1B, summarized in Fig. 1C). Only higher concentrations of anti-CD3 mAb (>1 μg/mL), as used in the original published work and our initial experiments, recapitulated the inhibition of sCTLA-4 secretion Selleck Venetoclax (n > 8). In contrast, lower concentrations of the mAb (<0.1 μg/mL) increased sCTLA-4 production, while retaining the ability to induce proliferative responses. Having demonstrated for the first time that sCTLA-4 secretion can be enhanced by Ag stimulation of T cells, the next question was whether this isoform has a role in regulating effector responses. We therefore determined the effects of supplementing human PBMC cultures with the isoform-specific mAb JMW-3B3, which can inhibit sCTLA-4 interaction
with the B7 receptor (Supporting Information Fig. 1F). Reduction in measurable culture supernatant levels of sCTLA-4 in the presence of the mAb was confirmed using standard anti-CTLA-4 reagents (Fig. 2A). Anti-sCTLA-4 mAb or IgG1 isotype control was added to healthy donor PBMC cultures left unstimulated or activated with the Ag PPD (Fig. 2). Blockade of sCTLA-4 consistently and significantly amplified cell proliferative (Fig. 2C, n = 15, p <
0.001, Wilcoxon), IFN-γ (p < 0.001), and IL-17 (p < 0.05) responses. This enhancement was Ag-dependent as proliferation and cytokine production by unstimulated PD-1/PD-L1 inhibition PBMCs showed little change when sCTLA-4 was blocked. The positive effects of the mAb on effector responses were supported by increases in the numbers of CD4+ T cells in responding cultures that expressed the respective Th1 and Th17 transcription factors T-bet and RORγt (Fig. 2D, summarized in 2E). The effects of selective sCTLA-4 Ab blockade with mAb JMW-3B3 on PBMC responses were compared with those obtained using commercially available anti-CTLA-4 antibodies that Unoprostone are often used routinely to assess mCTLA-4 function but are actually “pan-specific,” binding both membrane and soluble isoforms of CTLA-4. A representative example of these experiments is depicted in Fig. 3A, which compares the effects of JMW-3B3 with those of four commercially
available anti-CTLA-4 mAbs, and comparisons with a single anti-CTLA-4 mAb clone, BNI3, are summarized in Figure 3B (n = 10). Selective blockade of sCTLA-4 exhibited a stronger and more consistent, significant enhancing effect on Ag-driven PBMC responses than pan-specific blockade of total CTLA-4, which, overall, gave only a modest and variable increase in cell proliferation, and cytokine secretion (Fig. 3B). The results of selective blockade raise the prospect that inhibitory properties previously ascribed to mCTLA-4 may be at least partly due to secretion of the soluble isoform. In particular, since cells with a Treg-cell phenotype are an important source of mCTLA-4, it is reasonable to predict that sCTLA-4 expression may also be a feature of this population.