T follicular helper (Tfh) and regulatory (Tfr) cells are terminally differentiated cells found in germinal centers (GCs), specialized secondary lymphoid organ structures dedicated to antibody production. As such, follicular T (Tfol) cells are supposed to be specific for immunizing antigens, which has been reported for Tfh cells but is debated for Tfr cells. Here, we used high-throughput T cell receptor (TCR) sequencing to analyze the repertoires of Tfh and Tfr cells, at homeostasis and after immunization with self- or foreign antigens. We observed that, whatever the conditions, Tfh and Tfr cell repertoires are less diverse than those of effector T cells and Treg cells of the same tissues; surprisingly, these repertoires still represent thousands of different sequences, even after immunization with a single antigen that induces a 10-fold increase in Tfol cell numbers. Thorough analysis of the sharing and network of TCR sequences revealed that a specific response to the immunizing antigen can only, but hardly, be detected in Tfh cells immunized with a foreign antigen and Tfr cells immunized with a self-antigen. These antigen-specific responses are obscured by a global stimulation of Tfh and Tfr cells that appears to be antigen-independent. Altogether, our results suggest a major bystander Tfol cell activation during the immune response in the GCs.

Transformation of human T cells by herpesvirus saimiri allows the production of an unlimited number of T cells which express a functional T-cell receptor. In this study we transformed four T-cell lines derived from rheumatoid arthritis synovial membranes. The transformed T cells were mainly CD4+ and expressed the phenotype of activated T cells. They were grown for more than 1 year in the absence of mitogen or feeder cells, and three of them could be maintained without exogenous IL-2. The presence of viral DNA in the transformed cells was shown by in situ hybridization with a probe from the H-DNA region of the virus. No infectious virus could be recovered from the transformed cells. The relative proportion of the 24 different Vbeta families between the four transformed lines showed variations that increased with time. In the two T-cell lines transformed at an early stage of culture, the Vbeta2 family was maintained at about 10%. The dominant Vbeta2 clones that previously have been characterized in the patient were found in all transformed T-cell lines. We have thus shown the feasibility of obtaining transformed T cells from synovial membranes. They contain the dominant clones that are considered of potential importance for the disease, permitting further functional studies.

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Tolerogenic dendritic cells (DC) induce T-cell clonal deletion, anergy, generation and activation of regulatory T cells. In vitro production of TolDC has been accomplished, however the full molecular circuitry is not known. We aim to decipher the chemical signals and physical characteristics leading to T-cell tolerance in an artificial system. We have performed surface proteomic analysis of human peripheral blood cDC2 subset without and with in vitro stimulation with polyIC in vitro. The surface proteomics is based on biotinylation of sialic acids and the signal strength was 55-fold higher in the resting compared to the activated condition, presumably due to decreased sialation of glycoproteins in the activated cDC2. We found that label free quantification (LFQ), corrected for differences in sialation, agreed well with quantitative surface expression by flow cytometry. We combined the two datasets and ranked the top 120 glycoproteins with extracellular domains (ECD) > 60 amino acids by LFQ with approximately one third invariant, one third up-regulated/induced and one one-third down-regulated/lost on activation. The 120 ECD were expressed in HEK293 cells with C-terminal 10His tags and purified by Ni2+ affinity chromatography. Supported lipids bilayers (SLB) representing the tolerogenic and activating DC are being designed with different combinations of the 120 ECDs. We will adjust sialation to match resting and activated states. The SLB compositions will be tested for immunological synapse formation (fluorescent self-pMHC/CD80, ICAM-1 and CD58 for the cSMAC, pSMAC and dSMAC) and tolerance/activation spectrum with identification of relevant molecular combinations by machine learning.