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The prevalence of AIDS and mortality rates among HIV-infected individuals in Guangxi remain relatively high, potentially due to impaired CD4 + cell recovery. This study aims to identify factors hindering CD4 + cell recovery in people living with HIV. We conducted a retrospective study on people living with HIV in Guangxi, China, with data collection extending to the end of 2023. CD4 + T cells were categorized into "immunological responders" and "non-responders" based on CD4 + cell recovery after treatment. Multivariate logistic regression was used to analyze factors associated with the development of immunological non-responders. Recovery of CD4 + T lymphocytes was assessed using the Generalized Additive Mixed Model (GAMM) and Generalized Estimating Equations (GEE). Additionally, multivariate Cox regression identified factors influencing survival rates. Our findings indicated a 52.44% incidence of immunological non-responders after two years of treatment. Factors such as age, sex, education, occupation, infection route, pre-treatment CD4 + T cell count, HIV subtype, and treatment regimen were linked to immunological non-response. Specifically, male gender, education up to high school, farming occupation, heterosexual transmission, CRF01_AE subtype, pre-treatment CD4 + T cell count < 200/µL, and the 3TC + EFV + TDF regimen were identified as significant risk factors. Statistically significant differences in CD4 + T lymphocyte recovery rates were observed among different HIV subtypes (P < 0.05). Beyond age, sex, ethnicity, occupation, subtype, and treatment regimen, being an immunological non-responder was found to be a risk factor for both mortality and accelerated disease progression. The study highlights the complexity of factors affecting CD4 + cell recovery post-HIV treatment in Guangxi and underscores the need for vigilant clinical monitoring of people living with HIV, particularly those with low pre-treatment CD4 + T cell levels. [ABSTRACT FROM AUTHOR]

Anti‐CD19 Chimeric Antigen Receptor (CAR)‐T cell therapies have shown promise for treating B cell malignancies, but the clinical outcome is influenced by both the CAR‐T product and the patient's immune system. The role of γδ T cells in the context of CAR‐T cell therapy remains poorly understood. This study investigates the transcriptional heterogeneity, clonal expansion and dynamics of γδ T cells in patients undergoing anti‐CD19 CAR‐T cell therapy. Longitudinal single cell multi‐omics analysis was performed on γδ T cells from four patients receiving anti‐CD19 CAR‐T cell therapy. Single cell RNA‐seq, antibody‐based protein profiling (AbSeq) and full‐length TCRγδ sequences revealed clonally expanded populations displaying plasticity in T cell differentiation, and temporal dynamics of large clones, suggesting ongoing expansion and differentiation. Clonally expanded γδ T cells had heterogeneous gene expression profiles, occupying seven transcriptionally distinct clusters. Analysis of chemokine markers indicated cluster‐specific homing tendencies of circulating γδ T cells to peripheral tissues. We found unexpectedly high frequencies of Vδ1 and Vδ3 cells in the blood with distinct gene and protein expression profiles. This analysis provides insights into the dynamic and heterogeneous nature of γδ T cells following anti‐CD19 CAR‐T cell therapy, contributing valuable information for optimizing CAR‐T cell therapies in B cell malignancies. [ABSTRACT FROM AUTHOR]

Allogeneic hematopoietic stem cell transplantation (allo‐HSCT) is a widely used treatment for a variety of hematopoietic disorders, and also provides a valuable platform for investigating the development of donor‐derived immune cells in recipients post‐HSCT. The immune system remodels from the donor to the recipient during allo‐HSCT. However, little is known about the cell profile alterations as donor homeostasis rebalances to recipient homeostasis following HSCT. Here, multi‐omics technology is applied at both the single cell and bulk sample levels, as well as spectrum flow cytometry and fluorescent transgenic mouse models, to dissect the dynamics of the rebalanced homeostatic immune system in recipients after allo‐HSCT. The data reveal that all immune subpopulations observed in donors are successfully restored in recipients, though with varying levels of abundance. The remodeling of immune homeostasis exhibits different patterns in HLA‐matched and haploidentical HSCT, highlighting distinct biases in T cell reconstitution from the central and peripheral pathways. Furthermore, ZNF683 is critical for maintaining the persistence and quiescence of CD8 T‐cell in haploidentical HSCT. The research can serve as a foundation for developing novel strategies to induce immune tolerance. [ABSTRACT FROM AUTHOR]

Background: Progressive multifocal leukoencephalopathy (PML) is an often fatal disease of the central nervous system caused by opportunistic infection of John Cunningham Polyomavirus (JCV). There's still no antiviral therapeutic strategy which was generally recognized as effective. The prognosis may differ in patients with different pathological mechanisms and treatments. We aim to report the effectiveness of combined treatment of low-dose, long-term immunoglobulin and mirtazapine in a pathologically proved PML case. Case presentation: A patient presented with progressive acalculia, right-left confusion and visual neglection was recorded. She received 10-year immunosuppressive therapy for dermatomyositis. White matter lesions located in bilateral parietal lobe and callosum area symmetrically in MR scanning. JC virus analysis and brain biopsy in left parietal lobe were performed. The number of JCV copies was 2595 in CSF and 282,809 in brain specimen. Abundant foamy macrophages and the lymphatic cells were obvious in immunohistochemistry staining. Few SV-40 positive JC infected cell and more CD4 + and CD68 + cells were predominant. Immunosuppressive drugs were terminated after being diagnosed as PML for positive JCV and pathological characteristics. In addition, immunoglobulin (5 g/day) and mirtazapine (45 mg/day) were used. JC virus in CSF decreased to 0 after treatment for 4 months and was still negative in June 2023. The clinical symptoms improved, and white matter lesions recovered significantly. Conclusions: We demonstrated that the combination treatment of IVIG and mirtazapine was effective in PML. Low-dose, long-term immunoglobulin might regulate the immune status in our case with controlled inflammatory reaction instead of destructive virus spreading. The therapy may be a prospective option for PML. [ABSTRACT FROM AUTHOR]

Introduction: Immune reconstitution (IR) kinetics of paediatric patients underwent haploidentical haematopoietic stem cell transplantation (HSCT) with post‐transplant cyclophosphamide (PTCy) have not been extensively studied. We compared IR patterns of children receiving HSCT from haploidentical (n = 92) and HLA‐matched donors (n = 36), and analysed risk factors for viral infection in these patients. Methods: We prospectively measured lymphocyte subset numbers before HSCT and at 1, 3, 6 and 12 months after HSCT. Blood cytomegalovirus (CMV), Epstein–Barr virus, adenovirus, BK virus (BKV) and urine adenovirus and BKV viral loads were measured at designated time points. Results: The median numbers of total T and T helper cells at 1 month were significantly lower in the haploidentical group compared with the HLA‐matched group. Haploidentical HSCT recipients had significantly lower median numbers of several T cell subsets and B cells for 1 year after HSCT. The median NK cell count of the haploidentical group was lower at 1 month. BKV haemorrhagic cystitis, blood CMV and urine adenovirus reactivation were more frequently found in the haploidentical group. Post‐haploidentical HSCT patients receiving anti‐T lymphocyte globulin (ATG) had significantly lower median numbers of total T cells (at 1 month) and T helper cells (at 6 and 12 months) and higher rate of blood BKV reactivation compared with those without ATG. Conclusion: Paediatric patients who undergo haploidentical HSCT with PTCy are likely to have delayed IR and an increased risk of viral reactivation/infection compared with HLA‐matched HSCT. The addition of ATG to PTCy delayed T cell recovery and increased risk of BKV reactivation. [ABSTRACT FROM AUTHOR]

Background People with HIV-1 (PWH) age differently than the general population. Blood telomere length (BTL) attrition is a surrogate biomarker of immunosenescence and aging in PWH. BTL is reduced immediately after HIV-1 infection and recovers in PWH with long-term virologic suppression, but the extent of this recovery is unknown. Methods This prospective 6-year observational study assessed the evolution of BTL in PWH who were virologically suppressed. A cross-sectional analysis additionally compared BTL with age- and sex-matched blood donors and sex-matched persons older than 60 years from a general population cohort. DNA from whole blood was isolated, and relative BTL was determined by monochrome quantitative multiplex polymerase chain reaction assay and expressed as the ratio of telomere to single-copy gene (T/S). Results A total of 128 PWH were included in the prospective 6-year observational study. These same 128 PWH (median age, 55 years; 27.3% women) were compared cross-sectionally at 6-year follow-up with 128 age- and gender-matched blood donors (median age, 55 years) and 128 gender-matched individuals older than 60 years from a general population cohort (median age, 70 years). An inverse correlation between age and BTL was observed. The median BTL of PWH was shorter than their matched blood donors (T/S, 1.07 [IQR, 0.95–1.17] vs 1.28 [IQR, 1.12–1.48]; P <.001) but longer than the elderly population (T/S, 0.89 [IQR, 0.77–0.98], P <.001). PWH experienced a BTL increase at 6 years of 2.9% (T/S, 1.04 vs 1.07; P =.002). In PWH, age was associated with a shorter BTL (coefficient, −0.007 45, SE = 0.002 04, P =.002) and baseline lower CD4 count with a gain in BTL (coefficient, −0.000 06, SE = 0.000 02, P =.004). Shorter baseline BTL (odds ratio, 0.91 [95% CI,.87–.94]; P <.001) and higher glucose levels (odds ratio, 1.04 [95% CI, 1.02–1.07]; P =.003) were associated with a greater similarity of BTL to the elderly population. Conclusions PWH with long-term virologic suppression experience a trend toward an increased BTL after 6 years of follow-up. Middle-aged people with long-term controlled HIV-1 have a shorter BTL than expected for their chronologic age but longer than that of people 15 years older in the general population. [ABSTRACT FROM AUTHOR]

