Reconstitution of endogenous interferon alpha by recombinant interferon inhairy cell leukemia

Recombinant human IFN alpha (rhIFN-alpha) plays an important role in the tr eatment of hairy cell Leukemia (HCL). However, the mechanisms leading to it s beneficial effect are not completely clarified, and there is no informati on on IFN-alpha gene expression in this disease. Therefore, we investigated the pattern of IFN-alpha gene expression and protein production in HCL and their potential regulation by rhIFN-alpha. Blood samples from 10 patients with HCL and 8 healthy donors (HD) were investigated. Expression of IFN-alp ha mRNA was assessed by reverse transcription-PCR analysis in peripheral bl ood mononuclear cells (PBMCs) under basal conditions and on induction with rhIFN-alpha and polyionosinic-polycytidylic acid [poly(I.C)]. IFN-alpha con centrations in plasma and culture supernatants were measured by immunoassay s, and intracellular IFN-LU was evaluated by fluorescence-activated cell so rting analysis. Results showed that, in contrast to blood samples from HDs, freshly isolated PBMCs from untreated HCL patients did not express IFN-alp ha mRNA, whereas IFN-alpha transcripts were found in patients who were unde r rhIFN-alpha therapy. Plasma of untreated patients contained no, or extrem ely low levels of, IFN-alpha as compared with plasma of treated patients an d HDs. Ew vivo treatment of PBMCs with rhIFN-alpha or poly(I.C) resulted in a remarkable up-regulation of IFN-alpha at the mRNA and protein level. In HCL, however, the amounts of IFN-alpha protein remained less than in HD, In hibition of IFN-alpha transcription was Found after exposure of PBMCs to se rum from untreated patients. Finally, a reduced capacity to produce IFN-alp ha was found within B- cell, T-cell, and monocyte compartments in HCL patie nts, which could be enhanced by rhIFN-alpha. The results demonstrate the ab ility of rhIFN-alpha to up-regulate the expression of IFN-alpha gene and pr otein production and suggest that priming the production of endogenous IFN- alpha is a critical step in the mechanism of action of rhIFN-alpha in HCL.