T cell responses to recall antigens, alloantigen, and mitogen of HIV-infected patients receiving long-term combined antiretroviral therapy

Identification of a First Human Norovirus CD8+ T Cell Epitope Restricted to HLA-A*0201 Allele

Norovirus (NoV) causes a substantial global burden of acute gastroenteritis in all age groups and the development of NoV vaccine is a high priority. There are still gaps in understanding of protective NoV-specific immunity. Antibody mediated immune responses have been widely studied, but in contrast, the research on NoV-specific human T cell-mediated immunity is very limited. We have recently reported NoV capsid VP1-specific 18-mer peptide (¹³⁴SPSQVTMFPHIIVDVRQL¹⁵¹) to induce strong CD8⁺ T cell immune responses in healthy adult donors. This work extends to identify the precise NoV T cell epitope and the restricting human leucocyte antigen (HLA). Pentamer technology was used to detect HLA-A^*0201-restricted T cell-mediated responses to 10-mer peptide ¹³⁹TMFPHIIVDV¹⁴⁸ of four healthy adult blood donors. Immunogenicity of the 10-mer epitope was confirmed by ELISPOT IFN-γ and intracellular cytokine staining (ICS) on flow cytometry. A population of CD3⁺CD8⁺ T lymphocytes binding to HLA-A^*0201/TMFPHIIVDV pentamers was identified in two HLA-A^*0201-positive donors. Recognition of the 10-mer epitope by T cells resulted in a strong IFN-γ secretion as shown by ELISPOT assay. In addition, ICS confirmed that high proportion (31 and 59%) of the TMFPHIIVDV epitope-responsive CD3⁺CD8⁺ T cells in the two donors had multifunctional phenotype, simultaneously producing IFN-γ, IL-2 and TNF-α cytokines. In the present study novel human NoV HLA-A^*0201-restricted minimal 10-mer epitope ¹³⁹TMFPHIIVDV¹⁴⁸ in the capsid VP1 was identified. The HLA-peptide pentamer staining of T cells from healthy donor PBMCs and cytokine responses in ex-vivo ELISPOT and ICS assays suggest that this epitope is recognized during NoV infection and activates memory phenotype of the epitope-specific multifunctional CD8⁺ T cells. The importance of this epitope in protection from NoV infection remains to be determined.

Functionality and avidity of norovirus-specific antibodies and T cells induced by GII.4 virus-like particles alone or co-administered with different genotypes

Norovirus (NoV) is the main cause of acute gastroenteritis worldwide across all age groups. Current NoV vaccine candidates are based on non-infectious highly immunogenic virus-like particles (VLPs) produced in cell cultures in vitro. As NoVs infecting human population are highly divergent, it is proposed that the vaccine should contain at least two different NoV genotypes, potentially affecting the immunogenicity of each other. We investigated the immunogenicity of NoV GII.4 VLPs administered by intramuscular (IM) or intradermal (ID) injections to BALB/c mice either alone or co-delivered with genogroup I (GI) and other genogroup GII VLPs. Serum NoV-specific IgG binding antibody titers and antibody functionality in terms of avidity and blocking potential were assessed. Furthermore, the specificity and functional avidity of CD4⁺ and CD8⁺ T cell responses were analyzed using synthetic peptides previously identified to contain NoV VP1 P2 domain-specific H-2^d epitopes. The results showed that IM and ID immunization induced comparable GII.4-specific antibodies and T cell responses. Similar magnitude and functionality of antibodies and interferon-gamma producing T cells were developed using monovalent GII.4 VLPs or different genotype combinations. For the first time, degranulation assay using multicolor flow cytometry showed that NoV GII.4-specific CD8⁺ T cells had cytotoxic T lymphocyte phenotype. To conclude, our results demonstrate that there is no immunological interference even if up to five different NoV VLP genotypes were co-administered at the same time. Furthermore, no inhibition of NoV-specific antibody functionality or the magnitude, specificity and affinity of T cell responses was observed in any of the immunized animals, observations relevant for the development of a multivalent NoV VLP vaccine.

