CD4(+)CD25(+) T regulatory cells inhibit CD8(+) IFN-gamma production during acute and chronic FIV infection utilizing a membrane TGF-beta-dependent mechanism

Investigation of immune cell markers in feline oral squamous cell carcinoma

Squamous cell carcinoma is the most common oral cancer in the cat and presents as a locally aggressive lesion for which an effective therapeutic protocol remains elusive. Feline oral squamous cell carcinoma (OSCC) shares many clinical characteristics with human head and neck squamous cell carcinoma (HNSCC). Accordingly, present studies were conducted to determine similarities for immune markers shared by feline OSCC and human HNSCC. Biopsies harvested from a feline patient cohort-1 (n = 12) were analyzed for lymphoid cell infiltrates by immunohistochemistry (IHC). Results revealed unique patterns of T cell infiltration involving both neoplastic epithelium and stroma that were detected in most patient tumor biopsies (92%) examined by IHC staining for CD3. Intratumoral B cell infiltrates were detected within tumor stroma only, based on IHC staining for CD79a and CD20 for all patients within the same cohort-1. Infiltration of tumors by a regulatory CD4 T cell subset (Tregs) defined by expression of the forkhead transcription factor FoxP3, was also detected in biopsies from 57% of patients and involved infiltration of neoplastic epithelium and stroma. Patient biopsies were also examined for expression of immunomodulator cyclooxygenase (COX)-2 and revealed positive but weak staining of neoplastic epithelium in a significant proportion of cases (75%). Interestingly, COX-2 expression was detected in both neoplastic epithelium and stroma. Blood collected from a second cohort of feline OSCC patients (n = 9) revealed an increased frequency of circulating CD4+FoxP3+ T cells when compared to healthy adult controls (n = 7) (P = 0.045), although frequencies of CD4+CD25+FoxP3+ T cells were comparable between patients and healthy pet cat controls. Lastly, biopsies from feline OSCC patients were characterized for histologic subtype using a classification scheme previously described for human HNSCC. This analysis revealed the conventional subtype as the predominant variant (75%) with conventional subtypes split evenly between well differentiated and moderately differentiated carcinomas. Two cases were classified as papillary and one case as basaloid subtypes. Correlations between subtype, immune marker scores or circulating Treg frequencies and clinical characteristics or outcome were not detected, most likely due to small patient numbers within patient cohorts. However, findings from these studies provide a preliminary step in the characterization of immune and histologic markers that will be critical to defining prognostic immune markers for feline OSCC and potential targets for testing of immunotherapeutics also relevant to human HNSCC in future studies.

Histone Modulation Blocks Treg-Induced Foxp3 Binding to the IL-2 Promoter of Virus-Specific CD8⁺ T Cells from Feline Immunodeficiency Virus-Infected Cats

CD8⁺ T cells are critical for controlling HIV infection. During the chronic phase of lentiviral infection, CD8⁺ T cells lose their proliferative capacity and exhibit impaired antiviral function. This loss of CD8⁺ T cell function is due, in part, to CD4⁺CD25⁺ T regulatory (Treg) cell-mediated suppression. Our research group has demonstrated that lentivirus-activated CD4⁺CD25⁺ Treg cells induce the repressive transcription factor forkhead box P3 (Foxp3) in autologous CD8⁺ T cells following co-culture. We have recently reported that Treg-induced Foxp3 binds the interleukin-2 (IL-2), interferon-γ (IFN- γ), and tumor necrosis factor-α (TNF-α) promoters in virus-specific CD8⁺ T cells. These data suggest an important role of Foxp3-mediated CD8⁺ T cell dysfunction in lentiviral infection. To elucidate the mechanism of this suppression, we previously reported that decreased methylation facilitates Foxp3 binding in mitogen-activated CD8⁺ T cells from feline immunodeficiency virus (FIV)-infected cats. We demonstrated the reduced binding of Foxp3 to the IL-2 promoter by increasing methylation of CD8⁺ T cells. In the studies presented here, we ask if another form of epigenetic modulation might alleviate Foxp3-mediated suppression in CD8⁺ T cells. We hypothesized that decreasing histone acetylation in virus-specific CD8⁺ T cells would decrease Treg-induced Foxp3 binding to the IL-2 promoter. Indeed, using anacardic acid (AA), a known histone acetyl transferase (HAT) inhibitor, we demonstrate a reduction in Foxp3 binding to the IL-2 promoter in virus-specific CD8⁺ T cells co-cultured with autologous Treg cells. These data identify a novel mechanism of Foxp3-mediated CD8⁺ T cell dysfunction during lentiviral infection.

