Generation in culture of hematopoietic cells from human embryonic splanchnopleura–derived ACE⁺ and ACE⁻ cells. (A) The P-Sp and the rest of the embryo are shown during dissection of a 24-day human embryo. (B) Sorting of ACE⁺ and ACE⁻ cells after dissection of a 26-day human splanchnopleura showed that ACE⁺ cells represent less than 1% of the total population. (C) After 3-4 days of culture, only ACE⁺ cells gave rise to rounded cells, presumably hematopoietic colonies, adhering to the stromal cell layer. (D) Sorted ACE⁺ cells contain GM-CFU and more primitive HPP-CFU clonogenic progenitors (left). Fifteen-day colonies contain hematopoietic cells as confirmed by flow cytometric analysis after CD45 staining and by May-Grünwald-Giemsa coloration (right).