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Advances in liposome technology over the last decade has seen the development of stealth liposomes for drug delivery and cationic liposomes for gene delivery. Many of these liposome formulations are now in clinical trials for the treatment of a variety of malignancies. Whilst some clinical efficacy has been demonstrated, the goal of specific tumor targeting is yet to be attained. For this reason, antibodies have been attached to the surface of liposomes to produce immunoliposomes. These liposomes have shown preferential binding to specific tumor cells in animal models. The construction of the immunoliposome, and in particular the optimal method of antibody coupling to its surface is, however, yet to be determined. Despite these difficulties, immunoliposomes have demonstrated anti-tumor properties, both in vitro and in vivo, and show great promise as targeted delivery vehicles for the treatment of cancer.

We have generated a novel hematopoietic cell line which co-expresses lymphoid and myeloid cell surface markers. This cell line, termed E6-2TH, was derived from thymus tissue of a mouse which developed leukemia following lethal irradiation and reconstitution with retrovirally infected bone marrow progenitor cells. Infection was effected with a recombinant murine retrovirus containing v-erb-B. The cells which grew out from the thymus tissue were initially dependent on WEHI-3B conditioned medium as a source of exogenous growth factor, but progressed in culture to become growth factor independent. Flow cytometric analysis using lineage-specific surface markers demonstrated that the initial growth factor dependent cells co-expressed myeloid and B lymphoid antigens, while the derived growth factor independent cells expressed only antigens specific to the B lymphoid lineage. This result indicates a mixed lymphoid/myeloid phenotype in this cell line and subsequent lineage specialisation during in vitro tumor progression.