Norovirus-Specific Memory T Cell Responses in Adult Human Donors

Norovirus (NoV) is a leading cause of acute gastroenteritis in people of all ages worldwide. NoV-specific serum antibodies which block the binding of NoV virus-like particles (VLPs) to the cell receptors have been thoroughly investigated. In contrast, only a few publications are available on the NoV capsid VP1 protein-specific T cell responses in humans naturally infected with the virus. Freshly isolated peripheral blood mononuclear cells of eight healthy adult human donors previously exposed to NoV were stimulated with purified VLPs derived from NoV GII.4-1999, GII.4-2012 (Sydney), and GI.3, and IFN-γ production was measured by an ELISPOT assay. In addition, 76 overlapping synthetic peptides spanning the entire 539-amino acid sequence of GII.4 VP1 were pooled into two-dimensional matrices and used to identify putative T cell epitopes. Seven of the eight subjects produced IFN-γ in response to the peptides and five subjects produced IFN-γ in response to the VLPs of the same origin. In general, stronger T cell responses were induced with the peptides in each donor compared to the VLPs. A CD8⁺ T cell epitope in the shell domain of the VP1 (¹³⁴SPSQVTMFPHIIVDVRQL¹⁵¹) was identified in two subjects, both having human leukocyte antigen (HLA)-A^∗02:01 allele. To our knowledge, this is the first report using synthetic peptides to study NoV-specific T cell responses in human subjects and identify T cell epitopes.

Comprehensive evaluation of the immune risk phenotype in successfully treated HIV-infected individuals

Background

Despite successful treatment and CD4+ T-cell recovery, HIV-infected individuals often experience a profound immune dysregulation characterized by a persistently low CD4:CD8 T-cell ratio. This residual immune dysregulation is reminiscent of the Immune Risk Phenotype (IRP) previously associated with morbidity and mortality in the uninfected elderly (>85 years). The IRP consists of laboratory markers that include: a low CD4:CD8 T-cell ratio, an expansion of CD8+CD28- T-cells and cytomegalovirus (CMV) seropositivity. Despite the significant overlap in immunological phenotypes between normal aging and HIV infection, the IRP has never been evaluated in HIV-infected individuals. In this pilot study we characterized immune changes associated with the IRP in a sample of successfully treated HIV-infected subjects.

Methods

18 virologically suppressed HIV-infected subjects were categorized into 2 groups based on their IRP status; HIV+IRP+, (n = 8) and HIV+IRP-, (n = 10) and compared to 15 age-matched HIV uninfected IRP negative controls. All individuals were assessed for functional and phenotypic immune characteristics including: pro-inflammatory cytokine production, antigen-specific proliferation capacity, replicative senescence, T-cell differentiation and lymphocyte telomere length.

Results

Compared to HIV-infected subjects without an IRP, HIV+IRP+ subjects exhibited a higher frequency of TNF-α-producing CD8+ T-cells (p = 0.05) and a reduced proportion of CD8+ naïve T-cells (p = 0.007). The IRP status was also associated with a marked up-regulation of the replicative senescence markers CD57 and KLGR1, on the surface of CD8+T-cells (p = 0.004). Finally, HIV+IRP+ individuals had a significantly shorter mean lymphocyte telomere length than their non-IRP counterparts (p = 0.03).

Conclusions

Our findings suggest that, despite similar levels of treatment-mediated viral suppression, the phenotypic and functional immune characteristics of HIV+IRP+ individuals are distinct from those observed in non-IRP individuals. The IRP appears to identify a subset of treated HIV-infected individuals with a higher degree of immune senescence.

A novel H1N1 virus causes the first pandemic of the 21st century

A novel H1N1 virus of swine origin (H1N1v ) is currently spreading in humans, giving rise to the first pandemic in 40 years. The disease is of moderate severity but has notable differences from seasonal influenza. In contrast to seasonal influenza, those over 60 years are relatively spared, a likely consequence of the presence of H1N1v cross-neutralizing antibody in this age group. Most patients appear to have mild influenza-like illness and many of the complications leading to hospitalization and mortality occur in those with underlying disease conditions or pregnancy. Studies in animal models suggest that the novel H1N1v pandemic virus causes a more severe illness and appears to have a greater predilection for the alveolar epithelium than seasonal influenza viruses. As there are as yet little data on the pathogenesis and immunology of H1N1v infection in humans, we have reviewed relevant data from past pandemics, from seasonal influenza and avian influenza H5N1 to highlight key issues pertaining to pathogenesis and immunology.

