The principles of PK-tailored prophylaxis.

While prophylaxis with factor VIII (FVIII) is considered the first choice therapy for patients with severe haemophilia A the optimal prophylaxis regimen is still under scientific debate. A recent study demonstrated efficacy and safety of a PK-tailored prophylaxis regimen with rFVIII (ADVATE) aimed to maintain FVIII trough levels of ≥1% (19). The annual bleed rate (ABR) could be significantly reduced compared to the previous on-demand treatment period (p < 0.0001) and bodily pain, a health-related quality of life dimension of the SF-36v1 questionnaire also significantly improved (p = 0.0007). Thus PK-tailored prophylaxis with ADVATE might offer a valid alternative to standard prophylaxis. Open issues to be considered for implementation of PK-tailored prophylaxis are: What FVIII trough level is needed to prevent any bleed? Do patients with target joints need higher FVIII trough levels to stay bleed-free? Are there user-friendly tools available to calculate individualized PK-driven prophylaxis doses and frequency without the need for a full 9-sample PK curve? Current knowledge on these aspects as well as some considerations about the future of PK-tailored prophylaxis is discussed.

Monocytes of individual human subjects display heterogeneous bacterial uptake and antilisterial activity.

Peripheral blood monocytes (Mo) of normal human donors simultaneously exhibit two subsets differing in their functional activity towards the facultative intracellular bacterium Listeria monocytogenes. One subset (on average, 25% of total Mo) was characteristically able to ingest a large number of L. monocytogenes bacteria and permitted intracellular growth of these bacteria. The other Mo subpopulation (on average, 75% of total Mo) was far less active in phagocytosing L. monocytogenes and restricted intracellular L. monocytogenes growth. Electron microscopy revealed that the Listeria-permissive Mo subset allowed the bacteria to escape to the cytosol, a mechanism by which these bacteria evade the lethal attack of phagocytes. The Listeria-restrictive Mo subset, on the other hand, confined the bacteria to the phagolysosomes, where they were exposed to the killing mechanisms of the Mo. Permissiveness for L. monocytogenes growth was further associated with differences in the capacity of the Mo subsets to synthesize tumor necrosis factor alpha TNF-alpha), an important mediator in the defense against intracellular bacteria. Following challenge with L. monocytogenes, the Listeria-restrictive Mo subset secreted two to six times more TNF-alpha than did the Listeria-permissive Mo subset. Enhanced TNF-alpha secretion was paralleled by increased accumulation of TNF-alpha mRNA as assessed by quantitative PCR. Despite these functional differences, the two Mo subsets were indistinguishable with respect to expression of cell surface markers known to be involved in adherence and phagocytosis of microbes. A speculative physiological role of the two Mo subsets may lie in the dual function of Mo as microbicidal effector cells and accessory cells for antigen-specific immune reactions.