Evaluation of the interlaboratory concordance in quantification of human immunodeficiency virus-specific T cells with a gamma interferon enzyme-linked immunospot assay

Adenoviral-vectored epigraph vaccine elicits robust, durable, and protective immunity against H3 influenza A virus in swine

Current methods of vaccination against swine Influenza A Virus (IAV-S) in pigs are infrequently updated, induce strain-specific responses, and have a limited duration of protection. Here, we characterize the onset and duration of adaptive immune responses after vaccination with an adenoviral-vectored Epigraph vaccine. In this longitudinal study we observed robust and durable antibody responses that remained above protective titers six months after vaccination. We further identified stable levels of antigen-specific T cell responses that remained detectable in the absence of antigen stimulation. Antibody isotyping revealed robust class switching from IgM to IgG induced by Epigraph vaccination, while the commercial comparator vaccine failed to induce strong antibody class switching. Swine were challenged six months after initial vaccination, and Epigraph-vaccinated animals demonstrated significant protection from microscopic lesion development in the trachea and lungs, reduced duration of viral shedding, lower presence of infectious virus and viral antigens in the lungs, and significant recall of antigen-specific T cell responses following challenge. The results obtained from this study are useful in determining the kinetics of adaptive immune responses after vaccination with adjuvanted whole inactivated virus vaccines compared to adenoviral vectored vaccines and contribute to the continued efforts of creating a universal IAV-S vaccine.

Impact of Anti PD-1 Immunotherapy on HIV Reservoir and Anti-Viral Immune Responses in People Living with HIV and Cancer

The role of immune checkpoints (ICPs) in both anti-HIV T cell exhaustion and HIV reservoir persistence, has suggested that an HIV cure therapeutic strategy could involve ICP blockade. We studied the impact of anti-PD-1 therapy on HIV reservoirs and anti-viral immune responses in people living with HIV and treated for cancer. At several timepoints, we monitored CD4 cell counts, plasma HIV-RNA, cell associated (CA) HIV-DNA, EBV, CMV, HBV, HCV, and HHV-8 viral loads, activation markers, ICP expression and virus-specific T cells. Thirty-two patients were included, with median follow-up of 5 months. The CA HIV-DNA tended to decrease before cycle 2 (p = 0.049). Six patients exhibited a ≥0.5 log₁₀ HIV-DNA decrease at least once. Among those, HIV-DNA became undetectable for 10 months in one patient. Overall, no significant increase in HIV-specific immunity was observed. In contrast, we detected an early increase in CTLA-4 + CD4+ T cells in all patients (p = 0.004) and a greater increase in CTLA-4+ and TIM-3 + CD8+ T cells in patients without HIV-DNA reduction compared to the others (p ≤ 0.03). Our results suggest that ICP replacement compensatory mechanisms might limit the impact of anti-PD-1 monotherapy on HIV reservoirs, and pave the way for combination ICP blockade in HIV cure strategies.

Immunogenicity and safety of yellow fever vaccine in HIV-1-infected patients

OBJECTIVES

The objective of this study is to investigate immunogenicity and safety of the yellow fever vaccine (YFV) in HIV-infected (HIV+) patients with high CD4 T-cell counts.

DESIGN

In this prospective, comparative study of YFV-naive adults: 40 HIV+ under antiretroviral therapy (ART) with CD4 T-cell count above 350 cells/μl and plasma HIV-RNA less than 50 copies/ml for at least 6 months and 31 HIV-negative (HIV-) received one injection of the YF-17D strain vaccine.

METHODS

Serologic response was assessed by using a plaque reduction neutralizing test and YFV-specific T cells by using an INFγ-Elispot assay.

