Under the terms of the agreement, Spero takes control of the antibody—referred to internally as SP001—to target immune-mediated diseases where existing treatment options remain limited. The collaboration leverages Innovent’s initial research, which includes Phase 1 studies in healthy volunteers and patients with Sjögren's disease. Spero intends to launch a Phase 2 trial for IgG4-related disease by the second quarter of 2027, while Innovent will continue separate development of the drug for Sjögren's disease in China, with a Phase 2 study expected by early 2027.

IBI355 functions by blocking CD40L, a protein that acts as an upstream signal for immune activation. By inhibiting this pathway without depleting B-cells, the therapy aims to address the underlying causes of chronic inflammation and tissue damage. Spero’s CEO Esther Rajavelu stated that the acquisition provides a foundational asset for the company’s pivot toward immune-mediated therapeutics, noting the potential for the drug to be applied across a broader range of autoimmune conditions beyond its initial focus.