A boy with primary immunodeficiency, caused by a tyrosine kinase 2 (TYK2) mutation, presented with immune defects and a lifelong history of severe infections. Our aim was to determine whether allogeneic hematopoietic stem cell transplantation (HSCT) could restore the patient’s immune defenses and reduce susceptibility to infection. In the absence of a suitable HLA-matched blood relative to act as a donor, the patient received an allogeneic HSCT from unrelated donors. The patient’s clinical data were analyzed in the Children’s Hospital of Chongqing Medical University (Chongqing, China) before transplantation and during the 4-year follow-up period using a combination of western blotting (e.g., TYK2 and STAT levels), qRT-PCR (e.g., T cell receptor rearrangement excision circles, kappa deletion element recombination circles, and TYK2 transcript levels), and flow cytometry (e.g., lymphocyte subpopulations and CD107α secretion). We found that HSCT significantly reduced the incidence of severe infections, restored normal TKY2 levels, and reversed defects such as impaired JAK/STAT signaling in response to interferon-α or interleukin-10 treatment. Although the patient did not develop acute graft-versus-host disease (GVHD) after transplantation, he did experience chronic GVHD symptoms in a number of organs, which were effectively managed. Our findings suggest that HSCT is a feasible strategy for reconstituting the immune system in TYK2-deficient patients; however, the factors associated with GVHD and autoimmune thyroiditis development in TYK2-deficient patients undergoing HSCT warrant further investigation. [ABSTRACT FROM AUTHOR]

Background: People living with HIV are disproportionately represented among people with severe mpox. Mild and self‐limiting conjunctival involvement has been well‐documented, and severe ocular complications, including keratitis, corneal scarring, and the associated loss of vision, are increasingly recognized. Tecovirimat is the first‐line antiviral therapy for severe mpox, but data around the efficacy of systemic antiviral agents for mpox are limited, particularly in cases of ocular mpox. Case Report: Here, we describe a case of sight‐threatening necrotic blepharokeratoconjunctivitis in a person with advanced HIV, requiring an extended course of tecovirimat due to persistent mpox viral shedding for nearly 5 months. [ABSTRACT FROM AUTHOR]

Severe combined immunodeficiency (SCID) encompasses rare primary immunodeficiency disorders characterized by deficient T-cell development, which leads to a severely compromised immune system and susceptibility to life-threatening infections. Among SCID subtypes, IL7RA-SCID is caused by mutations in the interleukin 7 receptor alpha chain (IL7RA) and represents a significant subset of patients with limited treatment options. This study investigated the efficacy of a self-inactivating (SIN) alpharetroviral vector (ARV) engineered to deliver a codon-optimized IL7RA cDNA to restore T-cell development in Il7r-knockout mice. We compared the elongation factor 1 alpha short (EFS) promoter and the lymphoid-restricted Lck promoter for their ability to drive IL7RA expression and found that the EFS promoter enabled robust and sustained IL7RA expression that led to the functional rescue of T-lymphopoiesis in vitro and in vivo. Conversely, though effective in vitro, the Lck promoter failed to produce viable T-cell populations in vivo. Our results highlight the potential of using SIN-ARVs as a gene therapy (GT) strategy for treating IL7RA-SCID. Importantly, sustained production of T-lymphocytes was found in both primary and secondary transplant recipient animals with no adverse effects, supporting the safety and feasibility of this approach. Overall, this study provides valuable insights into the development of GT for IL7RA-SCID and underscores the clinical potential of an EFS-driven SIN-ARV to restore IL7RA-deficient immune function. [ABSTRACT FROM AUTHOR]

Abstract The prevalence of AIDS and mortality rates among HIV-infected individuals in Guangxi remain relatively high, potentially due to impaired CD4 + cell recovery. This study aims to identify factors hindering CD4 + cell recovery in people living with HIV. We conducted a retrospective study on people living with HIV in Guangxi, China, with data collection extending to the end of 2023. CD4 + T cells were categorized into “immunological responders” and “non-responders” based on CD4 + cell recovery after treatment. Multivariate logistic regression was used to analyze factors associated with the development of immunological non-responders. Recovery of CD4 + T lymphocytes was assessed using the Generalized Additive Mixed Model (GAMM) and Generalized Estimating Equations (GEE). Additionally, multivariate Cox regression identified factors influencing survival rates. Our findings indicated a 52.44% incidence of immunological non-responders after two years of treatment. Factors such as age, sex, education, occupation, infection route, pre-treatment CD4 + T cell count, HIV subtype, and treatment regimen were linked to immunological non-response. Specifically, male gender, education up to high school, farming occupation, heterosexual transmission, CRF01_AE subtype, pre-treatment CD4 + T cell count

Abstract Torque teno virus (TTV) viral load (VL), a component of the human virome, increases during immune suppression or dysregulation. This study aimed to explore TTV VL in youths living with vertically acquired HIV (YWVH) and its potential as an immunovirological marker. We performed an observational, retrospective study involving YWVH under antiretroviral treatment (ART) from the Spanish Cohort of HIV-infected children, adolescents, and vertically HIV-infected patients transferred to Adult Units (CoRISpe-FARO), compared to HIV-negative healthy donors (HD). Plasma TTV VL was assessed by qPCR. T-cell phenotype was analysed on cryopreserved peripheral blood mononuclear cells by flow cytometry. Correlations with baseline CD4 and CD8 and long-term virological evolution were examined. A total of 57 YWVH were compared with 23 HD. YWVH had a median CD4 T-cells of 736 cells/mm3 [IQR: 574–906], a median of 17 years [IQR: 14–20.5] since ART initiation, and 65 months [IQR: 39–116] under HIV-RNA virological control. TTV VL was higher among YWVH and in males compared with females (p

Abstract Background Progressive multifocal leukoencephalopathy (PML) is an often fatal disease of the central nervous system caused by opportunistic infection of John Cunningham Polyomavirus (JCV). There’s still no antiviral therapeutic strategy which was generally recognized as effective. The prognosis may differ in patients with different pathological mechanisms and treatments. We aim to report the effectiveness of combined treatment of low-dose, long-term immunoglobulin and mirtazapine in a pathologically proved PML case. Case presentation A patient presented with progressive acalculia, right-left confusion and visual neglection was recorded. She received 10-year immunosuppressive therapy for dermatomyositis. White matter lesions located in bilateral parietal lobe and callosum area symmetrically in MR scanning. JC virus analysis and brain biopsy in left parietal lobe were performed. The number of JCV copies was 2595 in CSF and 282,809 in brain specimen. Abundant foamy macrophages and the lymphatic cells were obvious in immunohistochemistry staining. Few SV-40 positive JC infected cell and more CD4 + and CD68 + cells were predominant. Immunosuppressive drugs were terminated after being diagnosed as PML for positive JCV and pathological characteristics. In addition, immunoglobulin (5 g/day) and mirtazapine (45 mg/day) were used. JC virus in CSF decreased to 0 after treatment for 4 months and was still negative in June 2023. The clinical symptoms improved, and white matter lesions recovered significantly. Conclusions We demonstrated that the combination treatment of IVIG and mirtazapine was effective in PML. Low-dose, long-term immunoglobulin might regulate the immune status in our case with controlled inflammatory reaction instead of destructive virus spreading. The therapy may be a prospective option for PML.

We evaluated immune cell subsets in patients with chronic lymphocytic leukemia (CLL) who received first-line therapy with 3 cycles of ibrutinib then 13 cycles of ibrutinib plus venetoclax in the minimal residual disease (MRD) cohort of the CAPTIVATE study (NCT02910583). Patients with Confirmed undetectable MRD (uMRD) were randomly assigned to placebo or ibrutinib groups; patients without Confirmed uMRD were randomly assigned to ibrutinib or ibrutinib plus venetoclax groups. We compared immune cell subsets in samples collected at 7 time points with age-matched healthy donors. CLL cells decreased within 3 cycles after venetoclax initiation; from cycle 16 onward, levels were similar to healthy donor levels (HDL; ≤0.8 cells per μL) in patients with Confirmed uMRD and slightly above HDL in patients without Confirmed uMRD. By 4 months after cycle 16, normal B cells had recovered to HDL in patients randomly assigned to placebo. Regardless of randomized treatment, abnormal counts of T cells, classical monocytes, and conventional dendritic cells recovered to HDL within 6 months (median change from baseline -49%, +101%, and +91%, respectively); plasmacytoid dendritic cells recovered by cycle 20 (+598%). Infections generally decreased over time regardless of randomized treatment and were numerically lowest in patients randomly assigned to placebo within 12 months after cycle 16. Sustained elimination of CLL cells and recovery of normal B cells were confirmed in samples from patients treated with fixed-duration ibrutinib plus venetoclax in the GLOW study (NCT03462719). These results demonstrate promising evidence of restoration of normal blood immune composition with ibrutinib plus venetoclax.

