Abstract
BackgroundCD40 activation of antigen presenting cells (APC) such as dendritic cells (DC) and B cells plays an important role in immunological licensing of T cell immunity. Agonist CD40 antibodies have been previously shown in murine models to activate APC and enhance tumor immunity; in humans, CD40-activated DC and B cells induce tumor-specific T cells in vitro. Although clinical translation of these findings for patients with cancer has been previously limited due to the lack of a suitable and available drug, promising clinical results are now emerging from phase I studies of the agonist CD40 monoclonal antibody CP-870,893. The most prominent pharmacodynamic effect of CP-870,893 infusion is peripheral B cell modulation, but direct evidence of CP-870,893-mediated B cell activation and the potential impact on T cell reactivity has not been reported, despite increasing evidence that B cells, like DC, regulate cellular immunity.MethodsPurified total CD19+ B cells, CD19+ CD27+ memory, or CD19+ CD27neg subsets from peripheral blood were stimulated in vitro with CP-870,893, in the presence or absence of the toll like receptor 9 (TLR9) ligand CpG oligodeoxynucleotide (ODN). B cell surface molecule expression and cytokine secretion were evaluated using flow cytometry. Activated B cells were used as stimulators in mixed lymphocyte reactions to evaluate their ability to induce allogeneic T cell responses.ResultsIncubation with CP-870,893 activated B cells, including both memory and naïve B cells, as demonstrated by upregulation of CD86, CD70, CD40, and MHC class I and II. CP-870,893-activated B cells induced T cell proliferation and T cell secretion of effector cytokines including IFN-gamma and IL-2. These effects were increased by TLR9 co-stimulation via a CpG ODN identical in sequence to a well-studied clinical grade reagent.ConclusionThe CD40 mAb CP-870,893 activates both memory and naïve B cells and triggers their T cell stimulatory capacity. Simultaneous TLR9 ligation augments the effect of CP-870,893 alone. These results provide further rationale for combining CD40 and TLR9 activation using available clinical reagents in strategies of novel tumor immunotherapy.
Highlights
CD40 activation of antigen presenting cells (APC) such as dendritic cells (DC) and B cells plays an important role in immunological licensing of T cell immunity
We studied the effect of CP-870,893 on B cell activation and B cell stimulation of T cells, and we analyzed the effects of co-stimulating B cells with the toll like receptor 9 (TLR9) agonist CpG ODN 2006
Because Toll-like receptor (TLR) agonists synergize with CD40 stimulation in vivo in mice and in vitro for human DC [25,26], we evaluated the additive effects of the TLR9 ligand CpG ODN 2006 on CP-870,893-stimulated B cells
Summary
CD40 activation of antigen presenting cells (APC) such as dendritic cells (DC) and B cells plays an important role in immunological licensing of T cell immunity. Resting APC may drive T cell tolerance and anergy, but fully activated APC - classically termed "licensed APC" - autonomously trigger effective and productive T cell responses [1]. This paradigm holds true for both dendritic cells (DC) and B cells. Ligation of CD40 on DC, for example, induces increased surface expression of costimulatory and MHC molecules, production of proinflammatory cytokines, and enhanced T cell triggering [11,12]. CD40 ligation on resting B cells increases antigen-presenting function and proliferation [11,12]
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