Scientists engineered yeast to make the immune‑boosting peptide thymosin‑alpha‑1 and fed the dried yeast to mice with a weakened immune system. The yeast‑produced peptide raised the mice's CD8+ T‑cell numbers, similar to a lab‑made peptide, showing it works when taken orally in this animal model.

We want to construct a yeast expression system for thymosin alpha1 (Talpha1) to make the orally administered Talpha1 preparation possible. The whole Talpha1 DNA fragment was obtained by PCR. After being digested with restriction enzymes, it was cloned into pYES2 vector. Sequencing was performed to identify the recombinant. The sequence of Talpha1 in recombinant coincided with the original one reported in Genbank. When pYES2-Talpha1 plasmid was transformed into yeast, galactose instead of glucose was used to induce Talpha1 expression. Western blot was performed to identify the quality of the expressed Talpha1. Dried yeast containing pYEST2-Talpha1 was fed to Balb/c mice whose immunities were inhibited by cyclophosphamide in advance. Synthesized Talpha1 peptide was used as positive control and empty yeast was used as negative control. Compared with the negative control group, both dried yeast containing pYEST2-Talpha1 and synthesized Talpha1 peptide can significantly increase the CD8+ level (22.74 +/- 1.09 and 18.77 +/- 4.72 vs 7.49 +/- 2.14, p < 0.01), while both of them had little effect on the CD4+ lymphocytes (61.86 +/- 6.94 and 65.91 +/- 4.78 vs 57.93 +/- 10.40,p > 0.05). We concluded that a high effective yeast expression system for Talpha1 was constructed successfully and the Talpha1 protein expressed by this system can improve CD8+ level in immune inhibited mice.