Inclusion Criteria:  SjS and MCTD:  • Fully vaccinated with any locally approved COVID-19 vaccination at least 4 weeks prior to baseline  SjS:  Unstimulated whole salivary flow rate of > 0 mL/min at screening Classification of Sjögren's Syndrome according to the 2016 ACR/EULAR criteria at screening Screening ESSDAI (based on weighted score) ≥ 5 from 8 defined domains (biologic, hematologic, articular, cutaneous, glandular, lymphadenopathy, renal, constitutional).  MCTD:  Diagnosis of MCTD based on criteria like a) Raynaud's phenomenon b) At least two of the four following signs: i) synovitis, ii) myositis, iii) swollen fingers and vi) interstitial lung disease Patients with overlap syndromes, i.e. patients meeting diagnostic criteria for systemic autoimmune disease other than MCTD may be included unless they have major organ involvement as judged by the investigator  Exclusion Criteria:  SjS and MCTD:  Prior use of B-cell depleting therapy within 6 months of baseline. For participants who received B-cell depleting therapy within 6 -12 months of baseline visit, B-cell count should be within normal range Prior treatment with any of the following within 3 months of baseline: CTLA4-Fc Ig (abatacept), Anti-TNF mAb, Intravenous Ig, Plasmapheresis, i.v. or oral cyclophosphamide, i.v. or oral cyclosporine A Screening CBC laboratory values as follows: Hemoglobin levels < 8 g/dL (< 5 mmol/L), Total leukocyte count < 2,000/µL (2 x 109/L), Platelets < 50,000/µL (50 x 109/L), Neutrophil count < 1,000/µL (1 x 109/L) Pregnant or nursing (lactating) women Women of child-bearing potential, defined as all women physiologically capable of becoming pregnant, unless they use a highly effective method of contraception  SjS:  Sjögren's Syndrome overlap syndromes where another autoimmune disease constitutes the primary illness Required regular use of medications known to cause, as a major side effect, dry mouth / eyes  Other protocol-defined inclusion/exclusion criteria may apply