Delaying a treatment switch in antiretroviral-treated HIV type 1-infected patients with detectable drug-resistant viremia does not have a profound effect on immune parameters: AIDS Clinical Trials Group Study A5115

Some patients are unable to achieve and maintain an undetectable plasma HIV-1 RNA level with combination antiretroviral therapy (ART) and are therefore maintained on a partially suppressive regimen. To determine the immune consequences of continuing ART despite persistent viremia, we randomized 47 ART-treated individuals with low to moderate plasma HIV-1 RNA levels (200-9999 copies/ml) to either an immediate switch in therapy or a delayed switch (when plasma HIV-1 RNA became > or =10,000 copies/ml). After 48 weeks of follow-up, naive and memory CD4+ T cell percents were comparable in the two groups. The proportion of subjects with a lymphocyte proliferative response to Candida, Mycobacterium avium-intracellulare complex, or HIV-gag was also not significantly different at week 48. Delaying a treatment switch in patients with partial virologic suppression and stable CD4+ T cells does not have profound effects on immune parameters.

Innate immune defenses in HIV-1 infection: prospects for a novel immune therapy

HIV-1 infection leads to a severe decrease of CD4(+) T lymphocytes, dysregulation of several leukocyte subpopulations and generalized immune activation, with the subsequent development of opportunistic infections and malignancies. Administration of highly active antiretroviral therapy (HAART) has been successful in reducing HIV-1 plasma viremia; however, the ability of HAART to restore immunocompetence appears incomplete, particularly in patients with chronic and advanced disease. Several components of the innate immune system have direct anti-HIV-1 effects, and studies to analyze the benefits of enhancing the function of the innate response during HIV-1 infection are increasing. Development of any complementary therapeutic approaches to HIV-1 infection, particularly those able to compensate for the limitations of HAART, and enhance the anti-HIV-1 innate immune activity would be of interest. The stimulation of innate immune responses using Toll-like receptor agonists, such as monophosphoryl lipid A and oligodeoxynucleotides with CpG motifs, are currently being investigated and their benefit in HIV-1-infected patients are under evaluation.

CD8+ cell noncytotoxic anti-HIV response: restoration by HAART in the late stage of infection

Highly active antiretroviral therapy (HAART) is currently the best HIV infection management strategy. However, its effects on the CD8+ T cell noncytotoxic anti-HIV response (CNAR) are not well known. We investigated if HAART has different effects on CNAR in patients at the intermediate and late stages of HIV infection. Untreated healthy HIV-infected subjects with a mean CD4+ T cell count of 606 cells/microl were examined as a reference group. Plasma viral load, CD4+ T cell count, and CNAR activity were measured at baseline and regular intervals for at least 48 weeks following initiation of HAART. Baseline CNAR activity in all subjects correlated inversely with viral load and directly with CD4 T+ cell counts. The level of CNAR in the latestage group was significantly lower than in the intermediate-stage and the healthy reference group (p < 0.01). Following initiation of HAART, substantial increases in CD4+ T cell counts and decreases in viral loads were observed in both groups, indicating treatment success. CNAR activity was found to be increased significantly during HAART, but only in the late-stage group (p < 0.01). This increase in CD8+ cell function was seen within 4 weeks of treatment initiation and resulted in levels of CNAR activity almost equal to those observed in the healthy reference subjects. Our findings suggest a beneficial effect on CNAR in those individuals with reduced activity, typically in late-stage infection.

Prognostic value of proliferative responses to HIV-1 antigen in chronically HIV-infected patients under antiretroviral therapy

BACKGROUND

In the chronic stage of HIV infection T cell proliferative responses to HIV antigens are rare, mostly of low level, and the influence of responses on antiretroviral therapy is not known.

OBJECTIVES

To determine a potential correlation between HIV-specific proliferative responses and the subsequent course of infection under antiretroviral therapy.

STUDY DESIGN

Proliferation assays were performed with freshly isolated blood mononuclear cells from 45 chronically HIV-infected HAART treated individuals using HIV-p24, other recall antigens, and mitogens as stimulants. Virus load was monitored at the time of stimulation and during 33 months follow-up.

