Small multivalent architectures mimicking homotrimers of the TNF superfamily member CD40L: delineating the relationship between structure and effector function.

Synthetic multivalent ligands, owing to the presence of multiple copies of a recognition motif attached to a central scaffold, can mediate clustering of cell surface receptors and thereby function as effector molecules. This paper dissects the relationship between structure and effector function of synthetic multivalent ligands targeting CD40, a cell surface receptor of the tumor necrosis factor receptor (TNF-R) superfamily. Triggering CD40 signaling in vivo can be used to enhance immunity against intracellular pathogens or tumors. A series of multimeric molecules has been prepared by systematically varying the shape and the valency of the central scaffold, the nature and the length of the linker as well as the sequence of the receptor binding motif. The data reported here (i) suggest that radial distribution of CD40-binding units and C3-symmetry are preferred for optimal binding to CD40 and signaling, (ii) underscore the importance of choosing an appropriate linker to connect the receptor binding motif to the central scaffold, and (iii) show the versatility of planar cyclic alpha- and beta-peptides as templates for the design of CD40L mimetics. In particular, the (Ahx)3-B trimeric scaffold-linker combination equally accommodated binding elements derived from distinct CD40L hot-spot regions including AA" loop and beta-strand E. The use of miniCD40Ls such as those reported here is complementary to other approaches (recombinant ligands, agonistic anti-receptor antibodies) and may find interesting therapeutic applications. Furthermore, the results disclosed in this paper provide the basis for future design of other TNF family member mimetics.

Cutting edge: small molecule CD40 ligand mimetics promote control of parasitemia and enhance T cells producing IFN-gamma during experimental Trypanosoma cruzi infection.

Host resistance to Trypanosoma cruzi infection depends on a type 1 response characterized by a strong production of IL-12 and IFN-gamma. Amplifying this response through CD40 triggering results in control of parasitemia. Two newly synthesized molecules (<3 kDa) mimicking trimeric CD40L (mini CD40Ls(-1) and (-2)) bind to CD40, activate murine dendritic cells, and elicit IL-12 production. Wild-type but not CD40 knockout mice exhibited a sharp decrease of parasitemia and mortality when inoculated with T. cruzi mixed with miniCD40Ls. Moreover, the immunosuppression induced by T. cruzi infection was impaired in mice treated with miniCD40Ls, as shown by proliferation of splenic lymphocytes, percentage of CD8(+) T cells, and IFN-gamma production. Mice surviving T. cruzi infection in the presence of miniCD40L(-1) were immunized against a challenge infection. Our results indicate that CD40L mimetics are effective in vivo and promote the control of T. cruzi infection by overcoming the immunosuppression usually induced by the parasites.

Macaque multimeric soluble CD40 ligand and GITR ligand constructs are immunostimulatory molecules in vitro.

CD40 ligand (CD40L) and GITR ligand (glucocorticoid-induced tumor necrosis factor receptor-related protein ligand [GITRL]) are tumor necrosis factor superfamily molecules that can be used as vaccine adjuvants. In a previous human immunodeficiency virus (HIV) DNA vaccine study in mice, we found that plasmids expressing multimeric soluble forms of trimeric CD40L (i.e., many trimers) were stronger activators of CD8(+) T-cell responses than were single-trimer soluble forms or the natural membrane-bound molecule. This report describes similar multimeric soluble molecules that were constructed for studies in macaques. Both two-trimer and four-trimer forms of macaque CD40L were active in B-cell proliferation assays using macaque and human cells. With human cells, four-trimer macaque GITRL costimulated CD4(+) T-cell proliferation and abrogated the immunosuppressive effects of CD4(+) CD25(+) regulatory T cells on a mixed leukocyte reaction. These molecular adjuvants provide new tools for vaccine development in the simian immunodeficiency virus system and other macaque models.

Solid-phase synthesis of CD40L mimetics.

The C3-symmetric molecule has been previously shown to mimic CD40 ligand (CD40L) homotrimers and to display effector functions. This molecule consists of a cyclic hexapeptide core containing the repetition of the D-Ala-L-Lys motif. The side chains of the lysine residues have been modified by appending the CD40L-derived sequence 143Lys-Gly-Tyr-Tyr146 via a 6-aminohexanoic acid residue as a spacer. The present report describes a general solid-phase synthesis approach to and related trimeric architectures. In addition, their CD40 binding properties as well as their effector functions have been evaluated.