The authors retract the 24 September 2009 article cited above, prepublished on 30 July 2009. They have recently learned that some of the cell lines used in their paper were inadvertently misidentified. Although the parental 697 and REH cell lines used to generate the Mer knockdown lines were authenticated by short tandem repeat (STR) analysis before publication, the transduced progeny were not analyzed until recently. The results of STR analysis indicate that the 697 shMer1A and 697 shMer1B cell lines are actually derived from the REH parental cell line. Importantly, the identities of the other 6 REH and 697 cell lines published in this study have been verified as authentic. Since this unfortunate discovery, the authors have generated new 697 Mer knockdown cell lines and authenticated their identity. These new cell lines are being used to replicate the original work. Data obtained to date support the overall findings and conclusions of the original report; these data will be described in a new manuscript. The authors sincerely apologize to the readers, reviewers, and editors of Blood for making this honest mistake.