HuM291 (NUVION), a humanized Fc receptor-nonbinding antibody against CD3, anergizes peripheral blood T cells as partial agonist of the T cell receptor

Background. Humanized Fc receptor (FcR)-nonbinding antibodies against CD3 are promising immunosuppressive agents that may overcome both the neutralizing response to and the cytokine release syndrome seen with conventional monoclonal antibodies against CD3, In addition, evidence from several murine models suggests that these recombinant antibodies may actively induce T cell unresponsiveness by a mechanism other than modulation of the T cell receptor (TCR) or T cell depletion. We hypothesized that FcR-nonbinding antibodies against CD3 could induce T cell unresponsiveness by acting as partial agonist ligands of the TCR and thus, inducing T cell anergy, Methods. To test this hypothesis, we examined the signaling and functional effects of HuM291 (Nuvion(TM)), a FcR-nonbinding humanized antibody against CD3, on primary human T cells. Results. Short exposure of human peripheral blood T lymphocytes to HuM291 caused a partial agonist type of signaling through the TCR characterized by incomplete phosphorylation of TCR zeta, failure to activate ZAP-70 and to phosphorylate LAT but activation of ERK-1/-2 and subsequent up-regulation of CD69 expression. These changes correlated with a dose-dependent induction of anergy in human, primary resting T cells, which was reversed by exogenous interleukin-2. Conclusions. The tolerogenic properties of FcR-nonbinding monoclonal antibodies against CD3 correlate with its ability to reproduce the biochemical and functional effects of TCR partial agonist ligands, Thus, generation of engineered antibodies against CD3 with low TCR oligomerization potential may provide a clinically applicable partial agonist-based strategy for the prevention of polyclonal T cell responses.