Fluorescent Signaling By Immune Cells

Autoimmune cells can now be closely observed in vivo. Scientists from the Max Planck Institute for Neurobiology in Martinsried/Germany succeeded in engineering intact immune cells carrying a gene encoding a fluorescent marker protein and in introducing these genetically modified cells into the organism. These labeled immune cells can be traced and functionally analyzed at any location in the body (Nature Medicine, July 1999).

Traditionally, cell biological processes are studied in cultured cells in vitro. The results allow, however, only limited conclusions about the real behavior of the analyzed cells in the living body since decisive factors, like influences of the natural environment and the cellular milieu, cannot be mimicked in vitro. Therefore, there have been many attempts to study T cells directly in vivo. This approach requires, however, an unequivocal identification of the respective cells.

A suitable technique which allows such an identification now has been developed by scientists from the Max Planck Institute for Neurobiology in Martinsried/Munich. They infected a certain immune cell type, namely CD4+ T lymphocyte, with a recombinant retrovirus into which a gene for the green fluorescent protein (GFP) had been inserted. During the infection the gene is introduced into the cells and stabily incorporated into their genomes. In contrast to previous approaches, this technique resulted in almost 100% gene transfer rate and in a life-long expression of the "fluorescent gene". The GFP gene is a physiological part of the jelly fish Aequorea Victoria and represents a unique biological label: it shines green when exposed to UV light.

CD4+ T cells play a central role in the coordination of the immune system. Accordingly, they are involved in most immune reactions including those directed against body-derived tissues, so called autoimmune reactions. Multiple sclerosis is one of those autoimmune diseases. The Max Planck scientists now show how disease-causing T cells can be visualized in the body. They introduced the GFP gene into T cells which are directed against a myelin protein of the central nervous system. Such genetically modified myelin-specific T lymphocytes maintain all their functional properties including their capability to evoke an autoimmune disease. In the animal model of experimental autoimmune encephalomyelitis, they induce symptoms resembling those of multiple sclerosis, such as paralysis, weight loss, and incontinence. Due to their green label, these disease-causing T cells can be located in every tissue of the body. Furthermore, for the first time these cells can be isolated ex vivo and tested for their functional properties without additional manipulations.

Another field of application of GFP-engineered T cells involves the examination of T cell-based immune memory. The scientists of the Max Planck Institute for Neurobiology could show that, under certain conditions, GFP-labeled T cells integrate into the immune system and can be traced and followed for long periods of time.

The new gene transfer technique with the introduction of GFP into T cells opens new insights into physiological processes of the immune system and inflammatory (auto)immune diseases. The method may lead to the development of novel therapeutic approaches. The scientists are currently evaluating the therapeutic potential of T cells. In the course of their immune surveillance, T cells migrate into nearly every tissue of the body. The scientists are now developing methods to arm T cells with various therapeutic genes and use them for genetically-based therapies.

Original article:Alexander Flügel, Michael Willem, Tomasz Berkowicz und Hartmut Wekerle: "Gene transfer into CD4+ T lymphocytes: Green fluorescent protein-engineered, encephalitogenic T cells illuminate brain autoimmune responses", Nature Medicine, Volume 5, Number 7, July 99, pp 843-847.