The researchers prospectively enrolled children aged 6 months to 15 years who were admitted to the pediatric burn service at UF Health Shands Children’s Hospital between December 2023 and July 2025. The cohort included 14 children with small burns and nine with moderate burns. Seven healthy controls younger than 16 were undergoing elective pediatric surgery. The investigators collected blood from burn patients on hospital day 2, with a window of one day either side, and obtained later samples when clinically feasible. Control blood was collected in the operating room after induction of anesthesia and before surgery. Because sampling times were partly determined by each child’s clinical course, serial specimens were not available from every participant at every interval, and the number included in each immune assay varied.

Monocyte HLA-DR was measured by flow cytometry in circulating CD14-positive monocytes. The researchers converted median fluorescence intensity into the average number of anti-HLA-DR antibodies bound per cell, a measure reported as ABC. This analysis included seven controls, 11 small-burn patients and six moderate-burn patients. Median HLA-DR expression was significantly lower in the moderate-burn group than in healthy controls, while the small-burn group did not differ significantly from either comparison group after statistical correction for multiple comparisons. The estimated Hodges–Lehmann location shift between the moderate-burn and control groups was minus 22,939 ABC, with an exact 96.50% confidence interval from minus 33,104 to minus 12,039. Individual values varied considerably, including substantial overlap between the small-burn and moderate-burn groups.

The investigators also assessed whether burn injury altered circulating myeloid-derived suppressor cells, or MDSCs, a heterogeneous collection of immature myeloid cells described in the study as having immunosuppressive activity. Flow-cytometric phenotyping of peripheral blood mononuclear cells was performed approximately one week after injury in seven controls, six small-burn patients and six moderate-burn patients. Total MDSCs and three subsets—monocytic, polymorphonuclear and early MDSCs—showed considerable person-to-person variation. Some measures appeared numerically higher in the moderate-burn group, but neither total frequencies, subset frequencies nor absolute subset counts differed significantly among the three groups. Absolute total MDSC counts were numerically higher in moderate-burn patients, with a median of 253,685 compared with 161,336 in controls and 117,892 in the small-burn group, but the difference was not statistically significant.

Functional responsiveness was tested with a whole-blood TNF-α ELISpot assay. Diluted blood was incubated for 24 hours with or without LPS, and spots representing TNF-α-secreting cells were counted and characterized. The day-2 analysis included seven controls, seven small-burn patients and eight moderate-burn patients. LPS increased the number of spots, their size and total expression within every cohort, demonstrating that all three groups retained the capacity to respond to the stimulus. Among stimulated samples, however, the moderate-burn group produced the strongest responses. Stimulated spot-forming units, spot size and total expression were significantly higher than in controls, while total expression was also significantly higher than in the small-burn group. The small-burn cohort did not differ significantly from controls.

The magnitude of the acute functional differences was appreciable. The estimated shift in stimulated spot-forming units between moderate-burn patients and controls was 294, with an exact 95.99% confidence interval of 36 to 506. The corresponding shifts were 1.203 for stimulated spot size, with a confidence interval of 0.3966 to 2.521, and 2,503 for total expression, with a confidence interval of 974.7 to 3,686. Compared with small-burn patients, the estimated difference in total expression was 2,229, with a confidence interval of 403.2 to 3,473. These results indicate that the heightened response was specific to the moderate-burn group in this cohort rather than evidence of a general rise in every burned child.

Exploratory analyses suggested that immune measures might also differ among children with and without inpatient complications, defined in the study as graft loss, wound infection, gastrointestinal infection or bacteremia. Among burn patients with available data, those who experienced complications had larger burns: a median of 25% TBSA, compared with 11% among those without complications. Those with complications also had lower day-2 monocyte HLA-DR expression, with a median of 28,603 ABC versus 40,910 ABC. Whole-blood LPS-induced TNF-α responses did not differ significantly by complication status. These observations were exploratory, and burn size was greater in the complication group, making it difficult to separate the independent effects of severity, clinical interventions and immune markers.

Only three moderate-burn patients provided samples for a descriptive comparison at six to eight weeks after injury. Their later samples showed lower spot-forming units and total TNF-α expression than their acute day-2 samples, while spot size appeared similar. The small and incomplete dataset was not subjected to inferential testing and cannot establish how immune responsiveness changes during recovery. It nevertheless points toward a possible difference between acute and later responses. More broadly, the assays captured different immune domains: monocyte HLA-DR was a cell-specific phenotypic measurement, whereas whole-blood ELISpot responses reflected an integrated cytokine response from multiple blood-cell populations and did not identify the cellular source of TNF-α.

