For optimal quality, memory CD8+ T cells require CD4+ T cell help. We have examined whether CD4+ T cells require CD27 to deliver this help, in a model of intranasal OVA protein immunization. CD27 deficiency reduced the capacity of CD4+ T cells to support Ag-specific CD8+ T cell accumulation at the tissue site after primary and secondary immunization. CD27-dependent CD4+ T cell help for the memory CD8+ T cell response was delivered during priming. It did not detectably affect formation of CD8+ memory T cells, but promoted their secondary expansion. CD27 improved survival of primed CD4+ T cells, but its contribution to the memory CD8+ T cell response relied on altered CD4+ T cell quality rather than quantity. CD27 induced a Th1-diagnostic gene expression profile in CD4+ T cells, which included the membrane molecule MS4A4B. Accordingly, CD27 increased the frequency of IFN-γ-and IL-2-producing CD4+ T cells. It did not affect CD40L expression. Strikingly, MS4A4B was also identified as a unique marker of CD8+ memory T cells that had received CD27-proficient CD4+ T cell help during the primary response. This apparent imprinting effect suggests a role for MS4A4B as a downstream effector in CD27-dependent help for CD8+ T cell memory.