Abstract Objectives The aim of this retrospective study was to investigate the influence of chemotherapy on the immune status of individual patients diagnosed with acute lymphoblastic leukemia (ALL) and to elucidate the clinical characteristics of immune reconstitution in ALL patients following chemotherapy. Methods Clinical data of children with ALL were gathered, including information on the number of lymphocyte subsets prior to chemotherapy, at the end of therapy, six months, and one year after the end of the treatment. Results A total of 146 children with ALL were included, and T cells, B cells, and NK cells all decreased to various degrees prior to treatment. The abnormal CD3 + T cell numbers group experienced a considerably higher mortality (21.9% vs. 6.1%) and recurrence rate (31.3% vs. 11.4%) compared to the normal group (P

Introduction: The use of integrase inhibitors within highly active antiretroviral therapy (HAART) has demonstrated benefits for individuals living with HIV. However, most comparisons are based on effectiveness against viral replication, with limited information on their impact on the immune system. Objective: To identify immunological outcomes in studies comparing in- tegrase inhibitors (INSTIs) with other drugs used as third agents in HAART. Methods: Systematic review of studies reporting patients treated with INS- TIs versus non-nucleoside reverse transcriptase inhibitors (NNRTIs) or pro-tease inhibitors (PIs) as the third drug in HAART. Immunological reconstitution outcomes were assessed, including CD4+ T lymphocyte count, CD4/ CD8 ratio, serum concentration of sCD14, D-dimer, and C-reactive protein, as well as the frequency and phenotype of T cells, functional capacity of T cells, and proviral DNA. Results: A total of 2804 studies were screened, 59 were evaluated in full text and four were included in the synthesis. A cohort study reported normalization of the CD4/CD8 ratio in patients initiating treatment with INSTIs compared to PIs or NNRTIs. However, this finding was not consistently replicated in other studies, and in one of them, this ratio was higher in those receiving efavirenz vs. dolutegravir. No evidence was found for other outcomes. Conclusions: The analyzed studies are inconclusive regarding differences in immunological reconstitution between INSTIs vs. PIs and NNRTIs.

Cladribine is a tablet preparation for the treatment of relapsing-remitting multiple sclerosis (RRMS), which is used as an immune reconstitution therapy. A population-based cohort study was conducted in 54 patients with RRMS who received cladribine tablets.Objective: to evaluate our own experience of treating patients with highly active MS (HAMS) with cladribine tablets in real-life clinical practice in the MS Centre of the Khanty-Mansi Autonomous Area (KhMAA) — Yugra.Material and methods. The data source is the register of MS patients of the KhMAA — Yugra. Cladribine tablets at a dose of 3.5 mg/kg of body weight were prescribed in two annual treatment cycles, each comprising 2 weeks with a treatment duration of 4—5 days — at the beginning of the first month and at the beginning of the second month. In 2021—2023, 54patients received therapy with cladribine tablets with an average frequency of exacerbations of 1.2 (62 exacerbations in 48 patients) within 12 months prior to therapy initiation. Before starting therapy and every 6 months thereafter, patients underwent magnetic resonance imaging (MRI) of the brain, cervical and thoracic regions MRI with contrast enhancement, assessment of neurological status using the Expanded Disability Status Scale (EDSS), complete blood count, monitoring of blood lymphocytes level and biochemical blood testing. After the first and second treatment courses with cladribine tablets, the lymphocyte level was assessed after 2 months and after 6 months.Results. It was found that the average frequency of exacerbations before the start of treatment was 1.2 per year; after treatment with cladribine tablets it was 0.05 per year, i.e. the average annual frequency of exacerbations fell by 92% in the first year of treatment. Before starting treatment with cladribine tablets, only six (11%) out of 54 patients had no exacerbations; after starting the treatment with cladribine tablets, 48 (89.5%) patients had no exacerbations. The results obtained exceed the results of the CLARITY study, in which the proportion of patients without exacerbations in the cladribine group was 79.7%. In addition, all patients had no disease activity on MRI after starting cladribine therapy compared to the baseline data before starting cladribine therapy, when Gd+ lesions were detected on T1-weighted images in 50 (92.5%) patients. There was also no increase in disability. The mean EDSS score remained stable (median 3.0) or decreased by 0.5—1 point. At the end of follow-up period, 49 (92%) out of 54 patients included in the analysis achieved NEDA-3 status. No adverse events were observed during patient follow-up.Conclusion. The experience with the use of cladribine in KhMAA is consistent with data from real-world clinical practice around the world in terms of efficacy, safety and results of randomized clinical trials. Cladribine tablets are a highly effective and safe treatment for HAMS. Further monitoring of patients is required to assess the long-term benefits and risks of cladribine.

Objectives: The aim of this retrospective study was to investigate the influence of chemotherapy on the immune status of individual patients diagnosed with acute lymphoblastic leukemia (ALL) and to elucidate the clinical characteristics of immune reconstitution in ALL patients following chemotherapy. Methods: Clinical data of children with ALL were gathered, including information on the number of lymphocyte subsets prior to chemotherapy, at the end of therapy, six months, and one year after the end of the treatment. Results: A total of 146 children with ALL were included, and T cells, B cells, and NK cells all decreased to various degrees prior to treatment. The abnormal CD3 + T cell numbers group experienced a considerably higher mortality (21.9% vs. 6.1%) and recurrence rate (31.3% vs. 11.4%) compared to the normal group (P < 0.05). T cells, B cells, and NK cells were all significantly compromised at the end of therapy compared to the beginning of chemotherapy, with B cells being more severely compromised (P < 0.001). At the end of treatment, levels of B cells, CD4 + T cells, CD4/CD8, IgG and IgM in low risk (LR) group were significantly higher than those in intermediate risk (IR) group (P < 0.01), and levels of NK cells in LR group were evidently lower than those in IR group (P < 0.001). Six months after the end of therapy, all the above indicators recovered (P < 0.001) except CD4/CD8 ratio (P = 0.451). Conclusions: The immune systems of the ALL patients were severely compromised upon therapy withdrawal, particularly the B cells. At six months after the therapy ended, the B cells were basically restored to normal level, while the T-cell compartment was not. The impaired numbers of CD3 + T cell may contribute to a weakened anti-tumor response, potentially leading to a poorer prognosis. [ABSTRACT FROM AUTHOR]

Gamma delta (γδ) T cells represent a minor fraction of human T cell repertoire but play an important role in mediating anti-infectious and anti-tumorous effects in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT). We performed a prospective study to analyze the effect of different transplant modalities on immune reconstitution of γδ T cells and subsets. CD3, CD4 and CD8 T cells were analyzed in parallel. Secondly, we examined the impact of γδ T cell reconstitution on clinical outcomes including acute Graft-versus-Host-Disease (aGvHD) and viral infections. Our cohort includes 49 pediatric patients who received unmanipulated bone marrow grafts from matched unrelated (MUD) or matched related (MRD) donors. The cohort includes patients with malignant as well as non-malignant diseases. Cell counts were measured using flow cytometry at 15, 30, 60, 100, 180 and 240 days after transplantation. Cells were stained for CD3, CD4, CD8, CD45, TCRαβ, TCRγδ, TCRVδ1, TCRVδ2, HLA-DR and combinations. Patients with a MRD showed significantly higher Vδ2+ T cells than those with MUD at timepoints +30, +60, +100 (p<0.001, respectively) and +180 (p<0.01) in univariate analysis. These results remained significant in multivariate analysis. Patients recovering with a high relative abundance of total γδ T cells and Vδ2+ T cells had a significantly lower cumulative incidence of grade II-IV aGvHD after transplantation (p=0.03 and p=0.04, respectively). A high relative abundance of Vδ2+ T cells was also associated with a lower incidence of EBV infection (p=0.02). Patients with EBV infection on the other hand showed higher absolute Vδ1+ T cell counts at days +100 and +180 after transplantation (p=0.046 and 0.038, respectively) than those without EBV infection. This result remained significant in a multivariate time-averaged analysis (q<0.1). Our results suggest a protective role of γδ T cells and especially Vδ2+ T cell subset against the development of aGvHD and EBV infection after pediatric HSCT. Vδ1+ T cells might be involved in the immune response after EBV infection. Our results encourage further research on γδ T cells as prognostic markers after HSCT and as possible targets of adoptive T cell transfer strategies. [ABSTRACT FROM AUTHOR]

Introduction: Adoption of allogeneic T cells directly supplements the number of T cells and rapidly induces T-cell immunity, which has good efficacy for treating some tumors and immunodeficiency diseases. However, poor adoptive T-cell engraftment and graft-versus-host disease (GVHD) limit the application of these methods. Alloreactive T-cell clones were eliminated from the donor T-cell repertoire, and the remaining T-cell clones were prepared as Tscm for T-cell adoptive treatment to reconstruct recipient T-cell immunity without GVHD. Methods: The subjects in this study included three different strains of mice. Lymphocytes from mice (C57BL/6) were used as the donor T-cell repertoire, from which the Tscm allo-reactive T cell clone was depleted (ATD-Tscm). This was confirmed by showing that the Tscm was not responsive to the alloantigen of the recipient (BALB/c). To prepare ATD-Tscm cells, we used recipient lymphocytes as a simulator, and coculture of mouse and recipient lymphocytes was carried out for 7 days. Sorting of non-proliferative cells ensured that the prepared Tscm cells were nonresponsive. The sorted lymphocytes underwent further expansion by treatment with TWS119 and cytokines for an additional 10 days, after which the number of ATD-Tscm cells increased. The prepared Tscm cells were transferred into recipient mice to observe immune reconstitution and GVHD incidence. Results: Our protocol began with the use of 1×107 donor lymphocytes and resulted in 1 ×107 ATD-Tscm cells after 17 days of preparation. The prepared ATD-Tscm cells exhibited a nonresponse upon restimulation of the recipient lymphocytes. Importantly, the prepared ATD-Tscm cells were able to bind long and reconstitute other T-cell subsets in vivo, effectively recognizing and answering the "foreign" antigen without causing GVHD after they were transferred into the recipients. Discussion: Our strategy was succeeded to prepare ATD-Tscm cells from the donor T-cell repertoire. The prepared ATD-Tscm cells were able to reconstitute the immune system and prevent GVHD after transferred to the recipients. This study provides a good reference for generating ATD-Tscm for T-cell adoptive immunotherapy. [ABSTRACT FROM AUTHOR]