RESULTS

YFV was well tolerated in both groups. Most participants had asymptomatic YFV viremia at day (D) 7 after vaccination (77% of HIV- and 82% of HIV+, P = 0.58), with higher plasma level of YFV RNA in HIV+ than in HIV- (median 2.46 log10 copies/ml (range: 1.15-4.16) and 1.91 log10 copies/ml (1.15-3.19), respectively, P = 0.011). A significant but transient decrease in CD4 cell counts was seen at D7 in both groups, more pronounced in HIV- than in HIV+ patients (-261.5 versus -111.5 cells/μl, respectively, P = 0.0003), but no HIV breakthrough was observed in plasma. All participants developed protective neutralizing antibody levels from D28 and up to 1 year after injection. At D91, fewer HIV+ than HIV- participants exhibited YFV T-cell response (20 versus 54%, respectively, P = 0.037).

CONCLUSION

At 1 year, YFV was immunogenic and well tolerated in HIV-infected adults under ART with CD4 T-cell counts above 350 cells/μl. However, a lower immunity of YFV T cells in HIV-infected patients was observed as compared with HIV- participants.

CLINICAL TRIALS REGISTRATION

NCT01426243.

What Is the most Important for Elite Control: Genetic Background of Patient, Genetic Background of Partner, both or neither? Description of Complete Natural History within a Couple of MSM

Background

We describe a homosexual man who strongly controlled HIV-1 for ten years despite lack of protective genetic background.

Methods

HIV-1 DNA was measured in blood and other tissues. Cell susceptibility was evaluated with various strains. HIV-1-specific (CD4 and CD8 activation markers and immune check points) and NK cells responses were assessed; KIRs haplotypes and HLA alleles were determined.

Findings

Two HIV-1 RNA copies/mL of plasma were detected in 2009, using an ultra-sensitive assay. HIV-DNA was detected at 1.1 and 2 copies/10⁶ PBMCs in 2009 and 2015 respectively, at 1.2 copies/10⁶ cells in rectal cells in 2011. WBs showed weak reactivity with antibodies to gp160, p55 and p25 from 2007 to 2014, remaining incomplete in 2017. CD4 T cells were susceptible to various strains including HIV_KON, a primary isolate of his own CRF02_AG variant. CD8 T cells showed a strong poly-functional response against HIV-Gag, producing mainly IFN-γ; a robust capacity of antibody-dependant cell cytotoxicity (ADCC) was observed in NK cells. Case patient was group B KIR haplotype. Neutralizing antibodies were not detected. CD4 and CD8 blood T cells showed normal proportions without increased activation markers. Phylogenetic analyses identified the same CRF02_AG variant in his partner. The patient and his partner were heterozygous for the CCR5ΔD32 deletion and shared HLA-B*07, C*07 non-protective alleles.

Interpretation

This thorough description of the natural history of an individual controlling HIV-1 in various compartments for ten years despite lack of protective alleles, and of his partner, may have implications for strategies to cure HIV-1 infection.

•

We described a MSM, elite controller despite pejorative genetic background.

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The patient had two HLA pejoratives alleles and no protective alleles.

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The partner was infected by the same strain.

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The genetic backgrounds of the patient and partner, and the virus could interact with each other to lead to elite control.

We considered all the evidence about elite control, HLA, ADCC and NK, using Medline/PubMed. We described a MSM, elite controller despite non-protective genetic background, explored extensively the patient: sequential WBs, RNA in plasma (ultrasensitive assay), DNA in PBMC/GALT, cell susceptibility, HIV-1 responses in PBMC/LNMC, neutralizing antibodies, CD3-CD56 + NK, ADCC, KIRs. He had one HLA pejorative and no protective alleles. The partner was infected by the same strain, his genetic background was studied. The genetic background of the exposed person, of the source, and the viral strain could interact with each other to lead to elite control.

Evaluation of T and B memory cell responses elicited by the pandemic H1N1 vaccine in HIV-infected and HIV-uninfected individuals

BACKGROUND

This study was to compare B and T memory cells elicited by a single dose monovalent 2009 influenza A (H1N1) vaccine (strain A/California/7/2009 H1N1) in HIV⁺ and HIV^- groups, and to analyze the impact of the prior seasonal vaccines to the immunogenicity of this vaccine.