Epigenetic Modulation of CD8⁺ T Cell Function in Lentivirus Infections: A Review

CD8⁺ T cells are critical for controlling viremia during human immunodeficiency virus (HIV) infection. These cells produce cytolytic factors and antiviral cytokines that eliminate virally- infected cells. During the chronic phase of HIV infection, CD8⁺ T cells progressively lose their proliferative capacity and antiviral functions. These dysfunctional cells are unable to clear the productively infected and reactivated cells, representing a roadblock in HIV cure. Therefore, mechanisms to understand CD8⁺ T cell dysfunction and strategies to boost CD8⁺ T cell function need to be investigated. Using the feline immunodeficiency virus (FIV) model for lentiviral persistence, we have demonstrated that CD8⁺ T cells exhibit epigenetic changes such as DNA demethylation during the course of infection as compared to uninfected cats. We have also demonstrated that lentivirus-activated CD4⁺CD25⁺ T regulatory cells induce forkhead box P3 (Foxp3) expression in virus-specific CD8⁺ T cell targets, which binds the interleukin (IL)-2, tumor necrosis factor (TNF)-α, and interferon (IFN)-γ promoters in these CD8⁺ T cells. Finally, we have reported that epigenetic modulation reduces Foxp3 binding to these promoter regions. This review compares and contrasts our current understanding of CD8⁺ T cell epigenetics and mechanisms of lymphocyte suppression during the course of lentiviral infection for two animal models, FIV and simian immunodeficiency virus (SIV).

Applications of the FIV Model to Study HIV Pathogenesis

Feline immunodeficiency virus (FIV) is a naturally-occurring retrovirus that infects domestic and non-domestic feline species, producing progressive immune depletion that results in an acquired immunodeficiency syndrome (AIDS). Much has been learned about FIV since it was first described in 1987, particularly in regard to its application as a model to study the closely related lentivirus, human immunodeficiency virus (HIV). In particular, FIV and HIV share remarkable structure and sequence organization, utilize parallel modes of receptor-mediated entry, and result in a similar spectrum of immunodeficiency-related diseases due to analogous modes of immune dysfunction. This review summarizes current knowledge of FIV infection kinetics and the mechanisms of immune dysfunction in relation to opportunistic disease, specifically in regard to studying HIV pathogenesis. Furthermore, we present data that highlight changes in the oral microbiota and oral immune system during FIV infection, and outline the potential for the feline model of oral AIDS manifestations to elucidate pathogenic mechanisms of HIV-induced oral disease. Finally, we discuss advances in molecular biology, vaccine development, neurologic dysfunction, and the ability to apply pharmacologic interventions and sophisticated imaging technologies to study experimental and naturally occurring FIV, which provide an excellent, but often overlooked, resource for advancing therapies and the management of HIV/AIDS.

T Regulatory Cell Induced Foxp3 Binds the IL2, IFNγ, and TNFα Promoters in Virus-Specific CD8+ T Cells from Feline Immunodeficiency Virus Infected Cats

Polyfunctional CD8⁺ T cells play a critical role in controlling viremia during AIDS lentiviral infections. However, for most HIV-infected individuals, virus-specific CD8⁺ T cells exhibit loss of polyfunctionality, including loss of IL2, TNFα, and IFNγ. Using the feline immunodeficiency virus (FIV) model for AIDS lentiviral persistence, our laboratory has demonstrated that FIV-activated Treg cells target CD8⁺ T cells, leading to a reduction in IL2 and IFNγ production. Furthermore, we have demonstrated that Treg cells induce expression of the repressive transcription factor, Foxp3, in CD8⁺ T cells. Based upon these findings, we asked if Treg-induced Foxp3 could bind to the IL2, TNFα, and IFNγ promoter regions in virus-specific CD8⁺ T cells. Following coculture with autologous Treg cells, we demonstrated decreased mRNA levels of IL2 and IFNγ at weeks 4 and 8 postinfection and decreased TNFα at week 4 postinfection in virus-specific CD8⁺ T cells. We also clearly demonstrated Treg cell-induced Foxp3 expression in virus-specific CD8⁺ T cells at weeks 1, 4, and 8 postinfection. Finally, we documented Foxp3 binding to the IL2, TNFα, and IFNγ promoters at 8 weeks and 6 months postinfection in virus-specific CD8⁺ T cells following Treg cell coculture. In summary, the results here clearly demonstrate that Foxp3 inhibits IL2, TNFα, and IFNγ transcription by binding to their promoter regions in lentivirus-specific CD8⁺ T cells. We believe this is the first description of this process during the course of AIDS lentiviral infection.

Immune recovery after fluid resuscitation in rats with severe hemorrhagic shock

OBJECTIVE

To investigate the effects of resuscitation with normal saline (NS), hypertonic saline (HTS), and hydroxyethyl starch (HES) on regulatory T cells (Tregs), helper T 1 (Th1)/Th2 and cytotoxic T 1 (Tc1)/Tc2 profiles in the treatment of hemorrhagic shock.

METHODS

Rats subjected to severe hemorrhagic shock were resuscitated for 30 min with NS (n=8), HTS (n=8), or HES (n=8); sham (n=8) and naive control (n=8) groups were used for comparison. Following fluid resuscitation, the whole shed blood was reinfused for 30 min, and the rats were observed with continuous hemodynamic monitoring for 120 min. CD4⁺CD25⁺Foxp3⁺ Treg proportions, Th1/Th2 and Tc1/Tc2 profiles in spleen were analyzed by three-color flow cytometry.