There is lack of guidance for immune monitoring and infection prevention after administration of ex vivo genetically modified hematopoietic stem cell therapies (GMHSCT). We reviewed current infection prevention practices as reported by providers experienced with GMHSCTs across North America and Europe, and assessed potential immunologic compromise associated with the therapeutic process of GMHSCTs described to date. Based on these assessments, and with consensus from members of the International Society for Cell & Gene Therapy (ISCT) Stem Cell Engineering Committee, we propose risk-adapted recommendations for immune monitoring, infection surveillance and prophylaxis, and revaccination after receipt of GMHSCTs. Disease-specific and GMHSCT-specific considerations should guide decision making for each therapy. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the kinetics of immune recovery following umbilical cord blood transplantation (UCBT) in adults who received a myeloablative conditioning (MAC) regimen and antithymocyte globulin (ATG). While the immune recovery kinetics has been extensively studied in pediatric UCBT recipients, limited data exist for adults. We conducted a comprehensive analysis of 221 consecutive adult patients who underwent UCBT with MAC and ATG at a single institution. Our objective was to evaluate the influence of patient, disease, and transplant factors, along with acute graft-versus-host disease (aGVHD), on immune reconstitution and overall survival. Our findings confirm a delayed recovery of T cells, while B and NK cell reconstitution exhibited rapid progress, with NK cell counts reaching normal levels within 3 months post-transplantation and B cells within 6 months. Within CD3+ T cells, CD8+ T cells also experienced a delayed recovery (12 months), but to a lesser extent compared to CD4+ T cells (18 months). Delayed immune recovery of T-cell subsets was associated with the development of aGVHD grade II-IV, older age, CMV negativity, and a female donor. Patients with lymphoproliferative diseases showed slower NK cell recovery. Our study demonstrates that adult patients undergoing MAC with ATG and receiving a single unit UCBT for hematologic malignancies experienced rapid reconstitution of NK and B cells. However, T cell recovery, particularly CD4+ T cells, was significantly delayed. To enhance T cell recovery, it may be crucial to consider UCB units with higher cellularity and optimize ATG doses in conditioning. [ABSTRACT FROM AUTHOR]

Background: Relapse remains a challenge after transplantation in pediatric patients with hematological malignancies. Myeloablative regimens used for disease control are associated with acute and long-term adverse effects. We used a CD45RA-depleted haploidentical graft for adoptive transfer of memory T cells combined with NK-cell addback and hypothesized that maximizing the graft-versus-leukemia (GVL) effect might allow for reduction in intensity of conditioning regimen. Methods: In this phase II clinical trial (NCT01807611), 72 patients with hematological malignancies (complete remission (CR)1: 25, ≥ CR2: 28, refractory disease: 19) received haploidentical CD34 + enriched and CD45RA-depleted hematopoietic progenitor cell grafts followed by NK-cell infusion. Conditioning included fludarabine, thiotepa, melphalan, cyclophosphamide, total lymphoid irradiation, and graft-versus-host disease (GVHD) prophylaxis consisted of a short-course sirolimus or mycophenolate mofetil without serotherapy. Results: The 3-year overall survival (OS) and event-free-survival (EFS) for patients in CR1 were 92% (95% CI:72–98) and 88% (95% CI: 67–96); ≥ CR2 were 81% (95% CI: 61–92) and 68% (95% CI: 47–82) and refractory disease were 32% (95% CI: 11–54) and 20% (95% CI: 6–40). The 3-year EFS for all patients in morphological CR was 77% (95% CI: 64–87) with no difference amongst recipients with or without minimal residual disease (P = 0.2992). Immune reconstitution was rapid, with mean CD3 and CD4 T-cell counts of 410/μL and 140/μL at day + 30. Cumulative incidence of acute GVHD and chronic GVHD was 36% and 26% but most patients with acute GVHD recovered rapidly with therapy. Lower rates of grade III-IV acute GVHD were observed with NK-cell alloreactive donors (P = 0.004), and higher rates of moderate/severe chronic GVHD occurred with maternal donors (P = 0.035). Conclusion: The combination of a CD45RA-depleted graft and NK-cell addback led to robust immune reconstitution maximizing the GVL effect and allowed for use of a submyeloablative, TBI-free conditioning regimen that was associated with excellent EFS resulting in promising long-term outcomes in this high-risk population. The trial is registered at ClinicalTrials.gov (NCT01807611). [ABSTRACT FROM AUTHOR]

Purpose: Patients with adenosine deaminase 1 deficient severe combined immunodeficiency (ADA-SCID) are initially treated with enzyme replacement therapy (ERT) with polyethylene glycol-modified (PEGylated) ADA while awaiting definitive treatment with hematopoietic stem cell transplant (HSCT) or gene therapy. Beginning in 1990, ERT was performed with PEGylated bovine intestinal ADA (ADAGEN®). In 2019, a PEGylated recombinant bovine ADA (Revcovi®) replaced ADAGEN following studies in older patients previously treated with ADAGEN for many years. There are limited longitudinal data on ERT-naïve newborns treated with Revcovi. Methods: We report our clinical experience with Revcovi as initial bridge therapy in three newly diagnosed infants with ADA-SCID, along with comprehensive biochemical and immunologic data. Results: Revcovi was initiated at twice weekly dosing (0.2 mg/kg intramuscularly), and monitored by following plasma ADA activity and the concentration of total deoxyadenosine nucleotides (dAXP) in erythrocytes. All patients rapidly achieved a biochemically effective level of plasma ADA activity, and red cell dAXP were eliminated within 2–3 months. Two patients reconstituted B-cells and NK-cells within the first month of ERT, followed by naive T-cells one month later. The third patient reconstituted all lymphocyte subsets within the first month of ERT. One patient experienced declining lymphocyte counts with improvement following Revcovi dose escalation. Two patients developed early, self-resolving thrombocytosis, but no thromboembolic events occurred. Conclusion: Revcovi was safe and effective as initial therapy to restore immune function in these newly diagnosed infants with ADA-SCID, however, time course and degree of reconstitution varied. Revcovi dose may need to be optimized based on immune reconstitution, clinical status, and biochemical data. [ABSTRACT FROM AUTHOR]

BackgroundImmunity reconstitution (IR) is crucial for pediatric patients undergoing hematopoietic stem cell transplantation (HSCT), but the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on lymphocyte subsets post-transplant remains unclear. Therefore, we assessed immune cell dynamics in children after SARS-CoV-2 infection.MethodsWe enrolled 42 children, including 21 post-HSCT SARS-CoV-2 infected and 21 matched, non-infected historical controls (1:1 matching based on propensity scores). The time from HSCT to SARS-CoV-2 infection in the infected group was determined by the beginning of follow-up for the non-infected group. The primary endpoint was 270-day IR kinetics post-infection.ResultsOur findings showed similar recovery trends between the infected group and non-infected group both in UCB and HID recipients. In the UCB cohort, the NK cell reconstitution in the infected group was poorer compared to the non-infected group, but this difference did not reach statistical significance (P = 0.178). Furthermore, HID transplantation might be a trend towards poor CD19+ T-cell reconstitution [hazard ratio (HR): 0.43, 95% CI: 0.18–1.04, p = 0.06]. No statistically significant difference was observed in terms of secondary infections across the UCB (P = 0.150) and HID (P = 0.980) cohorts as well as there was no discernible difference in overall survival between the two groups (P = 1).ConclusionsOur analysis reveals that SARS-CoV-2 might temporarily impaired the IR process in the short term, with recovery to a comparable trend as observed in non-infected patients approximately 9 months post-infection.

Abstract Allogeneic hematopoietic stem cell transplantation (allo‐HSCT) is a widely used treatment for a variety of hematopoietic disorders, and also provides a valuable platform for investigating the development of donor‐derived immune cells in recipients post‐HSCT. The immune system remodels from the donor to the recipient during allo‐HSCT. However, little is known about the cell profile alterations as donor homeostasis rebalances to recipient homeostasis following HSCT. Here, multi‐omics technology is applied at both the single cell and bulk sample levels, as well as spectrum flow cytometry and fluorescent transgenic mouse models, to dissect the dynamics of the rebalanced homeostatic immune system in recipients after allo‐HSCT. The data reveal that all immune subpopulations observed in donors are successfully restored in recipients, though with varying levels of abundance. The remodeling of immune homeostasis exhibits different patterns in HLA‐matched and haploidentical HSCT, highlighting distinct biases in T cell reconstitution from the central and peripheral pathways. Furthermore, ZNF683 is critical for maintaining the persistence and quiescence of CD8 T‐cell in haploidentical HSCT. The research can serve as a foundation for developing novel strategies to induce immune tolerance.

