Challenges and opportunities in targeting the CD28/CTLA-4 pathway in transplantation and autoimmunity

Immunization of recombinant NS3 protein (protease region) of dengue virus induces high levels of CTLA-4 and apoptosis in splenocytes of BALB/c mice

DENV infection outcomes depend on the host's variable expression of immune receptors and mediators, leading to either resolution or exacerbation. While the NS3 protein is known to induce robust immune responses, the specific impact of its protease region epitopes remains unclear. This study investigated the effect of recombinant NS3 protease region proteins from all four DENV serotypes on splenocyte activation in BALB/c mice (n = 5/group). Mice were immunized with each protein, and their splenocytes were subsequently stimulated with homologous antigens. We measured the expression of costimulatory molecules (CD28, CD80, CD86, CD152) by flow cytometry, along with IL-2 production, CD25 expression, and examined the antigen-specific activation of CD4 + and CD8 + T cells. Additionally, the expression of IL-1, IL-10, and TGF-β1 in splenocytes from immunized animals was assessed. Apoptosis was evaluated using Annexin V/PI staining and DNA fragmentation analysis. Stimulation of splenocytes from immunized mice triggered apoptosis (phosphatidylserine exposure and caspase 3/7 activation) and increased costimulatory molecule expression, particularly CD152. Low IL-2 production and low CD25 expression, as well as sustained expression of the IL-10 gene. These results suggest that these molecules might be involved in mechanisms by which the NS3 protein contributes to viral persistence and disease pathogenesis.

Application of CD25 and CTLA4 gene transcription levels in early prediction of acute graft-versus-host disease

Introduction

Our study investigated the potential of peripheral blood T cell CD25, CD28, and CTLA-4 gene transcription levels as predictive biomarkers for acute graft-versus-host disease (aGVHD) following allogeneic hematopoietic stem cell transplantation (allo-HSCT).

Methods

Real-time reverse transcription fluorescent quantitative PCR (RT-qPCR) analysis was conducted on day +7, +14, and +21 post-transplantation in patients undergoing allo-HSCT.

Results

Elevated levels of CD25 and CTLA-4 mRNA were found to be associated with the occurrence of aGVHD, as well as severe and gastrointestinal aGVHD. Receiver operating characteristic (ROC) curve analysis was utilized to assess the predictive value of each biomarker. Combined analysis of CD25 and CTLA-4 mRNA levels demonstrated promising predictive potential for aGVHD.

Conclusion

Our results confirmed that the transcription levels of CD25 and CTLA-4 genes could be used as early predictive biomarkers for aGVHD post-allo-HSCT.

Co-stimulatory pathway competitive assay development using Liquid chromatography-tandem mass spectrometry (LC-MS/MS)

T-cells play a significant role in the development of autoimmune diseases. The CD28-B7 costimulatory pathway is crucial for activating T-cells, and blocking this pathway is essential for treating autoimmune diseases. Therapeutic antibodies and fusion proteins that target costimulatory molecules like CD80, CD86, CTLA-4, and CD28 have been developed to explore the costimulation process and as targeted treatments. To advance our understanding of costimulation in autoimmunity and the inhibition of the costimulatory pathway, it is crucial to have an accurate, precise, and direct method for detecting and quantifying the soluble form of these molecules in body fluids and various biological systems. Herein, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for quantifying the four costimulatory proteins depending on the signature peptides derived from the soluble isoform of these proteins in multiple reaction monitoring (MRM) mode. The method was validated using the US FDA guidelines. The LOQ was determined as ∼0.5 nM for the four analytes, with quantification extended to 20 nM with a correlation coefficient of R2>0.998. The developed MRM method was used to analyze on-bead digested protein mixtures to establish a competitive assay for the CD28-B7 costimulatory pathway using CTLA4-Ig (Abatacept ™) as an FDA-approved drug for rheumatoid arthritis. The IC50 was determined to be 2.99 and 159.8 nM for sCD80 and sCD86, respectively. A straightforward MRM-based competitive assay will advance the knowledge about the costimulatory role in autoimmunity and the autoimmune therapeutic drug discovery, with the need for broad application on different in vitro and in vivo models to discover new targeted inhibitors.

