GFP-marked THP-1 cells (THP-1/GFP) coinjected with human LAGλ-1 MM tumor cells into C.B-17 SCID/SCID mice become incorporated into tumor blood vessels and express VEC markers. Human LAGλ-1 MM tumor cells were injected subcutaneously alone or in combination with THP-1/GFP monocytes into mice. Six weeks later, tumors were excised and immediately fixed with formalin. Tumor sections were prepared using standard histologic protocols. (A) Cells expressing GFP were determined using fluorescence and immunofluorescence was determined in sections stained with anti–human Tie-2 and anti-Dapi antibodies. (B) Another tumor blood vessel from a SCID mouse containing LAGλ-1 and THP-1/GFP cells was stained with anti–human CD144 (VE-cadherin) antibodies. Similarly, cells expressing GFP were determined using fluorescence and immunofluorescence was determined in sections stained with anti–human CD144 and anti-Dapi antibodies (100×/oil immersion, Olympus BX51; Olympus). (C) Human LAGλ-1 MM cells coinjected with THP-1 monocytes express VEC genes that are markedly reduced in the presence of anti-PTN antibodies. (i) Human LAGλ-1 MM cells were injected subcutaneously alone or in combination with THP-1 monocytes into mice. Six weeks later, tumors were excised and RNA was extracted. Expression of Tie-2, Flk-1, VWF, CD144, and GAPDH was determined using RT-PCR. (ii) Similarly, human LAGλ-1 MM or THP-1 cells were each injected subcutaneously alone or together into mice also treated twice weekly with intraperitoneal injections of either polyclonal goat anti–human PTN antibodies or control preimmune goat IgG. Six weeks later, tumors were excised and RNA was extracted. Tie-2 and GAPDH expression was determined using RT-PCR.