T-cell responses over time in a mild hemophilia A inhibitor subject: epitope identification and transient immunogenicity of the corresponding self-peptide.
BACKGROUND
Antibodies that neutralize factor (F) VIII activity, clinically referred to as 'inhibitors', complicate the treatment of hemophilia A patients; current tolerance and bypass strategies are extremely costly and sometimes ineffective. The development of inhibitors requires T-cell help.


OBJECTIVE
We characterized T-cell responses of a subject with mild hemophilia A with missense genotype A2201P for one year following his initial inhibitor response, with the goals of defining the primary epitope(s) and its (their) MHC Class II restriction. We investigated the possible involvement of regulatory T cells in modulating immune responses.


METHODS
The subject developed high-titer FVIII-neutralizing antibodies (250 BU mL(-1)) that declined over time to 8 BU ml(-1). His clotting activity was initially impaired (3%) but returned to baseline (8-10%) within four weeks. MHC Class II tetramers were used to analyze his CD4 T cells, which were stimulated with peptides spanning the C2 domain. Responses of total and CD25-depleted CD4 cells to sequences containing A2201 (native), P2201 (hemophilic), and other predicted T-cell epitopes were evaluated.


CONCLUSIONS
An HLA-DRA-DRB1*0101 restricted T-cell epitope containing the wild-type A2201 sequence was identified. Interestingly, peptides containing A2201 were recognized by CD4 T cells at all time points, whereas a P2201 peptide was recognized only near the initial peak response. The responsiveness of CD25-depleted CD4 cells to an A2201 peptide was enhanced 11 and 19 weeks following inhibitor detection, suggesting the possible involvement of CD4+CD25+ regulatory T cells in modulating immune responses. Patient-derived T-cell clones proliferated in response to C2 protein and to peptides containing A2201 but not P2201.
James
E A
EA
Benaroya Research Institute, Seattle, WA 98104, USA.
Kwok
W W
WW
Ettinger
R A
RA
Thompson
A R
AR
Pratt
K P
KP
D000328:Adult; D001323:Autoantibodies / Q000097:blood*; D001777:Blood Coagulation; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018604:Epitope Mapping; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D005169:Factor VIII / Q000235:genetics / Q000276:immunology*; D005838:Genotype; D015234:HLA-A Antigens / Q000235:genetics / Q000276:immunology*; D059811:HLA-DRB1 Chains; D006467:Hemophilia A / Q000097:blood / Q000235:genetics / Q000276:immunology*; D006801:Humans; D053645:Interleukin-2 Receptor alpha Subunit / Q000032:analysis; D008297:Male; D020125:Mutation, Missense; D010641:Phenotype; D017634:Self Tolerance; D012720:Severity of Illness Index; D013997:Time Factors
D001323:Autoantibodies; D018984:Epitopes, T-Lymphocyte; D015234:HLA-A Antigens; D059811:HLA-DRB1 Chains; C487961:HLA-DRB1*01:01 antigen; D053645:Interleukin-2 Receptor alpha Subunit; D005169:Factor VIII