CXCR4 and neoplasm: Bioluminescence imaging 48 hrs post-intracranial injection was similar between the two groups [mean photon flux for sc-U87-Luc: 6.78×106; and for shCXCR4-U87-Luc: 7.17×106] suggesting that CXCR4 was not required for tumor cell engraftment.