TIE2⁺ monocytes are found in human tumors. Flow cytometry analysis of the indicated tumor specimens, processed and analyzed as described in the text. FITC-conjugated anti-CD31 or anti-CD14, PE-conjugated anti-TIE2, or APC-conjugated anti-CD45 antibodies were used. (A) Breast carcinoma. Note that the gated CD31⁺CD45⁻ tumor-derived ECs are TIE2⁺ (red open line in the histogram on the right; filled line is the IgG isotype control). (B) Renal carcinoma. In this tumor specimen, approximately 2% of the tumor-derived cells are CD31⁺ (CD45⁻, not depicted) ECs. The wide majority of these CD31⁺ tumor-derived ECs are TIE2⁺. Note that a fraction of the tumor-derived cells are CD31⁻TIE2⁺ non-ECs (top right dot plot). In the same tumor sample, approximately 10% of tumor-derived cells are CD45⁺ hematopoietic cells. Only a minor fraction (12%) of these CD45⁺ cells are TIE2⁺ (bottom right dot plot). (C) Colon carcinoma (left) and nonneoplastic colon mucosa (right). In the tumor, 4% of the abundant CD45⁺ hematopoietic cells and most of the CD14⁺ monocytes are TIE2⁺. In the normal mucosa, CD45⁺ hematopoietic cells are much less abundant than in the tumor, and only a few TIE2⁺ cells are found. Note that CD14⁺ monocytes are not detected in the normal mucosa. (D) Lung adenocarcinoma (left) and nonneoplastic lung tissue (right). In the tumor, more than 30% of the cells are CD45⁺ hematopoietic cells, of which 6% are TIE2⁺. Most of the tumor-derived CD14⁺ monocytes are TIE2⁺. In the normal lung tissue, the CD45⁺ hematopoietic cells are TIE2⁻; note that CD14⁺ monocytes are not found in this tissue.