Cellular and Serologic Responses to Influenza Vaccination in Myeloproliferative Neoplasm Patients
Authors: How Chi-Joan , Nam Stella , Kok Charlene , Mukherjee Sonia , Bachanová Petra , Reeves Patrick , Hobbs Gabriela S. 
Published: December 2024

BACKGROUND
Patients with myeloproliferative neoplasms (MPNs) including essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF) experience immune dysregulation from clonal hematopoiesis, increased inflammation, and immunosuppressive treatments. Infection causes significant morbidity and mortality, and therefore annual influenza vaccination is recommended in all patients. However, the efficacy of influenza vaccine is unclear in the MPN population. We performed serologic testing and mass cytometry (CyTOF) to comprehensively profile innate and adaptive immunologic responses to influenza vaccination in MPN patients.

METHODS
Patients with a diagnosis of MPN by WHO 2016 criteria and eligible for influenza vaccination were recruited at Massachusetts General Hospital. Healthy participants with no history of malignancy were included as controls. Peripheral blood mononuclear cells (PBMCS) and plasma were collected at baseline and 1 month post-vaccination. All participants gave informed consent and the study protocol was approved by the Institutional Review Board.
Influenza hemagglutination inhibition (HAI) antibody titers against H1N1 and H3N2 were measured from patient and control sera. PBMC samples were labeled with a 45-antibody panel to characterize cell populations and functional markers and analyzed by CyTOF. Immune subsets and phenotypes were identified both manually and by computational clustering followed by statistical analyses by edgeR and ANOVA with Hidak correction.

RESULTS
22 MPN patients (9 ET, 7 MF, 1 PV, 3 MPN-U, 2 prefibrotic MF; 53.8% female; median age 61.84 years) and 12 healthy controls (75% female; median age 60) were enrolled and received quadrivalent influenza vaccination. Within MPN patients, 9 patients were on treatment with ruxolitinib, 10 patients were on hydroxyurea, and 3 patients were on no treatment.
In MPN patients, seroprotection as defined by a post-vaccination titer of &gt;1:40 occurred in 21/22 patients against H1N1 and 20/22 against H3N2; seroprotection occurred in all healthy controls, with no significant differences in post-vaccination HAI titers between MPN patients and controls for H1N1 (p=0.55) and H3N2 (p=0.19). Peptides from influenza were used to induce IFNg production and measured by CyTOF. Post-vaccination, peptide stimulation increased CD8+ IFNg+ T cells in healthy donors, while MPN showed a statistically significant increase in CD4+ IFNg+ T cells.
Additional analyses showed that after vaccination, MPN patients had increased CD123+ cells, diminished abundance of CXCR5+ B-cells, and an increased ratio of CD4+:CD8+ T-cells as compared to healthy controls. After vaccination, MPN patients demonstrated an increase in activated memory CD4+ T cells and proliferating NKT cells along with a diminution of activated neutrophils as compared to healthy controls. Vaccinated healthy controls exhibited increased CXCR5+ B cells, memory CD8+ Tbet+ T cells and naïve CD4+ T cells as compared to MPN patients. Stimulation with influenza specific peptides increased frequency of proliferating CD4+ T cells and CD8+ CD57+ (a marker of senescence) T cells in MPN patients, while healthy controls were increased in CD4+ CXCR5+ and activated memory CD8+ cells. Post vaccination we found that MF patients show decreased NKT cells, memory CD4+ T cells, and CD8+ IFNg+ T cells as compared to other MPN patients. MF patients also had a greater frequency of naïve CD8+ and memory CD8+ CCR6+ T cells compared to other MPN patients. These results suggest a greater immune dysregulation in MF patients. Patients treated with ruxolitinib showed expanded populations of NKT cells and decreased memory Th1 CD4+ CD57+ and memory CD8+ CCR6+ T cells compared to hydroxyurea-treated patients.

CONCLUSIONS
This is the first study to prospectively evaluate both antibody and cellular responses to influenza vaccination in MPN patients. Our results suggest that influenza vaccination has efficacy in MPNs based on adequate seroprotection rates and similar HAI titers between patients and healthy controls. However, all MPN patients display dysregulated cellular immune responses, with evidence of increased reliance on memory helper T cells (CD4+), as well as dysregulated B and cytolytic T cell (CD8+) responses. Further studies are needed to clarify whether these results translate into less clinical protection from influenza infection.