Assessment of CTLA-4 Gene Expression Levels on CD8+ T Cells in Renal Transplant Patients and Relation with Serum sCTLA-4 Levels

CTLA-4 (Cytotoxic T Lymphocyte Antigen-4) is an immune regulator molecule that is expressed on a variety of immune cells, including CD4+ and CD8+ T cells. After realizing the significance of this regulator molecule, researchers began to concentrate on its activation or inhibition in cancer. Even though there have been some studies on organ transplantation and autoimmunity, the role of the CTLA-4 molecule in renal transplantation has not been demonstrated. The goal of this study was to see how CTLA-4 gene expression and serum sCTLA-4 levels affected renal transplant patients. Peripheral blood samples were collected before and 1-3 months after renal transplantation from 29 recipients. CD8+ T lymphocytes were separated using magnetic beads and purity of the cells controlled by Flow cytometry. CTLA-4 mRNA levels were determined by Real-Time PCR while serum sCTLA-4 levels were assessed by ELISA. 55% of the patient had decreased level of CTLA-4 mRNA after transplantation when compared to pre-transplantation levels. Moreover 61% of the patient had lower serum sCTLA-4 levels after transplantation. sCTLA-4 levels were decreased 11% of the patients with rejection episode after transplantation when compared to stabile patients (5%). Kidney rejection is a complicated process influenced by numerous unknown factors. Several parameters should be evaluated together to precise rejection episodes or graft dysfunctions. Further research focused on the other immune checkpoint regulator molecules could give an opportunity to have an idea about the effect of these molecules on renal transplantation.

From glioma gloom to immune bloom: unveiling novel immunotherapeutic paradigms-a review

In tumor therapeutics, the transition from conventional cytotoxic drugs to targeted molecular therapies, such as those targeting receptor tyrosine kinases, has been pivotal. Despite this progress, the clinical outcomes have remained modest, with glioblastoma patients' median survival stagnating at less than 15 months. This underscores the urgent need for more specialized treatment strategies. Our review delves into the progression toward immunomodulation in glioma treatment. We dissect critical discoveries in immunotherapy, such as spotlighting the instrumental role of tumor-associated macrophages, which account for approximately half of the immune cells in the glioma microenvironment, and myeloid-derived suppressor cells. The complex interplay between tumor cells and the immune microenvironment has been explored, revealing novel therapeutic targets. The uniqueness of our review is its exhaustive approach, synthesizing current research to elucidate the intricate roles of various molecules and receptors within the glioma microenvironment. This comprehensive synthesis not only maps the current landscape but also provides a blueprint for refining immunotherapy for glioma, signifying a paradigm shift toward leveraging immune mechanisms for improved patient prognosis.

A better understanding of the role of the CTLA-CD80/86 axis in the treatment of autoimmune diseases

Autoimmune diseases are diseases in which the regulatory mechanisms of the immune response are disturbed. As a result, the body loses self-tolerance. Since one of the main regulatory mechanisms of the immune response is the CTLA4-CD80/86 axis, this hypothesis suggests that autoimmune diseases potentially share a similar molecular basis of pathogenesis. Hence, investigating the CTLA4-CD80/86 axis may be helpful in finding an appropriate treatment strategy. Therefore, this study aims to investigate the molecular basis of the CTLA4-CD80/86 axis in the regulation of the immune response, and then its role in developing some autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. As well, the main therapeutic strategies affecting the CTLA4-CD80/86 axis have been summarized to highlight the importance of this axis in management of autoimmune diseases.

