The Heparan Sulfate Mimetic PG545 Modulates T Cell Responses and Prevents Delayed-Type Hypersensitivity.

The heparan sulfate mimetic PG545 (pixatimod) is under evaluation as an inhibitor of angiogenesis and metastasis including in human clinical trials. We have examined the effects of PG545 on lymphocyte phenotypes and function. We report that PG545 treatment suppresses effector T cell activation and polarizes T cells away from Th17 and Th1 and toward Foxp3+ regulatory T cell subsets in vitro and in vivo. Mechanistically, PG545 inhibits Erk1/2 signaling, a pathway known to affect both T cell activation and subset polarization. Interestingly, these effects are also observed in heparanase-deficient T cells, indicating that PG545 has effects that are independent of its role in heparanase inhibition. Consistent with these findings, administration of PG545 in a Th1/Th17-dependent mouse model of a delayed-type hypersensitivity led to reduced footpad inflammation, reduced Th17 memory cells, and an increase in FoxP3+ Treg proliferation. PG545 also promoted Foxp3+ Treg induction by human T cells. Finally, we examined the effects of other heparan sulfate mimetics PI-88 and PG562 on lymphocyte polarization and found that these likewise induced Foxp3+ Treg in vitro but did not reduce Th17 numbers or improve delayed-type hypersensitivity in this model. Together, these data indicate that PG545 is a potent inhibitor of Th1/Th17 effector functions and inducer of FoxP3+ Treg. These findings may inform the adaptation of PG545 for clinical applications including in inflammatory pathologies associated with type IV hypersensitivity responses.

Natural Tr1-like cells do not confer long-term tolerogenic memory.

IL-10-producing Tr1 cells promote tolerance but their contributions to tolerogenic memory are unclear. Using 10BiT mice that carry a Foxp3-eGFP reporter and stably express CD90.1 following IL-10 production, we characterized the spatiotemporal dynamics of Tr1 cells in a house dust mite model of allergic airway inflammation. CD90.1+Foxp3-IL-10+ Tr1 cells arise from memory cells and rejoin the tissue-resident memory T-cell pool after cessation of IL-10 production. Persistent antigenic stimulation is necessary to sustain IL-10 production and Irf1 and Batf expression distinguishes CD90.1+Foxp3-IL-10+ Tr1 cells from CD90.1+Foxp3-IL-10- 'former' Tr1. Depletion of Tr1-like cells after primary sensitization exacerbates allergic airway inflammation. However, neither transfer nor depletion of former Tr1 cells influences either Tr1 numbers or the inflammatory response during subsequent allergen memory re-challenge weeks later. Together these data suggest that naturally-arising Tr1 cells do not necessarily give rise to more Tr1 upon allergen re-challenge or contribute to tolerogenic memory. This phenotypic instability may limit efforts to re-establish tolerance by expanding Tr1 in vivo.

Alternative NF-κB signaling controls peripheral homeostasis and function of regulatory T cells.

Regulatory T cells (Tregs) maintain immune homeostasis and play an important role in tissue regeneration after injury. Mutations affecting development or homeostasis of Tregs lead to immune pathologies in humans and are often fatal in mouse models. Although the pathways required for Treg development are being increasingly characterized, factors crucial for Treg homeostasis are not completely understood. Previously we have found a role for alternative NF-κB pathway in restricting T cell activation and Th17 differentiation. Here, by using the mouse model of uncontrolled alternative NF-κB signaling we identify a crucial intrinsic role of RelB signaling in regulating homeostasis and competitive fitness of Tregs. The failure of p100-/- Tregs to maintain the population of effector Tregs and efficiently suppress immune reactions results in lethal multiorgan Th1-mediated inflammation in Rag1-/- recipients. This inflammation is combined with severe lymphopenia and could be rescued by adoptive transfer of wild type Tregs. Thus in addition to its role in Th17 differentiation, RelB acts as a potent inhibitor of Treg effector functions. Our results point to RelB as a potential therapeutic target for Treg manipulation.

RelB regulates Th17 differentiation in a cell-intrinsic manner.

The role of the alternative NF-κB pathway is mainly attributed to the lymphoid organ formation and blood cancer. However, its involvement in lymphocyte differentiation is not clearly defined. Recently, we have shown that uncontrolled activation of alternative NF-κB in mice lacking the NF-κB inhibitory protein p100 (p100-/- mice) hinders plasmablast proliferation and diminishes T cell independent responses. Here we show that hyperactivation of this pathway leads to a cell-intrinsic T cell defects. p100-deficient T helper cells displayed both an activation and a proliferation defect in vitro. In addition, memory T cell formation was impaired in vivo. Moreover, p100-/- T cells failed to polarize into T helper 17 cells. This phenotype was dependent on increased RelB activation and suboptimal RORγt expression. Thus, our results demonstrate that RelB acts as a negative regulator of T cell activation and Th17 development. Targeting this pathway therefore could be beneficial in Th17-mediated pathologies.

Calix[4]arene methylenebisphosphonic acids as inhibitors of fibrin polymerization.

Calix[4]arenes bearing two or four methylenebisphosphonic acid groups at the macrocyclic upper rim have been studied with respect to their effects on fibrin polymerization. The most potent inhibitor proved to be calix[4]arene tetrakis-methylene-bis-phosphonic acid (C-192), in which case the maximum rate of fibrin polymerization in the fibrinogen + thrombin reaction decreased by 50% at concentrations of 0.52 × 10(-6) M (IC(50)). At this concentration, the molar ratio of the compound to fibrinogen was 1.7 : 1. For the case of desAABB fibrin polymerization, the IC(50) was 1.26 × 10(-6) M at a molar ratio of C-192 to fibrin monomer of 4 : 1. Dipropoxycalix[4]arene bis-methylene-bis-phosphonic acid (C-98) inhibited fibrin desAABB polymerization with an IC(50) = 1.31 × 10(-4) M. We hypothesized that C-192 blocks fibrin formation by combining with polymerization site 'A' (Aα17-19), which ordinarily initiates protofibril formation in a 'knob-hole' manner. This suggestion was confirmed by an HPLC assay, which showed a host-guest inclusion complex of C-192 with the synthetic peptide Gly-Pro-Arg-Pro, an analogue of site 'A'. Further confirmation that the inhibitor was acting at the initial step of the reaction was obtained by electron microscopy, with no evidence of protofibril formation being evident. Calixarene C-192 also doubled both the prothrombin time and the activated partial thromboplastin time in normal human blood plasma at concentrations of 7.13 × 10(-5) M and 1.10 × 10(-5) M, respectively. These experiments demonstrate that C-192 is a specific inhibitor of fibrin polymerization and blood coagulation and can be used for the design of a new class of antithrombotic agents.