Trichoderma reesei, a promising novel host for antibody production

The exceptional secretion capacity of the filamentous fungus Trichoderma reesei was harnessed for antibody production. T. reesei was able to assemble heterodimeric Fab fragments in active proteins, which were secreted into the culture medium. Reasonable yields were obtained when a Fab fragment was fused to a fungal cellulase, CBHI. The yield of this fusion protein, CBHI-Fab, was 150 mg/l, whereas the Fab fragment as such was produced in only 1 mg/l quantities. Studies on the positive role of the endogenous fusion preceding the antibody heavy chain were carried out. Unexpectedly, the CBHI fragment was shown to act favorably already at the transcriptional level either by stabilizing the messenger or enhancing transcription. At least one limiting step in secretion, which was overcome by the use of CBHI, was protein translocation into the lumen of the endoplasmic reticulum. Furthermore, it was shown that the CBHI-heavy Fd chain was produced in gram per liter range but most of it was cleaved inside the cell, resulting in the CBHI core-linker protein, which was then secreted to the culture medium as efficiently as extracellular T. reesei proteins.