CD4 and myeloid sarcoma: We found that early postpartum resumption of natalizumab did not reduce the risk of relapses in the first 6 months post partum, in line with the known biology of these early relapses in which a decline in circulating CD4+IFN-g–producing cells, typically beginning during late pregnancy, leads to postpartum MS relapses.23 Thus, early resumption was associated with a lower relapse rate in the entire postpartum year, as reported elsewhere,4,6 although natalizumab shows a very early effect on the development on gadolinium-enhancing lesions.24