Engineering of novel Class II Transactivator gene delivery systems as molecular adjuvants to improve genetic immunotherapies by inducing de novo MHC II expression in human cells

Abstract

Class II Transactivator (CIITA) induces transcription of MHC class II genes. This protein can potentially be used to improve genetic immunotherapies by converting non-immune cells into cells capable of presenting antigens to CD4+ T helper cells. However, CIITA expression is complex, tightly controlled and remains unclear whether distinct non-immune cells differ in the regulation of this transcription factor. In the present study, we describe a strategy to develop gene delivery systems capable of promoting the efficient expression of CIITA in non-immune cell lines and in primary human cells in an ex vivo skin explant model. A DNA plasmid and a lentiviral vector were produced, both carrying the human CIITA DNA sequence in silico designed to avoid cis-regulatory elements, and genetically optimized for expression efficacy in human cells. Different human cell types undergoing CIITA overexpression presented high-level de novo expression of MHC II molecules, validating the delivery systems as suitable tools for the evaluation of CIITA potential as a molecular adjuvant for genetic immunizations. Further, we directly compared different non-immune cells according to exogenous CIITA transcriptional activity, protein expression levels and proteasome degradation. Here we show for the first time that distinct types of non-immune cells differentially regulate the transcription factor, and ultimately the cell surface expression of MHC II, through a cell type-specific control of CIITA proteasomal degradation. Our findings contribute to the understanding of the CIITA post-translational regulation by non-immune cells, which can greatly influence the use of this regulator of MHC II genes as a vaccine adjuvant.