The study has important limitations. It was conducted at a single center with modest, assay-specific sample sizes, making it underpowered for modest differences and limiting generalizability. Nonsignificant results should not be interpreted as proof of equivalence. The cohort was predominantly male, no healthy control was African American, controls underwent diverse elective operations, and burn care—including surgery, transfusion, antibiotics, nutritional support and intensive care—varied with severity. The study was not designed to isolate those interventions’ effects. Burn depth was mixed, longitudinal sampling was incomplete, T-regulatory cells were not measured, and broader cytokine profiling and leukocyte functions such as phagocytosis, reactive oxygen species production and migration were not systematically assessed. All 30 participants were ultimately discharged in stable condition, and the research characterized early immune patterns rather than establishing that any marker predicts infection or other outcomes. Taken together, the results indicate that moderate pediatric burns were associated with concurrent phenotypic and functional innate immune alterations, rather than a uniformly weakened immune response.

Subject of Research: Early innate immune alterations in children with small and moderate burn injuries

Article Title: Moderate pediatric burn injury is associated with reduced monocyte HLA-DR expression and heightened whole-blood LPS-induced TNF-α responses

Article References: Wiggins, W. B., Rincon, J. C., Hernández-Ríos, M., Polcz, V., Rodhouse, C., Yoham, A. L., Richter, S., Cabral, A., Moldawer, L. L., Efron, P. A., Maile, R., & Larson, S. D. (2026). Moderate pediatric burn injury is associated with reduced monocyte HLA-DR expression and heightened whole-blood LPS-induced TNF-α responses. Frontiers in Pediatrics, 14, Article 1967322. https://doi.org/10.3389/fped.2026.1967322

Image Credits: AI Generated

DOI: 10.3389/fped.2026.1967322

Keywords: pediatric burns, innate immunity, monocyte HLA-DR, TNF-alpha, lipopolysaccharide, ELISpot, flow cytometry, myeloid-derived suppressor cells, immune dysregulation, Moderate, pediatric, burn

The research team, led by Frederica Dedo Partey of the Noguchi Memorial Institute for Medical Research at the University of Ghana, recruited healthy adults aged 18 to 60 from the Legon community in Accra who had completed a primary vaccination series at least six months earlier with one of four vaccines: AstraZeneca’s ChAdOx1-S, Moderna’s mRNA-1273, Pfizer-BioNTech’s BNT162b2, or Janssen’s Ad26.COV2.S. Blood was drawn at four time points — before the booster and at three, six, and nine months afterward — and peripheral blood mononuclear cells were isolated by density-gradient centrifugation, cryopreserved in liquid nitrogen, and later thawed for functional testing. A critical feature of the cohort is that every participant was nucleocapsid-seropositive at enrollment, indicating prior natural infection, and antibody levels remained stable throughout follow-up, confirming that no new infections occurred during the study. The findings therefore describe how boosters reshape cellular immunity on a background of hybrid immunity — the combination of vaccination and prior infection that most of the world’s population now carries.

Rather than testing crude pools of viral peptides, the researchers took a precision approach. They used NetMHCpan-4.1, a machine-learning tool trained on peptide binding and eluted-ligand data, to predict 10-mer peptides from the spike and nucleocapsid proteins that bind strongly to seven globally prevalent HLA class I supertypes: A01, A02, A03, A24, B07, B40, and B58. Because participants were not HLA-typed, selecting epitopes across these supertypes maximized population coverage and was particularly relevant for a West African cohort with extensive HLA diversity. The predicted epitopes were matched to pre-synthesized overlapping 15-mer peptides spanning the full spike protein (1,273 amino acids) and nucleocapsid protein (419 amino acids), based on the Wuhan reference strain. Each peptide was then tested individually in an ex vivo interferon-gamma ELISpot assay, with 200,000 peripheral blood mononuclear cells per well stimulated for 24 hours. This single-peptide design meant that every positive response could be assigned to a defined viral sequence — a level of resolution that proved essential to the study’s central discovery.

