Serumfree culture of the suspension cell line QB-Tn9-4s of the cabbage looper, Trichoplusia ni, is highly productive for virus replication and recombinant protein expression

Serumfree cultures of insect cells play an important role in the fields of protein engineering, medicine, and biology. In this paper, the suspension cell line QB-Tn9-4s of Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae) was successfully adapted to serumfree Sf-900 III medium and passaged for 52 generations. The adapted QB-Tn9-4s cells grew faster. Their population doubling time shortened from 27.4 hr in serum-containing medium to 24.1 hr, and their maximal density increased by 1.83-fold, reaching 3.50 ×10(6) cells/mL in serumfree culture in T-flasks. The cells readily adapted to spinner culture, with maximum cell density of 4.40 × 10(6) cells/mL in a spinner flask. Although the infection rate of Autographa californica multiple nucleopolyhedrovirus and production of occlusion bodies (OBs) of the adapted QB-Tn9-4s cells were 91.0% and 85.4 OBs/cell, respectively, similar to those of QB-Tn9-4s cells cultured in serum-containing medium and control BTI-Tn5B1-4 cells, their budded virus titer was 4.97 ×10(7) TCID50/mL, significantly higher than those of the latter two. In addition, the expression levels of β-galactosidase at six days postinfection and secreted alkaline phosphatase at seven days postinfection in the adapted QB-Tn9-4s cells reached 2.98 ± 0.15×10(4) IU/mL and 3.34 ± 0.13 IU/mL, respectively, significantly higher than those of QB-Tn9-4s and control BTI-Tn5B1-4 cultured in serum-containing media. The above findings establish a foundation for industrial production of virus and recombinant proteins in QB-Tn9-4s serumfree culture.

Expression of the green fluorescent protein carried by Autographa californica multiple nucleopolyhedrovirus in insect cell lines

A recombinant AcMNPV containing the green fluorescent protein (gfp) gene under the polyhedrin promoter (polh) was used to investigate the expression of the gfp gene as well as the production of recombinant extracellular virus in 14 continuous insect cell lines, including Heliothis virescens (BCIRL-HV-AM1), Helicoverpa zea (BCIRL-HZ-AM1), Anticarsia gemmatalis (BCIRL-AG-AM1), Trichoplusia ni (TN-CL1), Spodoptera frugiperda (IPLB-SF21), Spodoptera exigua (BCIRL/AMCY-Se-E1 and BCIRL/AMCY-Se-E5), Bombyx mori (BMN), Sf9 (a clone of IPLB-SF21), and five cell line clones of BCIRL-HV-AM1. The susceptibility of the cell lines to the recombinant virus (AcMNPV.GFP) was ascertained by calculating the mean percentage number of green light-emitting cells as well as by TCID50 titration of extracellular virus with fluorescence as a sign of infection. Of the 14 cell lines tested, all were permissive with varying degrees to AcMNPV.GFP, except BCIRL-HV-AMCL2 and BCIRL-HZ-AM1, both grown in serum-containing medium, and BMN, grown in serum-free medium, which were nonpermissive to the virus. Except for BCIRL/AMCY-Se-E1, IPLB-SF21, and four of the five BCIRL-HV-AM1 clones, all the other cell lines (BCIRL-HV-AM1, BCIRL-AG-AM1, TN-CL1, Se-E5, and Sf9) expressed detectable levels of GFP by 48 h postinoculation. The BCIRL/AMCY-Se-E1 and IPLB-SF21 cells, grown in serum-free medium (Ex-Cell 401), expressed detectable levels of GFP at 72 h postinoculation. By contrast, in BCIRL/AMCY-Se-E1 in serum-containing medium (Ex-Cell 401 + 10% FBS [fetal bovine serum]), GFP was detected at 48 h postinoculation. Furthermore, TN-CL1 cells produced the largest mean percentage number of fluorescent (76.6%) cells in both serum-containing and serum-free medium (64.8%) at 120 h postinoculation. All the BCIRL-HV-AM1 clones showed no GFP expression until 96 h postinoculation, and only then about 1% of the cell population fluoresced. The mean extracellular virus (ECV) production at 120 h postinoculation was highest in BCIRL/AMCY-Se-E5 cells grown in Ex-Cell 401 + 10% FBS (37.8 x 10% TCID50/ml) followed by BCIRL-HV-AM1 in TC199-MK (33.4 x 10(6) TCID50/ml). Only the BCIRL-HV-AMCL3 clone produced any substantial level of ECV at 120 h postinoculation (16.9 x 10(6) TCID50/ml). However, there was no significant correlation between ECV production and the mean percentage number of fluorescent cells. This study provides further information on the susceptibility of 14 insect cell lines to a recombinant AcMNPV containing the green fluorescent protein gene. This information might avail researchers with information to facilitate decisions as to what other cell lines are available for in vitro studies of the gfp gene.

Comparison of cell line maintenance procedures on insect cells used for producing baculoviruses

A gypsy moth cell line, IPLB-LdEIta, maintained under various conditions was tested for susceptibility to and productivity of two baculoviruses, the Autographa californica nucleopolyhedrovirus (AcMNPV) and Lymantria dispar nucleopolyhedrovirus (LdMNPV). The results suggest that cells maintained in serum-containing medium (modified TC100) were more susceptible (on the basis of titers in an endpoint assay) to LdMNPV than cells maintained in a serum-free medium (ExCell 400). Such a difference was not apparent with AcMNPV. Similarly, little difference existed in the proportion of cells containing occlusion bodies (OBs) a wk after inoculation with AcMNPV (i.e., the percent infected) in any LdEIta strains, although one combination of cells and medium (cells maintained in ExCell 400 but infected in TC100) showed a lower percent infection with LdMNPV. Even though the percentage of cells infected varied little, the number of OBs produced varied by 3 logs with AcMNPV and 11/2 logs with LdMNPV. In each case, cells normally grown in ExCell 400 and infected in the same medium produced the lowest number of OBs. However, productivity was improved when cells normally grown in ExCell 400 were infected in TC100. Even more interesting was that cells normally grown in TC100 produced more AcMNPV OBs when infected in ExCell 400 medium. This suggests that changing culture medium (regardless of the normal maintenance medium) can stimulate virus production. In addition to examining virus productivity in LdEIta cells in both serum-containing and serum-free media, I also tested a strain maintained at low temperature (17 degrees C) for over a yr. This maintenance protocol was not detrimental for LdMNPV productivity and was slightly stimulatory for production of AcMNPV.

The establishment of heliothine cell lines and their susceptibility to two baculoviruses

A total of eight cell lines were established from Helicoverpa armigera (3) and H. punctigera (5) embryos and ovaries. Cell lines were established and grown in TC100 and/or TC199-MK containing 10% fetal bovine serum. The serum-free medlium ExCell 400 was also used, with and without 10% supplemental fetal bovine serum, but failed to generate cell lines from fat bodies, embryos, or ovarian tissues. Cell lines consisted of heterogenous cell types ranging from oval to fibroblast-like. This is the first report on the successful establishment of cell lines from H. punctigera. Cell lines from the two species were distinguishable from each other by DAF-PCR, and noticeable differences in minor bands were observed among cell lines from the same species. All of the established cell lines from both species were susceptible to HzSNPV but did not replicate more virus than that of a H. zea cell line (BCIRL-HZ-AM1-A11). However, an H. punctigera cell line (HP1) replicated AcMNPV to the highest titer (1.0 X 10(8) 50% tissue culture infective dose/ml), and only one of the H. armigerm cell lines (HA1) was susceptible to this virus.