Genetic engineering of a Lymantria dispar nuclear polyhedrosis virus for expression of foreign genes

N-glycan structures of human transferrin produced by Lymantria dispar (gypsy moth) cells using the LdMNPV expression system

N-glycan structures of recombinant human serum transferrin (hTf) expressed by Lymantria dispar (gypsy moth) 652Y cells were determined. The gene encoding hTf was incorporated into a Lymantria dispar nucleopolyhedrovirus (LdMNPV) under the control of the polyhedrin promoter. This virus was then used to infect Ld652Y cells, and the recombinant protein was harvested at 120 h postinfection. N-glycans were released from the purified recombinant human serum transferrin and derivatized with 2-aminopyridine; the glycan structures were analyzed by a two-dimensional HPLC and MALDI-TOF MS. Structures of 11 glycans (88.8% of total N-glycans) were elucidated. The glycan analysis revealed that the most abundant glycans were Man1-3(+/-Fucalpha6)GlcNAc2 (75.5%) and GlcNAcMan3(+/-Fucalpha6)GlcNAc2 (7.4%). There was only approximately 6% of high-mannose type glycans identified. Nearly half (49.8%) of the total N-glycans contained alpha(1,6)-fucosylation on the Asn-linked GlcNAc residue. However alpha(1,3)-fucosylation on the same GlcNAc, often found in N-glycans produced by other insects and insect cells, was not detected. Inclusion of fetal bovine serum in culture media had little effect on the N-glycan structures of the recombinant human serum transferrin obtained.

Stable cell lines expressing baculovirus P35: resistance to apoptosis and nutrient stress, and increased glycoprotein secretion

The baculovirus P35 protein is a caspase inhibitor that prevents the induction of apoptosis during infection of Sf21 cells by Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV). P35 inhibits the induction of apoptosis in a broad range of cells and circumstances. In this study, we examined the effects of constitutive cellular P35 expression on the response of cells to stressful culture conditions and on protein production in AcMNPV infected cells. Sf9 cell lines expressing AcMNPV P35 or an epitope-tagged P35 protein were generated using a double selection technique, involving selection in the antibiotic G418, followed by a second round of selection by exposure to actinomycin D, a potent inducer of apoptosis in Sf9 cells. Clonal cell lines were generated and examined for (1) resistance to actinomycin D induced apoptosis, (2) resistance to nutrient deprivation, and (3) baculovirus expression of intracellular and secreted proteins. When compared with Sf9 cells, two P35-expressing cell lines (Sf9P35AcV5-1 and Sf9P35AcV5-3) showed increased resistance to actinomycin D-induced apoptosis and a profound resistance to nutrient deprivation. When these cell lines were infected with a recombinant baculovirus expressing a secreted glycoprotein (secreted alkaline phosphatase), expression of the glycoprotein from these cells exceeded that from the parental Sf9 cells and was comparable to expression levels obtained from Tn5B1-4 cells, the best available cell line for high-level expression. Increased levels of protein secretion in Sf9P35AcV5-1 and Sf9P35AcV5-3 cells appear to result from a prolonged infection cycle and accumulation of the secreted glycoprotein.

A field release of genetically engineered gypsy moth (Lymantria dispar L.) nuclear polyhedrosis virus (LdNPV)

The gypsy moth (Lymantria dispar L.) nuclear polyhedrosis virus was genetically engineered for nonpersistence by removal of the gene coding for polyhedrin production and stabilized using a coocclusion process. A beta-galactosidase marker gene was inserted into the genetically engineered virus (LdGEV) so that infected larvae could be tested for its presence using a colorimetric assay. In 1993, LdGEV-infected gypsy moths were released in a forested plot in Massachusetts to test for spread and persistence. A similar forested plot 2 km away served as a control. For 3 years (1993-1995), gypsy moths were established in the two plots in Massachusetts to serve as test and control populations. Each week, larvae were collected from both plots. These field-collected larvae were reared individually, checked for mortality, and then tested for the presence of beta-galactosidase. Other gypsy moth larvae were confined on LdGEV-contaminated foliage for 1 week and then treated as the field-collected larvae. The LdGEV was sought in bark, litter, and soil samples collected from each plot. To verify the presence of the LdGEV, polymerase chain reaction, slot blot DNA hybridization, and restriction enzyme analysis were also used on larval samples. Field-collected larvae infected with the engineered virus were recovered in the release plot in 1993, but not in subsequent years; no field-collected larvae from the control plot contained the engineered virus. Larvae confined on LdGEV-contaminated foliage were killed by the virus. No LdGEV was recovered from bark, litter, or soil samples from either of the plots.

Transfection techniques for producing recombinant baculoviruses

The production of recombinant baculoviruses usually employs cotransfection of insect tissue-culture cells with viral and transfer-plasmid DNAs. The preparation and storage of viral and plasmid DNAs suitable for optimal transfection of insect cells are discussed. Electroporation, calcium-phosphate, and lipofection transfection techniques are presented with a discussion of their relative advantages. The rates of recombinant virus formation are compared using viral infection/plasmid transfection protocols versus cotransfection of cells with transfer-plasmid and viral DNAs.