To investigate how the human γδ T cell pool is shaped during ontogeny and how it is regenerated after transplantation of hematopoietic stem cells (HSCs), we applied an RNA-based next-generation sequencing approach to monitor the dynamics of the repertoires of γδ T cell antigen receptors (TCRs) before and after transplantation in a prospective cohort study. We found that repertoires of rearranged genes encoding γδ TCRs (TRG and TRD) in the peripheral blood of healthy adults were stable over time. Although a large fraction of human TRG repertoires consisted of public sequences, the TRD repertoires were private. In patients undergoing HSC transplantation, γδ T cells were quickly reconstituted; however, they had profoundly altered TCR repertoires. Notably, the clonal proliferation of individual virus-reactive γδ TCR sequences in patients with reactivation of cytomegalovirus revealed strong evidence for adaptive anti-viral γδ T cell immune responses.
The innate and adaptive roles of γδ T cells and their clonal γδ T cell receptors (TCRs) in immune responses are still unclear. Recent studies of γδ TCR repertoire dynamics showed massive expansion of individual Vδ1+ γδ T cell clones during viral infection. To judge whether such expansion is random or actually represents TCR-dependent adaptive immune responses, information about their cognate TCR ligands is required. Here, we used CRISPR/Cas9-mediated screening to identify HLA-DRA, RFXAP, RFX5, and CIITA as required for target cell recognition of a CMV-induced Vγ3Vδ1+ TCR, and further characterization revealed a direct interaction of this Vδ1+ TCR with the MHC II complex HLA-DR. Since MHC II is strongly upregulated by interferon-γ, these results suggest an inflammation-induced MHC-dependent immune response of γδ T cells.
Hematopoietic stem cell transplantation (HSCT) is a curative treatment option for selected diseases of the hematopoietic system. In the context of HSCT, bloodstream infections caused by Gram-negative bacteria (GNB) significantly contribute to morbidity and mortality. Antibiotic treatment of bloodstream infections with carbapenem-resistant (CR) GNB presents a particular challenge. As a part of our infection control management, the admission of a patient who was known to be colonized with a CR Acinetobacter baumannii triggered an active weekly screening of all patients to determine the prevalence and potential transmission of CR GNB and CR Acinetobacter baumannii in particular. Over a 3 month period a total of 71 patients were regularly screened for colonization with CR GNB. Including the index patient, a total of three patients showed CR GNB colonization representing a prevalence of 4.2%. Nosocomial transmission of CR Acinetobacter baumannii or other CR GNB was not observed. However, the index patient developed a subsequent bloodstream infection with the CR Acinetobacter baumannii, therefore empiric antibiotic therapy based on the known resistance profile was initiated. A weekly prevalence screening for CR GNB might be an effective monitoring tool for potential transmission, may enhance existing infection control management concepts and may support the decision making for empiric antibiotic therapy.
Identification of immune phenotypes linked to durable graft-versus-leukemia (GVL) response following donor lymphocyte infusions (DLI) is of high clinical relevance. In this prospective observational study of 13 AML relapse patients receiving therapeutic DLI, we longitudinally investigated changes in differentiation stages and exhaustion markers of T cell subsets using cluster analysis of 30-color spectral flow cytometry during 24 months follow-up. DLI cell products and patient samples after DLI were analyzed and correlated to the clinical outcome. Analysis of DLI cell products revealed heterogeneity in the proportions of naïve and antigen experienced T cells. Cell products containing lower levels of effector memory (eff/m) cells and higher amounts of naïve CD4+ and CD8+ T cells were associated with long-term remission. Furthermore, investigation of patient blood samples early after DLI showed that patients relapsing during the study period, had higher levels of CD4+ eff/m T cells and expressed a mosaic of surface molecules implying an exhausted functional state. Of note, this observation preceded the clinical diagnosis of relapse by five months. On the other hand, patients with continuous remission retained lower levels of exhausted CD4+ eff/m T cells more than four months post DLI. Moreover, lower frequencies of exhausted CD8+ eff/m T cells as well as higher amounts of CD4+temra CD45RO+ T cells were present in this group. These results imply the formation of functional long-term memory pool of T cells. Finally, unbiased sample analysis showed that DLI cell products with low levels of eff/m cells both in CD4+ and CD8+ T cell subpopulations associate with a lower relapse incidence. Additionally, competing risk analysis of patient samples taken early after DLI revealed that patients with high amounts of exhausted CD4+ eff/m T cells in their blood exhibited significantly higher rates of relapse. In conclusion, differentially activated T cell clusters, both in the DLI product and in patients post infusion, were associated with AML relapse after DLI. Our study suggests that differences in DLI cell product composition might influence GVL. In-depth monitoring of T cell dynamics post DLI might increase safety and efficacy of this immunotherapy, while further studies are needed to assess the functionality of T cells found in the DLI.
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