Hematopoietic stem cell transplantation (HSCT)

The infusion of donor or autologous hematopoietic stem and progenitor cells following myeloablative or reduced-intensity conditioning to reconstitute the blood and immune system. HSCT is FDA-approved and the standard of care for a range of hematologic malignancies and certain non-malignant disorders (aplastic anemia, sickle cell disease, thalassemia, primary immunodeficiencies). In the aging context, HSCT is relevant on two distinct axes: (1) the well-documented donor-age effect, where older donors produce inferior transplant outcomes in the clinical setting, and (2) heterochronic HSCT — transplanting young-donor marrow into aged recipients to ask whether hematopoietic rejuvenation is achievable — which is currently limited to mouse models. HSC biology (cell-autonomous aging, clonal dynamics, niche interactions) is covered on hematopoietic-stem-cells; this page focuses on HSCT as a therapeutic modality.

Autologous vs allogeneic

Autologous HSCT: The patient’s own HSCs are collected (usually from mobilized peripheral blood), stored, and reinfused after high-dose conditioning chemotherapy. This eliminates graft-versus-host disease (GVHD) risk but also eliminates graft-versus-tumor (GVT) effect. Standard in myeloma and relapsed lymphoma. An aging-context note: autologous products are harvested from the patient’s own aging/potentially CHIP-bearing marrow, providing no immunological reset.

Allogeneic HSCT: HSCs from a related (sibling) or unrelated matched donor are infused. Full immunological reconstitution occurs from donor cells. For aging research, allogeneic HSCT is more relevant because it provides a genuine cellular replacement and immune reset from a genetically distinct donor — and because donor age significantly affects outcomes (see below).

Donor-age effects in clinical HSCT

Donor age is one of the strongest modifiable donor variables affecting recipient survival in unrelated-donor HSCT for hematologic malignancy.

Kollman 2001 — the foundational donor-age dataset

In a landmark analysis of 6,978 unrelated donor transplants across 295 centers, Kollman et al. demonstrated that donor age was the only donor trait independently associated with both overall and disease-free survival ¹. Five-year overall survival rates were 33%, 29%, and 25% for recipients of donors aged 18–30 years, 31–45 years, and >45 years respectively (P=0.0002). Younger donors also correlated with reduced incidence of chronic GVHD.

Kollman 2016 — updated analysis

An expanded analysis of 6,349 donor-recipient pairs in the training cohort (1988–2006), validated in a cohort of 4,690 pairs (2007–2011) ², confirmed the donor-age effect in the modern allele-level HLA-typing era: for every 10-year increment in donor age, there is a 5.5% increase in the hazard ratio for overall mortality (HR 1.005 per year; 95% CI, 1.002–1.009; P=.003). The optimal donor age band in this analysis was 18–32 years, with 5-year risk-adjusted OS of 36% vs 33% vs 29% for donor ages ≤32, 33–50, and >50 years respectively. This effect appears to operate through multiple mechanisms, including reduced T-cell repertoire diversity in older donors, increased GVHD severity, and potentially poorer hematopoietic reconstitution speed from aged HSCs with reduced regenerative capacity (see hematopoietic-stem-cells § Aging phenotype).

Donor age band	5-year OS (Kollman 2001)	Notes
18–30 years	~33%	Best outcomes
31–45 years	~29%	Intermediate
>45 years	~25%	Worst outcomes

Extrapolation table

Dimension	Status
Pathway conserved in humans?	yes — aged HSCs show conserved cell-intrinsic decline across mouse and human
Phenotype conserved in humans?	yes — clinical HSCT data are human
Replicated in humans?	yes — multiple large registry analyses

HSC aging and cell-intrinsic decline

Understanding why donor age matters requires understanding HSC aging. Two landmark papers established the cell-intrinsic basis for aged-HSC functional decline:

Rossi et al. 2005 showed that aged murine long-term HSCs exhibit intrinsic alterations independent of niche: upregulation of myeloid fate determinants, downregulation of lymphoid specification genes, elevated expression of leukemia-associated genes, and expanded self-renewal at the cost of lymphoid output ³. This provides the mechanistic basis for the myeloid skewing and immunosenescence observed with advancing donor age.