METHODS

Blood samples were collected before vaccination (day 0) and at days 28 and 180. Participants were categorized into HIV^-/LAIV, HIV^-/TIV and HIV⁺/TIV subgroups according to the trivalent live-attenuated or inactivated (LAIV or TIV) seasonal influenza vaccines they received previously. The IgG⁺ memory B cells (B_Mem) and IFNγ⁺ T cells were measured against antigens including the H1N1 vaccine, the hemagglutinin (HA) and neuraminidase (NA) proteins or peptide pools of the pandemic and the seasonal H1N1 strains, respectively.

RESULTS

Overall B_Mem responses increased significantly at day 28 but returned to baseline by day 180 in all three subgroups. The average frequency of the H1N1-specific B_Mem at day 28 for the HIV^-/LAIV, HIV^-/TIV and HIV⁺/TIV groups was 2.14%, 1.26% and 1.67%, respectively, and the average fold change was 14.39, 3.81 and 3.93, respectively. The differences of B_Mem between HIV^-/LAIV and the two TIV subgroups were significant. For the IFNγ response, the overall spot counts ranged widely between 0 and 958/10⁶ PBMCs. The group average spot counts to H1N1 vaccine was 89, 102, and 30 at day 28 for HIV^-/LAIV, HIV^-/TIV and HIV⁺/TIV subgroups, respectively. The average increase of IFNγ response at day 28 vs day 0 in all three subgroups did not reach 2-fold.

CONCLUSION

Participants with a prior LAIV seasonal vaccine, as compared to a TIV seasonal vaccine, responded significantly better to the monovalent H1N1 vaccine. Excluding LAIV participants, no difference was seen between the HIV⁺ and HIV^- subject groups in terms of B_Mem. The B_Mem response declined at 6months.

Risk factors for increased immune reconstitution in response to Mycobacterium tuberculosis antigens in tuberculosis HIV-infected, antiretroviral-naïve patients

Background

Little is known regarding the restoration of the specific immune response after combined antiretroviral therapy (cART) and anti-tuberculosis (TB) therapy introduction among TB-HIV patients. In this study, we examined the immune response of TB-HIV patients to Mycobacterium tuberculosis (Mtb) antigens to evaluate the response dynamics to different antigens over time. Moreover, we also evaluated the influence of two different doses of efavirenz and the factors associated with immune reconstitution.

Methods

This is a longitudinal study nested in a clinical trial, where cART was initiated during the baseline visit (D0), which occurred 30 ± 10 days after the introduction of anti-TB therapy. Follow-up visits were performed at 30, 60, 90 and 180 days after cART initiation. The production of IFN-γ upon in vitro stimulation with Mtb antigens purified protein derivative (PPD), ESAT-6 and 38 kDa/CFP-10 using ELISpot was examined at baseline and follow-up visits.

Results

Sixty-one patients, all ART-naïve, were selected and included in the immune reconstitution analysis; seven (11.5%) developed Immune Reconstitution Inflammatory Syndrome (IRIS). The Mtb specific immune response was higher for the PPD antigen followed by 38 kDa/CFP-10 and increased in the first 60 days after cART initiation. In multivariate analysis, the variables independently associated with increased IFN-γ production in response to PPD antigen were CD4⁺ T cell counts <200 cells/mm³ at baseline, age, site of tuberculosis, 800 mg efavirenz dose and follow-up CD4⁺ T cell counts. Moreover, the factors associated with the production of IFN-γ in response to 38 kDa/CFP-10 were detectable HIV viral load (VL) and CD4⁺ T cell counts at follow-up visits of ≥200 cells/mm³.

Conclusions

These findings highlight the differences in immune response according to the specificity of the Mtb antigen, which contributes to a better understanding of TB-HIV immunopathogenesis. IFN-γ production elicited by PPD and 38 kDa/CFP-10 antigens have a greater magnitude compared to ESAT-6 and are associated with different factors. The low response to ESAT-6, even during immune restoration, suggests that this antigen is not adequate to assess the immune response of immunosuppressed TB-HIV patients.

