New high-technology products for the treatment of haemophilia.

ABSTRACT

This review will focus on new technologies in development that promise to lead to further advances in haemophilia therapeutics. There has been continued interest in the bioengineering of recombinant factor VIII (rFVIII) and factor IX (rFIX) with improved function to overcome some of the limitations in current treatment, the high costs of therapy and to increase availability to a broader world haemophilia population. Bioengineered forms of rFVIII, rFIX or alternative haemostatic molecules may ultimately have an impact on improving the efficacy of therapeutic strategies for the haemophilias by improving biosynthesis and secretion, functional activity, half-life and immunogenicity. Preventing and suppressing inhibitors to factor (F) VIII remain a challenge for both clinicians and scientists. Recent experiments have shown that it is possible to obtain anti-idiotypic antibodies with a number of desirable properties (i) strong binding avidity to FVIII inhibitors; (ii) neutralization of inhibitory activity both in vitro and in vivo; (iii) cross-reactivity with antibodies from unrelated patients, and (iv) no interference with FVIII function. An alternative, although complementary approach, makes use of peptides derived from filamentous-phage random libraries. Mimotopes of FVIII can be obtained, which bind to the paratope of inhibitory activity and neutralize their activity both in vitro and in vivo. In this paper, we review advanced genetic strategies for haemophilia therapy. Until recently the traditional concept for gene transfer of inherited and acquired haematological diseases has been focused on how best to obtain stable insertion of a cDNA into a target-cell genome, allowing expression of a therapeutic protein. However, as gene-transfer vector systems continue to improve, the requirement for regulated gene transcription and hence regulated protein expression will become more critical. Inappropriate protein expression levels or expression of transferred cDNAs in non-intended cell types or tissues may lead to target-cell toxicity or activation of unwanted host immune responses. Regulated protein expression requires that the transferred gene be transferred with its own regulatory cassette that allows for gene transcription and translation approaching that of the normal gene in its endogenous context. New molecular techniques, in particular the use of RNA molecules, now allow for transcription of corrective genes that mimic the normal state.