That discovery concerns what actually drives the decline of T-cell immunity over time. Across the whole cohort, time had a powerful effect on total spike-specific interferon-gamma responses, with an omnibus F-test yielding F(3, 96.6) = 33.16 and a p-value of 8 × 10⁻¹⁵. Yet the median per-peptide response — the strength of each individual epitope-specific reaction — did not change significantly over the same period (F(3, 95.8) = 0.62, p = 0.606). The dissociation is striking: the waning of T-cell immunity after boosting was not caused by individual T-cell responses growing weaker, but by the immune system progressively dropping entire epitope specificities from its repertoire. The same pattern held within both booster groups separately, and the residual response stabilized after month six, with no significant difference between months six and nine.

The two booster platforms produced measurably different immune profiles. Participants boosted with the adenoviral vector Ad26.COV2.S showed significantly broader spike-specific epitope recognition — 70 positive peptide responses at month three compared with 34 in the BNT162b2 group, a difference with a p-value of 4.4 × 10⁻⁵ — and a subset of their responses persisted through month nine. The BNT162b2 recipients, by contrast, mounted higher cumulative interferon-gamma magnitude through month six, an advantage that was already present before the booster was administered (p = 0.012), suggesting it reflected their prior vaccination history rather than the booster itself. By month nine the picture had reversed, with the adenoviral-vector group showing higher — though not statistically significant — interferon-gamma levels. The authors propose a biological explanation rooted in platform mechanics: mRNA is inherently transient and subject to interferon-driven degradation, limiting the duration of antigen presentation, whereas adenoviral vectors support more prolonged antigen expression that may recruit subdominant T-cell clones and sustain a wider memory repertoire.

Vaccination strategy — whether the primary series and booster used the same platform — also left its mark. Within the Ad26.COV2.S group, homologous boosting (viral vector followed by viral vector) was associated with significantly broader epitope recognition at months zero, three, and nine, and this subgroup contributed the highest proportion of persistent responses at months six and nine. Two participants, J028 and J171, recognized at least one spike epitope at every time point, with J171 alone accounting for eight of the ten positive responses recorded at month nine. In the BNT162b2 group, no homologously boosted participant showed sustained responses across all post-booster time points, and no significant differences emerged between homologous and heterologous subgroups — a null result the authors attribute partly to limited statistical power. Notably, the finding that homologous adenoviral boosting outperformed heterologous regimens in breadth runs counter to the common assumption that anti-vector immunity undermines repeat adenoviral dosing.

Mapping the responses onto the spike protein revealed a dynamic immunodominance hierarchy. At baseline, recognition clustered in the N-terminal domain and the fusion peptide region — structurally exposed domains previously shown to harbor conserved T-cell epitopes. After boosting, recognition shifted toward the receptor-binding domain and subdomains 1/2, with peptides such as KLPDDFTGCV (amino acids 421–435) and IHADQLTPTW (amino acids 621–635) among the most frequently recognized at month three. By month nine, only nine spike peptides remained immunoreactive: three each from the N-terminal domain and fusion peptide region, and one each from the receptor-binding domain, subdomain 1/2, and the buried heptad repeat 2. The persistence of N-terminal and fusion-derived epitopes underscores their structural stability, while the rare recognition of a heptad repeat 2 peptide — a region largely hidden in the prefusion spike — hints at unusual HLA binding or exposure to post-fusion conformations.

The nucleocapsid arm of the study offered a natural experiment in memory maintenance without antigen restimulation. Because all administered vaccines encode only the spike protein, any nucleocapsid-specific T-cell responses must have been acquired through prior infection. Despite stable anti-nucleocapsid antibodies and no incident infection, these responses declined from 57 positive peptide reactions at baseline to just three at month nine — evidence that spike-based boosting does nothing to sustain cellular memory against non-spike antigens. Yet two nucleocapsid regions, YGANKDGIIW (amino acids 121–135) and VTPSGTWLTY (amino acids 321–335), were recognized at every one of the four time points. Their repeated immunogenicity, combined with the nucleocapsid protein’s high sequence conservation across coronaviruses, makes them leading candidates for inclusion in multi-epitope T-cell vaccines.

