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A conditionally replication-defective human cytomegalovirus (CMV) vaccine (V160) derived from AD169 and genetically engineered to express CMV pentameric complex (gH/gL/pUL128/pUL130/pUL131) was developed and evaluated for phase 1 vaccine safety and immunogenicity in CMV-seronegative and CMV-seropositive adults. Subjects received 3 doses of V160 or placebo on day 1, month 1, and month 6. Four vaccine dose levels, formulated with or without aluminum phosphate adjuvant, were evaluated. Injection-site and systemic adverse events (AEs) and vaccine viral shedding were monitored. CMV-specific cellular and humoral responses were measured by interferon-gamma ELISPOT and virus neutralization assay up to 12 months after last dose. V160 was generally well-tolerated, with no serious AEs observed. Transient, mild-to-moderate injection-site and systemic AEs were reported more frequently in vaccinated subjects than placebo. Vaccine viral shedding was not detected in any subject, confirming the nonreplicating feature of V160. Robust neutralizing antibody titers were elicited and maintained through 12 months postvaccination. Cellular responses to structural and nonstructural viral proteins were observed, indicating de novo expression of viral genes postvaccination. V160 displayed an acceptable safety profile. Levels of neutralizing antibodies and T-cell responses in CMV-seronegative subjects were within ranges observed following natural CMV infection. . NCT01986010.

Biomarkers that can be used to evaluate new interventions against latent tuberculosis infection (LTBI) and predict reactivation TB disease are urgently required. To evaluate ESAT-6 and CFP-10 (EC) IFN-γ ELISPOT as a biomarker for treatment efficacy in LTBI. This was a randomized, blinded, and placebo-controlled trial of INH in EC ELISPOT and Mantoux test positive participants. Participants received a 6-month course of 900 mg INH twice weekly or a matching placebo. INH acetylator genotypes were determined and urine tested for INH metabolites to confirm adherence. The proportion of positive responders for CFP-10 and ESAT-6 between treatment arms was compared using mixed effects logistic regression models. A Tweedie (compound Poisson) model was fitted to allow for zero inflation and overdispersion of quantitative response. The proportions of EC ELISPOT-positive subjects reduced over time (P < 0.001) but did not differ by study arm (P = 0.36). Median spot-forming units for ESAT-6 and CFP-10 also declined significantly with time (P < 0.001) but did not differ by study arm (P = 0.74 and 0.71, respectively). There was no evidence of an interaction between acetylator status and INH treatment with respect to ELISPOT results over time. In contacts with LTBI, INH therapy plays no role in observed decreases in Mycobacterium tuberculosis antigen-specific T-cell responses over time. IFN-γ ELISPOT is probably not a useful biomarker of treatment efficacy in LTBI. Clinical trial registered with www.clinicaltrials.gov (NCT 00130325).

•Viral vectored malaria vaccines adjuvanted with Matrix-M were well tolerated.•Addition of Matrix-M did not result in a reduction in cellular or humoral immunogenicity.•These vaccines adjuvanted with Matrix-M can be used safely in combination regimes with vaccines requiring an adjuvant. The use of viral vectors in heterologous prime-boost regimens to induce potent T cell responses in addition to humoral immunity is a promising vaccination strategy in the fight against malaria. We conducted an open-label, first-in-human, controlled Phase I study evaluating the safety and immunogenicity of Matrix-M adjuvanted vaccination with a chimpanzee adenovirus serotype 63 (ChAd63) prime followed by a modified vaccinia Ankara (MVA) boost eight weeks later, both encoding the malaria ME-TRAP antigenic sequence (a multiple epitope string fused to thrombospondin-related adhesion protein). Twenty-two healthy adults were vaccinated intramuscularly with either ChAd63-MVA ME-TRAP alone (n=6) or adjuvanted with 25μg (n=8) or 50μg (n=8) Matrix-M. Vaccinations appeared to be safe and generally well tolerated, with the majority of local and systemic adverse events being mild in nature. The addition of Matrix-M to the vaccine did not increase local reactogenicity; however, systemic adverse events were reported more frequently by volunteers who received adjuvanted vaccine in comparison to the control group. T cell ELISpot responses peaked at 7-days post boost vaccination with MVA ME-TRAP in all three groups. TRAP-specific IgG responses were highest at 28-days post boost with MVA ME-TRAP in all three groups. There were no differences in cellular and humoral immunogenicity at any of the time points between the control group and the adjuvanted groups. We demonstrate that Matrix-M can be safely used in combination with ChAd63-MVA ME-TRAP heterologous prime-boost immunization without any reduction in cellular or humoral immunogenicity. Clinical Trials Registration NCT01669512.

