Expression of Hepatocyte Growth Factor and Mesenchymal-epithelial Transition Factor by Human T Cells

The cytokine hepatocyte growth factor (HGF) has been studied extensively since its discovery in the 1980’s, where it was identified as a mitogenic factor involved in the extraordinary ability of the liver to regenerate in rats. Since that time, HGF has been shown to be present in human serum and is mainly produced by cells of mesenchymal origin. Originally, HGF was named scatter factor because of its effects on in vitro cultured epithelial cells, where treatment resulted in monolayer disruption, motility, and scattering. Indeed, the effects of hepatocyte growth factor have been summarized as promoting motility, growth, and invasiveness. These effects occur through signal transduction by the receptor for hepatocyte growth factor, mesenchymal-epithelial transition factor (c-Met), a receptor tyrosine kinase that is expressed by epithelial cells in a wide range of tissues. The c-Met receptor is unique in that it has a C-terminal multifunctional docking site that can directly recruit several primary effectors and scaffold proteins. c-Met is the product of the proto-oncogene MET, and the effects of signaling by this receptor have been described as initiating a program of invasive growth. Accordingly, much of the existing body of research on this topic has been conducted within the context of cancer.

The production of hepatocyte growth factor protein by a human CD4⁺ T cell line was first reported in 2000. However, further study into T cell expression of HGF has not been published. Thus, there is a significant gap in the literature. Similarly, an innovative study on the expression of c-Met by T cells was first published in 1994. There, the researchers show that T cells responded to treatment with HGF protein, however they could not detect c-Met mRNA or protein expression by the cells. It was not until 2022 that expression of c-Met by human primary T cells was thoroughly proven. However, study of the gene expression of c-Met⁺ T cells remains sparse. This is partially due to the fact that c-Met expressing T cells are rare in the peripheral blood of healthy humans, which makes isolation of an adequate quantity of cells difficult.

This thesis proves the expression of HGF mRNA and protein by in vitro differentiated human primary CD4⁺ and CD8⁺ T cells. Furthermore, CD4⁺ T cells that have been differentiated into the T-helper 1 (Th1) subset are shown to be the most positive. In similar fashion, it confirms c-Met mRNA and protein expression by human primary CD4⁺ T cells and shows that cells that have been differentiated into the T-helper 2 (Th2) subset are the most positive. In addition, it demonstrates a method for the rapid enrichment of a viable fraction of T cells based on surface expression of c-Met protein, resulting in a pool of cells with higher MET gene expression. This method enabled the study of c-Met⁺ CD4⁺ T cell gene expression and phenotype through cellular indexing of transcriptomes and epitopes by sequencing, and of the bulk gene expression of c-Met enriched cell pools through bulk RNA-sequencing. Together, these findings indicate that HGF producing T cells could play a role in disease where Th1 are present, and that c-Met⁺ CD4⁺ T cells may be important during Th2 driven processes.