Weyand, Cornelia M.

Abstract Description The two key determinants of successful vaccines are the ability to induce a protective immune response and a long-lived immune memory. The mechanism determining durability and its contribution to the lower vaccine efficacy in older adults is elusive. We use varicella zoster virus (VZV) vaccination as a model that relies on cellular, not humoral immunity. We compared long-lived antigen-specific memory T cells in adults who were vaccinated at young (<20 years) or older age (>50 years) with a life-attenuated vaccine that confers sustained protection only in young age, or who received an adjuvanted subunit vaccine that is protective at older age. We stimulated PBMCs of vaccine recipients years after vaccination and collected VZV-reactive T cells for spectral flow cytometry and single-cell sequencing. While CD4 T cells were resilient to aging, VZV-specific CD8 T cells lost diversity and lacked stem-like features while gaining end-differentiated, NK-like signatures. These age-associated changes in CD8 T cells were not reversed with the effective subunit vaccine. Instead, this vaccine induced pro-inflammatory VZV-specific TH17 cells. TH17 cells in the less efficient vaccine response, albeit present, were skewed towards a FOXP3+ regulatory phenotype and deficient in TH1 polyfunctionality – a phenotypic shift that is in part controlled by lipid metabolic pathways. Our study uncovers traits of T cell dysfunction with age and informs vaccination efforts tailored towards healthy aging. Funding Sources NIH U19AI057266, R01AG045779, R01AI108891, R01AI129191, T32AG049672, Glenn Foundation for Medical Research Postdoctoral Fellowship, Robert and Arlene Kogod Center on Aging Career Development Award. Topic Categories Lymphocyte Differentiation and Peripheral Maintenance (LYM)

Abstract Superantigens encoded in the genome or released by bacteria have been identified as potent modulators of the murine immune system. High frequencies of mature or immature T cells are activated or intrathymically deleted when superantigens cross-link MHC class II molecules and the V beta element of the TCR. The V beta specificity discriminates superantigens from polyclonal T cell stimulators as well as specific Ag and determines the immunomodulatory role in shaping the T cell repertoire. A similar regulatory function of superantigens in the human immune system is less well established. Here, we have studied a series of human T cell clones sharing the TCR V beta 6 element and describe a surprising heterogeneity in their responsiveness to staphylococcal exotoxins. The V beta 6 gene segment had the ability to respond to all staphylococcal enterotoxins (SE); however, for individual T cell clones, there was a clear predominance of SE C3 reactivity compared to SE B and SE C2. The clonal heterogeneity of SE responsiveness did not correlate to sequence polymorphisms in the fourth hypervariable region of the V beta 6 segment, the presumptive binding site for superantigens. Superantigen reactivity was crucially influenced by the presenting HLA-DR molecule, especially when the superantigen served as a coligand, enhancing or suppressing the Ag-specific activation of the TCR. These data suggest that the correlation between human TCR V beta gene segments and superantigen responses is not stringent. Potential intrathymic deletion mechanisms controlled by superantigens may be less selective in humans and may result in a leakiness influenced by the host HLA-DR molecules.

Abstract We have studied the molecular diversity of the allogeneic TCR repertoire specific for the HLA-DR4 variant, DRB1*0404, by analyzing the V beta gene segment usage of CD4+ T cell clones from nine different donors and comparing the V beta repertoire in allospecific and unselected T cell populations. To investigate the forces shaping the repertoire of the alloreactive T cell response we compared the diversity of TCR specificities utilized in very similar and in disparate responder/stimulator combinations. Six of the responders shared the HLA-DRB1*0401 allele, which differs from the HLA-DRB1*0404 allele by only two amino acid substitutions at positions 71 and 86 of the HLA-DR beta 1 chain; three responders expressed HLA-DRB1 alleles with extensive polymorphisms compared with the stimulator HLA-DRB1 allele. In all nine responders, TCR specificities recruited to recognize HLA-DRB1*0404 were strongly biased toward the dominant usage of one to three V beta elements. Despite some degree of heterogeneity between different responders, the overall pattern was very similar with a hierarchy of TCR V beta elements expressed by HLA-DRB1*0404 specific T cells. A core group of V beta elements (V beta 6, 5, 2, 13.2, 18, and 7) was preferentially used, whereas other V beta elements including V beta 3, 4, and 8 were infrequently used or not used at all. Sequencing of the VDJ beta region from selected T cell clones showed no junctional bias associated with the preferential V beta gene segment usage. Surprisingly, the T cell diversity in focused and in complex alloreactive responses were equally biased. The finding that HLA-DR4+ and DR4- donors exhibited a similar bias supports the interpretation that the alpha-helical HLA-DR structure of the stimulator cell has a dominant contribution in shaping the alloreactive repertoire.