Abstract Rationale HIV–tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) is an immunopathological reaction to mycobacterial antigens induced by antiretroviral therapy. Prednisone reduces morbidity in TB-IRIS, but the mechanisms are unclear. Objectives To determine the effect of prednisone on the inflammatory response in TB-IRIS (antigen-specific effector T cells, cytokines, and chemokines). Methods Blood was taken from participants in a randomized placebo-controlled trial of prednisone for TB-IRIS, at 0, 2, and 4 weeks. Participants received prednisone at a dosage of 1.5 mg/kg/day for 2 weeks followed by 0.75 mg/kg/day for 2 weeks, or placebo at identical dosages. Measurements and Main Results Analyses included IFN-γ enzyme-linked immunospot (ELISPOT), reverse transcription-polymerase chain reaction on peripheral blood mononuclear cells after restimulation with heat-killed Mycobacterium tuberculosis, Luminex multiplex cytokine analysis of corresponding tissue culture supernatants, and Luminex multiplex cytokine analysis of serum. Fifty-eight participants with TB-IRIS (31 receiving prednisone, 27 receiving placebo) were included. In serum, significant decreases in IL-6, IL-10, IL-12 p40, tumor necrosis factor-α, IFN-γ, and IFN-γ–induced protein-10 concentrations during prednisone, but not placebo, treatment were observed. No differences in ELISPOT responses comparing prednisone and placebo groups were shown in response to ESAT-6 (early secreted antigen target-6), Acr1, Acr2, 38-kD antigen, or heat-killed H37Rv M. tuberculosis. Purified protein derivative ELISPOT responses increased over 4 weeks in the prednisone group and decreased in the placebo group (P = 0.007). Conclusions The beneficial effects of prednisone in TB-IRIS appear to be mediated via suppression of predominantly proinflammatory cytokine responses of innate immune origin, not via a reduction of the numbers of antigen-specific T cells in peripheral blood.

Monitoring antigen-specific T cells is critical for the study of immune responses and development of biomarkers and immunotherapeutics. We developed a novel multiplex assay that combines conventional immune monitoring techniques and immune receptor repertoire sequencing to enable identification of T cells specific to large numbers of antigens simultaneously. We multiplexed 30 different antigens and identified 427 antigen-specific clonotypes from 5 individuals with frequencies as low as 1 per million T cells. The clonotypes identified were validated several ways including repeatability, concordance with published clonotypes, and high correlation with ELISPOT. Applying this technology we have shown that the vast majority of shared antigen-specific clonotypes identified in different individuals display the same specificity. We also showed that shared antigen-specific clonotypes are simpler sequences and are present at higher frequencies compared to non-shared clonotypes specific to the same antigen. In conclusion this technology enables sensitive and quantitative monitoring of T cells specific for hundreds or thousands of antigens simultaneously allowing the study of T cell responses with an unprecedented resolution and scale.