The authors are candid about the study’s limitations. The timing and severity of participants’ pre-enrollment infections could not be established; the interval between primary vaccination and booster ranged from six to 24 months; HLA typing was not performed, so genotype-specific responses could not be assessed; and months six and nine testing was restricted to peptides positive at month three, meaning delayed or newly emerging responses would have been missed. The observed contraction in breadth should therefore be read as a narrowing among the month-three-positive epitopes rather than definitive proof of global epitope loss. Subgroup comparisons were also modestly powered. Even so, the study’s central message stands: the platform and strategy chosen for boosting shape not just how strong T-cell immunity is, but how wide and how long-lasting it remains. For next-generation vaccine design, the implication is clear — durable cellular protection may depend less on maximizing peak response magnitude than on preserving epitope breadth, and conserved targets in the spike N-terminal domain, the fusion peptide, and the nucleocapsid protein deserve priority in the vaccines meant to outpace viral evolution.

Subject of Research: Longitudinal durability and epitope breadth of SARS-CoV-2-specific T-cell responses after mRNA versus adenoviral-vector booster vaccination

Article Title: T-cell recognition of SARS-CoV-2 antigen peptides following booster vaccination with mRNA and viral-vectored COVID-19 vaccines

Article References: Maru, A. K., Kumi, P. K., Pobee, A. N. A., Appiah, N. Y. A., Koranteng, N. A. O., Brenko, T., Osei, F., Teye-Adjei, D., Agyekum, G., Akuffo, L., Dzabeng, F., Kyei-Baafour, E., Obiri-Yeboah, D., Aniweh, Y., Ofori, M. F., Kusi, K. A., & Partey, F. D. (2026). T-cell recognition of SARS-CoV-2 antigen peptides following booster vaccination with mRNA and viral-vectored COVID-19 vaccines. Frontiers in Cellular and Infection Microbiology, 16, Article 1947651. https://doi.org/10.3389/fcimb.2026.1947651

Image Credits: AI Generated

DOI: 10.3389/fcimb.2026.1947651

Keywords: SARS-CoV-2, T-cell immunity, booster vaccination, BNT162b2, Ad26.COV2.S, ELISpot, epitope breadth, hybrid immunity, nucleocapsid protein, spike protein, HLA class I, vaccine design

The study, led by Daniel Arroyo-Sánchez and Oscar Cabrera-Marante of the Immunology Department at Hospital Universitario 12 de Octubre and published in the Journal of Translational Medicine, set out to answer a deceptively simple question: what happens to the B cells of CVID patients when they are pushed to produce antibodies under controlled laboratory conditions? To find out, the researchers isolated peripheral blood mononuclear cells, the mixed population of immune cells circulating in the blood, from 20 patients with CVID and from healthy donors. These cells were then cultured in the laboratory with a carefully chosen cocktail of stimuli: interleukin-2, a cytokine that supports lymphocyte survival and proliferation, and R848, a synthetic compound that activates Toll-like receptors, the molecular sensors that normally alert B cells to microbial invasion and drive them toward antibody-secreting states.

The choice of stimulation is scientifically significant. Toll-like receptor signaling has become an increasingly important focus in immunodeficiency research because it mimics a key pathway used during natural infection and, notably, during vaccination. Recent clinical observations had shown that some CVID patients mount partial responses to mRNA vaccines, hinting that a residue of functional capacity might survive within their B-cell compartment. By combining IL-2 with R848, the team created conditions designed to coax out whatever antibody-producing potential the patients’ cells still possessed, and then to measure precisely how far that potential could carry them.

The results, tracked over a ten-day culture period, revealed a striking temporal pattern. In cultures from healthy controls, antibodies remained readily detectable in the culture supernatants throughout the observation window, a sign that the cells had successfully differentiated into antibody-secreting cells and sustained their output. In cultures from CVID patients, by contrast, the ability to sustain antibody production collapsed. By day 10, the patients’ cultures had failed to maintain antibody secretion, and the cellular composition of those cultures told its own story: a predominance of IgD-CD27- B cells, a subset that lacks the classical markers of activated memory cells and is generally associated with a less mature, less responsive state.

Crucially, the defect was not a simple absence of responsive cells. On day 6 of culture, the proportion of memory B cells in the patients’ cultures was comparable to that seen in healthy controls. This timing matters enormously for interpretation. It suggests that CVID B cells can initially be pushed toward a memory-like phenotype when stimulated through Toll-like receptors in the presence of IL-2, but that this apparent activation cannot be consolidated into durable antibody output. The failure, in other words, appears to lie in the later stages of the differentiation program, in the transition from an activated, memory-like state to a fully functional antibody-secreting plasma cell, rather than in the earliest steps of B-cell activation.

