Intravital imaging of stromal cell dynamics in tumors

Abstract

Tumor stroma, consisting of the extracellular matrix and multiple cell types such as immune cells, fibroblasts and vascular cells, contributes to the malignancy of solid tumors by a variety of mechanisms. Intravital imaging by different microscopy techniques, especially by confocal and multi-photon microscopy, has proven to be a powerful method for analyzing the cell-cell and cell-matrix interactions in the dynamic tumor microenvironments. Intravital imaging has fostered the acquisition of data on parameters such as motility of different cell types in distinct tumor regions or manipulated with defined challenges, kinetics of tumor cell killing by T cells or macrophage-assisted tumor cell extravasation, functionality of the vasculature, protease activity and metabolic state. Achieving the direct observation of intact tumors offered by intravital imaging provides unique insights into tumor biology that will continue to deepen our understanding of the processes leading to malignancy and of the ways they can be targeted.

Figure 1

A series of stills from a time lapse movie of over 4 hours of an early MMTV-PyMT tumor taken with a spinning confocal microscope. Tumor cells are visualized by the high transgenic expression of CFP under the β-actin promoter (blue). The c-fms promoter directs GFP expression to myeloid cell, mostly macrophages (green). Rhodamine-dextran (red) injected into the tail vein immediately before imaging accumulates first in the blood vessels, slowly leaks and is taken up by stromal macrophages, and eventually disappears from the blood vessels over time. Macrophages that have ingested dextran (arrows) remain sessile, whereas some other myeloid cells, especially on the tumor margins, are seen to migrate (arrowheads). The panels are maximum intensity projections of three z planes at 4 m intervals. The images have been modified to improve brightness and contrast.