Work

Non-Expanded PR1-Specific CTL Sort-Purified Directly From Cord Blood Lymphocytes Deplete Human AML In Vivo

Year: 2011

Type: article

Abstract: Relapse remains a significant problem following allogeneic stem cell transplantation (SCT) for AML. Adoptive transfer of leukemia-specific cytotoxic T lymphocytes (CTL), such as PR1-specific CTL, might be used to treat persistent leukemia after SCT by enhancing graft versus leukemia (GVL) while minimizing graft versus host disease (GVHD). A limitation of this approach is the limited persistence of adoptively transferred T cells in the recipient, due in part to the lengthy ex vivo expansion of low frequency cells necessary to obtain a sufficient cell number. We chose to study PR1-CTL derived from umbilical cord blood (UCB) based on our observation that UCB PR1-CTL are increased 100- to 1,000-fold compared to adult peripheral blood (PB), suggesting UCB might be a rich source of PR1-CTL. Because UCB is associated with a decreased risk of GVHD, in part because of the predominance of naive T cells, it may also be a preferred platform to transfer GVL with minimal risk of GVHD. We found the frequency of PR1-CTL in UCB to be 0.007 to 0.345% (mean 0.117%; n = 57) of CD8+ cells compared with a frequency of < 0.001% in healthy adult PB. Therefore, we hypothesized that a sufficient number of PR1-CTL from UCB could be obtained by PR1/HLA-A2 tetramer-based cell sorting and infused without further expansion to mediate GVL. To test this, CD8+ T cells from HLA-A2+ UCB units were first enriched via whole blood negative immunodensity separation. Enriched cells were sorted (> 98% purity) into PR1-CTL and PR1-CTL-depleted CD8+ cells (PDC) and briefly activated ex vivo for 48 hours with soluble anti-CD3/anti-CD28 + IL-2. After 48 hours, PR1-CTL specifically lysed PR1-pulsed T2 cells although 95% of PR1-CTL and PDC retained a CCR7+CD45RA+ naive phenotype. Next, 1 × 104 cells were infused into NOD/SCID mice engrafted for 7 days with 2-4 × 106 human AML blasts. Three separate experiments were performed. Two weeks after adoptive transfer, AML in bone marrow (BM) of PR1-CTL treated mice decreased 27% (range 21%-32%; p < 0.02) compared to untreated mice, and by 23% (range 4%-47%; p = NS) compared to mice receiving PDC. Moreover, AML in the PB of PR1-CTL treated mice decreased 47% (range 30%-61%, p < 0.04) compared to untreated mice, and by 58% (range 48%-68%; p < 0.01) compared to mice receiving PDC. These data justify clinical studies to determine whether PR1-CTL isolated directly from UCB can be used to enhance GVL without increased GVHD.

Source: Transplantation and Cellular Therapy

DOI: 10.1016/j.bbmt.2010.12.175