Rossi et al. 2007 demonstrated that accumulated DNA damage (not merely niche signals) causally limits aged HSC function under stress, with DNA-repair-deficient mice recapitulating the aged-HSC phenotype at young ages ⁴.

Beerman et al. 2010 further showed that clonal expansion of myeloid-biased HSC subtypes — not uniform decline of all HSCs — is the primary driver of aging-associated hematopoietic skewing ⁵. This has direct implications for HSCT: aged donors harbor an HSC pool that is functionally and clonally restructured relative to young donors.

Florian et al. 2012 (Geiger group) identified elevated Cdc42 activity as causally linked to HSC aging and demonstrated that pharmacological Cdc42 inhibition restores aged HSC polarity, H4K16ac epigenetic patterns, and functional capacity to young-like levels ⁶. This is the most direct evidence that aged-HSC dysfunction is at least partially reversible — relevant to both the ex vivo preparation of older-donor HSCs and to the concept of rejuvenating a recipient’s endogenous stem cell pool post-transplant. needs-human-replication

Heterochronic HSCT — aging-rejuvenation evidence

Heterochronic HSCT (young-donor marrow → aged host) is the conceptually simplest test of whether hematopoietic rejuvenation is achievable via cell replacement.

Mouse evidence

The most directly relevant mouse study by Jazbec et al. 2022 ⁷ examined non-myeloablative heterochronic bone marrow transplantation in aged female BALB/c mice. Recipients (n=60) started receiving transplants at 14 months and were transplanted again at 16 and 18(19) months (eight injections total, 125.1 ± 15.6 million nucleated BM cells per animal). Young inbred BALB/c male donors (7–13 weeks) were used to enable chimerism tracking via Y-chromosome PCR. At 21 months, BM donor chimerism averaged 18.7 ± 9.6%. Results:

Improved innate immune markers: increased neutrophil counts in spleen (p=0.015) and BM (p=0.014)
Improved adaptive immune markers: increased central memory T-helper cells (p=0.040), effector/memory Tc cells (p=0.033), B1a and B1b cells in peritoneal cavity (p=0.006 and p<0.001)
Borderline-significant enhancement of lymphocyte proliferative capacity (PHA+PMA stimulation, p=0.056)

Critical null finding: Despite these immune improvements, the treatment did not significantly extend lifespan (median 706 days BMT vs 761 days SHAM; log-rank test NS; Cox HR 1.224, p=0.480) and did not reduce frailty index scores (FI p=0.356). The authors concluded that partial chimerism (~18.7%) in a non-conditioned setting may be insufficient to translate immune gains into longevity or frailty outcomes, and that the aged host HSC niche may actively impede engraftment. needs-replication long-term-unknown

Extrapolation table for heterochronic mouse data

Dimension	Status
Pathway conserved in humans?	partial — hematopoietic reconstitution biology is broadly conserved; immunosenescence drivers are partially conserved
Phenotype conserved in humans?	unknown — no human heterochronic HSCT for aging has been attempted
Replicated in humans?	no — preclinical only

Mechanistic basis and limitations

The Geiger-lab Cdc42 work ⁶ suggests that cell-intrinsic HSC aging is reversible, which supports the possibility that young donor HSCs engrafted in an aged host might maintain youth-like functional output. However, several barriers exist:

Niche competition. Aged host niches favor aged-phenotype HSCs. Young donor HSCs may be outcompeted by residual host HSCs unless myeloablation is near-complete.
Inflammatory milieu. Aged hosts exhibit chronic low-grade inflammation (inflammaging) that may impair young donor HSC function and accelerate their aging post-engraftment.
GVHD risk. The regimens required for high chimerism carry substantial GVHD morbidity in elderly recipients — a compounding safety problem for an indication that is not life-threatening cancer.
Engraftment-vs-aging timescale. Even with full chimerism, the aging clock in non-hematopoietic tissues is unchanged; hematopoietic rejuvenation may produce immune benefits without reversing aging in brain, skeletal muscle, or vasculature.

Donor-derived CHIP: clonal hematopoiesis transmission via HSCT

clonal-hematopoiesis (CHIP) accumulates in all aging individuals. When an older donor harbors CHIP clones and donates HSCs, those clones can be transmitted to the recipient and clonally expand in the engrafted host.

