The Ubiquitin E3 Ligase Cbl-b in T Cells Tolerance and Tumor Immunity

The implication of the immune system in tumor surveillance is proven and widely accepted. However, anti-cancer immunotherapy is still difficult due to insufficient activation, immune suppression and tolerance induction. The ubiquitin E3 ligase Cbl-b, is a member of the Cbl (Casitas B-lineage Lymphoma) protein family and was identified as a key dominant “tolerogenic” factor in T cells that directly regulates T-cell activation by controlling activation thresholds and the requirement for co-stimulation. Intriguingly, Cbl-b deficient mice spontaneously reject a variety of cancers including spontaneous solid tumors and hematopietic malignancies. Mechanistically, modulation of Cbl-b in T cells controls activation of tumor-reactive cytotoxic T cells in vivo and might circumvent several limitations of T cell immunotherapy. Therefore manipulation of Cbl-b might provide us with a unique opportunity for future immune treatment of human disorders such as autoimmunity, chronical viral infections, or cancer.