ABSTRACT Despite the success in the management of HIV with antiretroviral therapy (ART), people with HIV (PWH) have a heightened state of immune activation and inflammation, and an estimated 10%–40% demonstrate poor CD4 T-cell reconstitution, thereby increasing their mortality and morbidity risk burden. Soluble immunoregulatory proteins that function in lymphocyte activation or inhibition are elevated in PWH and associate with T-cell dysfunction, HIV persistence, and are predictive of comorbid outcomes. Here, we measured a panel of 35 circulating immunoregulatory proteins in 116 PWH with variations in CD4 T-cell counts (poor CD4 trajectory: 500 cells/μl, n = 82) by Luminex. Participants were enrolled in the AIDS Clinical Trials Group Longitudinal Linked Randomized Trials cohort, had initiated ART on enrollment, and had been on suppressive ART for 1 year. Using non-parametric analysis, we found that the levels of CD276, ICOSL, BAFF, OX40, galectin-1, and galectin-9 were significantly higher in PWH with poor CD4 trajectories compared to individuals with immune-competent CD4 T-cell count. Notably, in logistic models, ICOSL and OX40 remained significant after adjusting for age and baseline plasma HIV RNA. Furthermore, Extreme Gradient Boosting machine learning models comprising co-stimulatory and inhibitory checkpoint proteins yielded high accuracy in classification of individuals with poor CD4 trajectories. In summary, we identified a novel signature of circulating immunoregulatory proteins indicative of poor CD4 trajectories that may serve as potential targets to monitor and manage immune perturbations more accurately in PWH during suppressive ART.IMPORTANCEIt is essential to track immune perturbations related to insufficient CD4 T-cell recovery in PWH on suppressive ART as those with incomplete reconstitution are at a greater risk of non-AIDS-related morbidity and mortality. Several inflammatory soluble mediators have associated with poor immune reconstitution and adverse morbid outcomes in PWH, yet their implementation into routine clinical care to guide management remains inconsistent. Circulating immune checkpoint proteins have been linked to dysregulated immune pathways during suppressive ART and may serve as improved surrogate markers of clinical relevance. Here we investigate soluble lymphocyte-associated immunoregulatory proteins in virally suppressed PWH with no reported co-morbid outcomes and varying CD4 T-cell counts, to reveal underlying pathways that remain perturbed despite ART. This novel signature of immunoregulatory markers pertaining to poor CD4 T-cell trajectories uncover previously overlooked immune checkpoints as important targets for clinical monitoring of PWH in the setting of durable viral suppression by ART.

Objective To explore the effect of the precise diagnosis and treatment of a case of acute graft-versus-host disease （aGVHD） with rash as the main manifestation under the guidance of immune monitoring. Methods Clinical data and diagnosis and treatment of a child with high-risk acute myeloid leukemia who developed intractable rash after receiving unrelated umbilical cord blood transplantation were retrospectively analyzed. Using the keywords of “hematopoietic stem cell transplantation”“immune reconstitution” and “acute graft-versus-host disease”， relevant literatures were searched from PubMed， Web of Science， CNKI and Wanfang databases， and relevant cases were collected and analyzed. Results Hematopoietic reconstruction was successfully achieved in this 1 year 9 months old girl. On day 22 after transplantation， the skin of head and back neck of the patient showed dense red papules （approximately 19% in area）， with obvious itching. Under the treatment of oral tacrolimus and topical hormone drugs， the rash was not alleviated （area>90%）. Meanwhile， the proportion of CD3+ cells， CD8+ cells， CD3+CD69+cells and CD3+HLA-DR+cells was significantly increased， and the proportion of Treg cells was decreased. The immune indexes supported T lymphocyte activation， then diagnosis of gradeⅡaGVHD （skin grade 3） was made， and the immunosuppressive regimen was strengthened. During this period， the skin rash of the child subsided， but recurred， and accompanied by obvious skin desquamation. The proportion of CD3+ cells， CD8+ cells， and CD3+HLA-DR+cells remains relatively high， supporting the diagnosis of aGVHD. Therefore， the anti-GVHD regimen was adjusted and strengthened， and the aGVHD of the child’s skin was mitigated. Regular monitoring showed that the primary disease was completely relieved， the implantation rate was 100%， and the immune reconstitution was stable. During 32-month follow-up after transplantation， the child obtained disease-free survival. Nine relevant literatures were retrieved， all of which demonstrated that the increased proportion of early CD3+ cells， CD8+ cells， activated T lymphocytes and Treg downregulation were associated with the occurrence of aGVHD. Conclusions The dynamic monitoring of the immune status of patients after allogeneic hematopoietic stem cell transplantation is helpful to evaluate their immune reconstitution and disease status （such as， aGVHD）， thereby assisting clinicians to formulate a reasonable immunosuppressive regimen and bring favorable prognosis to patients.

BACKGROUND: Severe combined immunodeficiency (SCID) comprises rare inherited disorders of immunity that require definitive treatment through hematopoietic cell transplantation (HCT) or gene therapy for survival. Despite successes of allogeneic HCT, many SCID patients experience incomplete immune reconstitution, persistent T-cell lymphopenia, and poor long-term outcomes. OBJECTIVE: We hypothesized that CD4+ T-cell lymphopenia could be associated with a state of T-cell exhaustion in previously transplanted SCID patients. METHODS: We analyzed markers of exhaustion in blood samples from 61 SCID patients at a median of 10.4 years after HCT. RESULTS: Compared to post-HCT SCID patients with normal CD4+ T-cell counts, those with poor T-cell reconstitution showed lower frequency of naive CD45RA+/CCR7+ T cells, recent thymic emigrants, and TCR excision circles. They also had a restricted TCR repertoire, increased expression of inhibitory receptors (PD-1, 2B4, CD160, BTLA, CTLA-4), and increased activation markers (HLA-DR, perforin) on their total and naive CD8+ T cells, suggesting T-cell exhaustion and aberrant activation, respectively. The exhaustion score of CD8+ T cells was inversely correlated with CD4+ T-cell count, recent thymic emigrants, TCR excision circles, and TCR diversity. Exhaustion scores were higher among recipients of unconditioned HCT, especially when further in time from HCT. Patients with fewer CD4+ T cells showed a transcriptional signature of exhaustion. CONCLUSIONS: Recipients of unconditioned HCT for SCID may develop late post-HCT T-cell exhaustion as a result of diminished production of T-lineage cells. Elevated expression of inhibitory receptors on their T cells may be a biomarker of poor long-term T-cell reconstitution.

Non-Hodgkin lymphoma (NHL) is among the five most common pediatric cancer diagnoses in children and adolescents and consists of a heterogeneous group of lymphoid tissue malignancies –with B-cell-derived NHL accounting for nearly 80% of cases. Novel and high-throughput diagnostic tools have significantly increased our understanding of B-NHL biology and molecular pathogenesis, leading to new NHL classifications and treatment options. This retrospective cohort study investigated 17 cases of both mature B-cell NHL (Burkitt lymphoma or BL; Diffuse large B-cell lymphoma or DLBCL; Primary mediastinal large B-cell lymphoma or PMBCL; Follicular lymphoma or FL) and immature B-cell progenitor NHL (B-lymphoblastic lymphoma or BLL) that were treated in a tertiary Pediatric Hematology-Oncology Department during the last 20 years. Modern NHL protocols for children, adolescents, and young adults, along with the addition of rituximab, are safe and efficient (100% overall survival; one relapse). Elevated ESR was more prevalent than elevated LDH. Analyses have focused on immune reconstitution (grade ≥3 infections, lymphocyte and immunoglobulin levels recovery) and body-mass-index changes post-treatment, late effects (in 53% of patients), and the presence of histology markers BCL2, BCL6, CD30, cMYC, and Ki-67%. One patient was diagnosed with a second malignant neoplasm (papillary thyroid cancer). [ABSTRACT FROM AUTHOR]

Background: The immune reconstitution after allogeneic hematopoietic stem cell transplantation (allo‐HSCT) is crucial for preventing infections and relapse and enhancing graft‐versus‐tumor effects. B cells play an important role in humoral immunity and immune regulation, but their reconstitution after allo‐HSCT has not been well studied. Methods: In this study, we analyzed the dynamics of B cells in 252 patients who underwent allo‐HSCT for 2 years and assessed the impact of factors on B‐cell reconstitution and their correlations with survival outcomes, as well as the development stages of B cells in the bone marrow and the subsets in the peripheral blood. Results: We found that the B‐cell reconstitution in the bone marrow was consistent with the peripheral blood (p = 0.232). B‐cell reconstitution was delayed by the male gender, age >50, older donor age, the occurrence of chronic and acute graft‐versus‐host disease, and the infections of fungi and cytomegalovirus. The survival analysis revealed that patients with lower B cells had higher risks of death and relapse. More importantly, we used propensity score matching to obtain the conclusion that post‐1‐year B‐cell reconstitution is better in females. Meanwhile, using mediation analysis, we proposed the age‐B cells‐survival axis and found that B‐cell reconstitution at month 12 posttransplant mediated the effect of age on patient survival (p = 0.013). We also found that younger patients showed more immature B cells in the bone marrow after transplantation (p = 0.037). Conclusion: Our findings provide valuable insights for optimizing the management of B‐cell reconstitution and improving the efficacy and safety of allo‐HSCT. [ABSTRACT FROM AUTHOR]

