Intracellular concentrations of Ca(2+) modulate the strength of signal and alter the outcomes of cytotoxic T-lymphocyte antigen-4 (CD152)-CD80/CD86 interactions in CD4(+) T lymphocytes

High intracellular calcium amounts inhibit activation-induced proliferation of mouse T cells: Tert-butyl hydroquinone as an additive enhancer of intracellular calcium

Optimal T cell activation is critical to orchestrate adaptive immune responses. Calcium is critical for T cell activation and integrates signaling pathways necessary to activate key transcription factors. In fact, patients with calcium channelopathies are immunodeficient. Here, we investigated the effects of different concentrations of intracellular calcium on activation of mouse T cells. High intracellular calcium amounts inhibited in vitro T cell proliferation as evidenced by a decreased cell cycling-to-hypodiploidy ratio in two models of activation: the combination of phorbol 12-myristate 13-acetate (PMA) and Ionomycin (an ionophore)/Thapsigargin (a SERCA inhibitor) or plate bound anti-CD3 and anti-CD28. High intracellular calcium amounts increased the production of reactive oxygen species (ROS) in T cells activated with PMA and Ionomycin and scavenging excess ROS using N-acetyl cysteine (NAC) rescued the decrease in cycling-to-hypodiploidy ratio. To test the universality of our observations, we studied the effects of tert-Butylhydroquinone (tBHQ), a SERCA inhibitor and Nrf2 activator. tBHQ alone did not increase intracellular calcium amounts but the intracellular calcium amounts increased when tBHQ was used in combination with PMA. Also, tBHQ inhibited T cell activation in a dose-dependent manner in both in vitro models of T cell activation. Importantly, intraperitoneal injection of tBHQ ameliorated Dextran Sodium Sulfate (DSS)-induced colitis in mice as evidenced by rescue of colon length shortening and lower disease activity index. Overall, this study identifies high calcium amounts as a potential target to lower T cell activation. The implications of these observations are discussed in the context of calcium modulating drugs that are used to treat various diseases.

Mechanical Properties Affect Primary T Cell Activation in 3D Bioprinted Hydrogels

T cells play a critical role in the adaptive immune response of the body, especially against intracellular pathogens and cancer. In vitro, T cell activation studies typically employ planar (two-dimensional, 2D) culture systems that do not mimic native cell-to-extracellular matrix (ECM) interactions, which influence activation. The goal of this work was to study T cell responses in a cell line (EL4) and primary mouse T cells in three-dimensional (3D) bioprinted matrices of varied stiffness. Cell-laden hydrogels were 3D bioprinted from gelatin methacryloyl (GelMA) using a digital light processing (DLP)-based 3D bioprinter operated with visible light (405 nm). Mechanical characterization revealed that the hydrogels had pathophysiologically relevant stiffnesses for a lymph node-mimetic tissue construct. EL4, a mouse T cell lymphoma line, or primary mouse T cells were 3D bioprinted and activated using a combination of 10 ng/mL of phorbol myristate acetate (PMA) and 0.1 μM of ionomycin. Cellular responses revealed differences between 2D and 3D cultures and that the biomechanical properties of the 3D bioprinted hydrogel influence T cell activation. Cellular responses of the 2D and 3D cultures in a soft matrix (19.83 ± 2.36 kPa) were comparable; however, they differed in a stiff matrix (52.95 ± 1.36 kPa). The fraction of viable EL4 cells was 1.3-fold higher in the soft matrix than in the stiff matrix. Furthermore, primary mouse T cells activated with PMA and ionomycin showed 1.35-fold higher viable cells in the soft matrix than in the stiff matrix. T cells bioprinted in a soft matrix and a stiff matrix released 7.4-fold and 5.9-fold higher amounts of interleukin-2 (IL-2) than 2D cultured cells, respectively. Overall, the study demonstrates the changes in the response of T cells in 3D bioprinted scaffolds toward engineering an ex vivo lymphoid tissue-mimetic system that can faithfully recapitulate T cell activation and unravel pathophysiological characteristics of T cells in infectious biology, autoimmunity, and cancers.

