Early Decision: Effector and Effector Memory T Cell Differentiation in Chronic Infection

Human T-cell activation with Toxoplasma gondii antigens loaded in maltodextrin nanoparticles

Toxoplasmosis is the most prevalent parasitic zoonosis worldwide, causing ocular and neurological diseases. No vaccine has been approved for human use. We evaluated the response of peripheral blood mononuclear cells (PBMCs) to a novel construct of Toxoplasma gondii total antigen in maltodextrin nanoparticles (NP/TE) in individuals with varying infectious statuses (uninfected, chronic asymptomatic, or ocular toxoplasmosis). We analyzed the concentration of IFN-γ after NP/TE ex vivo stimulation using ELISA and the immunophenotypes of CD4+ and CD8+ cell populations using flow cytometry. In addition, serotyping of individuals with toxoplasmosis was performed by ELISA using GRA6-derived polypeptides. Low doses of NP/TE stimulation (0.9 μg NP/0.3 μg TE) achieved IFN-γ-specific production in previously exposed human PBMCs without significant differences in the infecting serotype. Increased IFN-γ expression in CD4+ effector memory cell subsets was found in patients with ocular toxoplasmosis with NP/TE but not with TE alone. This is the first study to show how T-cell subsets respond to ex vivo stimulation with a vaccine candidate for human toxoplasmosis, providing crucial insights for future clinical trials.

Enrichment of effector memory T cells in the CD4 and CD8 T cell compartment during chronic graft versus host disease in children

BACKGROUND

During allogeneic Hematopoietic stem cell transplantation (HSCT), frequent pathological scenarios include graft versus host disease (GVHD) and viral infections. We hypothesized if exogenous stimulus as alloantigen and viral antigens might impact on central and effector memory T cells in pediatric recipients.

PATIENTS AND METHODS

Subjects included 21 pediatric recipients and 20 healthy children (control group). Peripheral blood samples of patients were collected along the first 712 days post-HSCT. T cell phenotyping of naïve, central, and effector memory T cells (TCMs and TEMs, respectively) was conducted using flow cytometry. Viral nucleic acids were detected using real-time PCR.

RESULTS

T cell reconstitution was not reached after 1 year post-HSCT. Chronic GVHD was associated with increased numbers of naïve CD4 T cells (p < 0.05) as well as an increase in TEM and TCM cells of the CD4 (p < 0.0001 and p < 0.05, respectively) and CD8 T cell TEM (p < 0.0001). and TCM (p < 0.001) populations too. Moreover, BK and Epstein-Barr viruses were the main viral pathogens detected (<104 copies), which were associated with a decrease in all T cell compartments.

CONCLUSION

During chronic GVHD, alloantigen persistence generates TEM cell enrichment among CD4 and CD8 T cells, and viral infections are associated with deficient recovery of T cells after HSCT.

Angiotensin II-Induced Memory γδ T Cells Sensitize Mice to a Mild Hypertensive Stimulus

BACKGROUND

Memory T cells develop during an initial hypertensive episode, sensitizing mice to develop hypertension from further mild hypertensive challenges. We hypothesized that memory γδ T cells develop after a hypertensive challenge and sensitize mice to develop hypertension in response to a subsequent mild hypertensive challenge.

METHODS

The first aim was to profile memory γδ T cells after a 14-day pressor dose angiotensin II (AngII) infusion (490 ng/kg/min, subcutaneously) in male mice. The second aim was to deplete γδ T cells during a second 14-day subpressor dose AngII challenge (140 ng/kg/min, subcutaneously) in mice pre-exposed to an initial pressor dose AngII challenge. The third aim was to transfer 2.5 × 105 live pre-activated or not γδ T cells from mice that had received a 14-day pressor dose AngII infusion or sham treatment, to naive recipient mice stimulated with a subpressor dose AngII infusion.

RESULTS

Effector memory γδ T cells increased 5.2-fold in mesenteric vessels and perivascular adipose tissue, and 1.8-fold in mesenteric lymph nodes in pressor dose AngII-infused mice compared with sham-treated mice. Mice depleted of γδ T cells had 14 mm Hg lower systolic blood pressure (SBP) elevation than control mice from day 7 to 14 of subpressor dose AngII infusion. Adoptive transfer of γδ T cells from hypertensive mice induced an 18 mm Hg higher SBP elevation compared with a subpressor dose AngII infusion vs. γδ T cells transferred from sham-treated mice.

CONCLUSIONS

Memory γδ T cells develop in response to hypertensive stimuli, and contribute to the pathogenesis of hypertension.

IL-12 and IL-27 Promote CD39 Expression on CD8+ T Cells and Differentially Regulate the CD39+CD8+ T Cell Phenotype

Tumor-specific CD8+ T cells are critical components of antitumor immunity; however, factors that modulate their phenotype and function have not been completely elucidated. Cytokines IL-12 and IL-27 have recognized roles in promoting CD8+ T cells' effector function and mediated antitumor responses. Tumor-specific CD8+ tumor-infiltrating lymphocytes (TILs) can be identified based on surface expression of CD39, whereas bystander CD8+ TILs do not express this enzyme. It is currently unclear how and why tumor-specific CD8+ T cells uniquely express CD39. Given the important roles of IL-12 and IL-27 in promoting CD8+ T cell functionality, we investigated whether these cytokines could modulate CD39 expression on these cells. Using in vitro stimulation assays, we identified that murine splenic CD8+ T cells differentially upregulate CD39 in the presence of IL-12 and IL-27. Subsequently, we assessed the exhaustion profile of IL-12- and IL-27-induced CD39+CD8+ T cells. Despite the greatest frequency of exhausted CD39+CD8+ T cells after activation with IL-12, as demonstrated by the coexpression of TIM-3+PD-1+LAG-3+ and reduced degranulation capacity, these cells retained the ability to produce IFN-γ. IL-27-induced CD39+CD8+ T cells expressed PD-1 but did not exhibit a terminally exhausted phenotype. IL-27 was able to attenuate IL-12-mediated inhibitory receptor expression on CD39+CD8+ T cells but did not rescue degranulation ability. Using an immunogenic neuro-2a mouse model, inhibiting IL-12 activity reduced CD39+CD8+ TIL frequency compared with controls without changing the overall CD8+ TIL frequency. These results provide insight into immune regulators of CD39 expression on CD8+ T cells and further highlight the differential impact of CD39-inducing factors on the phenotype and effector functions of CD8+ T cells.