Regulating the regulatory T cells as cell therapies in autoimmunity and cancer

Regulatory T cells (Tregs), possess a pivotal function in the maintenance of immune homeostasis. The dysregulated activity of Tregs has been associated with the onset of autoimmune diseases and cancer. Hence, Tregs are promising targets for interventions aimed at steering the immune response toward the desired path, either by augmenting the immune system to eliminate infected and cancerous cells or by dampening it to curtail the damage to self-tissues in autoimmune disorders. The activation of Tregs has been observed to have a potent immunosuppressive effect against T cells that respond to self-antigens, thus safeguarding our body against autoimmunity. Therefore, promoting Treg cell stability presents a promising strategy for preventing or managing chronic inflammation that results from various autoimmune diseases. On the other hand, Tregs have been found to be overactivated in several forms of cancer, and their role as immune response regulators with immunosuppressive properties poses a significant impediment to the successful implementation of cancer immunotherapy. However, the targeting of Tregs in a systemic manner may lead to the onset of severe inflammation and autoimmune toxicity. It is imperative to develop more selective methods for targeting the function of Tregs in tumors. In this review, our objective is to elucidate the function of Tregs in tumors and autoimmunity while also delving into numerous therapeutic strategies for reprogramming their function. Our focus is on reprogramming Tregs in a highly activated phenotype driven by the activation of key surface receptors and metabolic reprogramming. Furthermore, we examine Treg-based therapies in autoimmunity, with a specific emphasis on Chimeric Antigen Receptor (CAR)-Treg therapy and T-cell receptor (TCR)-Treg therapy. Finally, we discuss key challenges and the future steps in reprogramming Tregs that could lead to the development of novel and effective cancer immunotherapies.

Transplantation elicits a clonally diverse CD8+ T cell response that is comprised of potent CD43+ effectors

CD8+ T cells mediate acute rejection of allografts, which threatens the long-term survival of transplanted organs. Using MHC class I tetramers, we find that allogeneic CD8+ T cells are present at an elevated naive precursor frequency relative to other epitopes, only modestly increase in number after grafting, and maintain high T cell receptor diversity throughout the immune response. While antigen-specific effector CD8+ T cells poorly express the canonical effector marker KLRG-1, expression of the activated glycoform of CD43 defines potent effectors after transplantation. Activated CD43+ effector T cells maintain high expression of the coreceptor induced T cell costimulator (ICOS) in the presence of CTLA-4 immunoglobulin (Ig), and dual CTLA-4 Ig/anti-ICOS treatment prolongs graft survival. These data demonstrate that graft-specific CD8+ T cells have a distinct response profile relative to anti-pathogen CD8+ T cells and that CD43 and ICOS are critical surface receptors that define potent effector CD8+ T cell populations that form after transplantation.

ICI-based therapies: A new strategy for oral potentially malignant disorders

Oral potentially malignant disorders (OPMDs) are linked with an escalated risk of developing cancers, particularly oral squamous cell carcinoma (OSCC). Since prevailing therapies cannot effectively forestall the exacerbation and recurrence of OPMDs, halting their malignant progression is paramount. The immune checkpoint serves as a cardinal regulator of the immune response and the primary cause of adaptive immunological resistance. Although the exact mechanism remains elusive, elevated expression of multiple immune checkpoints in OPMDs and OSCC relative to healthy oral mucosa has been ascertained. This review delves into the immunosuppressive microenvironment of OPMDs, the expression of diverse immune checkpoints such as programmed death receptor-1 (PD-1) and programmed death receptor-1 ligand (PD-L1) in OPMDs, and the potential application of corresponding inhibitors. In addition, synergistic strategies incorporating combined immune checkpoint inhibitors, such as cGAS-STING, costimulatory molecules, cancer vaccines, and hydrogels, are discussed to gain a more comprehensive understanding of the role and application of immune checkpoint inhibitors (ICIs) in oral carcinogenesis.

The prognostic and therapeutic potentials of CTLA-4 in hematological malignancies

INTRODUCTION

Hematological Malignancies (HMs) are a group of progressive, difficult-to-treat, and highly recurrent diseases. A suppressed phenotype of the immune system is present in HMs and growing evidence indicates the role of Cytotoxic T lymphocyte-Associated protein 4 (CTLA-4) in the course of HMs.

AREAS COVERED

This article reviews the recent literature on the role of CTLA-4 in different subtypes of HMs. Here, the studies on the expression pattern, its effect on the prognosis of different HMs, and polymorphisms of CTLA-4 have been elaborated. Finally, the effect of targeting CTLA-4 in vitro and in vivo, as well as in clinical trials, is discussed.

