A Study to Investigate the Long-term Safety and Efficacy of Belimumab in Adults With Interstitial Lung Disease (ILD) Associated With Systemic Sclerosis (SSc) and Other Connective Tissue Diseases (CTD) (BLISSconneCTD-OLE)

This is an open label extension (OLE) study of an ongoing randomized controlled parent clinical studies 218224 (NCT05878717) and 221672 (NCT06572384) which aim to assess the efficacy and safety of belimumab on reducing the decline in lung function in participants with interstitial lung disease associated with diffuse cutaneous systemic sclerosis (dcSSc-ILD) and interstitial lung disease associated with other connective tissue diseases (CTD-ILD), respectively. The OLE study will describe how well tolerated belimumab will be long term, and whether it might continue to slow progression of lung function decline, slow overall disease progression and improve quality of life.

Inclusion Criteria: * Participants with SSc-ILD or other CTD-ILDs that have completed either study 218224 or 221672 through to and including the Week 52 visit and are not considered treatment failure, defined as meeting either of the following criteria: * Discontinuation of study medication during study 218224 or 221672 for any reason. * Participants with SSc should have an area of uninvolved or mildly thickened skin that, in the opinion of the investigator, would allow subcutaneous (SC) injection at the abdomen or the front, middle region of the thigh. * Participant is capable and willing to self-administer the study medication or has a caregiver/healthcare professional who is capable and willing to administer the study medication throughout the study. * Female participants: A female participant is eligible to participate if she is not pregnant or breastfeeding, and one of the following conditions applies: Is a woman of non-childbearing potential (WONCBP) or is a woman of childbearing potential (WOCBP) and using a contraceptive method that is highly effective, with a failure rate of less than (\) 480 millisecond (msec) at Week 52 of parent study 218224 or study 221672.