Dynamic changes in TIGIT expression on the T-cell surface and TIGIT-mediated T-cell dysfunction in the brains of mice with chronic Toxoplasma gondii infection

The immunosuppressive receptor TIGIT plays a vital role in the regulation of the immune system's response to pathogens. However, the expression pattern of this receptor in mouse brains during infection with Toxoplasma gondii cysts is not known. Here, we provide evidence of immunological changes and TIGIT expression in infected mouse brains through flow cytometry and QPCR. The obtained results show that TIGIT expression on brain T cells rose considerably after infection. T. gondii infection triggered the conversion of TIGIT+ TCM cells to TIGIT+ TEM cells and reduced their cytotoxicity. During the whole period of T. gondii infection, high intensity and persistent expression of IFN-γ and TNF-α in brain and serum of mice. This study shows that chronic T. gondii infection increases TIGIT expression on brain T cells and affects their immune function.

Regulatory roles of MicroRNA in shaping T cell function, differentiation and polarization

T lymphocytes are an integral component of adaptive immunity with pleotropic effector functions. Impairment of T cell activity is implicated in various immune pathologies including autoimmune diseases, AIDS, carcinogenesis, and periodontitis. Evidently, T cell differentiation and function are under robust regulation by various endogenous factors that orchestrate underlying molecular pathways. MicroRNAs (miRNA) are a class of noncoding, regulatory RNAs that post-transcriptionally control multiple mRNA targets by sequence-specific interaction. In this article, we will review the recent progress in our understanding of miRNA-gene networks that are uniquely required by specific T cell effector functions and provide miRNA-mediated mechanisms that govern the fate of T cells. A subset of miRNAs may act in a synergistic or antagonistic manner to exert functional suppression of genes and regulate pathways that control T cell activation and differentiation. Significance of T cell-specific miRNAs and their dysregulation in immune-mediated diseases is discussed. Exosome-mediated horizontal transfer of miRNAs from antigen presenting cells (APCs) to T cells and from one T cell to another T cell subset and their impact on recipient cell functions is summarized.

Expression of TIGIT in splenic and circulatory T cells from mice acutely infected with Toxoplasma gondii

The surface protein TIGIT (T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif (ITIM) domain) has been characterized as an important regulator of cell-mediated immune responses in various infections. However, TIGIT expression in immune cells of mice infected with Toxoplasma gondii has not been investigated. Here, we detected TIGIT expression and related phenotypes by flow cytometry and real-time PCR in splenic and circulatory T cells of mice infected with the T. gondii RH strain. We found that the expression of TIGIT on the surface of CD4⁺ T cells and CD8⁺ T cells from the spleen and peripheral blood mononuclear cells decreased in the early stage, but increased significantly in the late stage of acute T. gondii infection in mice. Importantly, TIGIT expression was positively correlated with lesions in the murine spleen. In addition, T. gondii-specific TIGIT⁺T_CM cells in the spleen were activated and transformed into TIGIT⁺ T_EM cells. Hematoxylin and eosin staining of spleen sections and real-time PCR showed that the severity of splenic lesions was positively correlated with the T. gondii load. This study demonstrates that acute T. gondii infection can regulate the expression of TIGIT in T cells and affect immune cell function.

Molecular Diversity of Clinically Stable Human Kidney Allografts

IMPORTANCE

Clinical decision and immunosuppression dosing in kidney transplantation rely on transplant biopsy tissue histology even though histology has low specificity, sensitivity, and reproducibility for rejection diagnosis. The inclusion of stable allografts in mechanistic and clinical studies is vital to provide a normal, noninjured comparative group for all interrogative studies on understanding allograft injury.

OBJECTIVE

To refine the definition of a stable allograft as one that is clinically, histologically, and molecularly quiescent using publicly available transcriptomics data.

DESIGN, SETTING, AND PARTICIPANTS

In this prognostic study, the National Center for Biotechnology Information Gene Expression Omnibus was used to search for microarray gene expression data from kidney transplant tissues, resulting in 38 studies from January 1, 2017, to December 31, 2018. The diagnostic annotations included 510 acute rejection (AR) samples, 1154 histologically stable (hSTA) samples, and 609 normal samples. Raw fluorescence intensity data were downloaded and preprocessed followed by data set merging and batch correction.

MAIN OUTCOMES AND MEASURES

The primary measure was area under the receiver operating characteristics curve from a set of feature selected genes and cell types for distinguishing AR from normal kidney tissue.

