Screening, Identification And Functionalanalysis Of Mouse Thymus Targeted Phage Peptide

The thymus gland is a central lymphoid organ for the output of the mature T cell. Although the function of the thymus for the maturation of the T cell may be halted after puberty in human, it may serve as a place to preserve the unwanted autoreactive T cell repertoire, which leads to proliferation or malignancy in the thymus. Of great importance, in humans thymoma may trigger the self-specific unwanted autoreactive inmate T cells, which result in the autoimmune diseases. The high degree of molecular conservation in the thymus microenvironment between mouse and human has been revealed. Moreover, the thymus in mouse preserves its immunological function during the whole life. So mouse was selected to study thymus.Heterogeneity of the vasculature in different organs has been well documented by the method of in vivo phage display. Using this technology, several peptide ligands that home to tissue-specific vascular endothelial cell have been isolated. Such peptide ligands not only directed against organ specific vascular surface molecules but also triggered functional changes of the organ.Previous study suggested using in vivo phage display, targeted phage particles to the lymphoid organ can be selected, which might result in the change of immune response. This strategy may improve targeted immunotherapy. We hypothesized mouse thymus targeted phage peptide might trigger functional change of thymus immunity, which could be used to selectively modulate immunological function of thymus.In this study, we performed three iterative rounds of in vivo panning in mice using a phage display random peptide library and separated phage peptide CHAQGSAEC homing to mouse thymus. Immunohistochemistry and competitive binding assay of cognate synthesis peptide confirmed that the phage peptide CHAQGSAEC can bind specifically to thymus blood vessels in mice. Furthermore, phage peptide CHAQGSAEC and cognate synthetic peptide CHAQGSAEC can inhibit the bioactivity of thymus output in vivo by the analysis of T cell receptor excision circle expression in the peripheral blood.These results confirmed the hypothesis and suggested mouse thymus targeted phage peptide isolated by in vivo phage display can trigger functional change of thymus immunity. The peptide selectively modulates immunological function of thymus and can be used to study unwanted autoreactive thymus function and modulate the immune response. The study also indicated the feasibility of the in vivo phage display for the identification of targeted vector, and may be useful to identify the targeted peptide ligand of tumor in the animal model of cancer in our following study.