IL-3 affects endothelial cell-mediated smooth muscle cell recruitment by increasing TGFβ activity:: potential role in tumor vessel stabilization

Interleukin-3 (IL-3) express ion by tumor-infiltrating lymphocytes (TILs) and its effects on vessel assembly were evaluated. TILs from 'in situ' human breast cancers expressed CD4/CD25 antigens and IL-3. An injection of Matrigel containing SMC and IL-3 or basic-fibroblast growth factor ( bFGF) into SCID mice confirmed the neoangiogenetic effect of both factors. However, in response to IL-3, but not to bFGF, only few SMC became incorporated into the nascent vessels. To evaluate the possibility that signals emanated by the nascent vasculature in the presence of IL-3 may negatively regulate SMC recruitment, conditioned media ( CM) from IL-3-treated endothelial cells (EC) or SMC were tested for their biological effects on SMC and EC. CM from IL-3-treated SMC stimulated the migration of EC. In contrast, the migration of SMC was not affected by CM from IL-3-stimulated EC; however, it was greatly enhanced by blocking transforming growth factor beta (TGFbeta) activity. TGFbeta immunoenzymatic assay demonstrated the following: (i) the absence of TGFbeta activity in CM from IL-3-stimulated EC; (ii) a barely detectable TGFbeta activity in CM from IL-3-stimulated SMC; and (iii) the presence of TGFbeta activity in the supernatants of SMC stimulated with CM from IL-3-,but not from bFGF-stimulated EC. Increased TGFbeta mRNA expression was only detected in SMC stimulated with CM from IL-3-treated EC. Finally, the inhibitory signals induced by IL-3 in vivo were abrogated by the addition of the neutralizing TGFbeta antibody. Thus, the positive immunostaining for IL-3 by TILs in 'in situ' breast cancers sustains the possibility that early in tumor development, IL-3 can contribute to the chronic immaturity of these vessels.