RESULTS

Within the 28 data sets, the feature selection procedure identified a set of 6 genes (KLF4, CENPJ, KLF2, PPP1R15A, FOSB, TNFAIP3) (area under the curve [AUC], 0.98) and 5 immune cell types (CD4+ T-cell central memory [Tcm], CD4+ T-cell effector memory [Tem], CD8+ Tem, natural killer [NK] cells, and Type 1 T helper [TH1] cells) (AUC, 0.92) that were combined into 1 composite Instability Score (InstaScore) (AUC, 0.99). The InstaScore was applied to the hSTA samples: 626 of 1154 (54%) were found to be immune quiescent and redefined as histologically and molecularly stable (hSTA/mSTA); 528 of 1154 (46%) were found to have molecular evidence of rejection (hSTA/mAR) and should not have been classified as stable allografts. The validation on an independent cohort of 6 months of protocol biopsy samples in December 2019 showed that hSTA/mAR samples had a significant change in graft function (r = 0.52, P < .001) and graft loss at 5-year follow-up (r = 0.17). A drop by 10 mL/min/1.73m2 in estimated glomerular filtration rate was estimated as a threshold in allograft transitioning from hSTA/mSTA to hSTA/mAR.

CONCLUSIONS AND RELEVANCE

The results of this prognostic study suggest that the InstaScore could provide an important adjunct for comprehensive and highly quantitative phenotyping of protocol kidney transplant biopsy samples and could be integrated into clinical care for accurate estimation of subsequent patient clinical outcomes.

Immune Expression in Children With Vesicoureteral Reflux: A Pilot Study

OBJECTIVE

To perform an exploratory, descriptive pilot study of the systemic and local immune environment in patients with vesicoureteral reflux (VUR) and bladder-bowel dysfunction (BBD).

METHODS

Consecutive children with VUR undergoing intravesical ureteral reimplantation were enrolled. Patients were assessed for presence of BBD by reported patient history and validated questionnaire. Fresh blood and bladder tissue, collected at the time of surgery, were immediately processed for analysis. Immune cell compositions were determined via flow cytometry. Immune cell activation was also defined at the time of analysis. LegendPlex assay analysis was utilized to define levels of circulating chemokines and cytokines.

RESULTS

A total of 7 patients were enrolled. Although percentages of circulating immune cells in the blood of those with VUR/BBD and VUR alone were similar, within bladder tissue, VUR/BBD demonstrated increased immune infiltrates compared to VUR alone. Bladder sample analysis showed that B cells, and Effector Memory and Naïve T cell percentages were significantly increased in VUR/BBD patients compared to VUR patients. T cell expression of PD1 was increased in bladder tissues of BBD/VUR. Additionally, analysis of circulating neutrophils displayed significantly increased upregulation of PDL-1 in patients with VUR/BBD vs those with VUR only.

CONCLUSION

These pilot data suggest an immune-rich microenvironment is present within VUR. Severity of inflammation appeared to correlate with presence of BBD. This implies that targeting pelvic inflammation may be a novel therapy for children with VUR- or non-VUR-related BBD. Follow-up studies are currently underway.

Human and murine memory γδ T cells: Evidence for acquired immune memory in bacterial and viral infections and autoimmunity

γδ T cells are unconventional lymphocytes that could play a role in bridging the innate and adaptive immune system. Upon initial exposure to an antigen, some activated T cells become memory T cells that could be reactivated upon secondary immune challenge. Recently, subsets of γδ T cells with a restricted antigen repertoire and long-term persistence have been observed after clearance of viral and bacterial infections. These γδ T cells possess the hallmark ability of memory T cells to respond more strongly and proliferate to a higher extent upon secondary infection. Murine and primate models of Listeria monocytogenes and cytomegalovirus infection display these memory hallmarks and demonstrate γδ T cell memory responses. In addition, human and non-human primate infections with Mycobacterium tuberculosis, as well as non-human primate infection with monkeypox and studies on patients suffering from autoimmune disease (rheumatoid arthritis and multiple sclerosis) reveal memory-like responses corresponding with disease. Murine models of psoriatic disease (imiquimod) and parasite infections (malaria) exhibited shifts to memory phenotypes with repeated immune challenge. These studies provide strong support for the formation of immune memory in γδ T cells, and memory γδ T cells may have a widespread role in protective immunity and autoimmunity.

Low-dose influenza vaccine Grippol Quadrivalent with adjuvant Polyoxidonium induces a T helper-2 mediated humoral immune response and increases NK cell activity

The influenza vaccine Grippol® Quadrivalent (GQ) is a new vaccine, containing the adjuvant Polyoxidonium® and recombinant hemagglutinins from 4 strains of the influenza virus in amount of 5-6 μg of each hemagglutinin per human dose. These doses of antigens are about 3 times less than the standard dose recommended by WHO. We sought to characterize the immune response to the GQ vaccine and to determine the contribution of the adjuvant in this response. BALB/c mice were vaccinated with GQ or with adjuvant-free antigen mixtures (AGs). Then, the antibody response, the number of memory T cells in the spleen, and the functional properties of splenocytes were determined. The vaccine GQ has been shown to induce antibodies to all 4 influenza hemagglutinins. The vaccination with GQ caused a strong increase in the AG-induced proliferation and production of Th2 cytokines ex vivo. These effects were equal to effect achieved by standard dose of antigens. Vaccination also caused the accumulation of CD4⁺ large lymphocytes with the phenotype of central and effector memory T cells in the spleen. The GQ vaccine enhanced the cytolytic activity of natural killer (NK) cells, whereas the adjuvant-free mixture of AGs in lowered and standard doses did not affect NK activity. We did not find a noticeable response of Th1 and CD8⁺ T cells to vaccination. In vitro, the GQ vaccine stimulated the maturation of human monocyte-derived dendritic cells (DCs) enhancing the expression of HLA-DR, CD80, CD83, CD86 and ICOSL molecules. Polyoxidonium without AGs also induced expression of ICOSL, which plays an important role in T-dependent humoral immune response. In summary, the low-dose influenza vaccine GQ with Polyoxidonium adjuvant is immunogenic, induces a Th2-polarized T-cell response and CD4⁺ memory T cells maturation, activates the production of antibodies to influenza hemagglutinins, and increases the activity of NK cells.

