Thus, the improved immunization effect did not depend on a reduction of Treg numbers, but possibly (at least partly) on a functional inhibition of Tregs. As it has been shown that Tregs control B-cell expression of CD80 and CD86 via the coreceptor CTLA-4 , a potential mechanism enhancing the vaccination effect of trAbs in the combination setting may be mediated by CTLA-4 blockade on Tregs, thus fostering the induction of antitumor antibodies (Figure 4B). Further mechanistic studies, which should also address the role of follicular helper cells, are warranted.