The study is a Phase 2, multi-center, randomized, double-blind, placebo-controlled study to evaluate the effects of tibulizumab over 24 weeks (Period 1) in adult participants with systemic sclerosis, followed by an open-label extension period where all active participants will receive tibulizumab and will be evaluated for an additional 28 weeks (Period 2)

Inclusion Criteria:

• Male or female, 18 to 75 years of age
• Body mass index between 18.0 and 38.0 kg/m²
• Fulfills classification criteria for SSc according to ACR/EULAR 2013 criteria
• Has diffuse cutaneous SSc, defined as mRSS >0 over at least one skin area proximal to the elbows and/or knees, in addition to acral fibrosis
• Has had SSc (defined as the first non-Raynaud's phenomenon (RP) symptom or sign attributed to SSc) for ≤7 years
• mRSS ≥15 and ≤45 at screening. Additional requirements for participants ≥2 years to ≤7 years from SSc onset and RNA Polymerase III antibody positive
• FVC >50% predicted
• Diffusing capacity of the lungs for carbon monoxide (DLCO) ≥40% predicted (corrected for hemoglobin)

Exclusion Criteria:

• Has any of the following complications:

  • Left ventricular failure
  • Pulmonary arterial hypertension
  • Renal crisis within previous 6 months
  • Gastrointestinal dysmotility within previous 3 months
  • Digital ischemia with gangrene, amputation, or unscheduled hospitalization within previous 3 months

• Current rheumatic disease other than SSc that could interfere with assessment of SSc

• Lung disease requiring continuous oxygen therapy

• Evidence or suspicion of active or latent tuberculosis

• Active Crohn's Disease or ulcerative colitis