A short treatment of donor cells before transplantation was associated with lower graft-versus-host disease scores and higher survival in mouse transplant models. In the fully mismatched model, all 16 mice given vehicle-conditioned grafts died, compared with four of 18 mice given grafts conditioned with fluticasone propionate, venetoclax and IL-2. The authors described survival in the treated group as above 75%.
It was a graft-processing step performed outside the body. Donor splenocytes were exposed to vehicle or combinations of fluticasone propionate, venetoclax and IL-2 before being transplanted with uncultured donor bone marrow. Transplantation and subsequent grading were blinded.
A brief conditioning step changed the cell mix
The cell experiments focused on the balance between regulatory T cells, or Tregs, and conventional T cells, or Tcons. In 18-hour cultures, fluticasone plus either 10 or 100 nanomolar venetoclax was associated with viable Tregs at 56.0%, compared with 22.3% after fluticasone alone. Tcon viability was 0.2% with the drug combination, versus 3.1% with fluticasone alone.
The researchers then selected a shorter regimen: 3 nanomolar fluticasone propionate plus 100 nanomolar venetoclax for six hours. Under that condition, the reported Treg frequency rose from 7% to 31%, with minimal reported impact on Treg viability.
Adding 20 nanograms per millilitre of IL-2 to the six-hour combination was associated with a further increase in relative Treg frequency, from 38.0% without IL-2 to 51.0% with it. The experiment reported no viability differences in T cells or hematopoietic stem cells.
The result held in a second transplant model
In the fully mismatched experiment, the survival comparison included 16 vehicle-conditioned recipients and 18 FV2-conditioned recipients pooled from four independent experiments. The treated mice also had lower clinical scores for graft-versus-host disease than the vehicle group.
The researchers also tested a haploidentical transplant model, in which the analysis included 13 vehicle recipients and 12 FV2 recipients, alongside one bone-marrow-only reference mouse, pooled from two experiments. FV2 recipients regained weight similarly to the bone-marrow controls, had better appearance and higher survival than vehicle recipients, and showed 90% donor-derived granulocytes at 12 weeks.
Ten days after transplantation, the treated mice had a different immune profile from the vehicle group. Th1 frequency was 32.0% in FV2 recipients, compared with 80.1% in vehicle recipients. The treated group also had a lower Th17 frequency and more than 50% donor Tregs in the spleen.
What the study does and does not establish
The authors say the findings are mainly explained by a higher Treg-to-Tcon balance after six hours of conditioning. They also acknowledge that Tcon and CD8-positive T-cell numbers were about four times lower at day 10, which could itself contribute to the reduced graft-versus-host disease. So the result does not isolate the effect of a larger Treg proportion from the effect of removing other T cells.
The evidence is limited to mouse cells and mouse transplantation models. No human participants or clinical transplant outcomes were studied, and the work did not directly test whether the treatment preserves graft-versus-leukaemia or graft-versus-tumour activity in tumour-bearing recipients. The reported stem-cell experiment measured viability, not complete long-term stem-cell function, and sample sizes varied across the assays and models.
The haploidentical experiment used a different venetoclax concentration and exposure duration while retaining the FV2 label. Direct anti-tumour testing and longer-term assessment of stem-cell function remain open questions.
Study support and data
The experiments used several mouse lines and had institutional animal-care approval. The study was primarily supported by the Oxnard Foundation, with additional support from UC Irvine, National Cancer Institute and National Institutes of Health, American Cancer Society, and California Institute for Regenerative Medicine awards. The authors declared no commercial or financial relationships that could be construed as potential conflicts of interest.
The authors said raw data supporting the article's conclusions will be made available without undue reservation.
Paper data and sources
Original title: Short term ex vivo graft conditioning with venetoclax, fluticasone propionate, and IL-2 reduces graft versus host disease in mouse allogeneic hematopoietic cell transplantation
Authors: Ayala L, Ahmedani A, Zhou C et al.
Journal/Repository: Frontiers in immunology
Status: Peer-reviewed
First online: 2026-10-09
DOI: Not available
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