Hematopoietic growth factors in clinical hematology

Enhanced killing capacity of human Kupffer cells after activation with human granulocyte/macrophage-colony-stimulating factor and interferon gamma

In this study we investigated the effect of the cytokines human granulocyte/macrophage-colony-stimulating Factor (hGM-CSF) and interferon gamma (IFN gamma) on human Kupffer-cell-mediated cytotoxicity against the SW948 colon carcinoma cell line. Kupffer cells were isolated from small liver wedge biopsies, taken from 14 patients who had had abdominal surgery for colon carcinoma or partial hepatectomy. The cells were incubated with hGM-CSF (100 ng/ml), or with IFN gamma (100 U/ml) or with their combination and the percentage cytotoxicity was determined using a recently described modified assay. Additional experiments were performed with tumour-necrosis-factor-alpha (TNF alpha)-sensitive U937 cells as target. The TNF alpha secretion of Kupffer cells was measured and we evaluated the effect of TNF alpha on colon tumour targets. We performed human-Kupffer-cell-mediated cytotoxicity blocking experiments with anti-TNF alpha and used paraformaldehyde-fixed Kupffer cells to demonstrate lysis of TNF alpha-sensitive WEHI-164 cells and of SW948 cells. The overall cytotoxicity against SW948 caused by unactivated Kupffer cells (n = 14), and by Kupffer cells activated with hGM-CSF (n = 14), IFN gamma (n = 6) or their combination (n = 6) was respectively: 19.5 +/- 2.6%, 25.3 +/- 2.9%, 41 +/- 9.4% and 45.6 +/- 8% at E/T = 1 and 28.2 +/- 2.9%, 35.6 +/- 3.2%, 55.6 +/- 9.7% and 62.8% at E/T = 5. All differences were statistically significant (P < 0.05). No growth-promoting activity by hGM-CSF on the SW948 tumour cells was observed. U937 cells were highly susceptible to Kupffer-cell-mediated cytotoxicity. The TNF alpha secretion by human Kupffer cells increased in parallel to their cytotoxicity after incubation with these cytokines. Soluble TNF alpha had only a slight anti-proliferative effect on SW948 cells, while specific anti-TNF alpha blocked Kupffer cell cytotoxicity by up to 80%. Finally, paraformaldehyde-fixed Kupffer cells were able to lyse WEHI-164 and SW948 cells. This indicates that expression of cell-associated TNF alpha is the main cytolytic mechanism of human-Kupffer-cell-mediated cytotoxicity. The implications for the use of hGM-CSF and IFN gamma in vivo are discussed.

Transgenic animals as bioproducers of therapeutic proteins

Many human therapeutic proteins are currently produced with the aid of recombinant DNA technology in microbial bioreactors and a few also in large-scale animal cell cultures. Although extremely cost-efficient, the microbial production system has many inherent limitations. Micro-organisms, such as bacteria, can read the universal genetic code and hence produce human proteins with correct amino acid sequence, but cannot carry out post-translational modifications, such as glycosylation, or fold the newly synthesized protein properly to ultimately generate a biologically active entity. Moreover, even though the production of the proteins as such is inexpensive, the downstream processing of the final product may be extremely difficult and costly. Many of these disadvantages, especially the lack of post-translational modifications, can be overcome by employing large-scale animal cell cultures for the production of proteins of pharmaceutical interest. However, due to the long generation time and the requirement for rich culture media, the use of animal cell bioreactors is unacceptably expensive. With the advent of transgenic technology, the production of human pharmaceuticals in large transgenic animals has become more and more attractive. The use of targeted gene transfer, the expression of the transgene of interest can be directed to occur in the mammary gland of large farm animals, such as pigs, sheep, goats or dairy cattle, and hence the transgene product is ultimately being secreted into the milk. Although not yet in commercial use, the last few years have witnessed a remarkable progress in this area and proved the feasibility of the use of 'molecular farming' in high-quantity, low-cost production of valuable therapeutic or industrial proteins. While reviewing the progress of the field over the past few years, we discuss in somewhat greater detail aspects connected with the use of dairy cattle as bioproducers of human therapeutic proteins.