CD4+ T Cell–Derived IL-21 and Deprivation of CD40 Signaling Favor the In Vivo Development of Granzyme B–Expressing Regulatory B Cells in HIV Patients

IL-21 can induce both plasma cellsand regulatory B cells. In this article, we demonstrate that untreated HIV patients display CD4 + T cellswith enhanced IL-21 expression and high in vivo frequencies of regulatory B cellsoverexpressing the serine protease granzyme B. Granzyme B–expressing regulatory B cells(GraB cells) cellsfrom HIV patients exhibit increased expression of CD5, CD43, CD86, and CD147 but do not produce IL-10. The main functional characteristic of their regulatory activity is direct granzyme B–dependent degradation of the TCR-ζ–chain, resulting in significantly decreased proliferative T cellresponses. Although Th cellsfrom HIV patients secrete IL-21 in a Nef-dependent manner, they barely express CD40L. When culturing such IL-21 + CD40L − Th cellswith B cells, the former directly induce B celldifferentiation into GraB cells. In contrast, the addition of soluble CD40L multimers to T cell/ B cellcultures redirects B celldifferentiation toward plasma cells, indicating that CD40L determines the direction of IL-21–dependent B celldifferentiation. As proof of principle, we confirmed this mechanism in a patient lacking intact CD40 signaling due to a NEMO mutation. The majority of peripheral B cellsfrom this patient were GraB cellsand strongly suppressed T cellproliferation. In conclusion, GraB cellsrepresent potent regulatory B cellsin humans that are phenotypically and functionally distinct from B10 cellsand occur in early HIV infection. GraB cellsmay contribute significantly to immune dysfunction in HIV patients, and may also explain ineffective Ab responses after vaccination. The use of soluble CD40L multimers may help to improve vaccination responses in HIV patients.