Validation of an IFNγ/IL2 FluoroSpot assay for clinical trial monitoring

Background

The FluoroSpot assay, an advancement of the ELISpot assay, enables simultaneous measurement of different analytes secreted at a single-cell level. This allows parallel detection of several cytokines secreted by immune cells upon antigen recognition. Easier standardization, higher sensitivity and reduced labour intensity render FluoroSpot assays an interesting alternative to flow-cytometry based assays for analysis of clinical samples. While the use of immunoassays to study immunological primary and secondary endpoints becomes increasingly attractive, assays used require pre-trial validation. Here we describe the assay validation (precision, specificity and linearity) of a FluoroSpot immunological endpoint assay detecting Interferon γ (IFNγ) and Interleukin 2 (IL2) for use in clinical trial immune monitoring.

Methods

We validated an IFNγ/IL2 FluoroSpot assay to determine Epstein-Barr virus (EBV)-specific cellular immune responses (IFNγ, IL2 and double positive IFNγ + IL2 responses), using overlapping peptide pools corresponding to EBV-proteins BZLF1 and EBNA3A. Assay validation was performed using cryopreserved PBMC of 16 EBV-seropositive and 6 EBV-seronegative donors. Precision was assessed by (i) testing 16 donors using three replicates per assay (intra-assay precision/repeatability) (ii) using two plates in parallel (intermediate precision/plate-to-plate variability) and (iii) by performing the assays on three different days (inter-assay precision/reproducibility). In addition, we determined specificity, linearity and quantification limits of the assay. Further we tested precision across the two assay systems, IFNγ/IL2 FluoroSpot and the corresponding enzymatic single cytokine ELISpot.

Results

The validation revealed: (1) a high intra-assay precision (coefficient of variation (CV) 9.96, 8.85 and 13.05 %), intermediate precision (CV 6.48, 10.20 and 12.97 %) and reproducibility (CV 20.81 %, 12,75 % and 12.07 %) depending on the analyte and antigen used; (2) a specificity of 100 %; (3) a linearity with R² values from 0.93 to 0.99 depending on the analyte. The testing of the precision across the two assay systems, adduced a concordance correlation coefficient p_c = 0.99 for IFNγ responses and p_c = 0.93 for IL2 responses, indicating a large agreement between both assay methods.

Conclusions

The validated primary endpoint assay, an EBV peptide pool specific IFNγ/IL2 FluoroSpot assay was found to be suitable for the detection of EBV-specific immune responses subject to the requirement of standardized assay procedure and data analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0932-7) contains supplementary material, which is available to authorized users.

Defining ELISpot cut-offs from unreplicated test and control wells

In the absence of replication of wells, empirical criteria for enzyme-linked immunospot (ELISpot) positivity use fixed differences or ratios between spot forming units (SFU) counts between test and control. We propose an alternative approach which first identifies the optimally variance-stabilizing transformation of the SFU counts, based on the Bland-Altman plot of the test and control wells. The second step is to derive a positivity threshold from the difference in between-plate distribution functions of the transformed test and control SFU counts. This method is illustrated using 1309 assay results from a cohort study of influenza in Vietnam in which some, but not all, of the peptide pools have clear tendencies for SFU counts to be higher in test than control wells.

Broad and cross-clade CD4+ T-cell responses elicited by a DNA vaccine encoding highly conserved and promiscuous HIV-1 M-group consensus peptides

