Loss of N-terminal charged residues of mouse CD3 epsilon chains generates isoforms modulating antigen T cell receptor-mediated signals and T cell receptor-CD3 interactions

T-Cell-Specific Loss of the PI-3-Kinase p110α Catalytic Subunit Results in Enhanced Cytokine Production and Antitumor Response

Class IA phosphatidylinositol 3-kinase (PI3K) catalytic subunits p110α and p110δ are targets in cancer therapy expressed at high levels in T lymphocytes. The role of p110δ PI3K in normal or pathological immune responses is well established, yet the importance of p110α subunits in T cell-dependent immune responses is not clear. To address this problem, mice with p110α conditionally deleted in CD4⁺ and CD8⁺ T lymphocytes (p110α^-/-ΔT) were used. p110α^-/-ΔT mice show normal development of T cell subsets, but slightly reduced numbers of CD4⁺ T cells in the spleen. "In vitro," TCR/CD3 plus CD28 activation of naive CD4⁺ and CD8⁺ p110α^-/-ΔT T cells showed enhanced effector function, particularly IFN-γ secretion, T-bet induction, and Akt, Erk, or P38 activation. Tfh derived from p110α^-/-ΔT cells also have enhanced responses when compared to normal mice, and IL-2 expanded p110α^-/-ΔT CD8⁺ T cells had enhanced levels of LAMP-1 and Granzyme B. By contrast, the expansion of p110α^-/-ΔT iTreg cells was diminished. Also, p110α^-/-ΔT mice had enhanced anti-keyhole limpet hemocyanin (KLH) IFN-γ, or IL-4 responses and IgG1 and IgG2b anti-KLH antibodies, using CFA or Alum as adjuvant, respectively. When compared to WT mice, p110α^-/-ΔT mice inoculated with B16.F10 melanoma showed delayed tumor progression. The percentage of CD8⁺ T lymphocytes was higher and the percentage of Treg cells lower in the spleen of tumor-bearing p110α^-/-ΔT mice. Also, IFN-γ production in tumor antigen-activated spleen cells was enhanced. Thus, PI3K p110α plays a significant role in antigen activation and differentiation of CD4⁺ and CD8⁺ T lymphocytes modulating antitumor immunity.

Sepsis in preterm infants causes alterations in mucosal gene expression and microbiota profiles compared to non-septic twins

Sepsis is a life-threatening condition in preterm infants. Neonatal microbiota plays a pivotal role in the immune system maturation. Changes in gut microbiota have been associated to inflammatory disorders; however, a link with sepsis in the neonatal period has not yet been established. We aimed to analyze gut microbiota and mucosal gene expression using non-invasively obtained samples to provide with an integrative perspective of host-microbe interactions in neonatal sepsis. For this purpose, a prospective observational case-control study was conducted in septic preterm dizygotic twins and their non-septic twin controls. Fecal samples were used for both microbiota analysis and host genome-wide expression using exfoliated intestinal cells. Gene expression of exfoliated intestinal cells in septic preterm showed an induction of inflammatory and oxidative stress pathways in the gut and pro-oxidant profile that caused dysbiosis in the gut microbiota with predominance of Enterobacteria and reduction of Bacteroides and Bifidobacterium spp.in fecal samples, leading to a global reduction of beneficial anaerobic bacteria. Sepsis in preterm infants induced low-grade inflammation and oxidative stress in the gut mucosa, and also changes in the gut microbiota. This study highlights the role of inflammation and oxidative stress in neonatal sepsis on gut microbial profiles.

Heterogeneous CD3 expression levels in differing T cell subsets correlate with the in vivo anti-CD3-mediated T cell modulation

The tolerogenic anti-CD3ε monoclonal Abs (anti-CD3) are promising compounds for the treatment of type 1 diabetes. Anti-CD3 administration induces transient T cell depletion both in preclinical and in clinical studies. Notably, the said depletion mainly affects CD4(+) but not CD8(+) T cells. Moreover, type 1 diabetes reversal in preclinical models is accompanied by the selective expansion of CD4(+)Foxp3(+) T regulatory (Treg) cells, which are fundamental for the long-term maintenance of anti-CD3-mediated tolerance. The mechanisms that lead to this immune-shaping by affecting mainly CD4(+) T effector cells while sparing CD4(+)Foxp3(+) Treg cells have still to be fully elucidated. This study shows that CD3 expression levels differ from one T cell subset to another. CD4(+)Foxp3(-) T cells contain higher amounts of CD3 molecules than do CD4(+)Foxp3(+) and CD8(+) T cells in both mice and humans. The said differences correlate with the anti-CD3-mediated immune resetting that occurs in vivo after anti-CD3 administration in diabetic NOD mice. Additionally, transcriptome analysis demonstrates that CD4(+)Foxp3(+) Treg cells are significantly less responsive than are CD4(+)Foxp3(-) T cells to anti-CD3 treatment at a molecular level. Thus, heterogeneity in CD3 expression seems to confer to the various T cell subsets differing susceptibility to the in vivo tolerogenic anti-CD3-mediated modulation. These data shed new light on the molecular mechanism that underlies anti-CD3-mediated immune resetting and thus may open new opportunities to improve this promising treatment.