To probe the molecular roots of that failure, the researchers turned to transcriptomic analysis, sequencing the gene expression profiles of the cultured cells. The comparison between patients and healthy controls uncovered a coherent pattern of dysregulation. Genes related to antibody production were expressed at lower levels in the patients’ cells, consistent with the observed collapse in antibody secretion. Genes involved in adhesion and in proinflammatory signaling were also downregulated, pointing to a broader failure of the activated B cell to adopt the full behavioral repertoire of a responding immune cell, including the physical interactions with other immune cells that normally support germinal-center-like reactions in the culture dish.

Perhaps most intriguingly, the patients’ cells showed increased expression of genes associated with immune inhibitory responses. This shift toward an inhibitory program provides a mechanistic explanation for the paradox that has long defined CVID: B cells that are present, sometimes numerous, and capable of at least partial activation, yet chronically unable to deliver protective antibodies. If the cells are actively ramping up inhibitory pathways in response to stimulation, then the defect may not be a passive inability to respond but an active regulatory brake, one that engages precisely when the cells should be committing to antibody production.

The analysis of soluble factors in the culture supernatants reinforced this picture. Compared with healthy controls, the patients’ cultures contained lower concentrations of APRIL, a cytokine that plays a well-established role in supporting B-cell survival and the differentiation of antibody-secreting cells, and lower levels of interferon-alpha, an antiviral cytokine with important immunoregulatory functions. At the same time, the patients’ supernatants showed higher concentrations of BTLA, an inhibitory receptor of the CD28 family that delivers dampening signals to lymphocytes. The combination is telling: the patients’ cultures were simultaneously deprived of positive differentiation signals and enriched for inhibitory ones, a molecular environment stacked against sustained antibody output.

Taken together, the study’s findings sketch a coherent model of B-cell dysfunction in CVID. When stimulated through Toll-like receptors, the cells of these patients can begin the journey toward activation and memory differentiation, but they cannot sustain it. Their gene expression programs drift away from antibody production, adhesion, and inflammation and toward immune inhibition, while their soluble environment loses the supportive cytokines that healthy cultures provide. The researchers suggest that these insights into functional impairment after Toll-like receptor stimulation may be directly relevant to the B-cell dysfunction observed in patients with CVID, and they may help explain why some patients show only partial responses to vaccines that depend heavily on this signaling pathway.

The work also carries practical implications for the future. An in vitro assay that reliably distinguishes the functional profile of CVID B cells from healthy ones could, with further validation, help stratify patients, identify those with residual responsiveness, and guide more individualized approaches to immunoglobulin replacement and vaccination strategies. The study was approved by the Institutional Ethics Committee of Hospital Universitario 12 de Octubre and conducted with written informed consent from all participants, whose willingness to donate blood samples the authors explicitly acknowledged. Funded through Spanish COVID-19 research projects and supported by the genomic analysis group of the Spanish National Cancer Research Centre, the research exemplifies how translational immunology can turn a bedside mystery, why vaccinated patients remain vulnerable, into a bench-side mechanism, one inhibitory signal at a time.

Subject of Research: B-cell functional impairment in common variable immunodeficiency assessed by in vitro Toll-like receptor stimulation

Article Title: Common variable immunodeficiency: B cells' impairment in an in vitro assay

Article References: Arroyo-Sánchez, D., Chivite-Lacaba, M., González-Cuadrado, C., Almendro-Vázquez, P., Bermejo Olivera, F. J., Andara-Cordero, L. A., Garcinuño, S., Velasco-Sidro, M., Nieto-López, C., Alfocea Molina, Á., Cantonad Ruigómez, C., Pascual Palacios, L., Pleguezuelo-Garrote, D. E., Paz-Artal, E., & Cabrera-Marante, O. (2026). Common variable immunodeficiency: B cells' impairment in an in vitro assay. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08821-8

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08821-8

Keywords: common variable immunodeficiency, B cells, antibody production, Toll-like receptor, R848, interleukin-2, transcriptomics, ELISPOT, flow cytometry, APRIL, BTLA, primary immunodeficiency