T-cell based vaccine approaches have emerged to counteract HIV-1/AIDS. Broad, polyfunctional and cytotoxic CD4⁺ T-cell responses have been associated with control of HIV-1 replication, which supports the inclusion of CD4⁺ T-cell epitopes in vaccines. A successful HIV-1 vaccine should also be designed to overcome viral genetic diversity and be able to confer immunity in a high proportion of immunized individuals from a diverse HLA-bearing population. In this study, we rationally designed a multiepitopic DNA vaccine in order to elicit broad and cross-clade CD4⁺ T-cell responses against highly conserved and promiscuous peptides from the HIV-1 M-group consensus sequence. We identified 27 conserved, multiple HLA-DR-binding peptides in the HIV-1 M-group consensus sequences of Gag, Pol, Nef, Vif, Vpr, Rev and Vpu using the TEPITOPE algorithm. The peptides bound in vitro to an average of 12 out of the 17 tested HLA-DR molecules and also to several molecules such as HLA-DP, -DQ and murine IA^b and IA^d. Sixteen out of the 27 peptides were recognized by PBMC from patients infected with different HIV-1 variants and 72% of such patients recognized at least 1 peptide. Immunization with a DNA vaccine (HIVBr27) encoding the identified peptides elicited IFN-γ secretion against 11 out of the 27 peptides in BALB/c mice; CD4⁺ and CD8⁺ T-cell proliferation was observed against 8 and 6 peptides, respectively. HIVBr27 immunization elicited cross-clade T-cell responses against several HIV-1 peptide variants. Polyfunctional CD4⁺ and CD8⁺ T cells, able to simultaneously proliferate and produce IFN-γ and TNF-α, were also observed. This vaccine concept may cope with HIV-1 genetic diversity as well as provide increased population coverage, which are desirable features for an efficacious strategy against HIV-1/AIDS.

ELISpot for measuring human immune responses to vaccines

The enzyme-linked immunosorbent spot (ELISpot) assay is one of the most commonly used methods to measure antigen-specific T cells in both mice and humans. Some of the primary reasons for the popularity of the method are that ELISpot is highly quantitative, can measure a broad range of magnitudes of response and is capable of assessing critical cellular immune-related activities such as IFN-γ secretion and granzyme B release. Furthermore, ELISpot is adaptable not only to the evaluation of a variety of T-cell functions, but also to B cells and innate immune cells. It is no wonder that ELISpot has evolved from a research tool to a clinical assay. Recent Phase I and II studies of cancer vaccines, tested in a variety of malignancies, have suggested that ELISpot may be a useful biomarker assay to predict clinical benefit after therapeutic immune modulation. This article will discuss the most common applications of ELISpot, overview the efforts that have been undertaken to standardize the assay and apply the method in the analysis of human clinical trials, and describe some important steps in the process of developing a clinical-grade ELISpot.

Relationship between regulatory T cells and immune activation in human immunodeficiency virus-infected patients interrupting antiretroviral therapy

Persistent immune activation plays a central role in driving Human Immunodeficiency Virus (HIV) disease progression. Whether CD4+CD25+ regulatory T cells (Tregs) are harmful by suppressing HIV-specific immune responses and/or beneficial through a decrease in immune activation remains debatable. We analysed the relationship between proportion and number of regulatory T cells (Tregs) and immune activation in HIV-infected patients interrupting an effective antiretroviral therapy (ART). Twenty-five patients were included in a substudy of a prospective multicenter trial of treatment interruption (TI) (ANRS 116). Proportions and numbers of Tregs and the proportion of activated CD4 and CD8 T cells were assessed at baseline and month 12 (M12) of TI. Specific anti-HIV CD4 and CD8 responses were investigated at baseline and M12. Non parametric univariate analyses and multivariate linear regression models were conducted. At baseline, the proportion of Tregs negatively correlated with the proportion of HLA-DR⁺CD8⁺T cells (r = −0.519). Following TI, the proportion of Tregs increased from 6.3% to 7.2% (p = 0.029); absolute numbers of Tregs decreased. The increase in the proportion of HLA-DR⁺CD38⁺CD8⁺T cells was significantly related to the increase in proportion of Tregs (p = 0.031). At M12, the proportion of Tregs did not negatively correlate with CD8 T-cell activation. Nevertheless, Tregs retain a suppressive function since depletion of Treg-containing CD4⁺CD25⁺ cells led to an increase in lymphoproliferative responses in most patients studied. Our data suggest that Tregs are efficient in controlling residual immune activation in patients with ART-mediated viral suppression. However, the insufficient increase in the proportion and/or the decrease in the absolute number of Tregs result in a failure to control immune activation following TI.