RESULTS

The proportion of CD4⁺CD25⁺Foxp3⁺ Tregs and ratios of Th1/Th2 and Tc1/Tc2 did not differ among control, sham, and HTS groups, but were significantly lower in NS and HES groups (both P<0.05 vs. sham); NS and HES levels were similar. The level of Tc1 was significantly increased in HTS (P<0.05 vs. sham), and levels of Tc2 were increased in NS, HES, and HTS groups compared to sham (all P<0.05), but did not differ from each other.

CONCLUSIONS

HTS resuscitation has a greater impact on immune system recovery than NS or HES by preserving the proportion of Tregs and maintaining the balance between Th1/Th2 and Tc1/Tc2 cells in the spleen. Thus, HTS resuscitation provides potential immunomodulatory activity in the early stage after hemorrhagic shock.

Micro-RNA 10a Is Increased in Feline T Regulatory Cells and Increases Foxp3 Protein Expression Following In Vitro Transfection

CD4⁺CD25⁺Foxp3⁺ T regulatory (Treg) cells are activated during the course of lentiviral infection and exhibit heightened suppressor function when compared to Treg cells from uninfected controls. Foxp3 is essential to Treg cell function and multiple studies have documented that lentivirus-activated Treg cells exhibit heightened Foxp3 expression when compared to Treg cells from uninfected controls. Our hypothesis was that lentivirus-induced micro-RNAs (miRNAs) contribute to heightened Treg cell suppressor function by stabilizing Foxp3 expression. We demonstrated that CD4⁺CD25⁺ T cells from both feline immunodeficiency virus infected (FIV⁺) cats and uninfected control cats exhibit increased miRNA 10a and 21 levels compared to autologous CD4⁺CD25- T cells but there was no difference in the levels of these miRNAs when Treg cells from FIV⁺ cats were compared to Treg cells from uninfected controls. Further, there was no increase in Foxp3 mRNA following transfection of miRNA 10a or 21 into a feline cell line. However, transfection with miRNA 10a resulted in increased Foxp3 protein expression.

Immunomodulatory Effect of Nigella sativa Oil on T Lymphocytes in Patients with Rheumatoid Arthritis

BACKGROUND AND OBJECTIVES

Abundant evidence indicates the involvement of CD4(+), CD8(+), and CD4(+)CD25(+) T lymphocytes in the induction and/or protection of rheumatoid arthritis (RA). We aimed to investigate the modulatory effect of Nigella sativa (NS) oil on the selected T cell subset percentage in females with RA.

METHODS

A randomized, double-blinded placebo-controlled, 2 months, parallel-group clinical trial was conducted. Forty-three female patients (20-50 years) with mild to moderate RA were recruited and assigned into NS (n = 23) and placebo (n = 20) groups to receive one gram of NS oil, or starch, capsule in two divided doses, respectively. The disease activity scores of 28 joints (DAS28) were calculated and percentages of CD4(+), CD8(+), and CD4(+)CD25(+) T cells were examined using flow cytometry.

RESULTS

Treatment with NS led to significant reduction of the serum high-sensitivity C-reactive protein (hs-CRP) level and DAS-28 score and an improved number of swollen joints compared with baseline and placebo groups. A relatively comparable CD4(+) T cell percentage was observed in the NS and placebo groups either in baseline or the end of study. The treatment also resulted in reduced CD8(+), and increased CD4(+)CD25(+) T cell percentage and the CD4(+)/CD8(+) ratio as compared to placebo and baseline. A negative significant correlation between changes in CD8(+) and changes in CD4(+)CD25(+) T cells and a positive significant correlation between changes in CD4(+)CD25(+) T cells and changes in the CD4(+)/CD8(+) ratio was observed in the NS group.

CONCLUSION

This study gives strength to the potential relevance of NS in clinical management of RA through modulation of T lymphocytes.

Phenotypic and functional analysis of CD1a+ dendritic cells from cats chronically infected with feline immunodeficiency virus

Numerous studies suggest dendritic cell (DC) dysfunction is central to the dysregulated immune response during HIV infection; however, in vivo studies are lacking. In the present study we used feline immunodeficiency virus (FIV) infection of cats as a model for HIV-1 infection to assess the maturation and function of dendritic cells, in vivo and in vitro. We compared CD1a+ DC migration, surface phenotype, endocytosis, mixed leukocyte reaction (MLR) and regulatory T cell (Treg) phenotype induction by CD1a+ cells isolated from lymph nodes of FIV-infected and control cats. Results showed that resident CD1a+ DC in lymph nodes of chronically FIV-infected cats are phenotypically mature, can stimulate normal primary T cell proliferation, override Treg suppression and do not skew toward Treg induction. In contrast, FIV infection had deleterious effects on antigen presentation and migratory capacity of CD1a+ cells in tissues.

