Abstract
Tumors consist of a heterogeneous population of neoplastic cells infiltrated by an equally heterogeneous collection of nonneoplastic cells that comprise the tumor microenvironment. Tumor growth, invasion, and metastasis depend on multiple interactions between these cells. To assess their potential as therapeutic targets or vehicles for tumor specific delivery of therapeutic agents, we examined the contribution of bone marrow derived cells (BMDCs) to the intestinal tumor microenvironment. Hematopoietic stem cells expressing the enhanced green fluorescent protein (eGFP) were transplanted into lethally irradiated ApcMin/+ mice, and their engraftment was analyzed by confocal microscopy. The results showed abundant infiltration of eGFP cells into the small intestine, colon, and spleen compared to heart, muscle, liver, lung, and kidney. Within the intestine, there was a pronounced gradient of engraftment along the anterior to posterior axis, with enhanced infiltration into adenomas. Immunofluorescence analysis showed that osteopontin was expressed in tumor stromal cells but not in nontumor stromal populations, suggesting that gene expression in these cells is distinct. Tumor vasculature in ApcMin/+ mice was chaotic compared to normal intestinal regions. Our data suggest that BMDCs can be harnessed for tumor-targeted therapies to enhance antitumor efficacy.