C3dCR2

C3dCR2 is a recombinant fusion construct used in immunology that couples the complement fragment C3d to the extracellular portion of the B cell co-receptor CR2 (CD21). The design aims to exploit the natural C3d–CR2 interaction to enhance B cell responses to co-administered antigens, serving as a molecular adjuvant in vaccine contexts.

Mechanism and function: C3dCR2 binds to CR2 on B cells, which is part of the B cell co-receptor complex that also includes CD19 and CD81. When an antigen bound by the B cell receptor (BCR) is presented together with C3dCR2, the engagement of CR2 lowers the threshold for B cell activation and promotes stronger signaling through the BCR–co-receptor complex. This can lead to enhanced germinal center formation, affinity maturation, and higher antigen-specific antibody titers in preclinical models.

Applications and research status: C3dCR2 has been explored as a strategy to improve the immunogenicity of protein antigens in animal studies. It is studied primarily as a research tool for vaccine design and immunotherapy, rather than as an approved therapy. Variants may differ in the precise fusion configuration or in how the C3d and CR2 components are presented.

Production and considerations: The construct is typically produced as a recombinant protein or as part of a genetic fusion in experimental vaccine platforms. Research considerations include ensuring targeted B cell activation without inducing undesirable autoimmunity, preserving protein stability, and achieving scalable manufacturing.

See also: Complement system, CR2, C3d, B cell activation, vaccine adjuvant.