T cell costimulation, checkpoint inhibitors and anti-tumor therapy

The hallmarks of the adaptive immune response are specificity and memory. The cellular response is mediated by T cells which express cell surface T cell receptors (TCRs) that recognize peptide antigens in complex with major histocompatibility complex (MHC) molecules on antigen presenting cells (APCs). However, binding of cognate TCRs with MHC-peptide complexes alone (signal 1) does not trigger optimal T cell activation. In addition to signal 1, the binding of positive and negative costimulatory receptors to their ligands modulates T cell activation. This complex signaling network prevents aberrant activation of T cells. CD28 is the main positive costimulatory receptor on naı¨ve T cells; upon activation, CTLA4 is induced but reduces T cell activation. Further studies led to the identification of additional negative costimulatory receptors known as checkpoints, e.g. PD1. This review chronicles the basic studies in T cell costimulation that led to the discovery of checkpoint inhibitors, i.e. antibodies to negative costimulatory receptors (e.g. CTLA4 and PD1) which reduce tumor growth. This discovery has been recognized with the award of the 2018 Nobel prize in Physiology/Medicine. This review highlights the structural and functional roles of costimulatory receptors, the mechanisms by which checkpoint inhibitors work, the challenges encountered and future prospects.

Aberrant Peripheral Immune Function in a Good Syndrome Patient

Good's syndrome (GS) is often accompanied by recurrent respiratory infections and chronic diarrhea. The main purpose was to evaluate the peripheral immune status of a GS patient after thymoma resection. Twenty healthy volunteers were recruited as healthy controls (HCs). Flow cytometry was applied to determine the proportions of circuiting CD4⁺ T cells, CD8⁺ T cells, γδT cells, and regulatory T (Treg) cells in our GS patient. We also examined the proliferation capability of ex vivo CD4⁺ T cells and detected the levels of cytokines interferon- (IFN-) γ and interleukin-17A secreted by ex vivo immune cells from this GS patient. Compared with healthy control subjects, this GS patient had fewer B cells, an inverted ratio of CD4⁺/CD8⁺ cells, and more Treg cells in his peripheral blood. Additionally, the patient's Vδ2 T cell levels were significantly decreased despite having a normal percentage of γδT cells. Ex vivo peripheral CD4⁺ T cells from the patient showed insufficient proliferation and division potential as well as excessive expression of PD-1. Moreover, IFN-γ was predominantly derived from CD8⁺ T cells in this GS patient, rather than from CD4⁺ T cells and γδT cells. This GS patient had impaired T and B cell immunological alternations and cytokine disruptions after thymectomy. Detailed research should focus on therapies that can adjust the immune status in such patients for a better outcome.

Decreased CTLA4(+) and Foxp3(+) CD25(high)CD4(+) cells in induced sputum from patients with mild atopic asthma

BACKGROUND

Details of the comparisons between airway and peripheral blood regulatory T cells (Tregs) in patients with atopic asthma are still unclear. The objective of this study is to investigate the profiles of both airway and circulating Tregs in atopic asthma.

METHODS

We measured the numbers of Tregs and eosinophils in induced sputum and peripheral blood in 28 patients with mild atopic asthma and compared these with numbers in 18 healthy controls. The frequency (%) of Tregs (surface CTLA4+, intracellular Foxp3+, and CTLA4+Foxp3+ on CD25highCD4+ T cells) in sputum and blood was determined by intracellular 5-color flow cytometry. We also correlated the numbers with the level of airway hyperresponsiveness (AHR) in asthmatics.

