Introduction: Biomarkers predictive of vaccine response are needed to determine the optimal timing of immunization post-transplantation. We previously found that low T-cell ELISPOT responses to influenza vaccination were associated with lower likelihood of seroconversion. We hypothesize that baseline T-cell responses to a panel of HLA-restricted, influenza-specific epitopes correlate with fold increase in hemagglutination inhibition (HI) titers following influenza vaccination in pediatric solid organ transplant (SOT) recipients. Methods: PBMC and sera were collected from SOT recipients and healthy children before and after administration of the 2015/16 quadrivalent inactivated influenza vaccine. Seroconversion was defined as a 4-fold HI titer increase. Pre-immunization T-cell function was assessed by flow cytometry with intracellular cytokine staining to identify CD3+/CD69+/IFN-γ+ cells after stimulation with Staphylococcal enterotoxin B (SEB); pokeweed mitogen (PM); or peptide pool of influenza, CMV, and EBV-specific epitopes. Results: 34 children (mean age 12±5y; 18 kidney, 3 heart, 1 kidney/liver, 12 controls) were enrolled. Median time from transplant was 3y (range 4w–14y). 24%, 56%, 18% and 25% seroconverted to H1N1, H3N2 and 2 influenza B strains, respectively. 13 (62%) children did not convert to any strain. Nonseroconverters were more likely to be SOT recipients (84% vs 52%, p=0.06). Among SOT, nonseroconverters were more likely to have recent rejection (27% vs 0%, p=0.06). Percent of activated T cells after stimulation with SEB (1.2% vs 0.6%; p=0.2) and PM (0.4% vs 0.2%; p=0.2) did not differ significantly between seroconverters vs. nonseroconverters. However seroconverters had significantly greater T cell responses compared to nonseroconverters after stimulation with viral peptide pool (median 0.02%, IQR 0.02-0.05% vs 0.007%, IQR 0.002-0.01%; p=0.04). Conclusions: A more vigorous T-cell response to a viral peptide pool of influenza-specific epitopes was associated with greater likelihood of seroconversion following influenza immunization. If confirmed in a larger cohort, this assay could be used to predict the ideal time to immunize individual SOT recipients.

CITATION INFORMATION: Mayer E, Altrich M, Cordes C, Fausett S, Tepp J, Albrecht R, Fernandez-Sesma A, Herold B, Ramos I, Madan R. T Cell Responses to Viral Peptide Stimulation Predict Influenza Vaccine-Induced Seroconversion in Pediatric Solid Organ Transplant Recipients. Am J Transplant. 2017;17 (suppl 3).

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