HOXA5 and neoplasm: Although the TIE2 promoter is also expressed in some hematopoietic stem cells, including a subset of monocytes that can contribute to tumor angiogenesis [41,42], the number of these cells infiltrating developing neoplastic skin in K14-HPV16 mice is low (L. Coussens, unpublished), and thus consistent with undetectable levels of the HoxA5 transgene in peripheral blood or bone marrow cells.