Association between oral health status and retrovirus test results in cats

OBJECTIVE

To determine associations between oral health status and seropositivity for FIV or FeLV in cats.

DESIGN

Cross-sectional survey.

ANIMALS

5,179 cats.

PROCEDURES

Veterinarians at veterinary clinics and animal shelters completed online training on oral conditions in cats and then scored oral health status of cats with no known history of vaccination against FIV. Age, sex, and results of an ELISA for retroviruses were recorded. Results were analyzed by means of standard logistic regression with binary outcome.

RESULTS

Of 5,179 cats, 237 (4.6%) and 186 (3.6%) were seropositive for FIV and FeLV, respectively, and of these, 12 (0.2%) were seropositive for FIV and FeLV. Of all 5,179 cats, 1,073 (20.7%) had gingivitis, 576 (11.1%) had periodontitis, 203 (3.9%) had stomatitis, and 252 (4.9%) had other oral conditions (overall oral disease prevalence, 2,104/5,179 [40.6%]). Across all age categories, inflammatory oral disease was associated with a significantly higher risk of a positive test result for FIV, compared with the seropositivity risk associated with other oral diseases or no oral disease. Stomatitis was most highly associated with risk of FIV seropositivity. Cats with any oral inflammatory disease were more likely than orally healthy cats to have a positive test result for FeLV. Increasing age was associated with a higher prevalence of oral disease in retrovirus-seronegative cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Inflammatory oral disease was associated with an increased risk of seropositivity for retroviruses in naturally infected cats. Therefore, retroviral status of cats with oral inflammatory disease should be determined and appropriate management initiated.

IL10, TGF beta1, and IFN gamma modulate intracellular signaling pathways and cytokine production to control Toxoplasma gondii infection in BeWo trophoblast cells

Considering that interleukin 10 (IL10), transforming growth factor beta1 (TGFB1), and interferon gamma (IFNG) are involved in the susceptibility of BeWo trophoblast cells to Toxoplasma gondii infection, the aim of the present study was to investigate the effector mechanisms triggered by these cytokines in the control of T. gondii in BeWo cells. For this purpose, infected/uninfected BeWo cells were treated with IL10, TGFB1 (50 ng/ml), and IFNG (20 or 100 ng/ml) in order to verify the phosphorylation of signal transducers and activators of transcription 1 (STAT1), STAT3, and Smad2, parasite intracellular proliferation, as well as the Th1/Th2/IL17A cytokine production. The treatment of BeWo cells with IL10 and TGFB1 favored T. gondii proliferation, and these findings were associated with STAT3 and Smad2 phosphorylation, respectively (P < 0.05). Also, these cytokine treatments were able to down-modulate TNF alpha (TNFA) and IL6 production (P < 0.05). Low concentration of IFNG was unable to control T. gondii infection but was able to trigger STAT1 phosphorylation and up-regulate IL6 and IL17A production; whereas a high concentration of IFNG was unable to activate STAT1 but down-modulated IL6 and TNFA and increased T. gondii proliferation (P < 0.05). IL10, TGFB1, and IFNG regulate a differential T. gondii proliferation in BeWo cells because they distinctly trigger intracellular signaling pathways and cytokine production, especially IL6 and TNFA. Our data open new windows to understand the mechanisms triggered by IL10, TGFB1, and IFNG at the maternal-fetal interface in the presence of T. gondii, contributing to recognizing the importance of these effector mechanisms involved in the vertical transmission of this parasite.

Modulating DNA methylation in activated CD8+ T cells inhibits regulatory T cell-induced binding of Foxp3 to the CD8+ T Cell IL-2 promoter

We have previously demonstrated that CD4(+)CD25(+) regulatory T cells (Tregs) activated during the course of feline immunodeficiency virus (FIV) infection suppress CD8(+) CTL function in a TGF-β-dependent fashion, inhibiting IFN-γ and IL-2 production and inducing G1 cell-cycle arrest. In this article, we describe the molecular events occurring at the IL-2 promoter leading to suppression of IL-2 production. These experiments demonstrate that Foxp3 induced by lentivirus-activated Tregs in the CD8(+) target cells binds to the IL-2 promoter, actively repressing IL-2 transcription. We further demonstrate that the chronic activation of CD8(+) T cells during FIV infection results in chromatin remodeling at the IL-2 promoter, specifically, demethylation of CpG residues. These DNA modifications occur during active transcription and translation of IL-2; however, these changes render the IL-2 promoter permissive to Foxp3-induced transcriptional repression. These data help explain, in part, the seemingly paradoxical observations that CD8(+) T cells displaying an activation phenotype exhibit altered antiviral function. Further, we demonstrate that blocking demethylation of CpG residues at the IL-2 promoter inhibits Foxp3 binding, suggesting a potential mechanism for rescue and/or reactivation of CD8(+) T cells. Using the FIV model for lentiviral persistence, these studies provide a framework for understanding how immune activation combined with Treg-mediated suppression may affect CD8(+) T cell IL-2 transcription, maturation, and antiviral function.

