J Korean Med Sci.  2026 Mar;41(9):e87. 10.3346/jkms.2026.41.e87.

Dynamics of Varicella Zoster Virus-Specific Immune Reconstitution and Impact of Varicella Vaccination in Pediatric Allogeneic Hematopoietic Stem Cell Transplant Recipients

• Kim G
• Lee S
• Lee Y
• Yoo R
• Kim JH
• Kang SH
• Kim H
• Koh KN
• Im HJ
• Lee J

• KMID: 2578992
• DOI: http://doi.org/10.3346/jkms.2026.41.e87

Abstract

Background
Varicella-zoster virus infection poses a significant risk to pediatric hematopoietic stem cell transplant recipients owing to compromised T-cell-mediated immunity. Although varicella-zoster virus-specific T-cell-mediated immunity is crucial for preventing reactivation, its reconstitution following allogeneic hematopoietic stem cell transplant in pediatric patients remains poorly characterized.
Methods
This prospective study assessed varicella-zoster virus-specific T-cell-mediated immunity in 32 pediatric allogeneic hematopoietic stem cell transplant recipients pretransplant and 1 and 3 months post-transplant using enzyme-linked immune absorbent spot assays. An extension study assessed varicella-zoster virus-specific T-cell-mediated immunity 2 years post-transplant in 15 recipients, including 8 after a single dose of varicella vaccination.
Results
Among the 32 recipients (median age, 10.5 years), only one experienced posthematopoietic stem cell transplant varicella-zoster virus infection. Median varicella-zoster virus-specific spot-forming cells were low during the first 3 months but increased significantly at 2 years (0 vs. 5.0/2.0 × 10⁵ peripheral blood mononuclear cells; P = 0.005), more evident in recipients with pre-hematopoietic stem cell transplant varicella-zoster virus R + serostatus (P = 0.006) and no prior varicella-zoster virus infection (P < 0.001). The presence of varicellazoster virus-specific T-cell-mediated immunity (≥ 1.0 spot-forming cells/2.0 × 10⁵ peripheral blood mononuclear cells) did not differ significantly by pre-hematopoietic stem cell transplant T-cell-mediated immunity status, serostatus, or vaccination history. Among seven recipients assessed at all five time points, recovery-level responses (≥ 5.0 spot-forming cells) increased from 28.6% pre-vaccination to 71.4% post-vaccination.
Conclusion
Varicella-zoster virus-specific T-cell-mediated immunity in pediatric hematopoietic stem cell transplant recipients remained low in the first 3 months but recovered significantly by 2 years post-hematopoietic stem cell transplant, with a boosting effect from varicella vaccination. Further studies are needed to assess the clinical significance of T-cell-mediated immunity and to guide personalized prevention strategies.

Keyword

Varicella-Zoster Virus; T Cell Immunity; Hematopoietic Stem Cell Transplantation; Children; Varicella Vaccines; Acyclovir Prophylaxis