EXPERT OPINION

According to the recent literature, CTLA-4 is overexpressed in different HMs, which is correlated with poor survival, while it is associated with better a prognosis in Chronic Lymphocytic Leukemia (CLL). Targeting CTLA-4 in Acute Myeloid Leukemia (AML), Sezary Syndrome (SS), Hodgkin's Lymphoma (HL), and so on, is helpful. While this is not recommended and may even be harmful in multiple myeloma (MM) and CLL. Also, it seems that certain CTLA-4 gene polymorphisms are efficient factors in the course of HMs. Future studies may broaden our knowledge regarding the role of CTLA-4 in HMs.

Abatacept for Treatment of Adults Hospitalized with Moderate or Severe Covid-19

BACKGROUND

We investigated whether abatacept, a selective costimulation modulator, provides additional benefit when added to standard-of-care for patients hospitalized with Covid-19.

METHODS

We conducted a master protocol to investigate immunomodulators for potential benefit treating patients hospitalized with Covid-19 and report results for abatacept. Intravenous abatacept (one-time dose 10 mg/kg, maximum dose 1000 mg) plus standard of care (SOC) was compared with shared placebo plus SOC. Primary outcome was time-to-recovery by day 28. Key secondary endpoints included 28-day mortality.

RESULTS

Between October 16, 2020 and December 31, 2021, a total of 1019 participants received study treatment (509 abatacept; 510 shared placebo), constituting the modified intention-to-treat cohort. Participants had a mean age 54.8 (SD 14.6) years, 60.5% were male, 44.2% Hispanic/Latino and 13.7% Black. No statistically significant difference for the primary endpoint of time-to-recovery was found with a recovery-rate-ratio of 1.14 (95% CI 1.00-1.29; p=0.057) compared with placebo. We observed a substantial improvement in 28-day all-cause mortality with abatacept versus placebo (11.0% vs. 15.1%; odds ratio [OR] 0.62 [95% CI 0.41- 0.94]), leading to 38% lower odds of dying. Improvement in mortality occurred for participants requiring oxygen/noninvasive ventilation at randomization. Subgroup analysis identified the strongest effect in those with baseline C-reactive protein >75mg/L. We found no statistically significant differences in adverse events, with safety composite index slightly favoring abatacept. Rates of secondary infections were similar (16.1% for abatacept; 14.3% for placebo).

CONCLUSIONS

Addition of single-dose intravenous abatacept to standard-of-care demonstrated no statistically significant change in time-to-recovery, but improved 28-day mortality.

TRIAL REGISTRATION

ClinicalTrials.gov ( NCT04593940 ).

Mechanism-driven strategies for prevention of rheumatoid arthritis

In seropositive rheumatoid arthritis (RA), the onset of clinically apparent inflammatory arthritis (IA) is typically preceded by a prolonged period of autoimmunity manifest by the presence of circulating autoantibodies that can include antibodies to citrullinated protein antigens (ACPA) and rheumatoid factor (RF). This period prior to clinical IA can be designated preclinical RA in those individuals who have progressed to a clinical diagnosis of RA, and an 'at-risk' status in those who have not developed IA but exhibit predictive biomarkers of future clinical RA. With the goal of developing RA prevention strategies, studies have characterized immune phenotypes of preclinical RA/at-risk states. From these studies, a model has emerged wherein mucosal inflammation and dysbiosis may lead first to local autoantibody production that should normally be transient, but instead is followed by systemic spread of the autoimmunity as manifest by serum autoantibody elevations, and ultimately drives the development of clinically identified joint inflammation. This model can be envisioned as the progression of disease development through serial 'checkpoints' that in principle should constrain or resolve autoimmunity; however, instead the checkpoints 'fail' and clinical RA develops. Herein we review the immune processes that are likely to be present at each step and the potential therapeutic strategies that could be envisioned to delay, diminish, halt or even reverse the progression to clinical RA. Notably, these prevention strategies could utilize existing therapies approved for clinical RA, therapies approved for other diseases that target relevant pathways in the preclinical/at-risk state, or approaches that target novel pathways.