Gibson et al. 2022 (JCO) provided the largest analysis to date of donor-derived clonal hematopoiesis and recipient outcomes after HSCT ⁸. Key findings:

Donor CH was detectable in 22.5% of donors ≥40 years (n=388/1,727); prevalence increased with age (12.6% at 40–49, 26.6% at 50–59, 41.2% at ≥60)
The most common driver mutations: DNMT3A (14.6%), TET2 (5.2%), ASXL1 — consistent with the CHIP spectrum in aging donors
Critically, the clinical effects of donor CH were gene-specific and prophylaxis-dependent: DNMT3A-CH (VAF ≥0.01) was associated with improved recipient OS (HR 0.78; 95% CI 0.62–0.98; P=.037) and PFS (HR 0.72; P=.003), and reduced relapse risk (sHR 0.74; P=.022) — apparently via augmented graft-versus-leukemia activity
However, DNMT3A-CH was also associated with increased chronic GVHD risk in patients receiving calcineurin-based prophylaxis (sHR 1.37; 95% CI 1.02–1.84; P=.04); this risk was not observed in patients receiving post-transplant cyclophosphamide (PTCy)
TET2-CH and other non-DNMT3A CH were not significantly associated with any outcome
Donor clones evolved to donor cell leukemia (DCL) in 8 cases (10-year cumulative incidence 0.7%), predominantly from mutations in MDS-associated splicing factors or TP53, not from common DNMT3A or TET2 CH

This has a nuanced implication for aging-targeted HSCT: the most common form of CH in older donors (DNMT3A) does not adversely affect recipient outcomes and may even benefit them via GVL effects. The primary concern for DCL is rare splicing-factor and TP53 mutations, not the ubiquitous age-related DNMT3A mutations. The calculations around CHIP screening in donor selection are therefore more complex than a simple “older donor CHIP = bad” framing. needs-replication (prospective trials with systematic CHIP screening lacking)

Current CHIP donor screening guidance

As of 2026, CHIP donor screening is not universally mandated. The Gibson 2022 data complicate any blanket exclusion policy: common DNMT3A-CH in donors is associated with improved recipient survival via GVL augmentation, and the GVHD risk can be mitigated by PTCy prophylaxis selection. The primary concern is rare (<1% of donors) splicing-factor or TP53 mutations that carry high DCL risk. For aging-rejuvenation applications — where GVL effect is irrelevant and safety risk tolerance is lower — the calculus shifts: DNMT3A-CH provides no survival benefit if there is no malignancy to suppress, and any GVHD risk is unacceptable in a non-malignant indication. CHIP screening for high-risk (non-DNMT3A/non-TET2) mutations would therefore be prudent in aging-rejuvenation trial design.

Translation status

Hematologic indications (FDA-approved)

Allogeneic HSCT is FDA-approved for acute and chronic leukemias, myelodysplastic syndromes, myelofibrosis, aplastic anemia, and several non-malignant hematologic diseases. For these indications, HSCT has strong human evidence and decades of outcomes data. The procedure carries substantial procedural mortality (transplant-related mortality 5–15% depending on conditioning intensity, disease, and center) and long-term morbidity from GVHD and secondary cancers.

Aging-rejuvenation use (preclinical only)

No human trials of HSCT for aging-rejuvenation exist as of 2026-05-06. The heterochronic-HSCT concept is supported only by mouse evidence, and the only direct heterochronic mouse trial ⁷ produced immune benefits but no lifespan extension.

For HSCT to enter aging-rejuvenation clinical development, several barriers would need resolution:

Reducing conditioning toxicity for elderly recipients (reduced-intensity conditioning already exists but achieves lower chimerism)
CHIP-negative young donor availability (CHIP prevalence rises sharply with age; donors <30 have low CHIP prevalence)
Proof of heterochronic benefit in higher-chimerism models (the 2022 Jazbec BALB/c mouse study achieved only 18.7% chimerism in non-conditioned recipients; full myeloablative models with aging as the primary endpoint have not been published)
Non-malignant regulatory path (FDA/EMA would require a defined clinical indication with adequate risk-benefit — “aging” is not currently recognized as a regulatory indication)

