Targeting apoptosis to induce stable mixed hematopoietic chimerism and long-term allograft survival without myelosuppressive conditioning in mice.

Induction of mixed hematopoietic chimerism results in donor-specific immunological tolerance by apoptosis-mediated deletion of donor-reactive lymphocytes. A broad clinical application of this approach is currently hampered by limited predictability and toxicity of the available conditioning protocols. We developed a new therapeutic approach to induce mixed chimerism and tolerance by a direct pharmacological modulation of the intrinsic apoptosis pathway in peripheral T cells.

The BH3-mimetic ABT-737 inhibits allogeneic immune responses.

Apoptosis controls the adaptive immune system through regulation of central and peripheral lymphocyte deletion. Therefore, substances that selectively interact with the intrinsic apoptosis pathway in lymphocytes offer unexplored opportunities to pharmacologically modulate the immune response. Here, we present evidence that the BH3-mimetic ABT-737 suppresses allogeneic immune responses.

Selection of T-cell receptors with a recurrent CDR3β peptide-contact motif within the repertoire of alloreactive CD8(+) T cells.

Peptide/MHC complexes recognized by alloreactive T lymphocytes (TLs) have been identified, but their contribution to in vivo allo-rejection is not known. We previously characterized the peptide pBM1, highly represented among endogenous H-2K(b) (K(b) )-associated peptides and critically required to induce full activation of H-2(k) monoclonal CD8(+) TLs expressing the cognate TCR-BM3.3.

How much can a T-cell antigen receptor adapt to structurally distinct antigenic peptides?

Binding degeneracy is thought to constitute a fundamental property of the T-cell antigen receptor (TCR), yet its structural basis is poorly understood. We determined the crystal structure of a complex involving the BM3.3 TCR and a peptide (pBM8) bound to the H-2K(bm8) major histocompatibility complex (MHC) molecule, and compared it with the structures of the BM3.

Distinct orientation of the alloreactive monoclonal CD8 T cell activation program by three different peptide/MHC complexes.

We have characterized three different programs of activation for alloreactive CD8 T cells expressing the BM3.3 TCR, their elicitation depending on the characteristics of the stimulating peptide/MHC complex. The high-affinity interaction between the TCR and the K(b)-associated endogenous peptide pBM1 (INFDFNTI) induced a complete differentiation program into effector cells correlated with sustained ERK activation.

Structural and kinetic basis for low affinity cross-reactivity in T cell allorecognition.

The alloreactive BM3.3TCR interacts with high affinity with H-2Kb loaded with the endogenous peptide pBM1 (INFDFNTI), and shows low affinity cross-reactivity for H-2Kb loaded with a viral peptide VSV8 (RGYVYQGL), CTL activity requiring 10(3)-fold higher peptide concentration and being highly sensitive to inhibition by anti-CD8 monoclonal antibody. VSV8 peptides substituted with pBM1/TCR contact residues (N6 and T7) retained low affinity characteristics and among pBM1 peptides substituted with residues Q6 and/or G7 present in VSV8, only pBM1(G7) was recognized, albeit with characteristics akin to those of VSV8.

A T cell receptor CDR3beta loop undergoes conformational changes of unprecedented magnitude upon binding to a peptide/MHC class I complex.

The elongated complementary-determining region (CDR) 3beta found in the unliganded KB5-C20 TCR protrudes from the antigen binding site and prevents its docking onto the peptide/MHC (pMHC) surface according to a canonical diagonal orientation. We now present the crystal structure of a complex involving the KB5-C20 TCR and an octapeptide bound to the allogeneic H-2K(b) MHC class I molecule. This structure reveals how a tremendously large CDR3beta conformational change allows the KB5-C20 TCR to adapt to the rather constrained pMHC surface and achieve a diagonal docking mode.