A method for constructing stable bioactive fusion proteins of the difficult to express
tumor necrosis factor superfamily (TNFSF), and particularly members CD40L (CD154) and
RANKL / TRANCE, with collecting, particularly pulmonary surfactant
protein D (SPD) is described. Single trimers of these proteins lack the full stimulatory
efficacy of the natural membrane forms of these proteins in many cases. The multimeric nature of these soluble fusion proteins enables them to engage multiple receptors on the responding cells, thereby, mimicking the effects of the membrane forms of these ligands. For CD40L-SPD, the resulting
protein stimulates B cells, macrophages, and dendritic cells, indicating its potential usefulness as a
vaccine adjuvant. The
large size of these fusion proteins makes them less likely to diffuse into the circulation, thereby limiting their potential
systemic toxicity. This property may be especially useful when these proteins are injected locally as a
vaccine adjuvant or tumor
immunotherapy agent to prevent them from diffusing away. In addition, these and other TNFSF-collectin fusion proteins present new possibilities for the expression of highly active, multimeric, soluble TNFSF members.