CXCR4 and neoplasm: By contrast, ACKR3 became markedly upregulated as up to 50% of the conditioned cells (ex vivo) expressed the receptor (Figure 1A and 1B), indicating that after localized tumor passage the presence of two populations existed, namely ACKR3+/CXCR4+ and ACKR3-/CXCR4+cells.