | 
 
 
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| E.5 End points | 
| E.5.1 | Primary end point(s) | 
Proportion of CRESS responders on ≥3 of 5 items at week 24. The 5 items are: − Systemic disease activity: clinESSDAI − Patient-reported symptoms: ESSPRI − Tear gland function: Schirmer’s test and OSS − Salivary gland function: UWSF rate and SGUS − Serology (serum IgG and/or RF) | 
 
 
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| E.5.1.1 | Timepoint(s) of evaluation of this end point | 
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| E.5.2 | Secondary end point(s) | 
• Change in the relative counts of lymphocytic infiltrate (stained for CD45) at week 24 • Change in B/B+T cell ratio at week 24 • Incidence and severity of TEAEs, AESIs, and SAEs by SOC and PT up to 35 weeks • Changes in vital sign measurements, ECG results, and clinical laboratory safety evaluations up to 35 weeks • Proportion of participants with minimal clinically important improvement in ESSDAI: improvement of ≥3 points in ESSDAI score at week 24 up to 24 weeks • Proportion of participants with low disease activity: ESSDAI score of <5 at week 24 up to 24 weeks • Proportion of participants with minimal clinically important improvement in clinESSDAI: improvement of ≥3 points in clinESSDAI score at week 24 up to 24 weeks • Proportion of participants with low disease activity: clinESSDAI score of <5 at week 24 up to 24 weeks • Proportion of participants with minimal clinically important improvement in ESSPRI: decrease of 1 point or ≥15% at week 24 up to 24 weeks • Change in ESSDAI score at week 24 • Change in clinESSDAI score at week 24 • Change in ESSPRI score at week 24 • Proportion of participants with STAR score of ≥5 at week 24 • Efgartigimod serum concentration-time profile • Values, changes from baseline, and percent reduction from baseline in total IgG levels in serum • Values, changes from baseline, and percent reduction from baseline in autoantibodies − Anti-Ro/ SS-A − Anti-La/ SS-B in serum • Incidence and prevalence of ADA against efgartigimod in serum | 
 
 
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| E.5.2.1 | Timepoint(s) of evaluation of this end point | 
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| E.6 and E.7 Scope of the trial | 
| E.6 | Scope of the trial | 
| E.6.1 | Diagnosis |  No  | 
| E.6.2 | Prophylaxis |  No  | 
| E.6.3 | Therapy |  No  | 
| E.6.4 | Safety |  Yes  | 
| E.6.5 | Efficacy |  Yes  | 
| E.6.6 | Pharmacokinetic |  Yes  | 
| E.6.7 | Pharmacodynamic |  Yes  | 
| E.6.8 | Bioequivalence |  No  | 
| E.6.9 | Dose response |  No  | 
| E.6.10 | Pharmacogenetic |  No  | 
| E.6.11 | Pharmacogenomic |  No  | 
| E.6.12 | Pharmacoeconomic |  No  | 
| E.6.13 | Others |  No  | 
| E.7 | Trial type and phase | 
| E.7.1 | Human pharmacology (Phase I) |  No  | 
| E.7.1.1 | First administration to humans |  No  | 
| E.7.1.2 | Bioequivalence study |  No  | 
| E.7.1.3 | Other |  No  | 
| E.7.1.3.1 | Other trial type description |  | 
| E.7.2 | Therapeutic exploratory (Phase II) |  Yes  | 
| E.7.3 | Therapeutic confirmatory (Phase III) |  No  | 
| E.7.4 | Therapeutic use (Phase IV) |  No  | 
| E.8 Design of the trial | 
| E.8.1 | Controlled |  Yes  | 
| E.8.1.1 | Randomised |  Yes  | 
| E.8.1.2 | Open |  No  | 
| E.8.1.3 | Single blind |  No  | 
| E.8.1.4 | Double blind  |  Yes  | 
| E.8.1.5 | Parallel group |  Yes  | 
| E.8.1.6 | Cross over  |  No  | 
| E.8.1.7 | Other |  No  | 
| E.8.2 |  Comparator of controlled trial | 
| E.8.2.1 | Other medicinal product(s) |  No  | 
| E.8.2.2 | Placebo  |  Yes  | 
| E.8.2.3 | Other |  No  | 
| E.8.2.4 | Number of treatment arms in the trial | 2 | 
| E.8.3 | 
                                The trial involves single site in the Member State concerned
                             |  Yes  | 
| E.8.4 |  The trial involves multiple sites in the Member State concerned  |  No  | 
| E.8.5 | The trial involves multiple Member States |  Yes  | 
| E.8.5.1 | Number of sites anticipated in the EEA | 18 | 
| E.8.6 Trial involving sites outside the EEA | 
| E.8.6.1 | Trial being conducted both within and outside the EEA |  No  | 
| E.8.6.2 | Trial being conducted completely outside of the EEA |  No  | 
| E.8.7 | Trial has a data monitoring committee |  No  | 
| E.8.8 | 
                        Definition of the end of the trial and justification where it is not the last
                        visit of the last subject undergoing the trial
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| The end-of-study is defined as the date of the last participant’s last visit. | 
 
 
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| E.8.9 Initial estimate of the duration of the trial | 
| E.8.9.1 | In the Member State concerned years | 1 | 
| E.8.9.1 | In the Member State concerned months | 5 | 
| E.8.9.1 | In the Member State concerned days | 1 | 
| E.8.9.2 | In all countries concerned by the trial years | 1 | 
| E.8.9.2 | In all countries concerned by the trial months | 5 | 
| E.8.9.2 | In all countries concerned by the trial days | 1 |