A Study to Evaluate the Safety, Tolerability and Efficacy of MHV370 in Participants With Sjogren's Syndrome (SjS) or Mixed Connective Tissue Disease (MCTD)

Inclusion Criteria: SjS and MCTD: • Fully vaccinated with any locally approved COVID-19 vaccination including booster vaccinations if required by local guidelines 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), …