Abstract 152

Background: Natural killer cells (NK cells) are defined as CD56+CD3- cells, displaying a morphology of large granular lymphocytes (LGL cells). NK cells mediate unspecific immunity and are able to kill virus-infected and malignant transformed cells. Cytokine-stimulated NK cells may be useful in clinical trials of immunotherapy. We examined an immunomagnetic enrichment system, which allows a highly selective purification of CD56+ cells.

Material and Measurements: CD56+ cells were isolated by Magnetic Cell Separation (MACS), cord blood (n=12), adult controls (n=10). Cells were stained with T cell specific monoclonal antibodies CD3, CD4, CD8 and with CD56. Flow cytometric analysis was done on a FACScan.

Results: Mononuclear cells displayed a fraction of 9.5% CD56+ cells (range 0.7-21.3%) in neonates and a fraction of 16.6%(range 8.2-33.0%) in adults. Enriched cells (MACS) derived from neonates[adult controls] stained positive for CD56 with 97.2 ± 1.4%(±SD) [96.7 ± 0.7%]. CD56-specific coexpression of T cell markers differed markedly: CD8 was expressed to an extent of 43.6 ± 13.8% [50.8 ± 10.7%]. CD4 was found on CD56+ cells with 3.6± 3.1% [10.4 ± 7.7%]. CD3 displayed significant different values (p<0.02) of 7.2%, range 2.0-17.1%, in neonates, and 35.2%, range 14.3-75.7%, in adult controls.

Conclusions: The method of immunomagnetic isolation represents a powerful tool to enrich selectively CD56+ cell of cord blood and adult controls. Resulting cell populations differed in their coexpression of T cell markers. A remarkable fraction of adult CD56+ cells coexpressed CD3 and should therefore be considered as a T cell subset and not as a NK population. In contrast, the majority (>92%) of neonatal CD56+ cells displayed the NK cell specific CD56+CD3- phenotype.

Supported by fortüne 328, University of Tübingen