CD33 and acute lymphoblastic leukemia: In particular, in ALL-MSCs both at diagnosis and at later time points, contamination with hematopoietic cells was no longer detectable by P3 (negativity for CD14, CD33, CD45, CD80 and HLA-DR) and more than 98% of cells expressed the surface marker pattern (positivity for CD13, CD73, CD90, CD105 and HLA-I) typical of MSCs (Fig. 4A).