Molecular Aspects and Future Perspectives of Cytokine-Based Anti-cancer Immunotherapy

Cytokine-based immunotherapy is a promising field in the cancer treatment, since cytokines, as proteins of the immune system, are able to modulate the host immune response toward cancer cell, as well as directly induce tumor cell death. Since a low dose monotherapy with some cytokines has no significant therapeutic results and a high dose treatment leads to a number of side effects caused by the pleiotropic effect of cytokines, the problem of understanding the influence of cytokines on the immune cells involved in the pro- and anti-tumor immune response remains a pressing one. Immune system cells carry CD makers on their surface which can be used to identify various populations of cells of the immune system that play different roles in pro- and anti-tumor immune responses. This review discusses the functions and specific CD markers of various immune cell populations which are reported to participate in the regulation of the immune response against the tumor. The results of research studies and clinical trials investigating the effect of cytokine therapy on the regulation of immune cell populations and their surface markers are also discussed. Current trends in the development of cancer immunotherapy, as well as the role of cytokines in combination with other therapeutic agents, are also discussed.

An autophagy-inducing and TLR-2 activating BCG vaccine induces a robust protection against tuberculosis in mice

Mycobacterium bovis BCG is widely used as a vaccine against tuberculosis due to M. tuberculosis (Mtb), which kills millions of people each year. BCG variably protects children, but not adults against tuberculosis. BCG evades phagosome maturation, autophagy, and reduces MHC-II expression of antigen-presenting cells (APCs) affecting T-cell activation. To bypass these defects, an autophagy-inducing, TLR-2 activating C5 peptide from Mtb-derived CFP-10 protein was overexpressed in BCG in combination with Ag85B. Recombinant BCG85C5 induced a robust MHC-II-dependent antigen presentation to CD4 T cells in vitro, and elicited stronger TH1 cytokines (IL-12, IL-1β, and TNFα) from APCs of C57Bl/6 mice increasing phosphorylation of p38MAPK and ERK. BCG85C5 also enhanced MHC-II surface expression of MΦs by inhibiting MARCH1 ubiquitin ligase that degrades MHC-II. BCG85C5 infected APCs from MyD88 or TLR-2 knockout mice showed decreased antigen presentation. Furthermore, BCG85C5 induced LC3-dependent autophagy in macrophages increasing antigen presentation. Consistent with in vitro effects, BCG85C5 markedly expanded both effector and central memory T cells in C57Bl/6 mice protecting them against both primary aerosol infection with Mtb and reinfection, but was less effective among TLR-2 knockout mice. Thus, BCG85C5 induces stronger and longer lasting immunity, and is better than BCG against tuberculosis of mice.

Phenotypic and Functional Signatures of Herpes Simplex Virus-Specific Effector Memory CD73+CD45RAhighCCR7lowCD8+ TEMRA and CD73+CD45RAlowCCR7lowCD8+ TEM Cells Are Associated with Asymptomatic Ocular Herpes

HSV type 1 (HSV-1)-specific CD8⁺ T cells protect from herpes infection and disease. However, the nature of protective CD8⁺ T cells in HSV-1 seropositive healthy asymptomatic (ASYMP) individuals (with no history of clinical herpes disease) remains to be determined. In this study, we compared the phenotype and function of HSV-specific CD8⁺ T cells from HLA-A*02:01-positive ASYMP and symptomatic (SYMP) individuals (with a documented history of numerous episodes of recurrent ocular herpetic disease). We report that although SYMP and ASYMP individuals have similar frequencies of HSV-specific CD8⁺ T cells, the "naturally" protected ASYMP individuals have a significantly higher proportion of multifunctional HSV-specific effector memory CD8⁺ T cells (CD73⁺CD45RA^highCCR7^lowCD8⁺ effector memory RA (T_EMRA) and CD73⁺CD45RA^lowCCR7^lowCD8⁺ effector memory (T_EM) as compared with SYMP individuals. Similar to humans, HSV-1-infected ASYMP B6 mice had frequent multifunctional HSV-specific CD73⁺CD8⁺ T cells in the cornea, as compared with SYMP mice. Moreover, in contrast to wild type B6, CD73^-/- deficient mice infected ocularly with HSV-1 developed more recurrent corneal herpetic infection and disease. This was associated with less functional CD8⁺ T cells in the cornea and trigeminal ganglia, the sites of acute and latent infection. The phenotypic and functional characteristics of HSV-specific circulating and in situ CD73⁺CD8⁺ T cells, demonstrated in both ASYMP humans and mice, suggest a positive role for effector memory CD8⁺ T cells expressing the CD73 costimulatory molecule in the protection against ocular herpes infection and disease. These findings are important for the development of safe and effective T cell-based herpes immunotherapy.

