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The DPP4 (dipeptidyl peptidase-4) gene is located in the 2q24.2 region of human chromosome 2 and spans approximately 82 kb. It encodes a type II transmembrane serine exopeptidase—also known as T-cell surface antigen CD26 or adenosine deaminase complexing protein 2 (ADABP/ADCP2)—composed of 766 amino acids. This enzyme is highly expressed in various tissues, including the small intestine (RPKM 70.7) and placenta (RPKM 57.1), as well as in proximal enterocytes, prostatic glandular cells, T and B cells, macrophages, and dendritic cells; it exists in both transmembrane and soluble forms. Its primary function is the specific cleavage of X-proline or X-alanine dipeptides from the N-terminus of polypeptides. At least 63 substrates are currently known, including the incretin hormones GLP-1 and GIP; notably, because DPP4 rapidly degrades and inactivates GLP-1, it has become a key therapeutic target for type 2 diabetes. Beyond glucose regulation, DPP4 is deeply involved in a wide range of physiological and pathological processes, including immune modulation (acting as a T-cell co-stimulatory molecule to promote Th1/Th17 differentiation and inhibit Treg function), inflammatory responses, cell signaling (via pathways such as NF-κB and PI3K-AKT), lipid metabolism, bone turnover, tendon repair, and intestinal fibrosis.

Figure 1. Recombinant DPP4 CHO constitutively expressing DPP4.

Cell Resuscitation
1)Rapidly thaw the frozen cells in a 37 °C water bath for approximately 60 seconds. Once thawed (which may take slightly less or more than 60 seconds), immediately transfer the cell suspension from the cryovial into a 15 mL centrifuge tube containing 10 mL of pre-warmed  CHO-K1 Human DPP4 Cell complete culture medium.
2)Centrifuge cells at 1000 rpm for 5 min to remove medium, then resuspend cells in 5 mL of pre-warmed complete medium.
3)Transfer the cell suspension into a T25 culture flask and incubate at 37 °C with 5% CO₂.
4)After approximately 24–36 hours, replace the medium or passage the cells to remove non-adherent dead cells.

Subculturing procedure
1)When the cell density reaches the appropriate confluency for passaging, wash the cells with PBS, then add 1 mL trypsin to detach the cells. When more than 80% of the cells detach upon gently tapping the culture flask, add complete culture medium to terminate digestion. Gently pipette to obtain a single-cell suspension, transfer to a 15 mL centrifuge tube, and centrifuge at 1000 rpm for 5 minutes.

2)Discard supernatant after centrifugation. Resuspend cells in fresh medium to a single-cell suspension and transfer to a new culture flask for continued growth.

Cell Freezing
After trypsinization and centrifugation of cells from each T75 flask or 10 cm culture dish, discard the supernatant. Add 2 mL of cryopreservation medium (90% FBS + 10% DMSO), gently resuspend thoroughly, and aliquot into two cryovials. Immediately place the cryovials into a controlled-rate freezing container (e.g., Nalgene 5100-0001), fill with isopropanol to the indicated level, and store at −80 °C. After 24 hours, transfer the cryovials to liquid nitrogen for long-term storage.