Determination of rubella virus-specific cell-mediated immunity using IFN gamma-ELISpot

Immunity to rubella virus (RV) is conventionally determined by measuring specific immunoglobulin G (IgG). However, several individuals may be considered immune despite undetectable antibody levels. In the present study RV-specific interferon-gamma (IFN gamma)-ELISpot and rubella-IgG-ELISA were compared in 75 young adults aged between 20 and 30 years. In a subgroup, not only rubella-like particles (RLP), but also HPV77 rubella vaccine derived antigen was used in IFN gamma-ELISpot. The results from both, ELISA and ELISpot were independent of previous encounter to RV (vaccination, exanthematous disease, or childhood infection). There was no difference between RLP and RV vaccine antigen in IFN gamma-ELISpot response, and there was no correlation between IFN gamma-ELISpot and RV-specific IgG levels. IFN gamma-producing cells were found in 78.7% of all tested persons, and 83.8% of them were positive in ELISA. In almost all individuals seronegative for RV antibody, IFN gamma-producing cells were detected. Considering both humoral and cell-mediated immune responses, a positive RV immune reaction was seen in 98.6%. The results indicate that the IFN gamma-ELISpot can provide valuable additional information in seronegative individuals.

Immune and virological benefits of 10 years of permanent viral control with antiretroviral therapy

The effects of a 10-year control of HIV replication without viral blips with antiretroviral therapy were examined in progressors. CD4 cell counts did not plateau but showed a continuous increase until the 10th year. Ultrasensitive techniques showed very low plasma HIV RNA and cell-associated DNA levels. Robust memory T cell responses to HIV-p24 were higher than in 3-year treated patients and comparable to those of Elite controllers, whereas interferon-gamma-producing HIV-specific T cells were infrequent. Long-term and efficient antiretroviral therapy provides continuous benefits both on the immune system and on the HIV reservoirs.

Effect of methotrexate and anti-TNF on Epstein-Barr virus T-cell response and viral load in patients with rheumatoid arthritis or spondylarthropathies

INTRODUCTION

There is a suspicion of increased risk of Epstein-Barr virus (EBV)-associated lymphoproliferations in patients with inflammatory arthritides receiving immunosuppressive drugs. We investigated the EBV load and EBV-specific T-cell response in patients treated with methotrexate (MTX) or anti-TNF therapy.

METHODS

Data for patients with rheumatoid arthritis (RA) (n = 58) or spondylarthropathy (SpA) (n = 28) were analyzed at baseline in comparison with controls (n = 22) and after 3 months of MTX or anti-TNF therapy for EBV load and EBV-specific IFNgamma-producing T cells in response to EBV latent-cycle and lytic-cycle peptides.

RESULTS

The EBV load and the number of IFNgamma-producing T-cells after peptide stimulation were not significantly different between groups at baseline (P = 0.61 and P = 0.89, respectively). The EBV load was not significantly modified by treatment, for RA with MTX (P = 0.74) or anti-TNF therapy (P = 0.94) or for SpA with anti-TNF therapy (P = 1.00). The number of EBV-specific T cells was not significantly modified by treatment, for RA with MTX (P = 0.58) or anti-TNF drugs (P = 0.19) or for SpA with anti-TNF therapy (P = 0.39). For all patients, the EBV load and EBV-specific T cells were significantly correlated (P = 0.017; R = 0.21). For most patients, short-term exposure (3 months) to MTX or anti-TNF did not alter the EBV load or EBV-specific T-cell response but two patients had discordant evolution.

CONCLUSIONS

These data are reassuring and suggest there is no short-term defect in EBV-immune surveillance in patients receiving MTX or anti-TNF drugs. However, in these patients, long term follow-up of EBV-specific T-cell response is necessary and the role of non-EBV-related mechanisms of lymphomagenesis is not excluded.

The intracellular detection of MIP-1beta enhances the capacity to detect IFN-gamma mediated HIV-1-specific CD8 T-cell responses in a flow cytometric setting providing a sensitive alternative to the ELISPOT

BACKGROUND

T-cell mediated immunity likely plays an important role in controlling HIV-1 infection and progression to AIDS. Several candidate vaccines against HIV-1 aim at stimulating cellular immune responses, either alone or together with the induction of neutralizing antibodies, and assays able to measure CD8 and CD4 T-cell responses need to be implemented. At present, the IFN-gamma-based ELISPOT assay is considered the gold standard and it is broadly preferred as primary assay for detection of antigen-specific T-cell responses in vaccine trials. However, in spite of its high sensitivity, the measurement of the sole IFN-gamma production provides limited information on the quality of the immune response. On the other hand, the introduction of polychromatic flow-cytometry-based assays such as the intracellular cytokine staining (ICS) strongly improved the capacity to detect several markers on a single cell level.