T cells sit at the heart of adaptive immunity. Each one carries a T cell receptor generated by random recombination of gene segments, producing a repertoire of staggering diversity that can, in principle, recognize virtually any peptide fragment displayed on major histocompatibility complex molecules. When a T cell encounters its cognate peptide-MHC complex presented by an infected or malignant cell, it becomes activated, proliferates and executes effector functions such as cytokine secretion or direct killing. Because antigen-specific T cells typically exist at very low frequencies in peripheral blood, and because they are enormously heterogeneous in phenotype, function and receptor sequence, quantifying them accurately has challenged immunologists for decades. The new review emphasizes that no single assay can capture the full picture, and that the choice of method fundamentally shapes what a study can and cannot conclude.

The oldest approaches in the field rely on functional readouts of bulk cell populations. Lymphocyte proliferation assays, dating back to the 1970s, measure how many T cells divide in response to antigen stimulation, originally using radioactive tritiated thymidine incorporation and later shifting to fluorescent dyes such as CFSE that allow division tracking by flow cytometry. Cytotoxicity assays, most famously the chromium-51 release assay introduced in 1968, quantify the killing of labeled target cells. These methods remain informative for assessing whether a T cell population can proliferate or kill, but they provide little information about which cells are responsible, what phenotype they carry, or how they relate to protective immunity. The review notes that dye-based proliferation assays and their radioactive predecessors can differ in sensitivity for low-frequency responses, and that modern modifications preserve cell viability while enabling spectral flow cytometry analysis.

The enzyme-linked immunospot, or ELISPOT, assay transformed the field by allowing direct enumeration of individual antigen-reactive cells. Developed originally in 1983 to count antibody-secreting cells and adapted for T cell cytokines, ELISPOT detects the footprints of secreted molecules such as interferon-gamma on a membrane, with each spot corresponding to a single responding cell. Its sensitivity, relative simplicity and suitability for large clinical trials made it a workhorse of vaccine immunology, from hepatitis B studies in the 1990s through the massive COVID-19 vaccine programs, where it helped document T cell responses to BNT162b1 and booster regimens. The review highlights that decades of proficiency panels run by the Cancer Vaccine Consortium and harmonization guidelines for automated spot evaluation have made ELISPOT one of the most standardized functional assays available. Its extension, FluoroSpot, permits simultaneous detection of multiple cytokines, revealing polyfunctional response profiles that correlate more closely with protective immunity than single-cytokine counts.

Flow cytometry brought a decisive leap in information content. Intracellular cytokine staining, enabled by protein transport inhibitors such as brefeldin A, allows researchers to identify which T cells produce which cytokines while simultaneously measuring dozens of surface markers. The review traces the maturation of this approach from early two-color experiments through validated eight-color assays optimized for vaccine trials, up to contemporary spectral flow cytometry panels that approach fifty parameters. Alongside cytokine readouts, activation-induced marker assays exploit the upregulation of surface molecules such as CD154, CD137, OX40, CD25 and CD69 after antigen encounter. Because these markers appear without requiring intracellular fixation, they allow viable sorting of antigen-specific cells for downstream expansion or sequencing. The review notes that AIM assays have proven particularly valuable for detecting rare CD4 T cell responses, including those to SARS-CoV-2, that conventional cytokine assays miss, and that recent automated workflows have improved their reproducibility across laboratories.

Perhaps the most direct way to identify an antigen-specific T cell is to bind it with a soluble mimic of its ligand. Peptide-MHC multimers, introduced with tetramers in 1996, achieve this by clustering fluorescently labeled peptide-MHC complexes so that the low-affinity T cell receptor interaction becomes stable enough for detection. The review documents the steady engineering of these reagents: reversible multimers that can be stripped from cells after staining, conditional MHC ligands that allow on-demand peptide loading, dodecamers with enhanced avidity, affinity-matured class II reagents for robust CD4 staining, and combinatorial encoding schemes that pool dozens of differently labeled multimers in a single tube. DNA-barcoded multimers push the concept further, enabling screening of hundreds of specificities simultaneously by sequencing rather than fluorescence. Applied to COVID-19, malaria, celiac disease and cancer neoantigens, multimer staining provides phenotypic depth that functional assays cannot match, though it requires knowledge of the epitope and the restricting HLA allele.

