A preclinical model of double- versus single-unit unrelated cord blood transplantation

Abstract

Cord blood transplantation (CBT) with units containing total nucleated cell (TNC) dose >2.5 x 10(7)/kg is associated with improved engraftment and decreased transplant-related mortality. For many adults no single cord blood units are available that meet the cell dose requirements. We developed a dog model of CBT to evaluate approaches to overcome the problem of low cell dose cord blood units. This study primarily compared double- versus single-unit CBT. Unrelated dogs were bred and cord blood units were harvested. We identified unrelated recipients that were dog leukocyte antigen (DLA)-88 (class I) and DLA-DRB1 (class II) allele-matched with cryopreserved units. Each unit contained <or=1.7 x 10(7) TNC/kg. Recipients were given 9.2 Gy total-body irradiation (TBI) and DLA-matched unrelated cord blood with postgrafting cyclosporine and mycophenolate mofetil. After double-unit CBT, 5 dogs engrafted and 4 survived long term with 1 dominant engrafting unit and prompt immune reconstitution. In contrast, 0 of 5 dogs given single-unit CBT survived beyond 105 days (P = .03, log-rank test); neutrophil and platelet recovery was delayed (both P = .005) and recipients developed fatal infections. This new large animal model showed that outcomes were improved after double-unit compared to single-unit CBT. After double-unit CBT, the nonengrafted unit facilitates engraftment of the dominant unit.

Figure 1

The absolute neutrophil count (ANC) and platelet count per microliter (log₁₀ scale) from dogs receiving unrelated cord blood transplantation (CBT) on day 0 after 9.2 Gy TBI. A: Double-unit CBT group. B: Single-unit CBT group. Each line/symbol represents blood counts from individual dogs. ET= euthanized due to meeting defined criteria of poor condition after transplantation (for details, see Table 3 and Table 4).

Figure 2

Serial chimerism analyses from peripheral blood mononuclear cells for five dogs that received double unit unrelated cord blood transplantation. The first infused donor unit had the lower total cell dose. Each cord blood unit cell dose is shown in parenthesis (TNC × 10⁷/kg). Granulocyte chimerism for the dominant unit was consistently ≥ % PBMC chimerism (data not shown).

Figure 3

(A) Immune recovery of T- and B-cell subsets in 4 dogs after double unit unrelated cord blood transplantation (CBT). Shaded region indicates normal range of values (median ± 1 standard deviation from 20 untreated dogs). (B) Primary and secondary antibody titer response against the neoantigen sheep red blood cells injected on day +148-184 and +218-248 after CBT, respectively.