FIV in cats--a useful model of HIV in people?

The feline immunodeficiency virus (FIV) shares genomic organization, receptor usage, lymphocyte tropism, and induction of immunodeficiency and increased susceptibility to cancer with the human immunodeficiency virus (HIV). Global distribution, marked heterogeneity and variable host adaptation are also properties of both viruses. These features render the FIV-cat model suitable to explore many aspects of lentivirus-host interaction and adaptation, and to explore treatment and prevention of infection. Examples of fundamental discoveries that have emerged from study in the FIV-cat model concern two-receptor entrance strategies that target memory T-lymphocytes, host factors that restrict retroviral infection, viral strategies for replication in non-dividing cells, and identification of correlates of immunity to the virus. This article provides a brief overview of strengths and limitations of the FIV-cat model for comparative biology and medicine.

CD4+CD25+ T regulatory cells activated during feline immunodeficiency virus infection convert T helper cells into functional suppressors through a membrane-bound TGFβ / GARP-mediated mechanism

Background

We and others have previously reported that cell membrane-bound TGFβ (mTGFβ) on activated T regulatory (Treg) cells mediates suppressor function. Current findings suggest that a novel protein known as Glycoprotein A Repetitions Predominant (GARP) anchors mTGFβ to the Treg cell surface and facilitates suppressor activity. Recently, we have described that GARP⁺TGFβ⁺ Treg cells expand during the course of FIV infection. Because Treg cells are anergic and generally exhibit poor proliferative ability, we asked how Treg homeostasis is maintained during the course of feline immunodeficiency virus (FIV) infection.

Results

Here, we report that Treg cells from FIV⁺ cats express GARP and mTGFβ and convert T helper (Th) cells into phenotypic and functional Treg cells. Th to Treg conversion was abrogated by anti-TGFβ or anti-GARP treatment of Treg cells or by anti-TGFβRII treatment of Th cells, suggesting that Treg cell recruitment from the Th pool is mediated by TGFβ/TGFβRII signaling and that cell-surface GARP plays a major role in this process.

Conclusions

These findings suggest Th to Treg conversion may initiate a cascade of events that contributes to the maintenance of virus reservoirs, progressive Th cell immunosuppression, and the development of immunodeficiency, all of which are central to the pathogenesis of AIDS lentivirus infections.

Lentivirus-activated T regulatory cells suppress T helper cell interleukin-2 production by inhibiting nuclear factor of activated T cells 2 binding to the interleukin-2 promoter

Using the feline immunodeficiency virus (FIV) model for AIDS lentivirus infection, we previously demonstrated that Treg cells from FIV-infected cats up-regulate membrane-associated tumor growth factor beta (mTGF-ß) during the course of infection and that activated T lymphocytes up-regulate TGF-ß receptor II (TGF-ßRII) during the course of infection. Furthermore, we have demonstrated that autologous coculture of Tregs with Th cells from FIV-infected cats leads to suppression of interleukin (IL)-2 production and loss of proliferation in a TGF-ß-dependent fashion. Nuclear factor of activated T cells (NFAT) 2 has been identified as integral to effector Th cell maturation and function by promoting IL-2 transcription. Therefore, we questioned whether NFAT2 expression might be altered by TGF-β signaling. Feline NFAT2 exon sequences were identified based upon sequence homology to human and murine NFAT2. Following stimulation, IL-2 and NFAT2 mRNA levels were similarly increased in both FIV(-) and FIV(+) cats. Activated CD4(+)CD25(-) cells from both FIV(-) and FIV(+) cats cocultured with autologous CD4(+)CD25(+) cells or treated with TGF-β demonstrated decreased IL-2 production; however, NFAT2 mRNA levels were unaffected. Although NFAT2 mRNA levels were unaffected, chromatin immunoprecipitation (ChIP) for NFAT2 indicated decreased NFAT2 binding at the IL-2 promoter in suppressed Th cells. These data suggest that TGF-β-mediated Treg cell suppression of IL-2 transcription is modulated through alterations in NFAT2 binding to the IL-2 promoter.