Dyslipidemia in Renal Transplant Recipients

Dyslipidemia is a frequent complication after kidney transplantation (KT) and is an important risk factor for cardiovascular disease (CVD). Renal transplant recipients (RTRs) are considered at high, or very high, risk of CVD, which is a leading cause of death in this patient group. Despite many factors of post-transplant dyslipidemia, the immunosuppressive treatment has the biggest influence on a lipid profile. There are no strict dyslipidemia treatment guidelines for RTRs, but the ones proposing an individual approach regarding CVD risk seem most suitable. Proper diet and physical activity are the main general measures to manage dyslipidemia and should be introduced initially in every patient after KT. In the case of an insufficient correction of lipemia, statins are the basis for hypolipidemic treatment. Statins should be introduced with caution to avoid serious side-effects (e.g., myopathy) or drug-drug interactions, especially with immunosuppressants. To lower the incidence of adverse effects, and improve medication adherence, ezetimibe in combination with statins is recommended. Fibrates and bile sequestrants are not recommended due to their side-effects and variable efficacy. However, several new lipid-lowering drugs like Proprotein convertase subtilisin/Kexin type9 (PCSK9) inhibitors may have promising effects in RTRs, but further research assessing efficacy and safety is yet to be carried out.

Lessons from transmissible cancers for immunotherapy and transplant

The emergence of horizontal transmission of cancer between vertebrates is an issue that interests scientists and medical society. Transmission requires: (i) a mechanism by which cancer cells can transfer to another organism and (ii) a repressed immune response on the part of the recipient. Transmissible tumors are unique models to comprehend the responses and mechanisms mediated by the major histocompatibility complex (MHC), which can be transposed for transplant biology. Here, we discuss the mechanisms involved in immune-mediated tissue rejection, making a parallel with transmissible cancers. We also discuss cellular and molecular mechanisms involved in cancer immunotherapy and anti-rejection therapies.

Immunological lessons from CD28 deficiency in humans

In this issue of Cell, Casanova and colleagues examine three family members with a mutation that results in deficiency of the T cell co-stimulatory molecule CD28. These patients exhibit clinical symptoms due to human papillomavirus-2 and -4 infections, show increased levels of Epstein-Barr virus and cytomegalovirus in the blood, and respond poorly to vaccines.

ICOSL+ plasmacytoid dendritic cells as inducer of graft-versus-host disease, responsive to a dual ICOS/CD28 antagonist

Acute graft-versus-host disease (aGVHD) remains a major complication of allogeneic hematopoietic cell transplantation (HCT). CD146 and CCR5 are proteins that mark activated T helper 17 (Th17) cells. The Th17 cell phenotype is promoted by the interaction of the receptor ICOS on T cells with ICOS ligand (ICOSL) on dendritic cells (DCs). We performed multiparametric flow cytometry in a cohort of 156 HCT recipients and conducted experiments with aGVHD murine models to understand the role of ICOSL⁺ DCs. We observed an increased frequency of ICOSL⁺ plasmacytoid DCs, correlating with CD146⁺CCR5⁺ T cell frequencies, in the 64 HCT recipients with gastrointestinal aGVHD. In murine models, donor bone marrow cells from ICOSL-deficient mice compared to those from wild-type mice reduced aGVHD-related mortality. Reduced aGVHD resulted from lower intestinal infiltration of pDCs and pathogenic Th17 cells. We transplanted activated human ICOSL⁺ pDCs along with human peripheral blood mononuclear cells into immunocompromised mice and observed infiltration of intestinal CD146⁺CCR5⁺ T cells. We found that prophylactic administration of a dual human ICOS/CD28 antagonist (ALPN-101) prevented aGVHD in this model better than did the clinically approved belatacept (CTLA-4-Fc), which binds CD80 (B7-1) and CD86 (B7-2) and interferes with the CD28 T cell costimulatory pathway. When started at onset of aGVHD signs, ALPN-101 treatment alleviated symptoms of ongoing aGVHD and improved survival while preserving antitumoral cytotoxicity. Our data identified ICOSL⁺-pDCs as an aGVHD biomarker and suggest that coinhibition of the ICOSL/ICOS and B7/CD28 axes with one biologic drug may represent a therapeutic opportunity to prevent or treat aGVHD.

