Quantitative Contribution of IL2Rγ to the Dynamic Formation of IL2-IL2R Complexes

High common-γ cytokine receptor levels promote expression of Interleukin-2/Interleukin-7 receptor α-chains with implications on T-cell differentiation and function

Cytokines of the common-γ receptor chain (γc) family are crucial for T-cell differentiation and dysregulation of γc cytokine pathways is involved in the pathogenesis of autoimmune diseases. There is increasing evidence that the availability of the γc receptor (CD132) for the associated receptor chains has implications for T-cell functions. Here we studied the influence of differential γc expression on the expression of the IL-2Rα (CD25), the IL-7Rα (CD127) and the differentiation of activated naïve T cells. We fine-tuned the regulation of γc expression in human primary naïve T cells by lentiviral transduction using small hairpin (sh)RNAs and γc cDNA. Differential γc levels were then analysed for effects on T-cell phenotype and function after activation. Differential γc expression markedly affected IL-2Rα and IL-7Rα expression on activated naïve T cells. High γc expression (γc-high) induced significantly higher expression of IL-2Rα and re-expression of IL-7Rα after activation. Inhibition of γc caused lower IL-2Rα/IL-7Rα expression and impaired proliferation of activated naïve T cells. In contrast, γc-high T cells secreted significantly higher concentrations of effector cytokines (i.e., IFN-γ, IL-6) and showed higher cytokine-receptor induced STAT5 phosphorylation during initial stages as well as persistently higher pSTAT1 and pSTAT3 levels after activation. Finally, accelerated transition towards a CD45RO expressing effector/memory phenotype was seen especially for CD4+ γc-high naïve T cells. These results suggested that high expression of γc promotes expression of IL-2Rα and IL-7Rα on activated naïve T cells with significant effects on differentiation and effector cytokine expression.

Differential Effects of IL2Rα and IL15Rα over the Stability of the Common Beta-Gamma Signaling Subunits of the IL2 and IL15 Receptors

Interleukin (IL) 2 and IL15 are two members of the common gamma chain cytokine family, involved in the regulation of the T cell differentiation process. Both molecules use a specific alpha subunit, IL2Rα and IL15Rα, and share the same beta and gamma chains signaling receptors. The presence of the specific alpha subunit modulates the T cell ability to compete for both soluble cytokines while the beta and gamma subunits are responsible for the signal transduction. Recent experimental results point out that the specific alpha subunits modulate the capacity of IL2 and IL15 to induce the differentiation of stimulated T cells. In other membrane receptors, the outcome of the signal transduction has been associated with the strength of the interaction of the signaling subunits. Here, we investigate how IL2Rα and IL15Rα modulate the stability of their signaling complexes by combining molecular dynamics simulations and free energy calculations. Our simulations predict that IL2Rα binding destabilizes the β-γ_c interaction mediated by IL2, while IL15Rα has the opposite effect. These results explain the ability of IL2Rα and IL15Rα to modulate the signaling outcome and suggest new strategies for the development of better CD8⁺ T cell differentiation protocols for adoptive cell transfer (ACT).

Quantitative assessment of extracellular IL-1 regulation

IL-1 system is involved in the induction and maintenance of chronic inflammation associated with several autoimmune diseases and cancer, mainly due to its capacity to promote the secretion of inflammatory mediators. For this reason, several intracellular and extracellular mechanisms for this system have been fixed during the evolution. In spite of the large description of molecular interactions between IL-1 ligands and receptors, little is known about the relevance and limits of the extracellular regulatory mechanims in different scenarios. To tackle this problem, we developed and calibrated a mathematical model including all the known interactions between IL-1 ligands and IL-1Rs and calibrate it with experimental data of IL-1 binding to different cells. The model predicts that, independently on the IL-1Rs expression, IL-1α has more ability than IL-1β to induce IL-1 signaling, which suggests that both ligands can be equally relevant for the IL-1 related inflammation. On the other hand, at the cell level, IL-1 signaling is mainly controlled by IL-1R1 and IL-1R3 and not by IL-1R2. Moreover, the soluble form of IL-1R1 and IL-1RA have the highest capacity to prevent IL-1α while IL-1R2 and IL-1R1 and IL-1RA have a similar capacity to prevent IL-1β signaling. The soluble IL-1R3 has the lowest capacity to prevent IL-1 signaling and preferentially inhibits cells with low number of IL-1R3. In general, model predictions suggest several ways in which IL-1 controlling system may fail, developing IL-1 related inflammation.

Oscillatory IL-2 stimulus reveals pertinent signaling timescales of T cell responsiveness

Cell response to extracellular ligand is affected not only by ligand availability, but also by pre-existing cell-to-cell variability that enables a range of responses within a cell population. We developed a computational model that incorporates cell heterogeneity in order to investigate Jurkat T cell response to time dependent extracellular IL-2 stimulation. Our model predicted preferred timing of IL-2 oscillatory input for maximizing downstream intracellular STAT5 nuclear translocation. The modeled cytokine exposure was replicated experimentally through the use of a microfluidic platform that enabled the parallelized capture of dynamic single cell response to precisely delivered pulses of IL-2 stimulus. The in vitro results demonstrate that single cell response profiles vary with pulsatile IL-2 input at pre-equilibrium levels. These observations confirmed our model predictions that Jurkat cells have a preferred range of extracellular IL-2 fluctuations, in which downstream response is rapidly initiated. Further investigation into this filtering behavior could increase our understanding of how pre-existing cellular states within immune cell populations enable a systems response within a preferred range of ligand fluctuations, and whether the observed cytokine range corresponds to in vivo conditions.

Combining computational and experimental biology to develop therapeutically valuable IL2 muteins

High-dose IL2, first approved in 1992, has been used in the treatment of advanced renal cell carcinoma and melanoma. In these indications, IL2 induces long lasting objective responses in 5% to 20% of patients. However, toxicity and the unexpected expansion of regulatory T cells (Tregs) have limited its practical use and therapeutic impact, respectively. At the Center of Molecular Immunology in Havana, Cuba, a project was launched in 2005 to rationally design IL2 muteins that could be deployed in the therapy of cancer. The basic goal was to uncouple the pleiotropic effect of IL2 on different immune T cells, to obtain a mutein with a therapeutic index that was better than that achieved with wild type (wt) IL2. Using a combination of computational and experimental biology approaches, we predicted and developed two novel IL2 muteins with therapeutic potential. The first, designated no-alpha mutein, is an agonist of IL2R signaling with a reduced ability to expand Treg in vivo. In mice, the no-alpha mutein IL2 has higher antitumor activity and lower toxicity than wt IL2. It represents a potential best-in-class drug that has begun phase I/II clinical trials in solid tumors. The second, designated no-gamma mutein, is an antagonist of IL2R signaling, with some preferential affinity for Tregs. This mutein has antitumor activity in mice that likely derives from its ability to reduce Treg accumulation in vivo. It represents a first-in-class drug that offers a novel strategy to inhibit Treg activity in vivo.