The molecular interactions that mediate signaling of T and B lymphocytes, both during development and in activation of mature T and B cells, are not fully understood. Genetic and biochemical approaches have therefore been taken to address these questions. Costimulatory B7 molecules (B7-1 or CD80; and B7-2 or CD86) are known to bind to T cell costimulatory receptors CD28 and CTLA4. Engagement of CD28 is know to transduce signals in T cells that play a critical role in T cell activation. TCR mediated activation of T cells to proliferation and IL2 secretion was enhanced in mice deficient in the adapter molecule cbl-b, suggesting a negative regulatory role for cbl-b under these conditions. Cbl-b deletion in fact reversed the inability of CD28-deficient mice to generate T cell-dependent Ig class switched primary and secondary antibody responses. Surprisingly, however, cbl-b deletion did not reverse the functional defect of B7 (CD80/CD86) deficient mice, indicating an unexpected difference between the requirement for CD28 and for CD28 ligand B7 molecules. Moreover, cbl-b inactivation substantially reversed the immune response defect in mice deficient in both CD28 and B7. Overall, these results suggest the unanticipated conclusion that the expression of CD28 has a strong negative regulatory effect on immune response in the absence of its B7 ligands. The mechanism underlying these effects is under study employing CD28 mutant transgenes. The relationship between members of the cbl family and other critical adapter molecules has been studied. Experiments have indicated that inactivation of c-cbl (but not cbl-b) completely reverses the lethal phenotype caused by SLP-76 deficiency. In addition, c-cbl inactivation partially reverses the defect in T cell development caused by deficiency in SLP-76 or LAT, resulting in fact in a marked hyperplasia of peripheral CD4 T cells. These findings indicate an unanticipated SLP-76 (and LAT) independent signaling pathway that is facilitated by c-cbl inactivation. The biochemical basis for these effects is under study, using SLP-76 mutants to dissect the structure-function relationships in this pathway. SLP-65 (also termed BLNK) is an adapter molecule that plays a central role in development of B cells, and mice deficient in BLNK manifest severe impairment in early as well as late stages of B cell development. We have observed that inactivation of c-cbl results in substantial rescue of early B cell development by facilitating signaling through the pre-BCR, demonstrating that c-cbl negatively regulates a BLNK-independent pathway of early B cell maturation. The observation that cbl-b inactivation can enhance T cell responses to TCR signaling, and can bypass requirements for CD28 costimulation has been translated to studies of tumor rejection. Inactivation of cbl-b enhances the ability of mice to reject tumors that do not express costimulatory ligands (CD80 or CD86), and that grow progressively in wild type mice. Cbl-b inactivation also dramatically inhibits the incidence of thymic lymphomas in ATM-deficient mice. These findings identify a novel strategy for enhancing T cell-mediated tumor immunotherapy by modulating regulatory influences on T cell activation.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Intramural Research (Z01)
Project #
1Z01BC009281-21
Application #
7592603
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
21
Fiscal Year
2007
Total Cost
$746,520
Indirect Cost
Name
National Cancer Institute Division of Basic Sciences
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Williams, Joy A; Lumsden, Joanne M; Yu, Xiang et al. (2008) Regulation of thymic NKT cell development by the B7-CD28 costimulatory pathway. J Immunol 181:907-17
Song, Haifeng; Zhang, Juan; Chiang, Y Jeffrey et al. (2007) Redundancy in B cell developmental pathways: c-Cbl inactivation rescues early B cell development through a B cell linker protein-independent pathway. J Immunol 178:926-35
Chiang, Jeffrey Y; Jang, Ihn Kyung; Hodes, Richard et al. (2007) Ablation of Cbl-b provides protection against transplanted and spontaneous tumors. J Clin Invest 117:1029-36
Williams, Joy A; Hathcock, Karen S; Klug, David et al. (2005) Regulated costimulation in the thymus is critical for T cell development: dysregulated CD28 costimulation can bypass the pre-TCR checkpoint. J Immunol 175:4199-207
Chiang, Y Jeffrey; Sommers, Connie L; Jordan, Martha S et al. (2004) Inactivation of c-Cbl reverses neonatal lethality and T cell developmental arrest of SLP-76-deficient mice. J Exp Med 200:25-34
Zhang, Juan; Chiang, Yungping J; Hodes, Richard J et al. (2004) Inactivation of c-Cbl or Cbl-b differentially affects signaling from the high affinity IgE receptor. J Immunol 173:1811-8