Lineages of human T-cell clones, including T helper 17/T helper 1 cells, isolated at different stages of anti–factor VIII immune responses

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Abstract
The development of neutralizing antibodies (inhibitors) after factor VIII (FVIII) infusions is a serious complication that affects approximately one-quarter of hemophilia A patients who have access to replacement therapy. To investigate the differentiation of naive T cells into FVIII-specific helper T cells that promote B-cell activation and antibody secretion, HLA-DRA-DRB1*0101-restricted T-cell clones that respond to a specific epitope in FVIII were isolated from a mild hemophilia A subject (the proband) 19 weeks and 21 months after his development of a high-titer inhibitor. Clones responding to the same epitope were also isolated from his multiply infused brother, who has not developed a clinically significant inhibitor. The 19-week proband clones were T helper (TH)17/TH1- or TH1/TH2-polarized, whereas all 8 clones isolated 21 months postinhibitor development were TH2-polarized cells. In contrast, all 6 clones from the brother who did not develop an inhibitor were TH1-polarized, indicating that tolerance to FVIII can be maintained even with circulating TH1-polarized cells that respond vigorously to in vitro FVIII stimulation. This is the first evidence that TH17/TH1-polarized cells play a role in hemophilic immune responses to FVIII. Furthermore, this is the first report of successful isolation and expansion of antigen-specific human TH17/TH1 clones using standard culture conditions.