RESULTS

The cumulative analysis of 275 samples from 31 different HIV-1 infected individuals using an ICS staining procedure optimized by our laboratories revealed that, following antigenic stimulation, IFN-gamma producing T-cells were also producing MIP-1beta whereas T-cells characterized by the sole production of IFN-gamma were rare. Since the analysis of the combination of two functions decreases the background and the measurement of the IFN-gamma+ MIP-1beta+ T-cells was equivalent to the measurement of the total IFN-gamma+ T-cells, we adopted the IFN-gamma+ MIP-1beta+ data analysis system to evaluate IFN-gamma-based, antigen-specific T-cell responses. Comparison of our ICS assay with ELISPOT assays performed in two different experienced laboratories demonstrated that the IFN-gamma+ MIP-1beta+ data analysis system increased the sensitivity of the ICS up to levels comparable to the sensitivity of the ELISPOT assay.

CONCLUSION

The IFN-gamma+ MIP-1beta+ data evaluation system provides a clear advantage for the detection of low magnitude HIV-1-specific responses. These results are important to guide the choice for suitable highly sensitive immune assays and to build reagent panels able to accurately characterize the phenotype and function of responding T-cells. More importantly, the ICS assay can be used as primary assay to evaluate HIV-1-specific responses without losing sensitivity in comparison to the ELISPOT assay.

Precision and linearity targets for validation of an IFNgamma ELISPOT, cytokine flow cytometry, and tetramer assay using CMV peptides

BACKGROUND

Single-cell assays of immune function are increasingly used to monitor T cell responses in immunotherapy clinical trials. Standardization and validation of such assays are therefore important to interpretation of the clinical trial data. Here we assess the levels of intra-assay, inter-assay, and inter-operator precision, as well as linearity, of CD8+ T cell IFNgamma-based ELISPOT and cytokine flow cytometry (CFC), as well as tetramer assays.

RESULTS

Precision was measured in cryopreserved PBMC with a low, medium, or high response level to a CMV pp65 peptide or peptide mixture. Intra-assay precision was assessed using 6 replicates per assay; inter-assay precision was assessed by performing 8 assays on different days; and inter-operator precision was assessed using 3 different operators working on the same day. Percent CV values ranged from 4% to 133% depending upon the assay and response level. Linearity was measured by diluting PBMC from a high responder into PBMC from a non-responder, and yielded R2 values from 0.85 to 0.99 depending upon the assay and antigen.

CONCLUSION

These data provide target values for precision and linearity of single-cell assays for those wishing to validate these assays in their own laboratories. They also allow for comparison of the precision and linearity of ELISPOT, CFC, and tetramer across a range of response levels. There was a trend toward tetramer assays showing the highest precision, followed closely by CFC, and then ELISPOT; while all three assays had similar linearity. These findings are contingent upon the use of optimized protocols for each assay.

Results and harmonization guidelines from two large-scale international Elispot proficiency panels conducted by the Cancer Vaccine Consortium (CVC/SVI)