The most defensible near-term path mirrors the logic in aav-tert: start with a non-malignant indication where aging-related hematopoietic failure is the primary pathology — aplastic anemia, hypocellular MDS, or severe CHIP with clonal dominance in elderly patients. This would allow young-donor heterochronic HSCT within a regulated indication, with aging-related endpoints as secondary outcomes. needs-human-replication

Gaps and limitations

No heterochronic HSCT lifespan data in mice beyond partial chimerism. The 2022 Biomolecules study showed immune improvements without lifespan extension at 18.7 ± 9.6% chimerism in BALB/c mice. Whether full myeloablative conditioning and higher chimerism would extend lifespan is unknown. needs-replication
Aging inflammatory niche is unaddressed. Heterochronic HSCT replaces the cellular hematopoietic compartment but does not modify the aged systemic milieu (elevated IL-6, TNF-α, GDF11/GDF15 dysregulation). Young donor HSCs engrafted in a pro-inflammatory aged host may age more rapidly than expected. no-mechanism
CHIP transmission risk is gene-specific and prophylaxis-dependent. The Gibson 2022 JCO data show that DNMT3A-CH improves survival via GVL but increases chronic GVHD risk under calcineurin-based prophylaxis (mitigated by PTCy). The subset of donors with rare splicing-factor or TP53 mutations carries high DCL risk. Prospective trials with systematic CHIP screening are lacking; the absolute risk estimates and their prophylaxis interaction need replication in independent cohorts. needs-replication
Donor-age effect mechanisms are multi-factorial. It is not clear what fraction of the ~5.5% per decade HR increment for mortality from older donors (Kollman 2016; HR 1.005/yr; confirmed in validation cohort) is attributable to HSC cell-intrinsic aging vs T-cell repertoire narrowing vs CHIP transmission vs reduced cell dose from older donors. This complicates interpretation of the donor-age literature for rejuvenation applications. no-mechanism
No aging-specific clinical trials. Current trial registries contain no recruiting HSCT trials with anti-aging or rejuvenation primary endpoints (ClinicalTrials.gov v2 search, 2026-05-06). long-term-unknown

Cross-references

hematopoietic-stem-cells (cell biology of HSCs; aging phenotype; CHIP genetics — the canonical home for HSC cell-biology claims referenced here)
clonal-hematopoiesis (CHIP as phenotype; mutation spectrum; cardiovascular and leukemia risk)
stem-cell-exhaustion (parent hallmark page)
aav-tert (HSCT context for telomere gene therapy; ex vivo HSC TERT delivery as near-term translational path)
mesenchymal-stem-cell-therapy (sibling R23a page — paracrine-dominant mechanism vs HSCT’s replacement-dominant mechanism)
ipsc-derived-cell-therapy (sibling R23a page — rejuvenation via fully reprogrammed cell product)
in-vivo-partial-reprogramming-therapy (sibling R23a page — in situ epigenetic reset without cell transplantation)
inflammaging (implicit stub — the aged systemic milieu that may undermine heterochronic HSCT benefit)
immunosenescence (downstream consequence of HSC aging that HSCT could theoretically reverse)
hallmarks-of-aging — stem-cell-exhaustion and genomic-instability are the primary hallmarks targeted