Mesothelin virus-like particle immunization controls pancreatic cancer growth through CD8+ T cell induction and reduction in the frequency of CD4+ foxp3+ ICOS- regulatory T cells

Our previous study has shown that mesothelin (MSLN) is a potential immunotherapeutic target for pancreatic cancer. Here, we further studied the immunogenicity of chimeric murine MSLN-virus-like particles (mMSLN-VLPs), their ability to break tolerance to mMSLN, a self-antigen, and deciphered the mechanism of immune responses elicited by mMSLN-VLP immunization using a pancreatic cancer (PC) mouse model. In addition to what we have found with xenogeneic human MSLN-VLP (hMSLN-VLP), mMSLN-VLP immunization was able to break the tolerance to intrinsic MSLN and mount mMSLN-specific, cytotoxic CD8⁺ T cells which led to a significant reduction in tumor volume and prolonged survival in an orthotopic PC mouse model. Furthermore, CD4⁺foxp3⁺ regulatory T cells (Tregs) were progressively decreased in both spleen and tumor tissues following mMSLN-VLP immunization and this was at least partly due to elevated levels of IL-6 production from activated plasmocytoid dendritic cell (pDC)-like cells following mMSLN-VLP immunization. Moreover, mMSLN-VLP treatment mainly reduced the frequency of the CD4⁺foxp3⁺ICOS⁻ Treg subset. However, mMSLN-VLP induced IL-6 production also increased ICOSL expression on pDC-like cells which supported the proliferation of immunosuppressive CD4⁺foxp3⁺ICOS⁺ Treg cells. This study reveals that mMSLN-VLP immunization is capable of controlling PC progression by effectively mounting an immune response against mMSLN, a tumor self-antigen, and altering the immunosuppressive tumor microenvironment via activation of pDCs-like cells and reduction in the frequency of CD4⁺foxp3⁺ICOS⁻ Treg cells. However, combination therapies will likely need to be used in order to target residual CD4⁺foxp3⁺ICOS⁺ Treg cells.

Infection with feline immunodeficiency virus directly activates CD4+ CD25+ T regulatory cells

Lentivirus infection activates CD4(+) CD25(+) T regulatory (Treg) cells. Activation of Treg cells may be due to direct virus infection or chronic antigenic stimulation. Herein we demonstrate that in vitro feline immunodeficiency virus (FIV) infection, but not UV-inactivated virus, activates Treg cells as measured by immunosuppressive function and upregulation of GARP, FoxP3, and membrane-bound transforming growth factor β (TGF-β). These data demonstrate for the first time that AIDS lentiviruses infect and activate Treg cells, potentially contributing to immune dysfunction.

Feline glycoprotein A repetitions predominant anchors transforming growth factor beta on the surface of activated CD4(+)CD25(+) regulatory T cells and mediates AIDS lentivirus-induced T cell immunodeficiency

Using the feline immunodeficiency virus (FIV) model for AIDS-lentivirus infection, our laboratory has previously demonstrated that T regulatory (Treg) cell-mediated immune T and B cell dysfunction contributes to lentivirus persistence and chronic disease through membrane bound transforming growth factor beta (mTGFb). Studying Treg cells in the context of infection has been problematic as no inducible marker for activated Treg cells had been identified. However, recent reports in human Treg studies have described a novel protein, glycoprotein A repetitions predominant (GARP), as a unique marker of activated human Treg cells that anchors mTGFb. Herein we extend these studies to the feline Treg system, identifying feline GARP and demonstrating that human and feline GARP proteins are homologous in structure, expression pattern, and ability to form a complex with TGFb. We further demonstrate that GARP and TGFb form a complex on the surface of activated Treg cells and that these GARP(+)TGFb(+) Treg cells are highly efficient suppressor cells. Analysis of expression of this Treg activation marker in the FIV-AIDS model reveals an up-regulation of GARP expressing Treg cells during chronic FIV infection. We demonstrate that the GARP(+) Treg cells from FIV-infected cats suppress T helper cells in vivo and that blocking GARP or TGFb eliminates this suppression. These data suggest that GARP is expressed in complex with TGFb on the surface of activated Treg cells and plays an important role in TGFb(+) Treg-mediated T cell immune suppression during lentivirus infection.

B lymphocyte inhibition of anti-tumor response depends on expansion of Treg but is independent of B-cell IL-10 secretion

The mechanisms by which B lymphocytes inhibit anti-tumor immunity remain poorly understood. Murine EMT-6 mammary tumors grow readily in immune competent mice (BALB/c), but poorly in B-cell-deficient μ(-/-) BALB/c mice (BCDM). T regulatory cell (Treg) expansion and function were impaired in BCDM compared with BALB/c. In this study, we compared tumor growth, Treg cell proliferation, tumor lymphocyte infiltration and cytolytic T cell activity in BALB/c, BCDM and BCDM partially reconstituted with B cells by adoptive transfer (BCDM+B). Partial reconstitution of BCDM with adoptively transferred B cells restored EMT-6 tumor growth, which was independent of IL-10 secretion by B cells. Instead, high frequencies of intratumoral B cells were associated with increased recruitment and proliferation of Treg cells within the tumor microenvironment. The B-cell-dependent accumulation of Treg within the tumor microenvironment was associated with reduced tumor infiltration by CD49+ NK and CD8+ T cells and reduced cytotoxic T cell activity against EMT-6 targets. Our studies indicate that tumor-dependent immunosuppression of T-cell-mediated anti-tumor immunity is coordinated within the tumor microenvironment by B-cell-dependent cross talk with Treg cells, which does not require production of IL-10 by B cells.

