Application of blood and immunodeficiency gene detection in the diagnosis of hemophagocytic lymphohistiocytosis patients

Characteristics and specific differential gene analysis of the TCR immune repertoire in secondary adult HLH lymphocytes

BACKGROUND

Hemophagocytic lymphohistiocytosis (HLH) is a severe, life-threatening, and hyperinflammatory disorder characterized by excessive immune activation and systemic immune dysregulation. Despite advancements in diagnosis, the underlying alterations in the immune repertoire in HLH remain poorly understood. This study aimed to characterize remodeling in the T cell receptor (TCR) immune repertoire in patients with HLH, focusing on V(D)J gene usage, complementarity-determining region 3 (CDR3) diversity, and clonotypic distribution, to better understand the immunological basis of the disease.

METHODS

Thirty individuals were enrolled, including 16 untreated patients with HLH(U group), 4 patients with HLH undergoing post-induction therapy (T group), and 10 healthy controls (Hc group). Peripheral blood TCRβ sequencing was performed to analyze V(D)J gene usage, CDR3 length distribution, and repertoire diversity. The relative diversity index (RDI) and hierarchical clustering of V-J pairing frequencies were applied to evaluate immune repertoire alterations. Statistical analyses included one-way ANOVA and Wilcoxon rank-sum tests to assess group differences, with a significance threshold of P < 0.05.

RESULTS

Compared to healthy individuals, patients with HLH exhibited significant alterations in TCR diversity, including increased CDR3 length variability and shifts in V(D)J gene usage (P < 0.05). In particular, TRBV5-1 and TRBJ2-7 expression was observed in patients with HLH. The V-J pairing analysis demonstrated that HLH samples clustered distinctly from healthy controls, suggesting immune dysregulation. RDI analysis revealed a significantly higher diversity in the M-HLH group than in the non-M-HLH group (P < 0.05), indicating higher clonal expansion in the malignant subgroup. Following induction therapy, TCR diversity showed partial recovery (P < 0.05);however, the immune repertoire remained distinct from that of healthy individuals (P < 0.05).

CONCLUSIONS

HLH is associated with profound immune repertoire remodeling, particularly in V-J gene pairing and CDR3 diversity. The RDI values and significant differences in gene pairing suggest antigen-driven clonal expansion in patients with HLH. Immune repertoire profiling may act as an effective biomarker for HLH classification and disease monitoring. Further studies with larger cohorts and longitudinal data are required to validate these findings and explore their clinical application in HLH.

Human Immune Responses to Epstein-Barr Virus Highlighted by Immunodeficiencies

Inborn errors of immunity (IEIs) represent unique in natura models that uncover key components of immunity in humans, in particular those that predispose to infections. Epstein-Barr virus (EBV) is one of the most common opportunistic infectious agents in humans and is responsible for several diseases, including infectious mononucleosis, nonmalignant and malignant lymphoproliferative disorders, hemophagocytic lymphohistiocytosis, and smooth muscle and epithelial tumors. For most individuals, EBV infection persists for life without pathological consequences. IEIs that do not predispose to EBV infection suggest that innate and humoral responses are not necessary or redundant for the immune response to EBV. IEIs associated with high susceptibility to EBV infection provide unequivocal genetic proof of the central role of CD8+ T cell responses in immunity to EBV. They also highlight the distinct steps and pathways required for, on the one hand, the effector cytotoxic functions of CD8+ T cells and, on the other hand, the expansion and maturation of cytotoxic CD8+ T cells.

Genetic and clinical characteristics of primary hemophagocytic lymphohistiocytosis in children

To analyze the genetic variation and prognosis of primary hemophagocytic lymphohistiocytosis (pHLH) in children and the clinical features of isolated central nervous system HLH (CNS-HLH). We retrospectively analyzed the clinical and genetic data of 480 HLH children admitted to our hospital from September 2017 to September 2022. There were 66 patients (13.75%) with pHLH, and the median age was 3.21 years (0.17-12.92 years). Variants in UNC13D (22/66, 33.33%), PRF1 (20/66, 30.30%) and XIAP (11/66, 16.67%) were the most common. More CNS involvement was observed in pHLH patients than in secondary hemophagocytic lymphohistiocytosis (sHLH) patients (50% vs. 25.3%, P = 0.001). Eight pHLH patients had isolated CNS-HLH at onset, which progressed to systemic HLH within 10-30 days to several years. Among them, five patients who underwent hematopoietic stem cell transplantation (HSCT) survived without CNS sequelae, and the three patients who did not undergo HSCT died of disease progression or recurrence. Determination of natural killer (NK) cell cytotoxicity and CD107a levels had low sensitivity and specificity in the diagnosis of pHLH, especially in patients with PRF1 and XIAP mutations. The 3-year overall survival (OS) was significantly lower in pHLH patients than in sHLH patients (74.5% ± 14.7% vs. 89.2% ± 3.53%, P = 0.021) and in patients with CNS involvement than in those without (53.8% ± 26.07% vs. 94.4% ± 10.58%, P = 0.012). There was a significant difference in OS among pHLH patients with different gene variants (P = 0.032); patients with PRF1 variants had poor 3-year OS, and patients with XIAP variants had good 3-year OS (50% ± 28.22% and 100%, respectively). pHLH patients with distinct variants have different prognoses. Isolated CNS-HLH patients are easily misdiagnosed, and HSCT may be beneficial for these patients. Determination of NK cell cytotoxicity and CD107a levels cannot precisely distinguish pHLH from sHLH.

Inherited human ITK deficiency impairs IFN-γ immunity and underlies tuberculosis

Inborn errors of IFN-γ immunity can underlie tuberculosis (TB). We report three patients from two kindreds without EBV viremia or disease but with severe TB and inherited complete ITK deficiency, a condition associated with severe EBV disease that renders immunological studies challenging. They have CD4+ αβ T lymphocytopenia with a concomitant expansion of CD4-CD8- double-negative (DN) αβ and Vδ2- γδ T lymphocytes, both displaying a unique CD38+CD45RA+T-bet+EOMES- phenotype. Itk-deficient mice recapitulated an expansion of the γδ T and DN αβ T lymphocyte populations in the thymus and spleen, respectively. Moreover, the patients' T lymphocytes secrete small amounts of IFN-γ in response to TCR crosslinking, mitogens, or forced synapse formation with autologous B lymphocytes. Finally, the patients' total lymphocytes secrete small amounts of IFN-γ, and CD4+, CD8+, DN αβ T, Vδ2+ γδ T, and MAIT cells display impaired IFN-γ production in response to BCG. Inherited ITK deficiency undermines the development and function of various IFN-γ-producing T cell subsets, thereby underlying TB.