Safety is measured using AEs, including clinical significant changes in vital signs, laboratory test abnormalities and clinical tolerability of abatacept, and using serious AEs

mITT population includes all of the randomized participants who received at least one dose of study medication.

The efficacy of treatment on skin fibrosis will be measured by changes from baseline to month 12 in mRSS, a measure of skin thickness. mRSS scores have a range from 0 to 51, with higher score indicating greater severity of SSc (worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

Patient global assessment for overall disease represents the patient's assessment of the patient's global scleroderma on a 0 (excellent) -10 (extremely poor) Likert scale. Higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

This assessment represents the physician's assessment of the patient's current disease activity on a 0 (excellent) -10 (extremely poor) Likert scale. Higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

FVC is Forced vital capacity, a measure of lung function. FVC % Predicted is calculated using equations from Hankinson [Hankinson JL, Odencrantz JR, Fedan KB. Spirometric reference values from a sample of the general U.S. population. Am J Respir Crit Care Med. 1999;159(1):179-87], incorporating age, gender, and race. It is calculated as the (FVC Observed / FVC predicted) * 100, where FVC predicted is calculated relative to a reference population.

mITT population includes all of the randomized participants who received at least one dose of study medication.

FVC = forced vital capacity, a measure of lung function

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI overall score ranges from 0 (no disability) to 3 (severe disability). Higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

Scleroderma-Health Assessment Question Disability Index visual analogue scales (VAS) assess the burden of digital ulcers, Raynaud's, gastrointestinal involvement, breathing, and overall disease. The VAS scale for disease severity ranges from 0 (no disease) to 150 (very severe). A higher score means a worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

Scleroderma-Health Assessment Question Disability Index visual analogue scales (VAS) assess the burden of digital ulcers, Raynaud's, gastrointestinal involvement, breathing, and overall disease. The VAS scale for how much breathing problems interfered with daily activities ranges from 0 (do not limit activities) to 150 (very severe limitation). A higher score means a worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

Scleroderma-Health Assessment Question Disability Index visual analogue scales (VAS) assess the burden of digital ulcers, Raynaud's, gastrointestinal involvement, breathing, and overall disease. The VAS scale for how much Raynaud's interfered with daily activities ranges from 0 (does not limit activities) to 150 (very severe limitation). A higher score means a worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

Scleroderma-Health Assessment Question Disability Index visual analogue scales (VAS) assess the burden of digital ulcers, Raynaud's, gastrointestinal involvement, breathing, and overall disease. The VAS scale for how much finger ulcers interfered with daily activities ranges from 0 (do not limit activities) to 150 (very severe limitation). A higher score means a worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

Scleroderma-Health Assessment Question Disability Index visual analogue scales (VAS) assess the burden of digital ulcers, Raynaud's, gastrointestinal involvement, breathing, and overall disease. The VAS scale for how much intestinal problems interfered with daily activities ranges from 0 (do not limit activities) to 150 (very severe limitation). A higher score means a worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

28 joints are assessed for swelling (positive or negative). The number of swollen joint count ranges from 0 to 28. A higher number indicates worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

28 joints are assessed for tenderness (positive or negative). The number of tender joint counts ranges from 0 to 28. A higher number indicates worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the physical function domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., better outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the anxiety domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the depression domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the fatigue domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the sleep disturbance domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e.,worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the pain interference domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the ability to participate in social roles and activities domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., better outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 29-item short-form health-reported quality of life measures (PROMIS-29) were administered. The transformed score (T-score) for the pain intensity domain was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The SCTC GIT is the UCLA Scleroderma Clinical Trial Consortium Gastrointestinal Instrument. It assesses scleroderma-related gastrointestinal symptoms. The composite score ranges from 0 to 2.83; 0 indicates better health and higher score indicates worse health.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The American College of Rheumatology Combined Response Index in Systemic Sclerosis is a composite endpoint. It is determined in a 2-step process. The first step assesses whether the patient has had a significant decline in renal or cardiopulmonary involvement. If none of these apply, the second step assesses the probability of improvement by measuring changes in five outcomes and integrating them into a single number using an equation described in Khanna D, Berrocal VJ, et al. [The American College of Rheumatology Provisional Composite Response Index for Clinical Trials in Early Diffuse Cutaneous Systemic Sclerosis. Arthritis and Rheumatology. 2016; 68(2):299-311.]. It incorporates changes in the modified Rodnan skin score, percent predicted forced vital capacity (FVC), patient and physician global assessments, and SHAQ-DI over 1 year. The score ranges from 0 to 1; a higher score indicates better outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 8-question short-form health-reported quality of life measure fatigue domain was administered. The transformed score (T-score) was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

mITT population includes all of the randomized participants who received at least one dose of study medication.

The Patient-Reported Outcomes Measurement Information System (PROMIS) 4-question short-form health-reported quality of life measure sleep disturbance domain was administered. The transformed score (T-score) was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., better outcome).

Modified Intent-to-Treat population includes all of the randomized participants who received at least one dose of study medication

The Patient-Reported Outcomes Measurement Information System (PROMIS) 8-question short-form health-reported quality of life measure sleep impairment domain was administered. The transformed score (T-score) was used, where 50 (10) is the mean (standard deviation) of a relevant reference population. Higher scores equals more of the concept being measured (i.e., worse outcome).

Modified Intent-to-Treat population includes all of the randomized participants who received at least one dose of study medication

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.

The HAQ-DI is the Health Assessment Question Disability Index that assesses the extent of a patient's functional ability. The HAQ-DI subscore ranges from 0 (no disability) to 3 (severe disability). A higher score means worse outcome.

mITT population includes all of the randomized participants who received at least one dose of study medication.