Objective To investigate the long-term safety and effectiveness of withdrawal of hepatitis B immuneglobulin (HBIG) and/or nucleos(t)ide analogues (NAs) to prevent hepatitis B virus (HBV) reinfection in liver transplant recipients with hepatitis B-related diseases after successful vaccination. Methods Baseline data of 76 liver transplant recipients undergoing hepatitis B immune reconstitution after receiving hepatitis B vaccines were retrospectively analyzed. The vaccination and response, the follow-up results of respondents with HBIG and/or NAs withdrawal, and the reinfection of HBV after withdrawal of HBIG and/or NAs were analyzed. Results The time interval from liver transplantation to hepatitis B vaccination was 26 (20, 40) months. The time interval from vaccination to response was 15 (8,27) months. Initially, 76 recipients withdrew HBIG, and 36 recipients withdrew HBIG and NAs. During the follow-up, 12 of 76 recipients who withdrew HBIG resumed use of HBIG, and 16 of 36 recipients who withdrew HBIG and NAs resumed use of NAs. The withdrawal time of HBIG and NAs was 135 (98,150) and 133 (34,149) months, respectively. Sixteen respondents did not receive booster, and 36 respondents received boosters on a regular basis. The time interval between the first booster and HBIG withdrawal was 44 (11,87) months. No significant differences were observed in baseline data between the respondents with and without boosters (all P>0.05). During the follow-up, 9 recipients were lost to follow-up, 5 were re-infected with HBV, 3 died, and 1 recipient developed graft loss and underwent secondary liver transplantation. Among 5 recipients re-infected with HBV, 4 cases had virus mutation. Significant differences were found between re-infected and uninfected patients regarding withdrawal of NAs and hepatitis B e antigen (HBeAg) positive before transplantation (both P<0.05). Conclusions Long-term withdrawal of HBIG is feasible and safe for recipients with successful hepatitis B immune reconstitution after liver transplantation for hepatitis B-related diseases. Nevertheless, whether antiviral drugs can be simultaneously withdrawn remains to be validated. [ABSTRACT FROM AUTHOR]

Triple-negative breast cancer (TNBC) in humans is the most aggressive and deadly form of BC. Although TNBCs are about 15 percent of the total number of BC cases, they are associated with the highest mortalities. Current treatment options are limited, and most modalities are toxic and have not increased the 5-year survival rates of TNBC. Many oncolytic viruses are emerging as potential therapies for TNBC. In this study, two Tanapoxvirus (TPV) recombinants, one expressing FliC and the other expressing mouse interleukin-2 (mIL-2), were assessed for their efficacy in an immuno-competent xenograft mouse model. MDA-MB-231 tumors were planted in BALB/c nude mice, treated, made immuno-competent via adoptive transfer of splenocytes from healthy BALB/c donors, and then monitored for 40 days. TPV/Δ2L/66R/FliC and TPV/Δ66R/mIL-2 demonstrated significant tumor reduction (p = 0.01602 and p = 0.03890, respectively) compared to the reconstituted control (RC), whereas wtTPV did not. Pathological analyses of treated tumors revealed cells consistent with lymphocyte and plasma cell morphology in reconstituted mice treated with TPV recombinants. Anti-viral plaque reduction assays conducted using harvested serum from treated animals indicated the presence of anti-TPV antibodies in mice reconstituted and treated with TPV that were missing from immune-deficient nude mice, including those exposed to TPV and of statistically equivalent serum concentrations to normal BALB/c mice immunized against TPV. The results suggest immuno-deficient BALB/c nude mice can become immuno-competent via adoptive transfer of splenocytes from genetically identical donors and allow for testing of tumor xenografts in a competent model system. The TPV recombinants tested should be further studied for the potential treatment of human TNBC. [ABSTRACT FROM AUTHOR]

Leukemia relapse following stem cell transplantation remains a significant barrier to long-term remission. Timely and balanced immune recovery after transplantation is crucial for preventing leukemia relapse. After an extensive literature search of PubMed and Web of Science through October 2023, we provide an overview of the dynamics of immune reconstitution and its role in controlling leukemia relapse. We also discuss strategies to promote immune reconstitution and reduce disease recurrence following allogeneic hematopoietic stem cell transplantation. Immune reconstitution after transplantation has substantial potential to prevent relapse and might predict disease recurrence and prognosis. High dimensional cytometry, multi-omics, and T cell repertoire analysis allow for a more comprehensive and detailed understanding of the immune system's dynamics post-transplantation, and contribute to the identification of rare immune cell subsets or potential biomarkers associated with successful immune reconstitution or increased risk of complications. Strategies to enhance the immune system, such as adoptive immunotherapy and cytokine-based therapy, have great potential for reducing leukemia relapse after transplantation. Future research directions should focus on refining patient selection for these therapies, implementing appropriate and timely treatment, investigating combination approaches to maximize therapeutic outcomes, and achieving a robust graft-versus-leukemia (GVL) effect while minimizing graft-versus-host disease (GVHD) for optimal results. [ABSTRACT FROM AUTHOR]

An individual's T-cell repertoire constantly changes under the influence of external and internal factors. Cells that do not receive a stimulatory signal die, while those that encounter and recognize a pathogen or receive a costimulatory signal divide, resulting in clonal expansions. T-cell clones can be traced by monitoring the presence of their unique T-cell receptor (TCR) sequence, which is assembled de novo through a process known as V(D)J rearrangement. Tracking T cells can provide valuable insights into the survival of cells after hematopoietic stem cell transplantation (HSCT) or cancer treatment response and can indicate the induction of protective immunity by vaccination. In this study, we report a bioinformatic method for quantifying the T-cell repertoire dynamics from TCR sequencing data. We demonstrate its utility by measuring the T-cell repertoire stability in healthy donors, by quantifying the effect of donor lymphocyte infusion (DLI), and by tracking the fate of the different T-cell subsets in HSCT patients and the expansion of pathogen-specific clones in vaccinated individuals. [ABSTRACT FROM AUTHOR]

The success of allogeneic hematopoietic cell transplantation (HCT) as therapy for hematologic conditions is negatively impacted by the occurrence of graft-versus-host disease (GVHD). Tissue damage, caused, for example, by chemotherapy and radiotherapy, is a key factor in GVHD pathogenesis. Innate lymphoid cells (ILCs) are important mediators of tissue repair and homeostasis. The presence of ILCs before, and enhanced ILC reconstitution after, allogeneic HCT is associated with a reduced risk to develop mucositis and GVHD. However, ILC reconstitution after allogeneic HCT is slow and often incomplete. A way to replenish the pool of ILC relies on the differentiation of hematopoietic progenitor cells (HPCs) into ILC. We developed an ex vivo stromal cell–containing culture system to study the capacity of HPCs to differentiate into all mature helper ILC subsets. ILC development depended on the source of HPCs. ILCs developed at high frequencies from umbilical cord blood– and fetal liver–derived HPC and at low frequencies when HPCs were obtained from allogeneic or autologous adult HCT grafts or healthy adult bone marrow. Although all helper ILC subsets could be generated from adult HPC sources, development of tissue protective ILC2 and NKp44+ ILC3 was notoriously difficult. Our data suggest that slow ILC recovery after allogeneic HCT may be related to an intrinsic incapability of adult HPC to develop into ILC. [ABSTRACT FROM AUTHOR]

Introduction: Immune reconstitution following antiretroviral therapy (ART) initiation is crucial to prevent AIDS and non‐AIDS‐related comorbidities. Patients with suppressed viraemia who fail to restore cellular immunity are exposed to an increased risk of morbidity and mortality during long‐term follow‐up, although the underlying mechanisms remain poorly understood. We aim to describe clinical outcomes and factors associated with the worse immune recovery and all‐cause mortality in people living with HIV (PLWH) from Latin America following ART initiation. Methods: Retrospective cohort study using the CCASAnet database: PLWH ≥18 years of age at ART initiation using a three drug‐based combination therapy and with medical follow‐up for ≥24 months after ART initiation and undetectable viral load were included. Patients were divided into four immune recovery groups based on rounded quartiles of increase in CD4 T‐cell count at 2 years of treatment (<150, [150, 250), [250, 350] and >350 cells/mm3). Primary outcomes included all‐cause mortality, AIDS‐defining events and non‐communicable diseases that occurred >2 years after ART initiation. Factors associated with an increase in CD4 T‐cell count at 2 years of treatment were evaluated using a cumulative probability model with a logit link. Results: In our cohort of 4496 Latin American PLWH, we found that patients with the lowest CD4 increase (<150) had the lowest survival probability at 10 years of follow‐up. Lower increase in CD4 count following therapy initiation (and remarkably not a lower baseline CD4 T‐cell count) and older age were risk factors for all‐cause mortality. We also found that older age, male sex and higher baseline CD4 T‐cell count were associated with lower CD4 count increase following therapy initiation. Conclusions: Our study shows that PLWH with lower increases in CD4 count have lower survival probabilities. CD4 increase during follow‐up might be a better predictor of mortality in undetectable PLWH than baseline CD4 count. Therefore, it should be included as a routine clinical variable to assess immune recovery and overall survival. [ABSTRACT FROM AUTHOR]

Introduction: Pneumocystis jirovecii pneumonia (PJP) is a rare complication of hematopoietic stem cell transplantation (HSCT). Primary prophylaxis for 6–12 months post‐HSCT is the standard approach. However, there is no consensus regarding the optimal duration of prophylaxis. Methods: We identified patients who developed PJP more than 1‐year post‐HSCT. All patients had previously received 12 months of PJP prophylaxis. PJP was diagnosed based on clinical findings and the detection of P. jirovecii in bronchoalveolar lavage (BAL) using polymerase chain reaction (PCR). The CD4+ T‐cell percentage was determined using flow cytometry. Data expressed as median (interquartile range). Results: Ten patients developed PJP at 17.5 months (16–24 months) post‐HSCT. PJP diagnosis occurred 5.5 months (3–15 months) after discontinuing prophylaxis. Eight patients received anti‐thymocyte globulin (ATG) as graft versus host disease (GVHD) prophylaxis. At diagnosis, only one patient had lymphopenia; all patients had CD4+ T‐lymphocyte counts ≥0.2 × 109/L (median 0.337 × 109/L). Three patients had concomitant bacterial infections. The clinical presentation was mild; only three required hospitalization, none of them required intensive care and there were no deaths. Conclusion: There is a need to develop risk‐adapted prophylactic strategies in the contemporary era using ATG‐based GVHD prophylaxis. [ABSTRACT FROM AUTHOR]