RESULTS

A proliferative response to HIV antigen stimulation was detectable in 7 of 45 patients (15.5% responders). This group showed elevated reactions against tetanus toxoid and tuberculin, whereas reactions against standard mitogens were equal in the HIV responder and nonresponder groups. None of the seven HIV-specific responders had a blood virus load rebound of more than 1000 genome copies/ml during follow-up, whereas in 50% of the non-responders higher virus rebounds occurred. CD4 cell levels were slightly higher in the responder group, but mostly independent of virus rebound within the non-responders. Only four patients with high and continuous virus rebound experienced a significant CD4 cell decline.

CONCLUSIONS

In patients under HAART, HIV-specific proliferative response is frequently related to anamnestic antigen responses and an enduring control of virus replication.

Proliferation responses to HIVp24 during antiretroviral therapy do not reflect improved immune phenotype or function

OBJECTIVE

To ascertain whether lymphoproliferation (LP) responses to HIVp24 in chronically infected patients treated with antiretroviral therapy (ART) predict an improved cytolytic T-cell phenotype or better in vivo immune function as measured by immunization responses.

METHODS

HIV-infected patients who started ART during chronic infection and who achieved viral suppression (HIV-RNA < 400 copies/ml for > 12 months) were grouped by the presence of strong [stimulation index (SI) > 10; n = 21] or absent (SI < 3; n = 18) LP to HIV-core antigen. The two groups were compared for functional immune responses to vaccination with diphtheria-toxoid, tetanus-toxoid and keyhole-limpet-hemocyanin, frequency of circulating naive and memory CD4+ and CD8+ T lymphocytes, maturation phenotype and expression of cytolytic molecules on total and HIV-specific CD8+ T cells, and frequency of memory CD4+ T cells with intracellular HIV-mRNA. Group comparisons were analyzed by non-parametric Mann-Whitney tests. Proportions were estimated by Pearson's chi analysis.

RESULTS

There were no differences between the groups in immune responses to vaccination or in the numbers or phenotype of circulating T cells. In a subgroup of HLA-A2+ or B8+ patients, HIV-reactive CD8+ T cells in both groups had similar expression of perforin, granzyme A and T-cell maturation markers (CD27, CD28, CCR7, CD62L). However, patients with SI > 10 in response to HIVp24 tended to more often have high levels of circulating CD4+ T cells with intracellular HIV-1 mRNA than did patients with SI < 3.

CONCLUSION

Following long-standing suppression of viral replication on ART, the presence of HIV-1 specific T-helper proliferation responses does not correlate with improved indices of immune phenotype or function but may reflect relatively higher levels of HIV-expression.

Response of human immunodeficiency virus-infected patients receiving highly active antiretroviral therapy to vaccination with 23-valent pneumococcal polysaccharide vaccine

Whether highly active antiretroviral therapy (HAART) impacts responses to 23-valent pneumococcal polysaccharide vaccine (PV) is not known. Immunoglobulin G (IgG) levels for 6 capsular polysaccharides in human immunodeficiency virus (HIV)-infected patients who had received > or =6 months of HAART were measured either after their first dose of PV (n=46) or after revaccination (n=41); control subjects had never received HAART and had received the first dose of PV (n=38). There were no significant differences in pre- or postvaccination IgG levels among these groups but for 1 capsular polysaccharide. The 3 groups had significant postvaccination increases in IgG levels to all capsular polysaccharides. The control group had a greater number of 2-fold responses than did the combined HAART groups (P<.05). Patients with a CD4 cell count of > or =200 cells/mm3 had a greater number of 2-fold responses than did those with a CD4 cell count of <200 cells/mm3 (P<.05). For revaccinated patients, postvaccination IgG levels were correlated with the CD4 cell count at the initial vaccination. The immunogenicity of PV among patients receiving long-term HAART is modest. It seems best to immunize HIV-infected patients early in the course of disease.

Interleukin-7 and immunorestoration in HIV: beyond the thymus

One of the hallmarks of untreated HIV infection is a progressive loss of effective immunity to both HIV-associated and non-HIV antigens. Combination antiretroviral therapy can frequently control viral replication, resulting in variable levels of immune reconstitution, but has not resulted in restoration of effective immunity to the virus. Understanding the limitations of immune reconstitution following highly active antiretroviral therapy (HAART) and identifying approaches to enhance immunity in this context may not only improve outcome for patients with HIV infection but could also provide insight for immune reconstitution in other conditions associated with T cell depletion.