The Cancer Vaccine Consortium of the Sabin Vaccine Institute (CVC/SVI) is conducting an ongoing large-scale immune monitoring harmonization program through its members and affiliated associations. This effort was brought to life as an external validation program by conducting an international Elispot proficiency panel with 36 laboratories in 2005, and was followed by a second panel with 29 participating laboratories in 2006 allowing for application of learnings from the first panel. Critical protocol choices, as well as standardization and validation practices among laboratories were assessed through detailed surveys. Although panel participants had to follow general guidelines in order to allow comparison of results, each laboratory was able to use its own protocols, materials and reagents. The second panel recorded an overall significantly improved performance, as measured by the ability to detect all predefined responses correctly. Protocol choices and laboratory practices, which can have a dramatic effect on the overall assay outcome, were identified and lead to the following recommendations: (A) Establish a laboratory SOP for Elispot testing procedures including (A1) a counting method for apoptotic cells for determining adequate cell dilution for plating, and (A2) overnight rest of cells prior to plating and incubation, (B) Use only pre-tested serum optimized for low background: high signal ratio, (C) Establish a laboratory SOP for plate reading including (C1) human auditing during the reading process and (C2) adequate adjustments for technical artifacts, and (D) Only allow trained personnel, which is certified per laboratory SOPs to conduct assays. Recommendations described under (A) were found to make a statistically significant difference in assay performance, while the remaining recommendations are based on practical experiences confirmed by the panel results, which could not be statistically tested. These results provide initial harmonization guidelines to optimize Elispot assay performance to the immunotherapy community. Further optimization is in process with ongoing panels.

Multicentric Castleman disease is associated with polyfunctional effector memory HHV-8-specific CD8+ T cells

Multicentric Castleman disease (MCD) is a devastating human herpesvirus 8 (HHV-8)-related lymphoproliferative disorder that occurs in immunocompromised persons. To determine the role of immune responses in MCD, we studied the frequency, antigenic repertoire, differentiation, and functional profile of HHV-8-specific CD8(+) T cells in MCD patients and in human immunodeficiency virus-coinfected asymptomatic HHV-8 carriers (AC). Screening CD8(+) T-cell responses with ELISpot interferon-gamma (IFN-gamma) assays using 56 peptides on 6 latent and lytic HHV-8 proteins showed that MCD and AC patients had responses of similar magnitude and antigenic repertoire and identified a new 10-mer human leukocyte antigen B7 CD8 epitope in K15. Intracellular IFN-gamma staining showed significantly more CD45RA(-)CCR7(-)CD27(-) CD8(+)IFN-gamma(+) cells (late phenotype) and significantly fewer CCR7(-)CD27(+)CD45RA(-) cells (early and intermediate phenotype) in MCD than in AC patients. This phenotypic shift was not found for Epstein-Barr virus-specific CD8(+) T cells tested as controls. HHV-8 viral loads were negatively correlated with early and intermediate effector memory cells. HHV-8-specific T cells were polyfunctional (secretion of IFN-gamma, tumor necrosis factor-alpha, macrophage inflammatory protein-1beta, and/or CD107a) in both MCD and AC patients. In conclusion, MCD is not associated with a lack of HHV-8-specific CD8(+) T cells or limitation of their functional profile. Their differentiation increases with HHV-8 viral load. These results offer new insight into the pathophysiology of MCD.

The Th1 immune response against HIV-1 Gag p24-derived peptides in mice expressing HLA-A02.01 and HLA-DR1

Using HLA-DR1-transgenic H-2 class II knockout mice, we identified two new HLA-DR1-restricted HIV-1 Gag p24-derived epitopes (Gag(321-340 )and Gag(331-350)) and confirmed the immunogenicity of seven that have been previously described. The human relevance was confirmed for the two new ones (Gag(321-340 )and Gag(331-350)) assaying peripheral blood mononuclear cells from HLA-DR1(+) HIV-1-infected long-term asymptomatic subjects and showing that Gag(331-350) could prime CD4(+) T cells from two HLA-DR1(+) HIV-1 seronegative donors in vitro. Seven of these epitopes, structurally conserved among HIV-1 clade B isolates, were selected for a comparative evaluation of their Th1 helper potential by immunizing HLA-A02.01/HLA-DR1-transgenic, H-2 class I/class II knockout mice with recombinant mouse invariant chain constructs in which each helper epitope was inserted in association with two reporter HIV-1-derived HLA-A02.01-restricted CD8(+) T cell epitopes. A T helper effect was demonstrated in all cases, and was particularly strong with epitopes Gag(301-320),Gag(321-340 )and Gag(271-290), which should, therefore, be considered in the design of new vaccines.