The enzyme-linked immunosorbent spot (EliSpot) assay and its fluorescence-based version, FluoroSpot, are sensitive immunoassays commonly used to quantify antigen-specific T and B lymphocytes and other immune cells in peripheral blood or homogenized tissues. Due to their high sensitivity, these assays are popular in clinical trials to evaluate the efficacy of immunotherapy and vaccines, which involve a high level of scrutiny to ensure valid study results. Besides industry consensus white papers and other research publications, there is no formal guidance for the industry on how to validate EliSpot and FluoroSpot assays to ensure their accurate performance for immune monitoring in clinical trials. Herein, we describe a comprehensive in vitro study using healthy human donor peripheral blood mononuclear cells (PBMCs) and model antigens to validate a double-color FluoroSpot assay for monitoring antigen-specific lymphocytes by detecting and quantifying IFN-γ and IL-2-producing lymphocytes. Validation parameters, acceptance criteria set-up, and assay limits—limit of detection (LOD), minimum positive control response, lower and upper limits of quantification (LLOQ and ULOQ)—were determined, and assay performance was demonstrated by assessing precision, specificity, linearity, and robustness. In addition, an inter-laboratory comparison demonstrated concordance between assay results from two laboratories. In summary, this study outlines a robust approach to EliSpot and FluoroSpot validation and demonstrates that the IFN-γ/IL-2 FluoroSpot assay is suitable for the reliable detection of antigen-specific immune responses from PBMC samples across laboratories and meets the current regulatory requirements for bioanalytical method validation. Graphical Abstract

We investigated the performance of enzyme linked immunospot (ELISpot) assay for the diagnosis of invasive aspergillosis (IA) in high-risk patients with hematologic malignancies. We prospectively enrolled two cohorts of patients undergoing intensive myelosuppressive or immunosuppressive treatments at high risk for IA. ELISpot was performed to detect Aspergillus-specific T cells producing Interleukin-10. In the discovery cohort, a derived cut-off of 40 spot forming cells (SFCs)/106 PBMCs has shown to correctly classify IA cases with a sensitivity and specificity of 89.5% and 88.6%, respectively. This cut-off is lowered to 25 SFC when considering the subset of possible IA patients, with sensitivity and specificity of 76% and 93%, respectively. The application of the 40 SFCs cut-off to the validation cohort resulted in a positivity rate of 83.3% in proven/probable cases and a negativity rate of 92.5% in possible/non-IA cases. Adopting the 25 SCFs cut-off, the assay resulted positive in 83.3% of proven/probable cases while it resulted negative in 66.7% of possible/non-IA cases. ELISpot shows promises in the diagnosis of IA and the possibility to use two distinct cut-offs with similar diagnostic performances according to patients' different pre-test probability of infection can widen its use in patients at risk.

The Enzyme-Linked ImmunoSpot (ELISPOT) assay is a highly sensitive and widely used technique for assessing antigen-specific cellular immune responses in cancer research. By enabling the quantification of cytokine secretion at the single-cell level, particularly interferon gamma (IFN-γ), ELISPOT provides a functional readout of T cell activity with applications in both preclinical and clinical settings. This systematic review presents a structured qualitative synthesis of 78 studies investigating the use of ELISPOT in cancer immunotherapy, including cancer vaccines, oncolytic viruses, cellular therapies, immune checkpoint inhibitors, and biomarker development. Studies were selected following PRISMA guidelines from PubMed, Scopus, and Embase, focusing on both clinical and preclinical research with translational relevance. The evidence indicates that ELISPOT is widely used to validate tumor-associated antigens and neoantigens, monitor antigen-specific T cell responses during cancer immunotherapy, including immune checkpoint blockade, cancer vaccines, and adoptive cell therapies, and characterize antigen-specific T cell function. However, only a limited subset of studies establishes direct associations between ELISPOT responses and clinically meaningful outcomes. In addition, substantial variability in assay protocols and reporting criteria limits cross-study comparability and reproducibility. Overall, ELISPOT remains a valuable tool for immune monitoring in cancer research. Still, its implementation as a clinically validated biomarker requires further standardization, prospective validation, and integration with complementary analytical approaches.

