Factor VIII Inhibitors in Previously Treated Haemophilia A Patients with a Double Virus-inactivated Plasma Derived Factor VIII Concentrate

Antibodies to factor VIII (inhibitors) are usually produced at the beginning of treatment with factor VIII and are rare in multitransfused patients. Such antibodies are deemed to be patient-related, as supported by the description of a number of associated risk factors. However, a second category of inhibitors has recently been identified, namely antibodies occurring in multitransfused patients as a result of exposure to a particular factor VIII concentrate. A first outbreak of product-related inhibitors was recently described. The present paper describes the second well-documented occurrence of such inhibitors.

Eight out of 140 multitransfused patients with severe haemophilia A developed an inhibitor to factor VIII shortly after changing treatment to a double-virus inactivated plasma-derived factor VIII concentrate. In addition to solvent-detergent treatment, this concentrate was pasteurised at 63° C for 10 hours. Exposure to the pasteurised product before inhibitor detection ranged from 9 to 45 days. Inhibitor titers varied between 2.2 and 60 Bethesda Units and recovery of transfused factor VIII ranged from 0.21 to 0.68 (expressed as IU/dl factor VIII rise per IU/kg administered). In contrast to usual inhibitors in haemophilia A patients, these product-related inhibitors showed complex inhibition kinetics. They were found specific for the factor VIII light chain. The inhibitors gradually declined when exposure to the pasteurised product was stopped, despite further treatment with other factor VIII concentrates. The present data stress the importance of carefully monitored clinical studies, both in previously treated and previously untreated patients, before introduction of a new or modified clotting factor concentrate.

Increased synapse formation obtained by T cell epitopes containing a CxxC motif in flanking residues convert CD4+ T cells into cytolytic effectors

The nature of MHC class II-binding epitopes not only determines the specificity of T cell responses, but may also alter effector cell functions. Cytolytic CD4+ T cells have been observed primarily in anti-viral responses, but very little is known about the conditions under which they can be elicited. Their potential as regulators of immune responses, however, deserves investigations. We describe here that inclusion of a thiol-disulfide oxidoreductase motif within flanking residues of class II-restricted epitopes results, both in vitro and in vivo, in elicitation of antigen-specific cytolytic CD4+ T cells through increased synapse formation. We show that both naïve and polarized CD4+ T cells, including Th17 cells, can be converted by cognate recognition of such modified epitopes. Cytolytic CD4+ T cells induce apoptosis on APCs by Fas-FasL interaction. These findings potentially open the way towards a novel form of antigen-specific immunosuppression.

A Naturally-Processed Universal T Cell Epitope Is Located Within a Conserved Region of Der p 2: Implications for Allergen Sensitization and Immunotherapy

<i>Background:</i> Major allergens could represent a ‘port of entry’ to allergen polysensitization. The immunogenic properties of Der p 2 T cell epitopes were evaluated to test this hypothesis. <i>Material and Methods:</i> T cells were obtained from regional lymph nodes of mice belonging to four different haplotypes and used in proliferation assays using Der p 2 or synthetic peptides. <i>Results:</i> T cells from recombinant (r) Der p 2-immunized Balb/c mice (H-2^d) proliferated to an immunodominant region encompassing residues 21–35, which also stimulates T cells of mice expressing three alternative haplotypes (H-2^b, H-2^k and H-2^s), indicating the presence of a universal T cell epitope. Epitope mapping identified Ile28 as a critical H-2-binding residue for all four different haplotypes. p21–35 presents a sequence homology with FIS, another universal T cell epitope. FIS priming boosts immune responses to distinct weak immunogens. Balb/c mice primed with p21–35 or FIS produced stronger immune responses to transferrin upon administration of the latter than unprimed mice. Besides, this procedure profoundly affected the overall B cell response to rDer p 2. <i>Conclusion:</i> An immunodominant T cell epitope of Der p 2 behaves as a universal epitope and enhances responses to related and unrelated coadministered antigens. These findings have implications for the understanding of allergen polysensitization and for immunotherapy.