Dissociated Humoral and Cellular Immune Responses to Recombinant Zoster Vaccine in Myeloproliferative Neoplasms Under JAK Inhibition: A Pilot Study.

Patients with myeloproliferative neoplasms (MPN) are at increased risk of herpes zoster, particularly during Janus kinase inhibitor (JAKi) therapy, yet the immunogenicity of recombinant zoster vaccine (RZV) in this setting remains incompletely characterized. We performed a prospective pilot translational study including 18 patients with MPN and a small age-matched healthy donor group (n = 4, descriptive reference only). Samples were collected at baseline, 21 days after the first dose, and 21 days after the second dose. Humoral response was assessed by anti-varicella-zoster virus (VZV) immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA), whereas antigen-specific cellular responses were evaluated after ex vivo stimulation with recombinant VZV glycoprotein E followed by flow cytometry and cytokine quantification. IgG levels increased over time in MPN patients, while cellular responses remained limited, heterogeneous, and not consistently enhanced. Cytokine production was low and variable across time points. Overall, RZV in MPN under JAKi was associated with detectable humoral responses but limited cellular activation, supporting an apparent discordance between humoral and cellular immune readouts under the experimental conditions used.