CD4 and myeloid sarcoma: This contrasts with the marked 70–95% depletion of CD4 T cells induced by alemtuzumab.11 This level of depletion by CD4‐specific mAb, including the lack of targeting of CD45RO+ T cells, suggests that the trials in MS were unlikely to have succeeded.6 This perceived failure questioned the role of CD4 T cells in MS and also supported the devaluing of the use of animal models of MS.8 However, such a failure could have been predicted if a few simple experiments had been performed before embarking on a clinical trial programme.