High-throughput sequencing of T cell receptors has opened an entirely orthogonal window on antigen-specific immunity. Rather than interrogating function or ligand binding, repertoire sequencing catalogs the receptor sequences themselves, revealing clonal expansions, shared public clonotypes and convergent responses across individuals. The review discusses the technical challenges that once limited this approach, including biases among sequencing platforms and the difficulty of pairing alpha and beta chains, and describes solutions ranging from unique molecular identifiers to single-cell methods that link receptor sequence with transcriptome. Computational tools such as GLIPH2 and tcrdist3 cluster receptors by sequence similarity to predict shared specificity, enabling antigen discovery from repertoire data alone. The authors emphasize that sequencing reveals which clones expanded but not what they do, making it most powerful when combined with functional or phenotypic assays on the same cells.

Single-cell multiomics now fuses these dimensions. Methods that pair TCR sequencing with single-cell RNA profiling allow researchers to perform reverse phenotyping, inferring antigen specificity from receptor sequence while simultaneously reading out the transcriptional state of each cell. The review cites applications ranging from identifying SARS-CoV-2-reactive T cell signatures to distinguishing tumor-reactive from bystander clonotypes in pancreatic cancer and brain metastases. Spatial technologies extend the analysis into tissue, with imaging mass cytometry, multiplex immunohistochemistry and spatially resolved TCR sequencing mapping where specific clonotypes reside within tumors and lymphoid structures. These approaches matter because blood-based monitoring may not reflect what happens at the site of disease, and because the spatial organization of immune cells increasingly predicts immunotherapy response, as demonstrated by the clinically validated Immunoscore in colon cancer.

Underlying all of these technologies is a set of preanalytical variables that the review treats with unusual rigor. How blood is drawn, how peripheral blood mononuclear cells are isolated, how samples are cryopreserved and thawed, which culture medium and serum are used, and how long samples sit before stimulation can each swing assay results dramatically. Validation studies have shown that optimized PBMC processing enhances detected response rates in HIV vaccine trials, that serum-free media support consistent ELISPOT performance, and that suboptimal freezing conditions can render samples unusable. The authors argue that careful sample handling is not a technical footnote but a determinant of whether an immunomonitoring program generates trustworthy data, and they call for cell fitness criteria and standardized operating procedures to be adopted broadly.

The review’s central message is one of complementarity rather than competition. Functional assays such as ELISPOT and intracellular cytokine staining answer whether T cells respond and what they secrete; activation-induced marker assays capture viable responding cells across the full repertoire; multimer staining delivers phenotype and frequency with single-epitope resolution; and sequencing connects specificity with clonal architecture and transcriptomic state. Harmonization efforts, from the MIATA reporting guidelines to international proficiency panels for ELISPOT, ICS and multimer assays, have progressively made results comparable across laboratories, a prerequisite for using immune biomarkers as endpoints in clinical trials. As personalized neoantigen vaccines, TCR-engineered cell therapies and mRNA platforms multiply, the authors conclude that thoughtful, multi-assay immunomonitoring, built on standardized sample handling and validated protocols, will remain the foundation for understanding and improving T cell-mediated immunity in the clinic.

Subject of Research: Comparative analysis of traditional and novel laboratory methods for quantifying and characterizing human antigen-specific T cells in immunomonitoring

Article Title: T cell immunomonitoring: a comparative analysis of traditional and novel methods to quantify and characterize human antigen-specific T cells

Article References: Lazzaro, S., Leroux-Roels, G., Janetzki, S., Salaun, B., Cook, L., Franke, K., Poschke, I., Bunse, L., Welters, M. J. P., Fehlings, M., Pattyn, S., Waerlop, G., Brix, L., Tubo, N. J., Molldrem, J. J., Denninger, V., van Esch, W. J. E., Kristensen, N. P., Mahnke, Y. D., … Koch, S. D. (2026). T cell immunomonitoring: a comparative analysis of traditional and novel methods to quantify and characterize human antigen-specific T cells. Nature Protocols. https://doi.org/10.1038/s41596-026-01453-8

Image Credits: AI Generated

DOI: 10.1038/s41596-026-01453-8

Keywords: T cells, immunomonitoring, ELISPOT, flow cytometry, peptide-MHC multimers, T cell receptor sequencing, single-cell multiomics, vaccines, cancer immunotherapy, assay harmonization, cytokines, antigen specificity