CD8+ clonality is associated with prolonged acute plasma viremia and altered mRNA cytokine profiles during the course of feline immunodeficiency virus infection

Acute lentiviral infection is characterized by early CD8(+) cytotoxic T cell (CTL) activity and a subsequent decline in plasma viremia. However, CD8(+) lymphocytes fail to eliminate the virus and a progressive T cell immune dysfunction develops during the course of chronic lentiviral infection. To further define this CD8(+) immune dysfunction we utilized PARR (PCR for antigen receptor rearrangements), a technique which measures clonally expanded lymphocyte populations by comparison of highly conserved T cell receptor (TCR) regions to identify the prevalence of clonal CD8(+) T cells following FIV infection. We then compared phenotype, mRNA profiles, CD8(+) proliferation and plasma viremia during acute and chronic infection for PARR positive (PARR(+)) and PARR negative (PARR(-)) Feline Immunodeficiency Virus (FIV) infected cats. We demonstrated that approximately forty percent of the FIV(+) cats examined exhibit CD8(+) clonality compared to none of the FIV(-) control cats. There were no phenotypic differences between PARR(+) and PARR(-) CD8(+) lymphocytes from FIV(+) cats but retrospective analysis of plasma viremia over the course of infection revealed a delayed peak in plasma viremia and a decline in lymphocyte counts were observed in the PARR(+) group during acute infection. CD8(+) lymphocytes isolated from chronically infected PARR(-) cats exhibited significantly higher mRNA expression of IFN-γ and IL-2 following mitogenic stimulation when compared to PARR(+) CD8(+) lymphocytes. These data suggest that clonal CD8(+) expansion may be related to impaired control of acute viremia and less effective CD8(+) anti-viral function. Using PARR to assess changes in CD8(+) clonality during the progression from acute to chronic FIV infection may help to better characterize the factors which contribute to CD8(+) anergy and lentiviral persistence.

Administration of Fozivudine tidoxil as a single-agent therapeutic during acute feline immunodeficiency virus infection does not alter chronic infection

Initiating combination antiretroviral therapy (ART) during acute HIV infection has been correlated with decreased viral set point and improved lymphocyte function. However, the long term effects of single-agent therapy administered only during the acute stage of infection (interrupted treatment) remain largely uncharacterized. In this study we provide longitudinal data using the feline immunodeficiency virus (FIV) model for HIV infection. Infected cats were treated with a prophylactic single-agent therapy, Fozivudine tidoxil (FZD), for six weeks, starting one day before infection. The initial acute infection study, reported elsewhere, demonstrated a decrease in plasma- and cell-associated viremia at two weeks post-infection (PI) in FZD-treated cats as compared to placebo-treated cats. We hypothesized that this early alteration in plasma- and cell-associated viremia would alter the virus set point and ultimately affect the outcome of chronic infection. Here we provide data at one, two and three years PI for plasma- and/or cell-associated viremia, total lymphocyte counts and CD4:CD8 ratios. There was no difference in viremia or cell counts between treated and nontreated groups at all time points tested. Contrary to our hypothesis, these results suggest that treatment with a single agent anti-retroviral drug during acute lentivirus infection does not significantly alter viral load and immune function during the chronic, asymptomatic stage of infection.

Regulatory T cells and Th17 cells in viral infections: implications for multiple sclerosis and myocarditis

In immune-mediated diseases, Treg and proinflammatory Th17 cells have been suggested to play either suppressor (beneficial) or effector (detrimental) roles, respectively. Tissue damage in viral infections can be caused by direct viral replication or immunopathology. Viral replication can be enhanced by anti-inflammatory responses and suppressed by proinflammatory responses. However, Tregs could suppress proinflammatory responses, reducing immunopathology, while Th17 cell-induced inflammation may enhance immunopathology. Here, the roles of Treg and Th17 cells depend on whether tissue damage is caused by direct virus replication or immunopathology, which differ depending on the virus, disease stage and host immune background. Although the precise mechanisms of tissue damage in multiple sclerosis and myocarditis are unclear, both viral replication and immune effector cells have been proposed to cause pathogenesis. Personalized medicine that alters the balance between Treg and Th17 cells may ameliorate viral pathology during infections.

The immunopathology of sepsis: pathogen recognition, systemic inflammation, the compensatory anti-inflammatory response, and regulatory T cells

Sepsis, the systemic inflammatory response to infection, represents the major cause of death in critically ill veterinary patients. Whereas important advances in our understanding of the pathophysiology of this syndrome have been made, much remains to be elucidated. There is general agreement on the key interaction between pathogen‐associated molecular patterns and cells of the innate immune system, and the amplification of the host response generated by pro‐inflammatory cytokines. More recently, the concept of immunoparalysis in sepsis has also been advanced, together with an increasing recognition of the interplay between regulatory T cells and the innate immune response. However, the heterogeneous nature of this syndrome and the difficulty of modeling it in vitro or in vivo has both frustrated the advancement of new therapies and emphasized the continuing importance of patient‐based clinical research in this area of human and veterinary medicine.