RESULTS

The mean frequencies of cells expressing CTLA4+ (19.4 ± 2.1%, p = 0.075), Foxp3+ (16.4 ± 3.3%, p = 0.001), and CTLA4+Foxp3+ (7.0 ± 1.1%, p = 0.008) in induced sputum from asthmatics were significantly lower than controls (27.2 ± 3.7%, 37.4 ± 4.7%, and 18.2 ± 3.6%, respectively), whereas in peripheral blood, there was no inter-group difference in the frequencies of cells expressing CTLA4+ (7.1 ± 1.5% vs 5.7 ± 1.7%, p > 0.05), Foxp3+ (35.7 ± 3.2% vs 21.1 ± 3.9%, p > 0.05), and CTLA4+Foxp3+ (6.6 ± 1.5% vs 4.2 ± 1.0%, p > 0.05). Moreover, the frequency of CD25highCD4+ cells expressing CTLA4+, but not Foxp3+, in induced sputum was associated with AHR (r = 0.60, p = 0.009) and airway eosinophilic inflammation (r = -0.60, p = 0.008) in asthmatics.

CONCLUSIONS

Airway, but not circulating, Tregs are decreased in mild atopic asthmatics, and are negatively correlated to an increase of airway eosinophilic inflammation and AHR.

Surfactant protein A integrates activation signal strength to differentially modulate T cell proliferation

Pulmonary surfactant lipoproteins lower the surface tension at the alveolar-airway interface of the lung and participate in host defense. Previous studies reported that surfactant protein A (SP-A) inhibits lymphocyte proliferation. We hypothesized that SP-A-mediated modulation of T cell activation depends upon the strength, duration, and type of lymphocyte activating signals. Modulation of T cell signal strength imparted by different activating agents ex vivo and in vivo in different mouse models and in vitro with human T cells shows a strong correlation between strength of signal (SoS) and functional effects of SP-A interactions. T cell proliferation is enhanced in the presence of SP-A at low SoS imparted by exogenous mitogens, specific Abs, APCs, or in homeostatic proliferation. Proliferation is inhibited at higher SoS imparted by different doses of the same T cell mitogens or indirect stimuli such as LPS. Importantly, reconstitution with exogenous SP-A into the lungs of SP-A(-/-) mice stimulated with a strong signal also resulted in suppression of T cell proliferation while elevating baseline proliferation in unstimulated T cells. These signal strength and SP-A-dependent effects are mediated by changes in intracellular Ca(2+) levels over time, involving extrinsic Ca(2+)-activated channels late during activation. These effects are intrinsic to the global T cell population and are manifested in vivo in naive as well as memory phenotype T cells. Thus, SP-A appears to integrate signal thresholds to control T cell proliferation.

Immunotherapeutic efficacy of Mycobacterium indicus pranii in eliciting anti-tumor T cell responses: critical roles of IFNγ

Mycobacterium indicus pranii (MIP) is approved for use as an adjuvant (Immuvac/Cadi-05) in the treatment of leprosy. In addition, its efficacy is being investigated in clinical trials on patients with tuberculosis and different tumors. To evaluate and delineate the mechanisms by which autoclaved MIP enhances anti-tumor responses, the growth of solid tumors consisting of Sp2/0 (myeloma) and EL4 (thymoma) cells was studied in BALB/c and C57BL/6 mice, respectively. Treatment of mice with a single intra-dermal (i.d.) injection of MIP 3 days after Sp2/0 implantation greatly suppresses tumor growth. MIP treatment of tumor bearing mice lowers Interleukin (IL)6 but increases IL12p70 and IFNγ amounts in sera. Also, increase in CD8(+) T cell mediated lysis of specific tumor targets and production of high amounts of IL2 and IFNγ by CD4(+) T cells upon stimulation with specific tumor antigens in MIP treated mice is observed. Furthermore, MIP is also effective in reducing the growth of EL4 tumors; however, this efficacy is reduced in Ifnγ(-/-) mice. In fact, several MIP mediated anti-tumor responses are greatly abrogated in Ifnγ(-/-) mice: increase in serum Interleukin (IL)12p70 amounts, induction of IL2 and lysis of EL4 targets by splenocytes upon stimulation with specific tumor antigens. Interestingly, tumor-induced increase in serum IL12p70 and IFNγ and reduction in growth of Sp2/0 and EL4 tumors by MIP are not observed in nonobese diabetic severe combined immunodeficiency mice. Overall, our study clearly demonstrates the importance of a functional immune network, in particular endogenous CD4(+) and CD8(+) T cells and IFNγ, in mediating the anti-tumor responses by MIP.