Cellular and humoral immunity elicited by influenza vaccines in pediatric hematopoietic-stem cell transplantation

Immunity induced by influenza vaccines following hematopoietic stem-cell transplantation (HSCT) is poorly understood.Here, 14 pediatric recipients (mean age: 6 years) received H1N1 (n = 9) or H1N1/H3N2 (n = 5) vaccines at a median of 5.7 months post-HSCT (HLA-identical related bone-marrow graft: 10/14). Fourteen clinically-matched non-vaccinated recipients were included as controls. Cellular response to vaccination was assessed by a T-cell proliferation assay. Humoral response was assessed by H1N1-specific antibody titration. IL2 and IFNγ responses to influenza were also evaluated by an intracellular cytokine accumulation method for some of the recipients.Higher proliferative responses to H1N1 (p = 0.0001) and higher H1N1-specific antibody titers (p < 0.02) were observed in vaccines opposed to non-vaccinated recipients. In some cases, proliferative responses to H1N1 developed while at the same time antibody titers did not reach protective (⩾1:40) levels. Most recipients vaccinated with only the H1N1 strain had proliferative responses to both H1N1 and H3N2 (median stimulation index H1N1: 96, H3N2: 126 in responders). Finally, IL2 responses predominated over IFNγ responses (p < 0.02) to influenza viruses in responders.In conclusion, H1N1 vaccination induced substantial cell-mediated immunity, and to a lesser extent, humoral immunity at early times post-HSCT. H1N1/H3N2 T-cell cross-reactivity and protective (IL2) rather than effector (IFNγ) cytokinic profiles were elicited.