MSC isolation and adherent expansion

• Use a basal culture medium reported for MSC expansion, fetal bovine serum or human serum as the culture supplement, phosphate-buffered saline for washing, and trypsin or trypsin-EDTA for passaging adherent cells;
• Collagenase-based digestion is used for adipose-derived stromal vascular fraction or umbilical cord matrix methods when enzymatic isolation is selected.

• Use flow-cytometry antibodies for CD105, CD73, CD90, CD45, CD34, CD14 or CD11b, CD79α or CD19, and HLA-DR to confirm MSC phenotype, and use lineage-differentiation staining readouts for osteogenic, adipogenic, and chondrogenic induction when identity confirmation is required.

• Use sterile tissue-culture plasticware for adherence-based selection, a biosafety cabinet and CO₂ incubator for aseptic mammalian-cell culture, a centrifuge for cell recovery and washing, an inverted microscope for morphology and confluence monitoring, and a flow cytometer for immunophenotyping.

• Prepare the tissue source under sterile conditions;
• Bone marrow mononuclear or whole marrow preparations can be plated for adherence-based MSC recovery, adipose tissue can be enzymatically processed to obtain stromal vascular fraction before adherent culture, and umbilical cord matrix can be processed by explant or enzymatic methods before adherent expansion.

• Prepare complete culture medium using the serum-supplemented conditions reported in the selected protocol paper, and pre-equilibrate medium before plating cells when routine mammalian-cell culture conditions are used.

• Plate the prepared cell suspension or tissue-derived fraction onto tissue-culture plastic and maintain cultures under standard MSC culture conditions so that non-adherent hematopoietic or debris-containing fractions can be removed during medium changes while adherent fibroblast-like colonies are retained.

• Replace medium during primary culture to remove non-adherent cells;
• In the mouse bone-marrow protocol, frequent medium changes and minimized trypsinization time were highlighted as core features for MSC isolation and culture.

• Expand adherent cells as a monolayer and passage before overgrowth when cells reach the confluence range used in the selected protocol;
• Lower plating density and shorter passage duration were reported to improve expansion yield and preservation of early progenitor features in human bone-marrow stromal cultures.

• For adipose-derived MSCs, digest adipose tissue to obtain stromal vascular fraction, culture the adherent fraction, and expand cells through serial passaging before characterization by morphology, immunophenotype, and differentiation assays.

• For umbilical cord matrix MSCs, either explant-based or enzymatic isolation can generate adherent MSC-like cells, and one comparative study found that a 10-mm tissue explant approach gave shorter primary-culture time, higher cell number, and higher proliferation than other tested umbilical cord matrix methods.

• Assess successful isolation by the appearance of adherent fibroblast-like colonies and expansion into a monolayer, then confirm MSC identity using the ISCT minimal criteria: positive CD105/CD73/CD90, negative hematopoietic-lineage markers, and in-vitro differentiation into osteoblasts, adipocytes, and chondroblasts.

• Compare cultures by passage number, morphology, expansion rate, and immunophenotype, because tissue source, isolation method, serum supplement, seeding density, and passage conditions can alter MSC yield and culture quality.

Low recovery of adherent MSC colonies:

Possible Cause
Source material or isolation method yields few colony-forming adherent progenitors.
Solution
Use adherence-based selection with medium changes for marrow cultures, consider stromal vascular fraction processing for adipose tissue, and consider the 10-mm explant method for umbilical cord matrix when that source is used.

Reduced expansion or loss of early progenitor features during culture:

Possible Cause
Passage conditions, plating density, and prolonged culture can affect yield and culture quality.
Solution
Use lower plating density and shorter passage duration when following human bone-marrow stromal expansion conditions designed to maximize early progenitor yield.

Culture cannot be classified as MSC after expansion:

Possible Cause
The adherent culture may contain non-MSC populations or incompletely characterized cells.
Solution
Do not classify the culture as MSC unless it meets plastic adherence, surface-marker, and tri-lineage differentiation criteria.