Passage of Stem Cells and Its Correlation with UC-MSC Stem Cell Therapy
In stem cell therapy, particularly UC-MSC (umbilical cord-derived mesenchymal stem cells) therapy for many patients the terms Passage 3 or P3 and Passage 4 or P4 mean something. These terms may sound scientific, yet they are critical to a proper understanding of the preparation and manipulation of stem cells in vitro (in laboratory).
A “passage” is simply the number of times one has expanded, or sub-cultured stem cells in culture. Stem cells are harvested from umbilical cord (up to 75% number of stem cell per gram tissue) and then cultured in a sterile environment for clinical application. Passage number increases each time the cells are allowed to expand from cell transfers into a new culture environment.
For example:
P1 indicates the first stage of expansion
P2 being the second stage expansion
P3 stage is the third expansion phase
P4 stands for the fourth phase of expansion
In other words, P3 and P4 are only a one-expansion stage apart. This difference is not as striking as many patients assume.
Why Do Patients Trust P3 Stem Cells More
Patients often ask for P3 stem cells because they mistakenly believe that since these are a lower passage number, the cells will be “younger,” fresher or stronger. This idea is partly understandable. Very high passage numbers may show lower competence, altered behavior or senescence in cell culture.
This led to P3 stem cells promoting as early-passage choice. In marketing terms may make P3 sound fancy as it implies the cells have gone through expansion less.
But there is a need to clarify this very cautiously. Stem cell quality is not measured solely by passage number P3 cell batch that have not passed appropriate laboratory testing could be of poor quality. By the way, a good P4 cell is made from an excellent batch as long as it meets stringent quality control standards.
FIGURE 1: UC-MSC STEM CELL THERAPY PASSAGE 3 VS. PASSAGE 4: UNDERSTANDING QUALITY PROFILE
Figure 1: (A) The cell culture expansion timeline demonstrating the passage process from isolation to Passage 4 (P4), highlighting that the difference between P3 and P4 is merely a single expansion stage. (B) Shifting the clinical rationale from a narrow marketing perspective (focusing solely on passage numbers) to clinical reality, where therapeutic outcomes rely on comprehensive biological function. (C) The multi-parametric Quality Control (QC) profile required for batch validation, including cell viability, sterility, positive/negative surface markers, and structural karyotyping. (D)Comprehensive physician-guided evaluation framework integrating validated cell products with personalized metabolic care and realistic therapeutic expectations.
So is P4 Stem Cell Therapy just a two-tier therapy compared to P3?
Short answer: No, P4 stem cells are not automatically worse than P3 stem cells.
Most lab and research settings still consider P4 the “early to middle passage range”. The really nasty problems typically show up with later passages, once cells have been expanded many more times. P3/P4 difference will almost always be smaller than the early-passage cells vs late passage ones.
Thus, patients should not always assume that P3 must be superior or that P4 is feeble. Its now not only an issue of “What passage are the cells?” but also “quality testing of the cells they passed.”
What is More Critical Than Passage Number?
For UC-MSC stem cell therapy of high quality, not only passage number. It is the comprehensive quality profile of the cell product.
Important quality indicators may include:
Cell viability
Sterility testing
Mycoplasma testing
Endotoxin testing
Cell surface marker profile
Cell morphology
Karyotype or genetic stability testing
Growth characteristics
Potency or functional testing
Proper donor screening
Controlled laboratory processing
For mesenchymal stem cells, standard identity testing often includes positive markers such as CD105, CD73, and CD90, and negative markers such as CD45, CD34, CD14 or CD11b, CD79 or CD19, and HLA-DR. These markers help confirm that the cells still meet accepted MSC characteristics.
This is why a properly tested P4 UC-MSC product can still be a high-quality stem cell product.
P3 vs P4: A Patient-Friendly Comparison
| Factor | P3 Stem Cells | P4 Stem Cells |
| Passage level | Early passage | Early-to-middle passage |
| Patient perception | Often seen as more premium | Sometimes misunderstood as lower quality |
| Real difference | Expanded one stage less than P4 | Expanded one stage more than P3 |
| Main concern | Quality still depends on QC | Quality still depends on QC |
| Clinical value | Can be good if QC passes | Can be equally reliable if QC passes |
| What matters most | Viability, sterility, identity, potency | Viability, sterility, identity, potency |
P4: Why it still might be a great choice
Under properly controlled laboratory conditions, P4 cells may retain most MSC stem cell characteristics. MSC stem cell are generally used in early-to-middle passage ranges in most research and clinical manufacturing contexts, with P4 falling within that preparation window deemed acceptable.
It implies that P4 should not be declined only because it is higher than the number of P3. There is only one culture step between P3 and P4. If the P4 cells exhibit solid viability, suitable MSC stem cell markers (i.e., expression of CD73 and other hematopoietic stem cell antigens), sterility testing is negative for bacteria or fungal infections; have stable morphology with a characteristic spindle-like shape in culture, capability to maintain their specific growth/expression patterns under standard expanded conditions along functional potency such properties make them highly compatible candidates as useful regenerative medicine.
What Your Doctor Should Tell You about P3 vs P4
The motivation behind P3 is extremely appealing, being an early passage however where the cells pass a stringent QC process I believe that there can be some justifications for P4 as well. High and consistent quality stem cells are well evaluated, especially given passage number. The key question is whether the cells are safe, alive, well-defined and biologically functional?
Conclusion
P3 vs P4 UC-MSC therapy in patients is an essential topic. P3 is often preferred by many because it sounds younger and early passage cells are usually referred to as P3. However, P4 stem cells do not make them automatically better than other classes. P4 remains a viable early to middle passage choice when cultured under the right laboratory conditions.
Those stem cells need not only a high passage number, but assessed for an entire quality control profile, viability, sterility and identity markers; morphology; genetic stability by karyotyping in vitro or genomic sequencing-based analysis of long-range haplotypes (SnwM); and potency. For responsible regenerative medicine, quality control is more important than marketing terms.