Systemic Immunomodulatory Effects of Combinatorial Treatment of Thalidomide and Dexamethasone on T Cells and Other Immune Cells

PURPOSE

In organ transplantation, the need for immune modulation rather than immune suppression has been emphasized. In this study, we investigated whether combinatorial treatments of with thalidomide (TM) and dexamethasone (DX) might be new approaches to induce systemic immunomodulation on T cells and other immune cells that regulate the expression of co-inhibitory molecules.

MATERIALS AND METHODS

Naïve splenic T cells from C57BL/6 mice were sort-purified and cultured in vitro for CD4+ T cell proliferation and regulatory T cell (Treg) conversion in the presence of TM or/and DX. Expression of cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) and programmed death-1 (PD-1) in proliferated and converted T cells was quantified by flow cytometry. We also quantified in vivo expression of CTLA-4 and PD-1 on splenic CD4+ T cells and other immune cells isolated from TM- or/and DX-treated mice. Mixed lymphocytes reactions (MLR) were performed to evaluate the capacity of immune cells in carrying out immune responses.

RESULTS

CTLA-4 expressions in effector T cells in vivo and in Tregs in vivo/vitro significantly increased upon TM/DX combinatorial treatment. Corresponding to increased CTLA-4 expression in T cells, the expression of ligand molecules for CTLA-4 significantly increased in splenic dendritic cells in TM/DX-treated groups. In addition, MLR results demonstrated that splenocytes isolated from TM/DX-treated mice significantly suppressed the proliferation of T cells isolated from other strains.

CONCLUSION

Based on these results, we suggest that TM/DX combinatorial treatments might be efficient immunomodulatory methods for regulating T cell immunity.

Kidney xenotransplantation: Recent progress in preclinical research

Kidney transplantation is the most effective treatment for end-stage renal disease, but is limited by the increasing shortage of deceased and living human donor kidneys. Xenotransplantation using pig organs provides the possibility to resolve the issue of organ supply shortage and is regarded as the next great medical revolution. In the past five years, there have been sequential advances toward the prolongation of life-supporting pig kidney xenograft survival in non-human primates, with the longest survival being 499 days. This progress is due to the growing availability of pigs with multi-layered genetic modifications to overcome the pathobiological barriers and the application of a costimulation blockade-based immunosuppressive regimen. These encouraging results bring the hope to initiate the clinical trials of pig kidney transplantation in the near future. In this review, we summarized the latest advances regarding pig kidney xenotransplantation in preclinical models to provide a basis for future investigation and potential clinical translation.

Autophagy-lysosome inhibitor chloroquine prevents CTLA-4 degradation of T cells and attenuates acute rejection in murine skin and heart transplantation

Background: The immune checkpoint cytotoxic T lymphocyte antigen-4 (CTLA-4), induced upon T cell activation but degraded quickly, has been targeted in the clinical therapy of advanced cancers and autoimmune diseases. However, whether inhibiting CTLA-4 degradation ameliorates transplant rejection remains unknown.

Methods: The CTLA-4 expression in activated murine T cells treated with the inhibitors mediating protein degradation was detected by flow cytometry (FCM). CD45.1 mice, which received TEa T cells and underwent heart transplantation, were administrated with the inhibitor. Subsequently, CTLA-4 expression of TEa T cells was analyzed. Murine skin and heart transplantation models were built, then the survival and histopathology of the allografts, and T cell subsets in the spleens of each group were compared.

Results: Chloroquine (CQ) was identified as an inhibitor of CTLA-4 degradation, which augmented both surface and total CTLA-4 expression in T cells. It considerably prolonged the skin and heart allograft survival time and reduced the infiltration of inflammatory cells in allografts. Besides decreasing the frequencies of the CD4⁺ and CD8⁺ effector T cells, especially IFN-γ producing T cells, CQ also increased the proportion of regulatory T cells in the spleen. The CTLA-4 blockade abrogated the benefits of CQ on the survival of heart allografts. Moreover, CQ enhanced CTLA-4 expression in activated human T cells and reduced the secretion of IFN-γ in human mixed lymphocyte reaction.