Characteristics of TCR/CD3 complex CD3{varepsilon} chains of regulatory CD4+ T (Treg) lymphocytes: role in Treg differentiation in vitro and impact on Treg in vivo

Tregs are anergic CD4(+)CD25(+)Foxp3(+) T lymphocytes exerting active suppression to control immune and autoimmune responses. However, the factors in TCR recognition underlying Treg differentiation are unclear. Based on our previous data, we hypothesized that Treg TCR/CD3 antigen receptor complexes might differ from those of CD4(+)CD25(-) Tconv. Expression levels of TCR/CD3, CD3ε,ζ chains, or other molecules involved in antigen signaling and the characteristics of CD3ε chains were analyzed in thymus or spleen Treg cells from normal mice. Tregs had quantitative and qualitatively distinct TCR/CD3 complexes and CD3ε chains. They expressed significantly lower levels of the TCR/CD3 antigen receptor, CD3ε chains, TCR-ζ chain, or the CD4 coreceptor than Tconv. Levels of kinases, adaptor molecules involved in TCR signaling, and early downstream activation pathways were also lower in Tregs than in Tconv. Furthermore, TCR/CD3 complexes in Tregs were enriched in CD3ε chains conserving their N-terminal, negatively charged amino acid residues; this trait is linked to a higher activation threshold. Transfection of mutant CD3ε chains lacking these residues inhibited the differentiation of mature CD4(+)Foxp3(-) T lymphocytes into CD4(+)Foxp3(+) Tregs, and differences in CD3ε chain recognition by antibodies could be used to enrich for Tregs in vivo. Our results show quantitative and qualitative differences in the TCR/CD3 complex, supporting the hyporesponsive phenotype of Tregs concerning TCR/CD3 signals. These differences might reconcile avidity and flexible threshold models of Treg differentiation and be used to implement therapeutic approaches involving Treg manipulation.

Biased binding of class IA phosphatidyl inositol 3-kinase subunits to inducible costimulator (CD278)

To better understand T lymphocyte costimulation by inducible costimulator (ICOS; H4; CD278), we analyzed proteins binding to ICOS peptides phosphorylated at the Y(191)MFM motif. Phosphorylated ICOS binds class IA phosphatidyl inositol 3-kinase (PI3-K) p85α, p50-55α and p85β regulatory subunits and p110α, p110δ and p110β catalytic subunits. Intriguingly, T cells expressed high levels of both p110α or p110δ catalytic subunits, yet ICOS peptides, cell surface ICOS or PI3-kinase class IA regulatory subunits preferentially coprecipitated p110α catalytic subunits. Silencing p110α or p110δ partially inhibited Akt/PKB activation induced by anti-CD3 plus anti-ICOS antibodies. However, silencing p110α enhanced and silencing p110δ inhibited Erk activation. Both p110α- and p110δ-specific inhibitors blocked cytokine secretion induced by TCR/CD3 activation with or without ICOS costimulus, but only p110α inhibitors blocked ICOS-induced cell elongation. Thus, p110α and p110δ are essential to optimal T cell activation, but their abundance and activity differentially tune up distinct ICOS signaling pathways.

N-terminal negatively charged residues in CD3varepsilon chains as a phylogenetically conserved trait potentially yielding isoforms with different isoelectric points: analysis of human CD3varepsilon chains

CD3varepsilon chains are essential to the structure, expression and signaling of T cell receptors. Here, we extend to human CD3varepsilon our previous data in mouse CD3varepsilon showing that, in T cells, proteolytic processing of the acidic N-terminal sequence of CD3varepsilon chains generate distinct polypeptide species that can be identified by two-dimension (IEF-SDS PAGE) electrophoresis and immunoblot. This was shown first by showing the processing of a fusion protein of GFP and the extracellular domain of mouse CD3varepsilon (mCD3GFP) expressed in Jurkat cells. Secondly, pI heterogeneity was also found in human CD3varepsilon chains immunoprecipitated from the surface of Jurkat cells or PHA blasts of human blood T lymphocytes. Comparison of CD3varepsilon chains from 27 different species shows that their N-terminal sequences share a strong acidic nature, despite the large differences in terms of length and composition, even among closely related species. Our results suggest that generation of CD3varepsilon chain isoforms with different N-terminal sequence and pI is a general phenomenon. Thus, as previously observed in the mouse, the relative abundance of CD3varepsilon chain species might regulate TCR/CD3 structure and function, including the strength of the interactions between CD3 dimers and the TCR clonotypic receptors, as well as TCR/CD3 activation thresholds. Interestingly, CD3varepsilon chains from 7 out of 27 species studied have putative N-glycosylation (NxS or NxT) motifs in their Ig extracellular domain. Their location, plus the conservation of residues involved in domain organization, the interactions with other CD3 chains, or the TCR, and signal triggering add new data useful to establish a permissive topology for the interaction between CD3 dimers and the TCR chains.