Fozivudine tidoxil as single-agent therapy decreases plasma and cell-associated viremia during acute feline immunodeficiency virus infection

BACKGROUND

Feline immunodeficiency virus (FIV) is a lentivirus that infects domestic and wild felidae and the course of disease is similar to that of human immunodeficiency virus infection. The thymidine nucleoside analog fozivudine (FZD) tidoxil is a lipid-zidovudine (ZDV) conjugate and member of the family of nucleoside reverse transcriptase (RT) inhibitors (NRTIs).

HYPOTHESIS

FZD administration to cats during acute FIV infection produces antiviral activity with fewer adverse effects than its parent compound ZDV (AZT).

ANIMALS

Male, neutered cats approximately 7 months of age (n = 12).

METHODS

FZD (45 mg/kg q12h, n = 6) or placebo (n = 6) was administered PO in a nonblinded trial for 6 weeks to cats infected with the NCSU(1) isolate of FIV. Peripheral blood was collected preinfection and at 2, 4, and 6 weeks postinfection for CBC, evaluation of CD4(+) and CD8(+) cell counts by flow cytometry, and quantification of plasma and cell-associated viremia by real time RT-PCR.

RESULTS

Treatment of cats with FZD during the acute stage of FIV infection decreased plasma and cell-associated viremia during the first 2 weeks of infection, but was not protective against FIV, as all cats were infected by 6 weeks.

CONCLUSIONS

At the dosage used in this study, treatment with FZD results in a short-term decrease in viral load with no adverse effects. Further investigation of FZD is warranted to assess pharmacokinetics, optimal dosage, and to directly compare the antiviral activity of FZD to ZDV in naturally infected cats.

CD4+CD25+ T regulatory cells from FIV+ cats induce a unique anergic profile in CD8+ lymphocyte targets

Background

Using the FIV model, we reported previously that CD4⁺CD25⁺ T regulatory (Treg) cells from FIV⁺ cats are constitutively activated and suppress CD4⁺CD25^- and CD8⁺ T cell immune responses. In an effort to further explore Treg-mediated suppression, we asked whether Treg cells induce anergy through the alteration of production of cyclins, cyclin-dependent kinases and their inhibitors.

Results

Lymphocytes were obtained from control or FIV⁺ cats and sorted by FACS into CD4⁺CD25⁺ and CD8⁺ populations. Following co-culture with CD4⁺CD25⁺ cells, CD8⁺ targets were examined by Western blot for changes in cyclins D₃, E and A, retinoblastoma (Rb) protein, as well as the cyclin dependent kinase inhibitor p21^cip1. Following co-culture with CD4⁺CD25⁺cells, we observed up-regulation of p21^cip1 and cyclin E, with down-regulation of cyclin D₃, in CD8⁺ cells from FIV⁺ cats. As expected, CD8⁺ targets from control cats were quiescent with little up-regulation of p21^cip1 and cyclin E. There was also a lack of Rb phosphorylation in CD8⁺ targets consistent with late G₁ cell cycle arrest. Further, IL-2 mRNA was down regulated in CD8⁺ cells after co-culture with CD4⁺CD25⁺ Treg cells. Following CD4⁺CD25⁺ co-culture, CD8⁺ targets from FIV⁺ cats also had increased Foxp3 mRNA expression; however, these CD8⁺Foxp3⁺ cells did not exhibit suppressor function.

Conclusions

Collectively, these data suggest that CD4⁺CD25⁺ Treg cells from FIV⁺ cats induce CD8⁺ anergy by disruption of normal G₁ to S cell cycle progression.

Prior mucosal exposure to heterologous cells alters the pathogenesis of cell-associated mucosal feline immunodeficiency virus challenge

BACKGROUND

Several lines of research suggest that exposure to cellular material can alter the susceptibility to infection by HIV-1. Because sexual contact often includes exposure to cellular material, we hypothesized that repeated mucosal exposure to heterologous cells would induce an immune response that would alter the susceptibility to mucosal infection. Using the feline immunodeficiency virus (FIV) model of HIV-1 mucosal transmission, the cervicovaginal mucosa was exposed once weekly for 12 weeks to 5,000 heterologous cells or media (control) and then cats were vaginally challenged with cell-associated or cell-free FIV.

RESULTS

Exposure to heterologous cells decreased the percentage of lymphocytes in the mucosal and systemic lymph nodes (LN) expressing L-selectin as well as the percentage of CD4+ CD25+ T cells. These shifts were associated with enhanced ex-vivo proliferative responses to heterologous cells. Following mucosal challenge with cell-associated, but not cell-free, FIV, proviral burden was reduced by 64% in cats previously exposed to heterologous cells as compared to media exposed controls.

CONCLUSIONS

The pathogenesis and/or the threshold for mucosal infection by infected cells (but not cell-free virus) can be modulated by mucosal exposure to uninfected heterologous cells.