A Simple-to-Perform ifn-γ mRNA Gene Expression Assay on Whole Blood Accurately Appraises Varicella Zoster Virus-Specific Cell-Mediated Immunity After Allogeneic Hematopoietic Stem Cell Transplantation

Herpes zoster, which is due to the reactivation of Varicella zoster virus (VZV), is a leading cause of morbidity after allogeneic hematopoietic stem cell transplantation (allo-HSCT). While cell-mediated immunity (CMI) is critical to inhibiting VZV reactivation, CMI is not routinely assessed due to a lack of reliable tests. In this study, we aimed to evaluate VZV-specific CMI among allo-HSCT recipients (n = 60) and healthy individuals (HI, n = 17) through a panel of three immune functional assays after ex vivo stimulation by VZV antigen: quantification of (i) IFN-gamma release in the supernatants, (ii) T-cell proliferation after a 7-day stimulation of peripheral blood mononuclear cells (PBMC), and (iii) measurement of the ifn-gamma mRNA gene expression level after 24 h of stimulation of a whole-blood sample. VZV responsiveness was defined according to IFN-gamma release from VZV-stimulated PBMC. Upon VZV stimulation, we found that allo-HSCT recipients at a median time of 6 [5-8] months post-transplant had lower IFN-gamma release (median [IQR], 0.34 [0.12-8.56] vs. 409.5 [143.9-910.2] pg/ml, P <.0001) and fewer proliferating T cells (0.05 [0.01-0.57] % vs. 8.74 [3.12-15.05] %, P <.0001) than HI. A subset of allo-HSCT recipients (VZV-responders, n = 15/57, 26%) distinguished themselves from VZV-non-responders (n = 42/57, 74%; missing data, n = 3) by higher IFN-gamma release (80.45 [54.3-312.8] vs. 0.22 [0.12-0.42] pg/ml, P <.0001) and T-cell proliferation (2.22 [1.18-7.56] % vs. 0.002 [0.001-0.11] %, P <.0001), suggesting recovery of VZV-specific CMI. Interestingly, VZV responders had a significant fold increase in ifn-gamma gene expression, whereas ifn-gamma mRNA was not detected in whole blood of VZV-non-responders (P <.0001). This study is the first to suggest that measurement of ifn-gamma gene expression in 24-h-stimulated whole blood could be an accurate test of VZV-specific CMI. The routine use of this immune functional assay to guide antiviral prophylaxis at an individual level remains to be evaluated.

Automated summary

This study evaluated Varicella zoster virus (VZV)-specific cell-mediated immunity (CMI) in allo-HSCT recipients and healthy individuals using immune functional assays. The results showed that allo-HSCT recipients had lower IFN-gamma release and T-cell proliferation after VZV stimulation compared to healthy individuals. A subset of allo-HSCT recipients showed recovery of VZV-specific CMI, which was indicated by higher IFN-gamma release and T-cell proliferation. Measurement of ifn-gamma gene expression in 24-hour stimulated whole blood could be an accurate test for VZV-specific CMI. The routine use of this immune functional assay for antiviral prophylaxis needs further evaluation.