Th1-like Plasmodium-Specific Memory CD4+ T Cells Support Humoral Immunity

Effector T cells exhibiting features of either T helper 1 (Th1) or T follicular helper (Tfh) populations are essential to control experimental Plasmodium infection and are believed to be critical for resistance to clinical malaria. To determine whether Plasmodium-specific Th1- and Tfh-like effector cells generate memory populations that contribute to protection, we developed transgenic parasites that enable high-resolution study of anti-malarial memory CD4 T cells in experimental models. We found that populations of both Th1- and Tfh-like Plasmodium-specific memory CD4 T cells persist. Unexpectedly, Th1-like memory cells exhibit phenotypic and functional features of Tfh cells during recall and provide potent B cell help and protection following transfer, characteristics that are enhanced following ligation of the T cell co-stimulatory receptor OX40. Our findings delineate critical functional attributes of Plasmodium-specific memory CD4 T cells and identify a host-specific factor that can be targeted to improve resolution of acute malaria and provide durable, long-term protection against Plasmodium parasite re-exposure.

Protection by and maintenance of CD4 effector memory and effector T cell subsets in persistent malaria infection

Protection at the peak of Plasmodium chabaudi blood-stage malaria infection is provided by CD4 T cells. We have shown that an increase in Th1 cells also correlates with protection during the persistent phase of malaria; however, it is unclear how these T cells are maintained. Persistent malaria infection promotes protection and generates both effector T cells (Teff), and effector memory T cells (Tem). We have previously defined new CD4 Teff (IL-7Rα^-) subsets from Early (Teff^Early, CD62L^hiCD27⁺) to Late (Teff^Late, CD62L^loCD27^-) activation states. Here, we tested these effector and memory T cell subsets for their ability to survive and protect in vivo. We found that both polyclonal and P. chabaudi Merozoite Surface Protein-1 (MSP-1)-specific B5 TCR transgenic Tem survive better than Teff. Surprisingly, as Tem are associated with antigen persistence, Tem survive well even after clearance of infection. As previously shown during T cell contraction, Teff^Early, which can generate Tem, also survive better than other Teff subsets in uninfected recipients. Two other Tem survival mechanisms identified here are that low-level chronic infection promotes Tem both by driving their proliferation, and by programming production of Tem from Tcm. Protective CD4 T cell phenotypes have not been precisely determined in malaria, or other persistent infections. Therefore, we tested purified memory (Tmem) and Teff subsets in protection from peak pathology and parasitemia in immunocompromised recipient mice. Strikingly, among Tmem (IL-7Rα^hi) subsets, only Tem^Late (CD62L^loCD27^-) reduced peak parasitemia (19%), though the dominant memory subset is Tem^Early, which is not protective. In contrast, all Teff subsets reduced peak parasitemia by more than half, and mature Teff can generate Tem, though less. In summary, we have elucidated four mechanisms of Tem maintenance, and identified two long-lived T cell subsets (Tem^Late, Teff^Early) that may represent correlates of protection or a target for longer-lived vaccine-induced protection against malaria blood-stages.

Malaria causes significant mortality but current vaccine candidates have poor efficacy and duration, as does natural immunity to malaria. T helper cells (CD4⁺) are essential to protection from malaria, but it is unknown what kinds of T cells would be both protective and long-lasting. Here, we explored the mechanisms of survival used by memory T cells in malaria, and their ability to protect immunodeficient animals from malaria. We identified four mechanisms by which memory T cells are maintained in chronic infection. We also showed that highly activated effector T cells protect better than memory T cells in general, however, effector T cells have a shorter lifespan suggesting a mechanism for short-lived immunity. In total, we identified two protective T cell subsets that are long-lived. Unfortunately, the memory T cell subset that protects, is not the predominant memory T cell population generated by natural infection, suggesting a mechanism for the poor immunity seen in malaria. Our work suggests that vaccines that induce these two T cell subsets may improve on current immunity from malaria infection and disease.

Cryptococcal-related meningoencephalitis in a patient with sarcoidosis and CD4 lymphocytopenia: thorough immunological characterization of lymphocyte homeostasis

Cryptococcal meningoencephalitis is the most common infective complication observed in patients with CD4 lymphocytopenia, including sarcoidosis. T-cell immunity is well characterized in HIV-related infections and data regarding immunity in cryptococcosis animal models is now available; on the contrary, little is known about the immune status in non-HIV-related infections. We report on reduced production of new T cells observed in a patient with sarcoidosis, CD4 lymphocytopenia, and cryptococcal-related meningoencephalitis. Although T cells presented with an intact proliferative capacity, they were oligoclonally expanded showing an effector memory phenotype. However, the deleterious activity of effector memory cells could have been controlled by the expansion of the regulatory T cell subset with the highest suppressive capability. This information provides a better understanding of the immune response to Cryptococcus occurring in non-HIV-associated cases, the predisposition to infection, and the role of different cell subtypes in controlling the disease in humans.

Early Inhibition of Fatty Acid Synthesis Reduces Generation of Memory Precursor Effector T Cells in Chronic Infection

Understanding the mechanisms of CD4 memory T cell (Tmem) differentiation in malaria is critical for vaccine development. However, the metabolic regulation of CD4 Tmem differentiation is not clear, particularly in persistent infections. In this study, we investigated the role of fatty acid synthesis (FAS) in Tmem development in Plasmodium chabaudi chronic mouse malaria infection. We show that T cell-specific deletion and early pharmaceutical inhibition of acetyl CoA carboxylase 1, the rate limiting step of FAS, inhibit generation of early memory precursor effector T cells (MPEC). To compare the role of FAS during early differentiation or survival of Tmem in chronic infection, a specific inhibitor of acetyl CoA carboxylase 1, 5-(tetradecyloxy)-2-furoic acid, was administered at different times postinfection. Strikingly, the number of Tmem was only reduced when FAS was inhibited during T cell priming and not during the Tmem survival phase. FAS inhibition during priming increased effector T cell (Teff) proliferation and strongly decreased peak parasitemia, which is consistent with improved Teff function. Conversely, MPEC were decreased, in a T cell-intrinsic manner, upon early FAS inhibition in chronic, but not acute, infection. Early cure of infection also increased mitochondrial volume in Tmem compared with Teff, supporting previous reports in acute infection. We demonstrate that the MPEC-specific effect was due to the higher fatty acid content and synthesis in MPEC compared with terminally differentiated Teff. In conclusion, FAS in CD4 T cells regulates the early divergence of Tmem from Teff in chronic infection.