Objective To explore the effect of the precise diagnosis and treatment of a case of acute graft-versus-host disease (aGVHD) with rash as the main manifestation under the guidance of immune monitoring. Methods Clinical data and diagnosis and treatment of a child with high-risk acute myeloid leukemia who developed intractable rash after receiving unrelated umbilical cord blood transplantation were retrospectively analyzed. Using the keywords of “hematopoietic stem cell transplantation”“immune reconstitution” and “acute graft-versus-host disease”, relevant literatures were searched from PubMed, Web of Science, CNKI and Wanfang databases, and relevant cases were collected and analyzed. Results Hematopoietic reconstruction was successfully achieved in this 1 year 9 months old girl. On day 22 after transplantation, the skin of head and back neck of the patient showed dense red papules (approximately 19% in area), with obvious itching. Under the treatment of oral tacrolimus and topical hormone drugs, the rash was not alleviated (area>90%). Meanwhile, the proportion of CD3+ cells, CD8+ cells, CD3+ CD69+ cells and CD3+ HLA-DR+ cells was significantly increased, and the proportion of Treg cells was decreased. The immune indexes supported T lymphocyte activation, then diagnosis of grade Ⅱ aGVHD (skin grade 3) was made, and the immunosuppressive regimen was strengthened. During this period, the skin rash of the child subsided, but recurred, and accompanied by obvious skin desquamation. The proportion of CD3+ cells, CD8+ cells, and CD3+ HLA-DR+ cells remains relatively high, supporting the diagnosis of aGVHD. Therefore, the anti-GVHD regimen was adjusted and strengthened, and the aGVHD of the child’s skin was mitigated. Regular monitoring showed that the primary disease was completely relieved, the implantation rate was 100%, and the immune reconstitution was stable. During 32-month follow-up after transplantation, the child obtained disease-free survival. Nine relevant literatures were retrieved, all of which demonstrated that the increased proportion of early CD3+ cells, CD8+ cells, activated T lymphocytes and Treg downregulation were associated with the occurrence of aGVHD. Conclusion The dynamic monitoring of the immune status of patients after allogeneic hematopoietic stem cell transplantation is helpful to evaluate their immune reconstitution and disease status (such as, aGVHD), thereby assisting clinicians to formulate a reasonable immunosuppressive regimen and bring favorable prognosis to patients. [ABSTRACT FROM AUTHOR]

Gamma delta (γδ) T cells represent a minor fraction of human T cell repertoire but play an important role in mediating anti-infectious and anti-tumorous effects in the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT). We performed a prospective study to analyze the effect of different transplant modalities on immune reconstitution of γδ T cells and subsets. CD3, CD4 and CD8 T cells were analyzed in parallel. Secondly, we examined the impact of γδ T cell reconstitution on clinical outcomes including acute Graft-versus-Host-Disease (aGvHD) and viral infections. Our cohort includes 49 pediatric patients who received unmanipulated bone marrow grafts from matched unrelated (MUD) or matched related (MRD) donors. The cohort includes patients with malignant as well as non-malignant diseases. Cell counts were measured using flow cytometry at 15, 30, 60, 100, 180 and 240 days after transplantation. Cells were stained for CD3, CD4, CD8, CD45, TCRαβ, TCRγδ, TCRVδ1, TCRVδ2, HLA-DR and combinations. Patients with a MRD showed significantly higher Vδ2+ T cells than those with MUD at timepoints +30, +60, +100 (p

BackgroundImmune reconstitution bone loss (IRBL) is a common side-effect of antiretroviral therapy (ART) in people with human immunodeficiency virus (PWH). Immune reconstitution bone loss acts through CD4+ T-cell/immune reconstitution-induced inflammation and is independent of antiviral regimen. Immune reconstitution bone loss may contribute to the high rate of bone fracture in PWH, a cause of significant morbidity and mortality. Although IRBL is transient, it remains unclear whether bone recovers, or whether it is permanently denuded and further compounds bone loss associated with natural aging.MethodsWe used a validated IRBL mouse model involving T-cell reconstitution of immunocompromised mice. Mice underwent cross-sectional bone phenotyping of femur and/or vertebrae between 6 and 20 months of age by microcomputed tomography (µCT) and quantitative bone histomorphometry. CD4+ T cells were purified at 20 months to quantify osteoclastogenic/inflammatory cytokine expression.ResultsAlthough cortical IRBL in young animals recovered with time, trabecular bone loss was permanent and exacerbated skeletal decline associated with natural aging. At 20 months of age, reconstituted CD4+ T cells express enhanced osteoclastogenic cytokines including RANKL, interleukin (IL)-1β, IL-17A, and tumor necrosis factor-α, consistent with elevated osteoclast numbers.ConclusionsImmune reconstitution bone loss in the trabecular compartment is permanent and further exacerbates bone loss due to natural aging. If validated in humans, interventions to limit IRBL may be important to prevent fractures in aging PWH.

BackgroundIn HIV infection, even under long-term antiretroviral therapy (ART), up to 20% of HIV-infected individuals fail to restore CD4+ T cell counts to the levels similar to those of healthy controls. The mechanisms of poor CD4+ T cell reconstitution on suppressive ART are not fully understood.MethodsHere, we tested the hypothesis that lipopolysaccharide (LPS) from bacteria enriched in the plasma from immune non-responders (INRs) contributes to blunted CD4+ T cell recovery on suppressive ART in HIV. We characterized plasma microbiome in HIV INRs (aviremic, CD4+ T cell counts < 350 cells/μl), immune responders (IRs, CD4+ T cell counts > 500 cells/μl), and healthy controls. Next, we analyzed the structure of the lipid A domain of three bacterial species identified by mass spectrometry (MS) and evaluated the LPS function through LPS induced proinflammatory responses and CD4+ T cell apoptosis in PBMCs. In comparison, we also evaluated plasma levels of proinflammatory cytokine and chemokine patterns in these three groups. At last, to study the causality of microbiome-blunted CD4+ T cell recovery in HIV, B6 mice were intraperitoneally (i.p.) injected with heat-killed Burkholderia fungorum, Serratia marcescens, or Phyllobacterium myrsinacearum, twice per week for total of eight weeks.FindingsINRs exhibited elevated plasma levels of total microbial translocation compared to the IRs and healthy controls. The most enriched bacteria were Burkholderia and Serratia in INRs and were Phyllobacterium in IRs. Further, unlike P. myrsinacearum LPS, B. fungorum and S. marcescens LPS induced proinflammatory responses and CD4+ T cell apoptosis in PBMCs, and gene profiles of bacteria-mediated cell activation pathways in THP-1 cells in vitro. Notably, LPS structural analysis by mass spectrometry revealed that lipid A from P. myrsinacearum exhibited a divergent structure consistent with weak toll-like receptor (TLR) 4 agonism, similar to the biological profile of probiotic bacteria. In contrast, lipid A from B. fungorum and S. marcescens showed structures more consistent with canonical TLR4 agonists stemming from proinflammatory bacterial strains. Finally, intraperitoneal (i.p.) injection of inactivated B. fungorum and S. marcescens but not P. myrsinacearum resulted in cell apoptosis in mesenteric lymph nodes of C57BL/6 mice in vivo.InterpretationThese results suggest that the microbial products are causally associated with INR phenotype. In summary, variation in blood microbial LPS immunogenicity may contribute to immune reconstitution in response to suppressive ART. Collectively, this work is consistent with immunologically silencing microbiome being causal and targetable with therapy in HIV.FundingThis work was supported by the National Institute of Allergy and Infectious Diseases (NIAID; R01 AI128864, Jiang) (NIAID; P30 AI027767, Saag/Health), the Medical Research Service at the Ralph H. Johnson VA Medical Center (merit grant VA CSRD MERIT I01 CX-002422, Jiang), and the National Institute of Aging (R21 AG074331, Scott). The SCOPE cohort was supported by the UCSF/Gladstone Institute of Virology & Immunology CFAR (P30 AI027763, Gandhi) and the CFAR Network of Integrated Clinical Systems (R24 AI067039, Saag). The National Center for Advancing Translational Sciences of the National Institutes of Health under Award Number UL1TR001450 (the pilot grant, Jiang). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Introduction: Cladribine tablet therapy is an efficacious treatment for multiple sclerosis (MS). Recently, we showed that one year after the initiation of cladribine treatment, T and B cell crosstalk was impaired, reducing potentially pathogenic effector functions along with a specific reduction of autoreactivity to RAS guanyl releasing protein 2 (RASGRP2). In the present study we conducted a longitudinal analysis of the effect of cladribine treatment in patients with RRMS, focusing on the extent to which the effects observed on T and B cell subsets and autoreactivity after one year of treatment are maintained, modulated, or amplified during the second year of treatment. Methods: In this case-control exploratory study, frequencies and absolute counts of peripheral T and B cell subsets and B cell cytokine production from untreated patients with relapsing-remitting MS (RRMS) and patients treated with cladribine for 52 (W52), 60 (W60), 72 (W72) and 96 (W96) weeks, were measured using flow cytometry. Autoreactivity was assessed using a FluoroSpot assay. Results: We found a substantial reduction in circulating memory B cells and proinflammatory B cell responses. Furthermore, we observed reduced T cell responses to autoantigens possibly presented by B cells (RASGRP2 and a-B crystallin (CRYAB)) at W52 and W96 and a further reduction in responses to the myelin antigens myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG) after 96 weeks. Conclusion: We conclude that the effects of cladribine observed after year one are maintained and, for some effects, even increased two years after the initiation of a full course of treatment with cladribine tablets. [ABSTRACT FROM AUTHOR]

