CD40-CD40L interactions are important for both antigen-dependent B-cell differentiation and effector and memory T-cell formation. The prevailing view is that CD40L is expressed on activated CD4(+) T cells, which enables them to provide help to high-affinity B cells in germinal centers and to license DCs for efficient induction of CD8(+) T-cell responses. Interestingly, CD8(+) T cells themselves can also express CD40L and, in this issue of the European Journal of Immunology, Thiel and colleagues [Eur. J. Immunol. 2013. 43: XXXX-XXXX] show that CD40L expression on these cells can be part of a self-sustaining feed-forward loop, in which expression of CD40L is induced by IL-12 and TCR signaling. This provides a paradigm shift in our thinking about the requirements of effector CD8(+) T-cell development and the role herein of CD4(+) T cells to provide help in this process. This article is protected by copyright. All rights reserved.