Repopulation of γ-irradiated Lewis lung carcinoma by malignant cells and host macrophage progenitors

Abstract

Summary.-Cellular repopulation in Lewis carcinoma irradiated with 60Co y-rays was examined by performing sequential cell-survival estimations using an in vitro soft-agar-colony assay. Following local irradiation (15-35 Gy) two distinct types of colony were seen: compact colonies with tightly packed cells and diffuse colonies with widely dispersed cells. Maximal diffuse colony formation in vitro was only obtained in the simultaneous presence of adequate numbers of compact colonies. After wholebody irradiation only compact colonies were observed.Only cell-survival data from compact colony counts correlated with cell survival estimated by the lung colony assay and we conclude that compact colonies are produced by clonogenic tumour cells. Cytochemical and immunological evidence showed that diffuse colonies were composed of macrophages. After local irradiation the initial kill of clonogenic tumour cells was dose dependent. At each dose level, repopulation began immediately and proceeded with a doubling time of about 1 day. Macrophage colony-forming cells (macrophage progenitors) per tumour were initially reduced by about 3 decades, but recovered very rapidly to reach pretreatment levels within 2 days.We conclude that at least two populations of clonogenic cells are present in Lewis lung carcinoma, tumour cells that repopulate irradiated tumours by in situ proliferation and host-macrophage progenitors that repopulate locally irradiated tumours by infiltration. The hazards of confusing host and tumour cell colonies in in vitro assay systems are stressed.

Macrophage migration and gene expression in response to tumor hypoxia

“…5 It is thought that TAMs are almost entirely derived from peripheral blood monocytes recruited into the tumor from the local circulation rather than the reservoir of resident macrophages already in the healthy tissue before tumor development. 6 Elevated expression of a number of monocyte chemoattractants by both tumor and stromal cells within tumors has been shown to positively correlate with increased TAMs numbers in many human tumors (reviewed in Ref. 7 ) and these are thought to drive the recruitment of monocytes from the bloodstream.…”

“…10 In addition, a number of cytokines and growth factors have also been implicated in the recruitment of monocytes into tumors. These include colony stimulating factor-1 (CSF-1), 6,11 vascular endothelial growth factor (VEGF), 12,13 endothelial monocyte-activating polypeptide II (EMAPII) 14 and endothelin-1. 15 It should be noted that much of the data linking the role of these chemoattractants to monocyte recruitment into tumors have come from descriptive studies correlating their expression with macrophage accumulation in various forms of human tumors.…”

Cell subpopulations dispersed from solid tumours and separated by centrifugal elutriation

“…One such factor arises from the observation that tumours may contain different proportions of neoplastic and non-neoplastic cells, and that these proportions may vary with tumour type (Evans, 1972;Russell et al, 1976;Stewart & Beetham, 1978; (Stephens et al, 1978;Stewart & Beetham, 1978). It is therefore important to evaluate the proportion of host and neoplastic cells in tumours and to assess the role of the non-neoplastic cells in clonogenic cellsurvival assays.…”

Clonal variation in the sensitivity of a murine mammary carcinoma to melphalan

“…Tumour disaggregation was performed as previously described (Stephens et al, 1978 suspension at a concentration of 5 x l04 cells per ml was divided into 2ml aliquots. These were gassed with 90% nitrogen, 5% CO2, 5% oxygen at 37°C for 1.5 to 2.5h.…”

“…Twelve to 14 days after preparation of the cultures colonies were counted, taking care to distinguish between 'compact' tumour cell colonies and 'diffuse' host cell colonies (Stephens et al, 1978 …”