Phage display-derived recombinant antibodies with TCR-like specificity against alpha-galactosylceramide and its analogues in complex with human CD1d molecules.

The glycolipid alpha-galactosylceramide (alpha-GalCer) is a potent activator of invariant natural killer T (iNKT) cells and has been shown to be an effective agent against cancer, infections and autoimmune diseases. The effectiveness of alpha-GalCer and its alkyl chain analogues depends on efficient loading and presentation by the antigen-presenting molecule CD1d. To monitor the ability of CD1d to present the glycolipids, we have used a phage display strategy to generate recombinant antibodies with T cell receptor-like (TCRL) specificity against the human CD1d (hCD1d)-alpha-GalCer complex. These Fab fragments were able to detect specifically hCD1d-alpha-GalCer complexes in cell-free systems such as surface plasmon resonance and ELISA, as well as on the surface of hCD1d(+) antigen-presenting cells (APC) by flow cytometry and immunofluorescence microscopy, the latter of which could also detect intracellular complexes. We show that our TCRL antibodies can stain dendritic cells from CD11c-hCD1d-transgenic mice administered in vivo with alpha-GalCer and its analogues. Furthermore, the antibody was also able to detect the presentation by hCD1d molecules of analogues of alpha-GalCer with the same polar head structure. Using this reagent, we were able to confirm directly that the alpha-GalCer analogue C20:2 preferentially loads onto cell surface CD1d rapidly without the need for internalization, while the loading of alpha-GalCer is improved with longer incubation times on professional APC. This reagent will be essential for assessing the loading and presenting capabilities of hCD1d of alpha-GalCer and its analogues.