Detection of rare allelic variants of the interferon-alpha 2 gene in human genomic DNA

Design and validation of an immuno-PCR assay for IFN-α2b quantification in human plasma

Aim: Nowadays, IFN-α is considered a promising therapeutic target for systemic lupus erythematosus. An immuno-PCR (iPCR) was developed to quantify low amounts of IFN-α in human plasma followed by a deep analysis of the methodologic robustness throughout quality by design approach. Results: An accurate, sensitive, selective and versatile iPCR was validated. The critical iPCR procedural steps were identified, applying a Plackett–Burman design. Also, this assay demonstrated an outstanding LOD of 0.3 pg/ml. A significant aspect relies on its high versatility to detect and quantify other cytokines in human plasma as the appropriate biotinylated antibody is employed. Conclusion: This reliable iPCR assay can be clinically used as an alternative method for quantitating and detecting low IFN-α2b concentrations in human plasma samples.

Expression of biologically active human interferon alpha 2b in the milk of transgenic mice

Interferon alpha 2b (IFNα-2b) is an important immune regulator widely used in clinic, for the treatment of chronic hepatitis, hairy cell leukemia, chronic myelogenous leukemia and multiple myeloma, etc. The clinically used IFNα-2b is generally produced by E.Coli, which lacks the post-translational O-glycosylation presents on naturally synthesized protein, and has a short serum half-life. In this study, a transgenic cassette pBCN-IFN-pA-CMV-EGFP was constructed, with a 5.2 kb beta-casein regulation fragment from Jersey cow and a 6×His tagged human Interferon alpha 2b (hIFNα-2b) gene fragment. By using pronuclear microinjection technique, transgenic mice were generated and the expression of IFNα-2b in the milk was assayed. The hIFNα-2b was correctly translated in milk of transgenic mice according to Western blot analysis. The expression level of hIFNα-2b was varied among the transgenic mice, and the highest one was about 29.71 μg/L. The recombinant protein exhibited biological activity in vitro by increasing the luminescence value and the MxA gene expression in established WISH cells, and the specific activity is approximately 2.8 × 10(7 )IU/mg. The expression of recombinant hIFNα-2b in mammary glands of transgenic mice constitutes an important step towards low-cost and full biological activity production of this protein drug in mammary gland bioreactor.

Stable high volumetric production of glycosylated human recombinant IFNalpha2b in HEK293 cells

Background

Mammalian cells are becoming the prevailing expression system for the production of recombinant proteins because of their capacity for proper protein folding, assembly, and post-translational modifications. These systems currently allow high volumetric production of monoclonal recombinant antibodies in the range of grams per litre. However their use for large-scale expression of cytokines typically results in much lower volumetric productivity.

Results

We have engineered a HEK293 cell clone for high level production of human recombinant glycosylated IFNα2b and developed a rapid and efficient method for its purification. This clone steadily produces more than 200 mg (up to 333 mg) of human recombinant IFNα2b per liter of serum-free culture, which can be purified by a single-step cation-exchange chromatography following media acidification and clarification. This rapid procedure yields 98% pure IFNα2b with a recovery greater than 70%. Purified IFNα2b migrates on SDS-PAGE as two species, a major 21 kDa band and a minor 19 kDa band. N-terminal sequences of both forms are identical and correspond to the expected mature protein. Purified IFNα2b elutes at neutral pH as a single peak with an apparent molecular weight of 44,000 Da as determined by size-exclusion chromatography. The presence of intramolecular and absence of intermolecular disulfide bridges is evidenced by the fact that non-reduced IFNα2b has a greater electrophoretic mobility than the reduced form. Treatment of purified IFNα2b with neuraminidase followed by O-glycosidase both increases electrophoretic mobility, indicating the presence of sialylated O-linked glycan. A detailed analysis of glycosylation by mass spectroscopy identifies disialylated and monosialylated forms as the major constituents of purified IFNα2b. Electron transfer dissociation (ETD) shows that the glycans are linked to the expected threonine at position 106. Other minor glycosylated forms and non-sialylated species are also detected, similar to IFNα2b produced naturally by lymphocytes. Further, the HEK293-produced IFNα2b is biologically active as shown with reporter gene and antiviral assays.

Conclusion

These results show that the HEK293 cell line is an efficient and valuable host for the production of biologically active and glycosylated human IFNα2b.

Confirmation of QTL on porcine chromosomes 1 and 8 influencing leukocyte numbers, haematological parameters and leukocyte function