Severe combined immunodeficient (SCID) mice serve as a critical model for human xenotransplantation studies, yet they often suffer from low engraftment rates and susceptibility to graft-versus-host disease (GVHD). Moreover, certain SCID strains demonstrate 'immune leakage', underscoring the need for novel model development. Here, we introduce an SCID mouse model with a targeted disruption of the dclre1c gene, encoding Artemis, which is essential for V(D)J recombination and DNA repair during T cell receptor (TCR) and B cell receptor (BCR) assembly. Artemis deficiency precipitates a profound immunodeficiency syndrome, marked by radiosensitivity and compromised T and B lymphocyte functionality. Utilizing CRISPR/Cas9-mediated gene editing, we generated dclre1c-deficient mice with an NOD genetic background. These mice exhibited a radiosensitive SCID phenotype, with pronounced DNA damage and defective thymic, splenic and lymph node development, culminating in reduced T and B lymphocyte populations. Notably, both cell lines and patient-derived tumor xenografts were successfully engrafted into these mice. Furthermore, the human immune system was effectively rebuilt following peripheral blood mononuclear cells (PBMCs) transplantation. The dclre1c-knockout NOD mice described herein represent a promising addition to the armamentarium of models for xenotransplantation, offering a valuable platform for advancing human immunobiological research. [ABSTRACT FROM AUTHOR]

The quality of immune reconstitution (IR) is crucial for the outcome of patients who received allogeneic hematopoietic stem cell transplantation (allo-HSCT), and is closely connected with infection, relapse and graft-versus-host disease (GvHD) which are the most important causes for transplantation failure. However, the IR pattern in the early stage after allo-HSCT, particularly haploidentical (HID) HSCT, remains unclear. In this retrospective study, we examined the T cell reconstitution of patients within the initial 30 days (n = 173) and 100 days (n = 122) after allo-HSCT with myeloablative condition (MAC), of which > 70% were HID HSCT, to assess the influence of IR on the transplant outcomes. By comparing 78 patients with good IR (GIR) to 44 patients with poor IR (PIR), we observed that GIR was associated with lower risk for Epstein–Barr virus (EBV) reactivation and cytomegalovirus (CMV) reactivation, but had no significant impacts on the survival outcomes (i.e., overall survival, event-free survival) and cumulative incidences of GvHD. Importantly, we found lymphocyte reconstitution pattern at day 30 after allo-HSCT would be a surrogate for IR evaluated at day 100. In the Cox proportional hazard model, early reconstitution of CD4+, CD4+CD25+, CD4+CD45RO+, CD4+CD25+CD27low, and CD8+ T cells at day 30 was reversely correlated with risk of EBV reactivation. Finally, we constructed a predictive model for EBV reactivation with CD8+ and CD4+CD45RO+ T cell proportions of the training cohort (n = 102), which was validated with a validation cohort (n = 37). In summary, our study found that the quality of IR at day 30 had a predictive value for the risk of EBV reactivation, and might provide guidance for close monitoring for EBV reactivation. [ABSTRACT FROM AUTHOR]

This study aims to develop and evaluate a model to predict the immune reconstitution among HIV/AIDS patients after antiretroviral therapy (ART). A total of 502 HIV/AIDS patients are randomized to the training cohort and evaluation cohort. Least absolute shrinkage and selection operator (LASSO) regression and multivariate logistic regression analysis are performed to identify the indicators and establish the nomogram for predicting the immune reconstitution. Decision curve analysis (DCA) and clinical impact curve (CIC) are used to evaluate the clinical effectiveness of the nomogram. Predictive factors included white blood cells (WBC), baseline CD4+ T‐cell counts (baseline CD4), ratio of effector regulatory T cells to resting regulatory T cells (eTreg/rTreg) and low‐density lipoprotein cholesterol (LDL‐C) and are incorporated into the nomogram. The area under the curve (AUC) is 0.812 (95% CI, 0.767∼0.851) and 0.794 (95%CI, 0.719∼0.857) in the training cohort and evaluation cohort, respectively. The calibration curve shows a high consistency between the predicted and actual observations. Moreover, DCA and CIC indicate that the nomogram has a superior net benefit in predicting poor immune reconstitution. A simple‐to‐use nomogram containing four routinely collected variables is developed and internally evaluated and can be used to predict the poor immune reconstitution in HIV/AIDS patients after ART. [ABSTRACT FROM AUTHOR]

Haploidentical hematopoietic stem cell transplantation (h-HSCT) is a therapeutic option to cure patients affected by hematologic malignancies. The kinetics and the quality of immune-reconstitution (IR) impact the clinical outcome of h-HSCT and limit the onset of life-threatening Human Cytomegalovirus (HCMV) infection/reactivation. Natural Killer (NK) cells are the first lymphocytes that recover after h-HSCT and they can provide rapid innate immune responses against opportunistic pathogens. By performing a longitudinal single-cell analysis of multiparametric flow-cytometry data, we show here that the persistence at high frequencies of CD158b1b2jneg/NKG2Apos/NKG2Cneg/NKp30pos/NKp46pos (KIRneg) NK cells is associated with HCMV infection/reactivation control. These KIRneg NK cells are "unlicensed", and are not terminal-differentiated lymphocytes appearing early during IR and mainly belonging to CD56bright/CD16neg and CD56bright/CD16pos subsets. KIRneg NK cells are enriched in oxidative and glucose metabolism pathways, produce interferon-γ, and are endowed with potent antiviral activity against HCMV ex vivo. Decreased frequencies of KIRneg NK cells early during IR are associated with clinically relevant HCMV replication. Taken together, our findings indicate that the prolonged persistence of KIRneg NK cells after h-HSCT could serve as a biomarker to better predict HCMV infection/reactivation. This phenomenon also paves the way to optimize anti-viral immune responses by enriching post-transplant donor lymphocyte infusions with KIRneg NK cells. [ABSTRACT FROM AUTHOR]

Background: Memory T cells are a heterogeneous population of immune cells that provide adaptive immunity. Its full recovery seems essential for graft-versus-tumor reactions that provide an opportunity for biological cure in patients with acute leukemia. The use of mismatched or haploidentical donors has increased, which has become possible because of modifications in graft versus host disease (GVHD) prophylaxis. Materials and Methods: Sixty-five leukemia patients (acute myeloid leukemia -- 40, acute lymphoblastic leukemia -- 25), median age 33 (17-61) years, underwent allo-HSCT from 2016 to 2019 in the National Research Centre for Hematology. Patients were divided into three groups based on the impact of GVHD prophylaxis on T cell recovery: horse antithymocyte globulin (ATG)-based regimen (n=32), horse ATG combined with posttransplant cyclophosphamide (PT-Cy) (n=18), and ex vivo T cell depletion (n=15). Results: The early period after transplantation (before day +100) was characterized by significantly lower absolute numbers of T naïve, memory stem and T central memory cells in peripheral blood in patients after ATG+PT-Cy-regimen or ex vivo T cell depletion than after ATG-based prophylaxis (p<0.05). Moreover, strong depletion of naïve T and memory stem cells prevents the development of GVHD, and determining the absolute number of CD8+ naïve T and memory stem cells with a cutoff of 1.31 cells per microliter seems to be a perspective in assessing the risks of developing acute GVHD (p=0.008). The dynamics of T cell recovery showed the involvement of either circulating or bone marrow resident T effector cells shortly after allogeneic transplantation in all patients, but the use of manipulated grafts with ex vivo T cell depletion requires the involvement of naïve and memory stem cells. There was no significant effect of T cell recovery on leukemia relapse after allogeneic transplantation. Conclusion: These experimental outcomes contribute to providing the best understanding of immunological events that occur early after transplantation and help in the rational choice of GVHD prophylaxis in patients who will undergo allogeneic transplantation. Our study demonstrated the comparable immunological effects of posttransplant cyclophosphamide and ex vivo T cell depletion and immunological inefficiency of horse ATG for GVHD prevention. [ABSTRACT FROM AUTHOR]

HLA antigen presentation and T‐cell mediated immunity are critical to control acute viral infection such as COVID‐19 caused by SARS‐CoV‐2. Recent data suggest that both the depth of peptide presentation and the breadth of the T‐cell repertoire are associated with disease outcome. It has also been shown that unexposed subjects can develop strong T‐cell responses against SARS‐CoV‐2 due to heterologous immunity. In this study, we explored the anti‐SARS‐CoV‐2 T‐cell repertoire by analyzing previously published T‐cell receptor (TCR) CDR3β immunosequencing data in a cohort of 116 healthy donors and in the context of immune reconstitution after allogeneic hematopoietic stem cell transplantation in 116 recipients collected during the pre‐COVID‐19 era. For this, 143,310 publicly available SARS‐CoV‐2 specific T‐cell sequences were investigated among the 3.5 million clonotypes in the cohort. We also performed HLA class I peptide binding predictions using the reference proteome of the virus and high resolution genotyping data in these patients. We could demonstrate that individuals are fully equipped at the genetic level to recognize SARS‐CoV‐2. This is evidenced by the 5% median cumulative frequency of clonotypes having their sequence matched to a SARS‐CoV‐2 specific T‐cell. In addition, any combination of HLA class I variants in this cohort is associated with a broad capacity of presenting hundreds of SARS‐CoV‐2 derived peptides. These results could be explained by heterologous immunity and random somatic TCR recombination. We speculate that these observations could explain the efficacy of the specific immune response against SARS‐CoV‐2 in individuals without risk factors of immunodeficiency and infected prior to vaccination. [ABSTRACT FROM AUTHOR]