A recombinant form of the monoclonal IgM antibody M12 isolated from a Waldenstrom macroglobulinaemia patient (rHIgM12) with potential immunomodulating activity. B7-DC cross-linking antibody rHIgM12B7 binds and crosslinks the B7 co-stimulatory family member B7-DC (PD-L2) on dendritic cells (DCs), antigen presenting cells (APCs) that play a crucial role in the human immune response. This results in enhanced activation of DCs; enhanced antigen-presenting activity; and increased production of immunomodulatory cytokines (especially interleukin 12); and may potentiate a specific cytotoxic T lymphocyte (CTL) response against Waldenstrom macroglobulinaemia B cells.