A genome wide search in European Wild Boar x Swedish Yorkshire (W x Y) inter-cross pigs has earlier identified quantitative trait loci (QTL) for leucocyte number and function on porcine chromosomes 1 and 8 (SSC 1 and 8). To verify the involvement of these chromosomal regions in the regulation of haematocrit (Hem) and haemoglobin (Hb) levels, leucocyte numbers and in vitro leukocyte functions (mitogen induced proliferation and IL-2 production, virus induced interferon-alpha production and neutrophil phagocytosis), animals of different genetic backgrounds were analysed. The animals comprised a back-cross sire family (n=47) of W x Y pigs and six crossbred [Y x Landrace (L)] sire families (n=191). They were genotyped for 16 genetic markers and an interval analysis was performed. On SSC1, a QTL close to S0082 on the q-arm that influenced numbers of white blood cells in L x Y pigs and numbers of band neutrophils and CD8(+) cells in W x Y pigs was identified (P<or=0.01). An additional SSC1 QTL was identified on the p-arm close to S0008 with influence on numbers of CD2(+) cells in W x Y pigs (P<or=0.05). On SSC8, a QTL influencing Hb (P<or=0.01) and Hem (P<or=0.05) levels was identified close to KIT in the W x Y pigs. For L x Y pigs, a second QTL, distal to KIT and close to S0069, on SSC8 influenced the numbers of MHCII(+) cells and mitogen induced proliferation (P<or=0.05), whilst the QTL close to KIT influenced the number of IgM(+) cells in these pigs (P<or=0.05). The results confirm the involvement of earlier identified regions of SSC1 and SSC8 on porcine immune parameters and some candidate genes were suggested.

Determination of interferon-alpha2 allele composition in the genomic DNA from healthy volunteers and leukemic patients in Japan

The three interferon-alpha2 (IFN-alpha2) sequences identified to date differ from each other in just two nucleotide positions, both of which result in changes in amino acids. Thus, the mature IFN-alpha2a protein product is characterized by a lysine residue at position 23 (AAA) and a histidine at position 34 (CAA), IFN-alpha2b has an arginine at position 23 (AGA) and histidine at position 34 (CAT), and IFN-alpha2c has arginine residues at both positions 23 (AGA) and 34 (CGT). These nucleotide variations in the DNA sequence can be distinguished by selective restriction enzyme analysis. We studied the distributions of the three IFN-alpha2 variants by analyzing chromosomal DNA from 103 Japanese volunteers and 33 patients with hematologic disorders. Fragments of 238 bp and 617 bp of the IFN-alpha2 gene containing codons 23 and 34 were amplified by PCR using specific primers, and the PCR products were analyzed with specific restriction nucleases to identify the IFN-alpha2 variant sequences. Only IFN-alpha2b gene was detected in normal volunteers, and no IFN-alpha2a gene was detected in Japanese subjects. However, IFN-alpha2c was detected in 4 of 33 (12.1%) patients with leukemia.

The incidence and clinical significance of antibodies to interferon-a in patients with solid tumors

It is well known that natural and recombinant proteins can cause antibody formation in the host. We have studied the incidence of binding and neutralizing antibodies in carcinoid patients (n = 327). All together 204 patients received interferon-alpha 2b (Intron-A), median does 15 MU range 9-35 MU/week subcutaneously and 51% of the patients developed binding antibodies by immunoassay and 17% showed positive neutralization assay but high titer antibodies (> 800 NU/ml) were only found in 4% of the patients. The median time until the development of binding antibodies was 26 months and neutralizing antibodies 25 months. Twenty-nine patients received interferon-alpha 2a (Roferon), median does 18 MU/week subcutaneously and 45% developed binding antibodies, 38% had positive neutralization assay and 28% presented high titer antibodies. Binding and neutralizing antibodies occurred at the same time after median six months of treatment. Patients treated with Wellferon (n = 45) and leukocyte interferon (n = 48), median dose of 15 MU/week subcutaneously did not develop any neutralizing antibodies. The majority of the interferon-alpha 2 antibodies were of the IgG isotype. The clinical relevance of the development of high titer neutralizing antibodies was evaluated in the patients. All together 17 patients developed high titer neutralizing antibodies and of these 12 patients showed loss of antitumor response measured as increased level of tumor markers and of tumor progression. In nine of these patients a switch to human leukocyte interferon reinstituted an antitumor response. Neutralizing antibodies against recombinant interferon-alpha 2a and 2b might occur in patients with carcinoid tumors. The incidence of high titer neutralizing antibodies is significantly higher in patients treated with interferon-alpha 2a compared to interferon-alpha 2b. A significant number of patients lost the antitumor effect during development of neutralizing antibodies at high titers, but human leukocyte interferon can be used as rescue treatment.

Transcription of interferon-alpha 2 alleles from virus-induced human leucocytes and lymphoblastoid cells of African origin

It has been previously shown that the genomic DNA of both the lymphoblastoid cell line (Namalwa) and certain human donors (of African origin) contain sequences corresponding to two allelic variants, b and c, of the interferon-alpha 2 gene (IFNA2). Little is known however about the relative expression of these two alleles in heterozygous cells. We have therefore examined the transcription of allelic variants of the human IFNA2 locus by both normal human leucocytes (from a heterozygous donor) and Namalwa cells. Analysis of cDNA clones identified sequences of both allelic variants, IFNA2b and c, indicating active transcription by both cell types. Analysis of tryptic and peptic peptides derived from purified IFN-alpha 2 also demonstrated both IFN-alpha 2b and IFN-alpha 2c proteins. Populations of virus induced heterozygous cells can therefore effectively transcribe and secrete both forms of IFN-alpha 2 simultaneously, with no apparent restrictions on expression of either allele.