Exclusion of host cells during spheroid formation from disaggregated solid tumours

Multicellular tumour spheroids have become widely used as a 3-dimensional in vitro model system in radiobiology and experimental chemotherapy (Sutherland & Durand, 1976; Yuhas et al., 1977; Haji-Karim & Carlsson, 1978; Twentyman, 1980). In general, however, spheroids have been initiated either from established tumour cell lines or from cell populations passaged in monolayer in vitro from solid tumours. There has been much recent interest in the possibility of growing spheroids directly from disaggregated clinical tumour material. Suspensions prepared from solid tumours generally contain a considerable population of normal host cells including macrophages, endothelial cells, lymphocytes and granulocytes (Siemann et al., 1981). The proportions will vary between tumour types, but investigation of two different sublines of the EMT6 mouse tumour have showed that 40% of the total cellular composition consists of macrophages (Stewart & Beetham, 1978; Siemann et al., 1981). We therefore decided to investigate whether spheroids derived from the established EMT6 mouse tumour or from