THY1 and neoplasm: Confocal microscopy images of CD90-labeled hBM-MSCs and CD45-labeled KG1a cells clearly demonstrated KG1a cell clumping and interactions with hBM-MSCs (day 10 post-printing) and the increase in KG1a cell number on day 21 post-printing, resulting in a higher cell density and tumor bulk (day 21 post-printing) (Fig. 4E).