Human cytomegalovirus (HCMV) usually establishes a lifelong latent infection after primary infection. Reactivation occurs sporadically and is controlled by cell-mediated immune response (CMIR). Monitoring of CMIR against CMV is mandatory in immunocompromised patients to adjust immunosuppressive drugs to prevent serious end-organ damage after CMV reactivation. Intracellular staining (ICS) and enzyme-linked immunospot (ELISPOT) quantifying CMV-specific T-cells are generally used as surrogate markers for CMIR against CMV. Whether the results of these 2 methods correlate well is not known. This study compared the numbers of CMV-specific T-cells identified by ELISPOT and ICS in healthy adult volunteers. Correlation with CMV serological status was explored. Thirty peripheral blood samples from healthy individuals were quantified for IFN-γ-producing cells after stimulation with whole CMV and IE1 using ICS, and IFN-γ-secreting cells after stimulation with whole CMV lysate and IE1 peptide pool using ICS and IFN-γ-secreting cells by ELISPOT. Anti-CMV IgG levels were analyzed concomitantly using a chemiluminescent microparticle immunoassay. There were 30 healthy participants, 15 (50%) male, with a mean age of 37.8 (± 7.6) years. Twenty-eight (93.3%) were seropositive against CMV. The CMV-specific CD3+ cells, as measured by ICS, were highly correlated with the spot numbers obtained by the ELISPOT, irrespective of CMV antigens used (whole CMV, r = 0.7677, p < 0.0001; IE1, r = 0.6516, p < 0.0001). The numbers of CMV-specific CD3+ cells quantified by IE1 stimulation by these 2 assays were statistically correlated with anti-CMV IgG levels (ICS, r = 0.5070, p = 0.004; ELISPOT, r = 0.4384, p = 0.015). Among the 30 participants, CMV-specific T cells were detected in all participants (100%), including the two seronegative individuals. The present study demonstrated that CMV-specific T-cells measured by ICS and ELISPOT assays were well correlated, suggesting that these assays could be used to monitor CMV-specific T-cells. CMV IgG levels may reflect prior CMV infection and CMV-specific cell-mediated immunity (CMIR) in immunocompetent individuals.

•An in vitro assay to detect de novo cross-primed CD8+ T-cell responses against HCV antigens.•10-day cocultures, allow rapid identification of functional HCV epitopes.•Identification of functional immunogenic and less immunogenic epitopes for cancer vaccines. For the rational design of epitope-specific vaccines, identifying epitopes that can be processed and presented is essential. As algorithm-based epitope prediction is frequently discordant with actually recognized CD8+ T-cell epitopes, we developed an in vitro CD8 T-cell priming protocol to enable the identification of truly and functionally expressed HLA class I epitopes. The assay was established and validated to identify epitopes presented by hepatitis C virus (HCV)-infected cells. In vitro priming of naïve CD8 T cells was achieved by culturing unfractionated PBMCs in the presence of a specific cocktail of growth factors and cytokines, and next exposing the cells to hepatic cells expressing the NS3 protein of HCV. After a 10-day co-culture, HCV-specific T-cell responses were identified based on IFN-γ ELISpot analysis. For this, the T cells were restimulated with long synthetic peptides (SLPs) spanning the whole NS3 protein sequence allowing the identification of HCV-specificity. We demonstrated that this protocol resulted in the in vitro priming of naïve precursors to antigen-experienced T-cells specific for 11 out of 98 SLPs tested. These 11 SLPs contain 12 different HLA-A*02:01-restricted epitopes, as predicted by a combination of three epitope prediction algorithms. Furthermore, we identified responses against 3 peptides that were not predicted to contain any immunogenic HLA class I epitopes, yet showed HCV-specific responses in vitro. Separation of CD8+ and CD8− T cells from PBMCs primed in vitro showed responses only upon restimulation with short peptides. We established an in vitro method that enables the identification of HLA class I epitopes resulting from cross-presented antigens and that can cross-prime T cells and allows the effective selection of functional immunogenic epitopes, but also less immunogenic ones, for the design of tailored therapeutic vaccines against persistent viral infections and tumor antigens.