CD40LG and synovial sarcoma: In vitro studies using peripheral blood mononuclear cells from healthy controls and SS patients have shown that the combined use of leflunomide (LEF) and hydroxychloroquine (HCQ) can dose-dependently inhibit the proliferation of T and B cells, and reduce levels of key pro-inflammatory cytokines (CXCL13, IFN-α, IFN-γ) and immunoglobulins (IgG, IgM) associated with SS pathology.