Quantitative characterization of CTLA4 trafficking and turnover using a combined in vitro and in silico approach

12 CTLA4 is an essential negative regulator of T cell immune responses and is a key checkpoint regulating 13 autoimmunity and anti-tumour immunity. Genetic mutations resulting in a quantitative defect in CTLA4 are 14 associated with the development of an immune dysregulation syndrome. Endocytosis of CTLA4 is rapid and 15 continuous with subsequent degradation or recycling. CTLA4 has two natural ligands, the surface transmembrane 16 proteins CD80 and CD86 that are shared with the T cell co-stimulatory receptor CD28. Upon ligation with 17 CD80/CD86, CTLA4 can remove these ligands from the opposing cells by transendocytosis. The efficiency of 18 ligand removal is thought to be highly dependent on the processes involved in CTLA4 trafficking. With a combined 19 in vitro-in silico study, we quantify the rates of CTLA4 internalization, recycling and degradation. We incorporate 20 experimental data from cell lines and primary human T cells. Our model provides a framework for exploring the 21 impact of altered affinity of natural ligands or therapeutic anti-CTLA4 antibodies and for predicting the effect of 22 clinically relevant CTLA4 pathway mutations. The presented methodology for extracting trafficking rates can be 23 transferred to the study of other transmembrane proteins. 24 1 not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/106898 doi: bioRxiv preprint first posted online Feb. 8, 2017;