CD8 cell dose predicts outcomes in allogeneic stem cell transplantation with reduced-intensity conditioning

FROM THE JOURNAL OF CLINICAL ONCOLOGY

Peripheral blood stem cell (PBSC) grafts with high doses of CD8 cells were associated with significantly lower relapse risk and improved survival in patients who were treated for hematologic malignancies with reduced-intensity conditioning (RIC) hematopoietic allogeneic stem cell transplantation (allo-HSCT), according to a report online in the Journal of Clinical Oncology.

A multivariate analysis showed that CD8 cell dose was an independent predictor of relapse (adjusted hazard ratio [aHR], 0.43; P = .009), relapse-free survival (aHR, 0.50; P = .006), and overall survival (aHR, 0.57; P = .04). The data showed a linear association between CD8 cell dose and outcomes, and further analysis identified an optimum cutoff of CD8 cell dose (0.72 x 108 CD8 cells per kg) to segregate survival outcomes. Patients who received grafts with CD8 cell doses above the cutoff had significantly improved regression-free and overall survival (P = .005 and P = .007, respectively).

“These findings indicate that improved survival after RIC transplantations could be achieved by optimizing donor selection and PBSC collection to increase the likelihood of mobilizing grafts containing high CD8 cell doses,” wrote Dr. Ran Reshef of the department of medicine at the Hospital of the University of Pennsylvania, Philadelphia, and colleagues (Journ. Clin. Onc. 2015 June 8 [ doi:10.1200/JCO.2014.60.1203 ]).

Younger donors were more likely to have CD8 cell doses above the cutoff (CD8hi), however, only 53% of donors younger than 30 years had CD8hi grafts. To find methods to predict graft composition during donor screening, the investigators studied 21 randomly selected allo-HSCT donors. They found no correlations between CD8 graft content and clinical variables such as weight, sex, viral serologies, or apheresis parameters. Donors with a higher proportion of CD8 cells donated grafts with higher CD8 cell dose, but the presence of higher CD4 counts negated this. Screening for the relative proportions of CD8 and CD4 cells identifies donors most likely to mobilize CD8hi grafts.

“This is also a practical consideration because the assay is rapid, is routinely performed in clinical laboratories, and can easily be done at the time of confirmatory HLA [human leukocyte antigen] typing,” the authors noted. Since the relationship between CD8 dose and survival is linear, the higher the dose the better, even if it is below the cutoff.

Previous studies showed conflicting results regarding the outcome of RIC transplantation with younger unrelated donors versus older sibling donors. Donor age inversely correlates with CD8 cell dose, and the results of this study showed that overall survival was significantly better with younger unrelated donors with a CD8hi graft, compared with older sibling donors (P = .03). No such benefit was observed with younger unrelated donors with CD8lo grafts (P = .28), indicating the benefit may rely on CD8 cell dose.

The study evaluated 200 patients with hematologic malignancy who underwent allo-HSCT with fludarabine plus busulfan conditioning from 2007 to 2014 at the Abramson Cancer Center, University of Pennsylvania in Philadelphia. The cumulative relapse incidence was 42% at 1 year and 47% at 5 years. The most common diseases in the cohort were acute myeloid leukemia, myelodysplastic syndrome, and non-Hodgkin lymphoma.

High CD8 dose was associated with an increased, but nonsignificant risk of chronic graft-versus-host disease (GVHD); the risk for nonrelapse mortality was not associated with cell doses.

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