Footnotes

doi:10.1182/blood.v98.7.2043 · Kollman C, Howe CW, Anasetti C, Antin JH, Davies SM, Filipovich AH, et al. · Blood 2001 · 98(7):2043–2051 · observational · n=6,978 unrelated donor transplants · model: human registry data (NMDP) · donor age independently associated with 5-year OS (33% vs 25% for ages 18–30 vs >45, P=0.0002); only donor trait independently associated with both OS and DFS · archive: local PDF available ↩
doi:10.1182/blood-2015-08-663823 · Kollman C, Spellman SR, Zhang MJ, et al. · Blood 2016 · 127(2):260–267 · observational · n=6,349 donor-recipient pairs (training cohort, 1988–2006) + n=4,690 (validation cohort, 2007–2011) · model: human registry data (CIBMTR/NMDP; allele-level 8/8 HLA-matched unrelated donors) · per 10-year donor age increment: HR for mortality +5.5% (HR 1.005/yr; 95% CI 1.002–1.009; P=.003); optimal donor age 18–32 years (5-year OS 36% vs 33% vs 29% for ≤32, 33–50, >50 yr) · archive: local PDF available (bronze OA; downloaded 2026-05-06) ↩
doi:10.1073/pnas.0503280102 · Rossi DJ, Bryder D, Zahn JM, Ahlenius H, Sonu R, Wagers AJ, Weissman IL · PNAS 2005 · 102(26):9194–9199 · in-vivo · model: C57BL/6 mouse HSCs; serial transplantation and gene expression profiling · cell-intrinsic myeloid bias, downregulated lymphoid genes, elevated leukemia-associated genes in aged HSCs · archive: local PDF available (green OA) ↩
doi:10.1038/nature05862 · Rossi DJ, Bryder D, Seita J, Nussenzweig A, Hoeijmakers J, Weissman IL · Nature 2007 · 447:725–729 · in-vivo · model: C57BL/6 mice and DNA-repair-deficient strains · accumulated DNA damage as causal mechanism of HSC functional decline with age; DNA-repair-deficient mice recapitulate aged-HSC phenotype at young age · archive: local PDF available (closed; downloaded) ↩
doi:10.1073/pnas.1000834107 · Beerman I, Bhattacharya D, Zandi S, Sigvardsson M, Weissman IL, Bryder D, Rossi DJ · PNAS 2010 · 107(12):5465–5470 · in-vivo · model: C57BL/6 mice; clonal tracking via transplantation · clonal expansion of myeloid-biased HSC subtypes (not uniform decline) drives hematopoietic aging; myeloid-biased HSCs have robust self-renewal · archive: local PDF available (green OA) ↩
doi:10.1016/j.stem.2012.04.007 · Florian MC, Dörr K, Niebel A, Daria D, Schrezenmeier H, Rojewski M, Filippi MD, Hasenberg A, Gunzer M, Scharffetter-Kochanek K, Zheng Y, Geiger H · Cell Stem Cell 2012 · 10(5):520–530 · in-vivo · model: C57BL/6 mouse HSCs; pharmacological Cdc42 inhibitor (CASIN) treatment · elevated Cdc42 causally linked to HSC aging; CASIN treatment restores polar cell frequency, H4K16ac patterns, and functional reconstitution capacity to young-like levels · archive: local PDF available (bronze OA; downloaded 2026-05-06) ↩ ↩²
doi:10.3390/biom12040595 · Jazbec K, Jež M, Švajger U, et al. · Biomolecules 2022 · 12(4):595 · in-vivo · model: aged female BALB/c mice (n=60 BMT, n=41 SHAM; transplanted at 14, 16, 18/19 months); young inbred male BALB/c donors (7–13 weeks); non-myeloablative whole-BM transplantation (125.1 ± 15.6 × 10⁶ cells/animal; 8 injections) · 18.7 ± 9.6% donor chimerism in BM at 21 months; improved innate (neutrophils) and adaptive (central memory Th, effector/memory Tc, B1a, B1b) immune markers; borderline lymphocyte proliferation benefit (p=0.056); no significant lifespan extension (706 vs 761 days median; log-rank NS) or frailty reduction (FI p=0.356) · archive: local PDF available (gold OA; downloaded 2026-05-06) ↩ ↩²
doi:10.1200/JCO.21.02286 · Gibson CJ, Kim HT, Zhao L, et al. · Journal of Clinical Oncology 2022 · J Clin Oncol 40:189–201 · observational · n=1,727 donors ≥40 years (Dana-Farber + Johns Hopkins, 2000–2016); targeted sequencing of 46 genes · model: human allogeneic HSCT recipients · CH present in 22.5% of donors; DNMT3A-CH (VAF ≥0.01) associated with improved OS (HR 0.78, P=.037), improved PFS (HR 0.72, P=.003), and reduced relapse (sHR 0.74, P=.022); DNMT3A-CH increased chronic GVHD risk with calcineurin-based prophylaxis (sHR 1.37, P=.04) but not with PTCy; DCL evolved from rare TP53/splicing-factor mutations, not DNMT3A/TET2; primary drivers DNMT3A (14.6%), TET2 (5.2%), ASXL1 · archive: local PDF available (hybrid OA) ↩

🧬 Aging Wiki

Explorer

hematopoietic-stem-cell-transplantation