What Plasma Level of Interferon-γ Indicates in Systemic Chronic Active Epstein-Barr Virus Infection

Background and Aim

Systemic chronic active Epstein-Barr virus infection (sCAEBV) is an intractable and progressive disease of which the symptoms include persistent or recurrent inflammation and harboring EBV-infected clonally proliferating T- or NK-cells. 24% of sCAEBV patients progress to hemophagocytic lymphohistiocytosis (HLH), a life-threatening condition. (Blood Adv. 2020;4:p2918) The presence of HLH at hematopoietic stem cell transplantation is associated with poor survival in sCAEBV (BMT. 2016;15;p879).

Interferon-γ (IFN-γ) plays pivotal roles in developing HLH, and antagonistic anti-IFN-γ antibody is effective against HLH (N Engl J Med 2020;382:p1811). In this study, we examined the plasma level of IFN-γ to investigate its impact on disease conditions of sCAEBV and its possibility as a therapeutic target.

Methods

sCAEBV was diagnosed based on following criteria which confirm with the definition of CAEBV in the WHO 2017 classification:

(1) elevated EBV-DNA load in peripheral blood (PB) (>10 ^2.5 copies/μg DNA)

(2) EBV infection of T- or NK-cells (see below) in the affected tissues or PB

(3) systemic inflammatory symptoms persisting for more than three months

(4) exclusion of other possible diagnoses: primary infection of EBV, autoimmune disease, congenital immunodeficiency, HIV, and other immunodeficiencies or underlying diseases with potential immunosuppression

Patients who fulfilled all criteria (1) to (4) were diagnosed as sCAEBV. (Blood Adv. 2020;4(13):2918-2926.)

We defined a patient's condition as active disease when presenting any of following persistent inflammation: fever, liver dysfunction, progressive skin lesions, vasculitis, or uveitis. The plasma concentration of IFN-γ was measured by high sensitivity cytokine beads assay. mRNA was measured by real-time RT-PCR using TaqMan ^® system.

Results

We examined 18 sCAEBV patients (CD4 type n = 7, CD8 type n = 1, and CD56 type n = 10). Their IFN-γ plasma levels were significantly higher than those of healthy donors. The levels in sCAEBV patients with active disease were higher than those with inactive disease. The mRNA expression of IFN-γ was detected in EBV-infected cells of all patients. A patient whose plasma IFN-γ was extremely high harbored HLH with markedly high expression of the mRNA of IFN-γ in EBV-infected cells, but there was no statistical correlation between the plasma IFN-γ levels and the mRNA levels of EBV-infected cells.

Discussion

Our findings infer IFN-γ's role in the inflammation of sCAEBV. The mRNA expression of IFN-γ was detected in EBV-infected cells of all patients. We discovered earlier that STAT3, a responsible transcriptional factor for IFN-γ expression, is constitutively activated in EBV-infected T- or NK-cells of CAEBV (Oncotarget.2018; 9;31077). Thus, we suspected that IFN-γ is produced by EBV-infected cells. Meanwhile, there was no statistical correlation between the plasma IFN-γ levels and the mRNA levels of EBV-infected cells as a whole. The proliferation of non-infected immunocompetent cells, such as NK cells, CD8-positive T cells, macrophages, and histiocytes, are often detected in the lesions of CAEBV. These cells also possibly produce IFN-γ.

sCAEBV patients accompanied by hemophagocytic lymphohistiocytosis (HLH) had significantly higher IFN-γ levels in the serum compared to those without HLH. There was a report on emapalumab's effect on primary HLH. We expect emapalumab, a human anti-IFN-γ, is effective to sCAEBV patients, particularly who is harboring HLH．

Conclusion

Plasma IFN-γ in sCAEBV indicates disease activity and potentially be a therapeutic target.