Hollow microneedle-mediated intradermal delivery of model vaccine antigen-loaded PLGA nanoparticles elicits protective T cell-mediated immunity to an intracellular bacterium

The skin is an attractive organ for immunization due to the presence of a large number of epidermal and dermal antigen-presenting cells. Hollow microneedles allow for precise and non-invasive intradermal delivery of vaccines. In this study, ovalbumin (OVA)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles with and without TLR3 agonist poly(I:C) were prepared and administered intradermally by hollow microneedles. The capacity of the PLGA nanoparticles to induce a cytotoxic T cell response, contributing to protection against intracellular pathogens, was examined. We show that a single injection of OVA-loaded PLGA nanoparticles, compared to soluble OVA, primed both adoptively transferred antigen-specific naïve transgenic CD8⁺ and CD4⁺ T cells with markedly high efficiency. Applying a triple immunization protocol, PLGA nanoparticles primed also endogenous OVA-specific CD8⁺ T cells. Immune response, following immunization with in particular anionic PLGA nanoparticles co-encapsulated with OVA and poly(I:C), provided protection against a recombinant strain of the intracellular bacterium Listeria monocytogenes, secreting OVA. Taken together, we show that PLGA nanoparticle formulation is an excellent delivery system for protein antigen into the skin and that protective cellular immune responses can be induced using hollow microneedles for intradermal immunizations.

Cryopreservation-related loss of antigen-specific IFNγ producing CD4+ T-cells can skew immunogenicity data in vaccine trials: Lessons from a malaria vaccine trial substudy

Ex vivo functional immunoassays such as ELISpot and intracellular cytokine staining (ICS) by flow cytometry are crucial tools in vaccine development both in the identification of novel immunogenic targets and in the immunological assessment of samples from clinical trials. Cryopreservation and subsequent thawing of PBMCs via validated processes has become a mainstay of clinical trials due to processing restrictions inherent in the disparate location and capacity of trial centres, and also in the need to standardize biological assays at central testing facilities. Logistical and financial requirement to batch process samples from multiple study timepoints are also key. We used ELISpot and ICS assays to assess antigen-specific immunogenicity in blood samples taken from subjects enrolled in a phase II malaria heterologous prime-boost vaccine trial and showed that the freeze thaw process can result in a 3–5-fold reduction of malaria antigen-specific IFNγ-producing CD3⁺CD4⁺ effector populations from PBMC samples taken post vaccination. We have also demonstrated that peptide responsive CD8⁺ T cells are relatively unaffected, as well as CD4⁺ T cell populations that do not produce IFNγ. These findings contribute to a growing body of data that could be consolidated and synthesised as guidelines for clinical trials with the aim of increasing the efficiency of vaccine development pipelines.

Chronic Plasmodium chabaudi Infection Generates CD4 Memory T Cells with Increased T Cell Receptor Sensitivity but Poor Secondary Expansion and Increased Apoptosis

Exposure to blood-stage malaria infection is often persistent, leading to generation of CD4 effector and effector memory T cells that contribute to protection. We showed previously that chronic exposure to blood-stage Plasmodium chabaudi offers the best protection from parasitemia and pathology in reinfection cases, correlating with an increase in Th1 cells. Although much is known about the features of resting or exhausted memory T cells (Tmem), little is known about the functional capacities of chronically stimulated but protective T cells. To determine the functional capacity of CD4 T cells generated by chronic infection upon reexposure to parasite, we compared their responses to known features of classical Tmem. The numbers of cytokine-producing T cells increased following infection in the polyclonal populations, suggesting an increase in pathogen-specific T cells. Malaria antigen-specific B5 T cell receptor (TCR) transgenic (Tg) T cells from chronic infection proliferated on reinfection and were highly sensitive to TCR stimulation without costimulation, as shown for Tmem in acute stimulations. However, B5 Tmem did not accumulate more than naive B5 T cells in vivo or in vitro and became apoptotic. Failure to accumulate was partly the result of chronic stimulation, since eliminating persistent parasites before reinfection slightly increased the accumulation of B5 Tg T cells upon reinfection. The levels of specific gamma interferon-positive, interleukin-10-positive T cells, which protect animals from pathology, increased after malaria infection. These data demonstrate that although chronic infection generates a protective T cell population with increased TCR sensitivity and cytokine production, they do not reexpand upon reexposure due to increased apoptosis.

