PMID: 20820193

Authors:

Yang H, Wang J, Du J, Zhong C, Zhang D, Guo H, Guo Y, Ding J

Title:

Structural basis of immunosuppression by the therapeutic antibody daclizumab.

Journal:

Cell Res. 2010 Sep 7.

Abstract:

Interleukin-2 (IL)-2 signaling plays a pivotal role in the activation of immune responses, and drugs that block this pathway have been shown to be effective for the immunosuppression in patients with organ transplantation to alleviate/eliminate allograft rejection. The first humanized monoclonal antibody (mAb) daclizumab falls into this category and shows high specificity and affinity against a key component of the IL-2 receptor complex, namely IL-2Ralpha. To reveal the molecular mechanism of the inhibition of the IL-2 signaling pathway by daclizumab, we determined the crystal structures of the daclizumab Fab in free form and in complex with the IL-2Ralpha ectodomain at 2.6 and 2.8 A resolution, respectively. The daclizumab Fab adopts a similar conformation in the presence or absence of the IL-2Ralpha ectodomain. The antigen-binding site of daclizumab is mainly composed of five complementarity determining regions (CDRs) that form a large positively charged surface depression and two flanking patches that are generally hydrophobic. The conformational epitope consists of several discontinuous segments of the IL-2Ralpha ectodomain, a large portion of which overlaps with the regions that interact with IL-2, suggesting that the binding of daclizumab to IL-2Ralpha would prevent the IL-2 binding to IL-2Ralpha and the subsequent formation of the IL-2/IL-2Ralphabetagamma(c) complex, and therefore block the IL-2 signaling pathway. These results also have implications for the design and development of improved mAb drugs targeting IL-2Ralpha.Cell Research advance online publication 7 September 2010; doi:10.1038/cr.2010.130.