Conclusion: Targeting CTLA-4 degradation provides a novel means to prevent transplant rejection and induce transplant tolerance.

Cowpox virus encodes a protein that binds B7.1 and B7.2 and subverts T cell costimulation

Costimulation is required for optimal T cell activation, yet it is unclear whether poxviruses dedicatedly subvert costimulation during infection. Here, we report that the secreted M2 protein encoded by cowpox virus (CPXV) specifically interacts with human and murine B7.1 (CD80) and B7.2 (CD86). We also show that M2 competes with CD28 and CTLA4 for binding to cell surface B7 ligands, with stronger efficacy against CD28. Functionally, recombinant M2 and culture supernatants from wild-type (WT) but not M2-deficient (∆M2) CPXV-infected cells can potently suppress B7 ligand-mediated T cell proliferation and interleukin-2 (IL-2) production. Furthermore, we observed increased antiviral CD4 and CD8 T cell responses in C57BL/6 mice challenged by ∆M2 CPXV compared with WT virus. These differences in immune responses to ∆M2 and WT CPXV were not observed in CD28-deficient mice. Taken together, our findings define a mechanism of viral sabotage of T cell activation that highlights the role of CD28 costimulation in host defense against poxvirus infections.

CD28 Deficiency Ameliorates Blast Exposure-Induced Lung Inflammation, Oxidative Stress, Apoptosis, and T Cell Accumulation in the Lungs via the PI3K/Akt/FoxO1 Signaling Pathway

Although CD28 is associated with the expression of inflammatory mediators, apoptosis-related protein, immunosuppression, and tumorigenesis, the effects of CD28 deficiency on blast exposure-induced lung injury have not been investigated. In this study, we have explored the effects of CD28 on blast exposure-induced lung injury and studied its potential molecular mechanisms. A mouse model of blast exposure-induced acute lung injury was established. Sixty C57BL/6 wild-type (WT) and CD28 knockout (CD28^−/−) mice were randomly divided into control or model groups. Lung tissue samples were collected 24 h and 48 h after blast injury. Histopathological changes and the expressions of inflammatory-related proteins were detected by hematoxylin-eosin, immunohistochemistry, and immunofluorescence staining. Apoptosis and oxidative stress were evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and reactive oxygen species (ROS). Inflammation, apoptosis, oxidative stress, and related pathway protein expression were studied by western blotting. In addition, the levels of CD3 and CD28 proteins were measured by flow cytometry. In the current study, we found that CD28 deficiency significantly inhibited blast exposure-induced increases in the lung weight/body weight ratio and wet weight/dry weight ratio; decreased the infiltration of CD44⁺ leukocytes, CD163⁺ macrophages, and CD3⁺ T cells into the lungs; reduced the expressions of proinflammatory cytokines including IL-1β, TNF-α, and IL-6; and markedly increased IL-10 expression. CD28 deficiency also significantly attenuated blast exposure-induced ROS, MDA5, and IREα expressions; increased SOD-1 expression; lowered the number of apoptotic cells and Bax, Caspase-3, and active Caspase-8 expressions; and increased Bcl-2 expression. Additionally, CD28 deficiency significantly ameliorated blast exposure-induced increases of p-PI3K and p-Akt and ameliorated the decrease in the p-FoxO1 expression. Our results suggest that CD28 deficiency has a protective effect on blast exposure-induced lung injury, which might be associated with the PI3K/Akt/FoxO1 signaling pathway.

Transplant research in nonhuman primates to evaluate clinically relevant immune strategies in organ transplantation

Research in transplant immunology using non-human primate (NHP) species to evaluate immunologic strategies to prevent rejection and prolong allograft survival has yielded results that have translated successfully into human organ transplant patient management. Other therapies have not proceeded to human translation due to failure in NHP testing, arguably sparing humans the futility and risk of such testing. The NHP transplant models are ethically necessary for drug development in this field and provide the closest analogue to human transplant patients available. The refinement of this resource with respect to colony MHC typing, reagent and assay development, and availability to the research community has greatly enhanced knowledge about transplant immunology and drug development.