Increased TNF-α/IFN-γ/IL-2 and Decreased TNF-α/IFN-γ Production by Central Memory T Cells Are Associated with Protective Responses against Bovine Tuberculosis Following BCG Vaccination

Central memory T cell (Tcm) and polyfunctional CD4 T cell responses contribute to vaccine-elicited protection with both human and bovine tuberculosis (TB); however, their combined role in protective immunity to TB is unclear. To address this question, we evaluated polyfunctional cytokine responses by CD4 T cell effector/memory populations from bacille Calmette–Guerin (BCG) vaccinated and non-vaccinated calves by flow cytometry prior to and after aerosol challenge with virulent Mycobacterium bovis. Polyfunctional cytokine expression patterns in the response by Tcm, effector memory, and effector T cell subsets were similar between BCG-vaccinated and M. bovis-infected calves, only differing in magnitude (i.e., infected > vaccinated). BCG vaccination, however, did alter the kinetics of the ensuing response to virulent M. bovis infection. Early after challenge (3 weeks post-infection), non-vaccinates had greater antigen-specific interferon-γ (IFN-γ)/tumor necrosis factor-α (TNF-α) and lesser IFN-γ/TNF-α/IL-2 responses by Tcm cells than did vaccinated animals. Importantly, these differences were also associated with mycobacterial burden upon necropsy. Polyfunctional responses to ESAT-6:CFP10 (antigens not synthesized by BCG strains) were detected in memory subsets, as well as in effector cells, as early as 3 weeks after challenge. These findings suggest that cell fate divergence may occur early after antigen priming in the response to bovine TB and that memory and effector T cells may expand concurrently during the initial phase of the immune response. In summary, robust IFN-γ/TNF-α response by Tcm cells is associated with greater mycobacterial burden, while IFN-γ/TNF-α/IL-2 response by Tcm cells are indicative of a protective response to bovine TB.

Long-Lived CD4+IFN-γ+ T Cells rather than Short-Lived CD4+IFN-γ+IL-10+ T Cells Initiate Rapid IL-10 Production To Suppress Anamnestic T Cell Responses during Secondary Malaria Infection

CD4⁺ T cells that produce IFN-γ are the source of host-protective IL-10 during primary infection with a number of different pathogens, including Plasmodium spp. The fate of these CD4⁺IFN-γ⁺IL-10⁺ T cells following clearance of primary infection and their subsequent influence on the course of repeated infections is, however, presently unknown. In this study, utilizing IFN-γ-yellow fluorescent protein (YFP) and IL-10-GFP dual reporter mice, we show that primary malaria infection-induced CD4⁺YFP⁺GFP⁺ T cells have limited memory potential, do not stably express IL-10, and are disproportionately lost from the Ag-experienced CD4⁺ T cell memory population during the maintenance phase postinfection. CD4⁺YFP⁺GFP⁺ T cells generally exhibited a short-lived effector rather than effector memory T cell phenotype postinfection and expressed high levels of PD-1, Lag-3, and TIGIT, indicative of cellular exhaustion. Consistently, the surviving CD4⁺YFP⁺GFP⁺ T cell-derived cells were unresponsive and failed to proliferate during the early phase of secondary infection. In contrast, CD4⁺YFP⁺GFP^- T cell-derived cells expanded rapidly and upregulated IL-10 expression during secondary infection. Correspondingly, CD4⁺ T cells were the major producers within an accelerated and amplified IL-10 response during the early stage of secondary malaria infection. Notably, IL-10 exerted quantitatively stronger regulatory effects on innate and CD4⁺ T cell responses during primary and secondary infections, respectively. The results in this study significantly improve our understanding of the durability of IL-10-producing CD4⁺ T cells postinfection and provide information on how IL-10 may contribute to optimized parasite control and prevention of immune-mediated pathology during repeated malaria infections.

A Recombinant Chimeric Ad5/3 Vector Expressing a Multistage Plasmodium Antigen Induces Protective Immunity in Mice Using Heterologous Prime-Boost Immunization Regimens

An ideal malaria vaccine should target several stages of the parasite life cycle and induce antiparasite and antidisease immunity. We have reported a Plasmodium yoelii chimeric multistage recombinant protein (P. yoelii linear peptide chimera/recombinant modular chimera), engineered to express several autologous T cell epitopes and sequences derived from the circumsporozoite protein and the merozoite surface protein 1. This chimeric protein elicits protective immunity, mediated by CD4(+) T cells and neutralizing Abs. However, experimental evidence, from pre-erythrocytic vaccine candidates and irradiated sporozoites, has shown that CD8(+) T cells play a significant role in protection. Recombinant viral vectors have been used as a vaccine platform to elicit effective CD8(+) T cell responses. The human adenovirus (Ad) serotype 5 has been tested in malaria vaccine clinical trials with excellent safety profile. Nevertheless, a major concern for the use of Ad5 is the high prevalence of anti-vector neutralizing Abs in humans, hampering its immunogenicity. To minimize the impact of anti-vector pre-existing immunity, we developed a chimeric Ad5/3 vector in which the knob region of Ad5 was replaced with that of Ad3, conferring partial resistance to anti-Ad5 neutralizing Abs. Furthermore, we implemented heterologous Ad/protein immunization regimens that include a single immunization with recombinant Ad vectors. Our data show that immunization with the recombinant Ad5/3 vector induces protective efficacy indistinguishable from that elicited by Ad5. Our study also demonstrates that the dose of the Ad vectors has an impact on the memory profile and protective efficacy. The results support further studies with Ad5/3 for malaria vaccine development.

Efficient tumor regression by adoptively transferred CEA-specific CAR-T cells associated with symptoms of mild cytokine release syndrome

Carcinoembryonic antigen (CEA) is a cell surface antigen highly expressed in various cancer cell types and in healthy tissues. It has the potential to be a target for chimeric antigen receptor (CAR)-modified T-cell therapy; however, the safety of this approach in terms of on-target/off-tumor effects needs to be determined. To address this issue in a clinically relevant model, we used a mouse model in which the T cells expressing CEA-specific CAR were transferred into tumor-bearing CEA-transgenic (Tg) mice that physiologically expressed CEA as a self-antigen. The adoptive transfer in conjunction with lymphodepleting and myeloablative preconditioning mediated significant tumor regression but caused weight loss in CEA-Tg, but not in wild-type mice. The weight loss was not associated with overt inflammation in the CEA-expressing gastrointestinal tract but was associated with malnutrition, reflected in elevated systemic levels of cytokines linked to anorexia, which could be controlled by the administration of an anti-IL-6 receptor monoclonal antibody without compromising efficacy. The apparent relationship between lymphodepleting and myeloablative preconditioning, efficacy, and off-tumor toxicity of CAR-T cells would necessitate the development of CEA-specific CAR-T cells with improved signaling domains that require less stringent preconditioning for their efficacy. Taken together, these results suggest that CEA-specific CAR-based adoptive T-cell therapy may be effective for patients with CEA⁺ solid tumors. Distinguishing the fine line between therapeutic efficacy and off-tumor toxicity would involve further modifications of CAR-T cells and preconditioning regimens.

