2.5 Stem Cell & Cellular Product Sources: Donor Selection Hierarchy

Stem Cell and Cellular Product Sources: Donor Selection

Clinical principle: Graft source and donor are selected together with disease, urgency, conditioning and GVHD-prophylaxis platform. Source comparisons are relative; one cell dose, engraftment day, incidence percentage or donor hierarchy does not fit every program.

1. Peripheral-Blood Stem Cells

PBSC donors receive a protocol-defined mobilization course, commonly G-CSF, and circulating mononuclear cells are collected by leukapheresis. Peripheral access is preferred when it can safely support the procedure; validated central access is used when needed. Nurses teach mobilization symptoms and splenic warning signs, assess vascular access and citrate toxicity, and preserve chain of identity through processing.

PBSC products commonly contain more CD34+ progenitors and mature T cells than marrow products. In many adult allogeneic comparisons they produce faster neutrophil and platelet recovery but more chronic GVHD than marrow. The magnitude varies with donor relationship, disease, conditioning, cell dose and prophylaxis. The collection team follows the requested product dose; a value near 2 × 10^6 CD34+ cells/kg is a common autologous minimum, but neither that value nor a higher target is a universal release rule for all autologous and allogeneic products.

2. Bone Marrow

Marrow is aspirated from the posterior iliac crests in an operating-room procedure under general or regional anesthesia. The collection plan balances the recipient’s requested cell dose against donor weight, estimated blood volume, baseline hemoglobin and allowable collection volume. Monitor consent, anesthesia risk, blood loss, hemodynamics, pain, wound care and recovery; iron or transfusion support is individualized.

Marrow generally contains fewer mature T cells than PBSC and may lower chronic-GVHD risk in selected comparisons, although recovery can be slower and graft-failure tradeoffs depend on platform. It is often considered when avoiding chronic GVHD is especially important, including selected nonmalignant or pediatric settings, but disease and patient age alone do not mandate one source. Marrow dose is commonly expressed as total nucleated cells and may also be assessed by CD34+ cells; the actual collection target belongs to the program request.

3. Umbilical Cord Blood

Cord blood is collected from placental/umbilical blood after birth, processed, tested and stored in a bank before a recipient is identified. Its banked availability can shorten donor-search time, and its immune biology permits greater HLA disparity than many adult-donor platforms. The limitations are low cell dose, slower hematopoietic/immune recovery in many recipients, infection and graft-failure risk, and limited ability to obtain another donation from the same unit.

Select a unit with the transplant program’s current algorithm, integrating high-resolution HLA data, total nucleated and CD34+ cell dose, viability/potency, bank quality, infectious and genetic screening, donor-specific antibodies and urgency. Historical 4/6 antigen matching or fixed single-/double-unit cell-dose cutoffs should not be treated as the only modern selection pathway; typing methods, expansion strategies and transplant platforms evolve.

4. Other Cellular Sources

The TCTCN outline also includes cells obtained from tumor and other cellular-therapy sources. For tumor-infiltrating lymphocyte therapy, autologous lymphocytes are procured from resected tumor, expanded/manufactured and returned after regimen-specific preparation. NK-cell, gene-modified hematopoietic-cell, donor-lymphocyte and commercial CAR T workflows can begin from autologous, allogeneic, cord, marrow, blood or tumor material. Each uses its own collection, manufacturing, storage, release, compatibility and toxicity plan; do not import an HCT graft-dose rule into a manufactured product.

5. Donor Selection Framework

Start with the disease goal, urgency, available donor types and intended transplant platform. Then integrate:

• HLA: required resolution and loci, DPB1 permissiveness where applicable, and platform-specific mismatch tolerance.
• Donor-specific antibody: assay confirmation, specificity, strength/trend and crossmatch/complement information when useful; avoid the targeted antigen when feasible or use the program’s desensitization plan.
• Donor age and health: younger age is often favorable when other critical factors are comparable, but donor suitability, match, availability and recipient urgency can outweigh it.
• Source and dose: collection feasibility, expected cell yield, marrow/PBSC/cord tradeoffs, recipient size and backup options.
• Infection and immunologic context: CMV relationship and other required donor testing, interpreted with recipient serostatus and the prevention plan.
• Sex and pregnancy history: may affect chronic-GVHD risk in some settings and is weighed with all other factors, not used as an automatic exclusion.
• ABO and logistics: ABO is secondary to critical HLA/clinical factors but affects processing and transfusion planning; travel, timing and reliability affect whether the graft can be collected safely.

A matched sibling or well-matched unrelated donor may be favored in many settings, while haploidentical, mismatched unrelated or cord options may provide the best timely graft for a particular patient. PTCy and other platforms have widened donor access but do not erase differences among donors or grafts. Document the multidisciplinary rationale and a backup plan.

6. Donor-Centered Safety and Ethics

A healthy donor receives no direct medical benefit. Evaluation and consent should be sufficiently independent from recipient pressure and must address collection options, common and serious risks, privacy, expenses, alternatives, follow-up and the right to withdraw. A minor donor requires guardian permission, developmentally appropriate assent/dissent attention, independent advocacy and pediatric-trained care. The team protects donor welfare while explaining that late withdrawal after recipient conditioning can create grave recipient risk.