Cblb, also known as Casitas B lymphoma-b, is an E3 ubiquitin ligase. It ubiquitinates proteins downstream of immune receptors, playing a key role in down-regulating positive signaling cascades within the immune system [4]. It is involved in multiple pathways including those related to T cell activation and regulation [3,4]. Genetic models, such as gene knockout (KO) mouse models, have been crucial in studying its functions.

In KO mouse models, T cell-specific deficiency of Cblb (along with Cbl) leads to hyper T follicular helper (Tfh) cell responses and lupus-like symptoms. This occurs as Cblb deficiency reduces the degradation of BCL6, which is upregulated by ICOS signaling [1]. In CD8+ T cells, genetic deletion of Cblb induces resistance to regulatory T cells (Tregs), through IFNγ induction and down-modulation of TGFβ/SMAD signaling, enhancing their anti-cancer effectiveness [2]. In human CD4+ T cells, CBLB-knockout cells are hyperproliferative, produce excessive IL-2, and are resistant to Treg suppression, overcoming it at transcriptional and translational levels [3]. Also, in mice with a Cblb mutation equivalent to that in human patients, T and B cell hyperproliferation is observed in response to antigen receptor cross-linking, along with increased Tregs that have normal in vitro suppressive function, but T effector cells are resistant to WT Treg suppression [4].

In conclusion, Cblb is an important E3 ubiquitin ligase in the immune system, regulating T cell-related signaling pathways. Studies using KO/CKO mouse models have revealed its role in autoimmune diseases like lupus and in cancer-related immune responses, highlighting its potential as a therapeutic target in these disease areas [1,2,3,4].

References:

1. Li, Xin, Sun, Weili, Huang, Mengxing, Lian, Zhe-Xiong, Gu, Hua. 2024. Deficiency of CBL and CBLB ubiquitin ligases leads to hyper T follicular helper cell responses and lupus by reducing BCL6 degradation. In Immunity, 57, 1603-1617.e7. doi:10.1016/j.immuni.2024.04.023. https://pubmed.ncbi.nlm.nih.gov/38761804/

2. Wolf, Dominik, Baier, Gottfried. . IFNγ Helps CBLB-Deficient CD8+ T Cells to Put Up Resistance to Tregs. In Cancer immunology research, 10, 370. doi:10.1158/2326-6066.CIR-22-0080. https://pubmed.ncbi.nlm.nih.gov/35362047/

3. Song, Jing, Anderson, Warren, Hu, Alex, Rawlings, David J, Buckner, Jane H. 2022. CBLB Deficiency in Human CD4+ T Cells Results in Resistance to T Regulatory Suppression through Multiple Mechanisms. In Journal of immunology (Baltimore, Md. : 1950), 209, 1260-1271. doi:10.4049/jimmunol.2200219. https://pubmed.ncbi.nlm.nih.gov/36165179/

4. Janssen, Erin, Peters, Zachary, Alosaimi, Mohammed F, Bertoli-Avella, Aida M, Geha, Raif S. 2022. Immune dysregulation caused by homozygous mutations in CBLB. In The Journal of clinical investigation, 132, . doi:10.1172/JCI154487. https://pubmed.ncbi.nlm.nih.gov/36006710/