IFN-γ Priming Effects on the Maintenance of Effector Memory CD4(+) T Cells and on Phagocyte Function: Evidences from Infectious Diseases

Although it has been established that effector memory CD4⁺ T cells play an important role in the protective immunity against chronic infections, little is known about the exact mechanisms responsible for their functioning and maintenance, as well as their effects on innate immune cells. Here we review recent data on the role of IFN-γ priming as a mechanism affecting both innate immune cells and effector memory CD4⁺ T cells. Suboptimal concentrations of IFN-γ are seemingly crucial for the optimization of innate immune cell functions (including phagocytosis and destruction of reminiscent pathogens), as well as for the survival and functioning of effector memory CD4⁺ T cells. Thus, IFN-γ priming can thus be considered an important bridge between innate and adaptive immunity.

Development and Function of Protective and Pathologic Memory CD4 T Cells

Immunological memory is one of the defining features of the adaptive immune system. As key orchestrators and mediators of immunity, CD4 T cells are central to the vast majority of adaptive immune responses. Generated following an immune response, memory CD4 T cells retain pertinent information about their activation environment enabling them to make rapid effector responses upon reactivation. These responses can either benefit the host by hastening the control of pathogens or cause damaging immunopathology. Here, we will discuss the diversity of the memory CD4 T cell pool, the signals that influence the transition of activated T cells into that pool, and highlight how activation requirements differ between naïve and memory CD4 T cells. A greater understanding of these factors has the potential to aid the design of more effective vaccines and to improve regulation of pathologic CD4 T cells, such as in the context of autoimmunity and allergy.

CD56+ T cells are increased in kidney transplant patients following cytomegalovirus infection

BACKGROUND

CD56+ T cells previously have been identified as potentially cytotoxic lymphocytes, and relative numbers are increased in some infectious diseases.

PATIENTS AND METHODS

Relative proportions of CD56+ T cells were measured by flow cytometry in groups of renal transplant patients differing in cytomegalovirus (CMV) status of donor (D) and recipient (R). These measurements were related to episodes of CMV viremia.

RESULTS

Patient groups in which recipients (R+) or donors (D+/R-) were CMV+ had significantly higher proportions of CD56+ T cells (5.11 ± 0.69% and 5.42 ± 1.01%, respectively) than the D-/R- group (1.9 ± 0.35%; P = 0.0018 and 0.017, respectively). In the high-risk D+/R- group, it was found that patients who had post-transplant CMV viremia had higher levels than those who remained CMV negative (9.09 ± 2.34% vs. 3.16 ± 1.22%; P = 0.01). CD56+ T cells from R+ and D+/R- groups had higher proportions of both CD4+ and CD8+ cells than the D-/R- group. When activation markers were examined, some CD56+ T cells from both CMV+ groups had a TEM phenotype, with significantly more expressing CD45RO and NKG2C, and less expressing CD28, CD62L, CD127, and CD161 compared to the D-/R- group. Some CD56+ T cells showed specificity for CMV antigens and similar proportions of CD8+ cells were positive for class I HLA-CMV tetramers containing immunodominant CMV peptides compared to the majority CD56- T cells.

CONCLUSION

The results show significant increases in proportions of CD56+ T cells in relation to CMV infection in renal transplant patients and suggest that these cells have a cytotoxic function against CMV-infected cells.

Early effector cells survive the contraction phase in malaria infection and generate both central and effector memory T cells

CD4 T cells orchestrate immunity against blood-stage malaria. However, a major challenge in designing vaccines to the disease is poor understanding of the requirements for the generation of protective memory T cells (Tmem) from responding effector T cells (Teff) in chronic parasite infection. In this study, we use a transgenic mouse model with T cells specific for the merozoite surface protein (MSP)-1 of Plasmodium chabaudi to show that activated T cells generate three distinct Teff subsets with progressive activation phenotypes. The earliest observed Teff subsets (CD127(-)CD62L(hi)CD27(+)) are less divided than CD62L(lo) Teff and express memory genes. Intermediate (CD62L(lo)CD27(+)) effector subsets include the most multicytokine-producing T cells, whereas fully activated (CD62L(lo)CD27(-)) late effector cells have a terminal Teff phenotype (PD-1(+), Fas(hi), AnnexinV(+)). We show that although IL-2 promotes expansion, it actually slows terminal effector differentiation. Using adoptive transfer, we show that only early Teff survive the contraction phase and generate the terminal late Teff subsets, whereas in uninfected recipients, they become both central and effector Tmem. Furthermore, we show that progression toward full Teff activation is promoted by increased duration of infection, which in the long-term promotes Tem differentiation. Therefore, we have defined markers of progressive activation of CD4 Teff at the peak of malaria infection, including a subset that survives the contraction phase to make Tmem, and show that Ag and cytokine levels during CD4 T cell expansion influence the proportion of activated cells that can survive contraction and generate memory in malaria infection.