Complement factor and T-cell interactions during alloimmune inflammation in transplantation

Complement factor and T-cell signaling during an effective alloimmune response plays a key role in transplant-associated injury, which leads to the progression of chronic rejection (CR). During an alloimmune response, activated complement factors (C3a and C5a) bind to their corresponding receptors (C3aR and C5aR) on a number of lymphocytes, including T-regulatory cells (Tregs), and these cell-molecular interactions have been vital to modulate an effective immune response to/from Th1-effector cell and Treg activities, which result in massive inflammation, microvascular impairments, and fibrotic remodeling. Involvement of the complement-mediated cell signaling during transplantation signifies a crucial role of complement components as a key therapeutic switch to regulate ongoing inflammatory state, and further to avoid the progression of CR of the transplanted organ. This review highlights the role of complement-T cell interactions, and how these interactions shunt the effector immune response during alloimmune inflammation in transplantation, which could be a novel therapeutic tool to protect a transplanted organ and avoid progression of CR.

Fates of CD8+ T cells in Tumor Microenvironment

Studies have reported a positive correlation between elevated CD8+ T cells in the tumor microenvironment (TME) and good prognosis in cancer. However, the mechanisms linking T cell tumor-infiltration and tumor rejection are yet to be fully understood. The cells and factors of the TME facilitate tumor development in various ways. CD8+ T cell function is influenced by a number of factors, including CD8+ T cell trafficking and localization into tumor sites; as well as CD8+ T cell growth and differentiation. This review highlights recent literature as well as currently evolving concepts regarding the fates of CD8+ T cells in the TME from three different aspects CD8+ T cell trafficking, differentiation and function. A thorough understanding of factors contributing to the fates of CD8+ T cells will allow researchers to develop new strategies and improve on already existing strategies to facilitate CD8+ T cell mediated anti-tumor function, impede T cell dysfunction and modulate the TME into a less immunosuppressive TME.

Toward Small-Molecule Inhibition of Protein-Protein Interactions: General Aspects and Recent Progress in Targeting Costimulatory and Coinhibitory (Immune Checkpoint) Interactions

Protein-Protein Interactions (PPIs) that are part of the costimulatory and coinhibitory (immune checkpoint) signaling are critical for adequate T cell response and are important therapeutic targets for immunomodulation. Biologics targeting them have already achieved considerable clinical success in the treatment of autoimmune diseases or transplant recipients (e.g., abatacept, belatacept, and belimumab) as well as cancer (e.g., ipilimumab, nivolumab, pembrolizumab, atezolizumab, durvalumab, and avelumab). In view of such progress, there have been only relatively limited efforts toward developing small-molecule PPI inhibitors (SMPPIIs) targeting these cosignaling interactions, possibly because they, as all other PPIs, are difficult to target by small molecules and were not considered druggable. Nevertheless, substantial progress has been achieved during the last decade. SMPPIIs proving the feasibility of such approaches have been identified through various strategies for a number of cosignaling interactions including CD40-CD40L, OX40-OX40L, BAFFR-BAFF, CD80-CD28, and PD-1-PD-L1s. Here, after an overview of the general aspects and challenges of SMPPII-focused drug discovery, we review them briefly together with relevant structural, immune-signaling, physicochemical, and medicinal chemistry aspects. While so far only a few of these SMPPIIs have shown activity in animal models (DRI-C21045 for CD40-D40L, KR33426 for BAFFR-BAFF) or reached clinical development (RhuDex for CD80-CD28, CA-170 for PD-1-PD-L1), there is proof-of-principle evidence for the feasibility of such approaches in immunomodulation. They can result in products that are easier to develop/ manufacture and are less likely to be immunogenic or encounter postmarket safety events than corresponding biologics, and, contrary to them, can even become orally bioavailable.