Clearance of CMV viremia and survival after double umbilical cord blood transplantation in adults depends on reconstitution of thymopoiesis

Abstract

Umbilical cord blood grafts are increasingly used as sources of hematopoietic stem cells in adults. Data regarding the outcome of this approach in adults are consistent with delayed and insufficient immune reconstitution resulting in high infection-related morbidity and mortality. Using cytomegalovirus (CMV)-specific immunity as a paradigm, we evaluated the status, mechanism, and clinical implications of immune reconstitution in adults with hematologic malignancies undergoing unrelated double unit cord blood transplantation. Our data indicate that CD8(+) T cells capable of secreting interferon-gamma (IFN-gamma) in a CMV-specific enzyme-linked immunosorbent spot (ELISpot) assay are detectable at 8 weeks after transplantation, before reconstitution of thymopoiesis, but fail to clear CMV viremia. Clearance of CMV viremia occurs later and depends on the recovery of CD4(+)CD45RA(+) T cells, reconstitution of thymopoiesis, and attainment of T-cell receptor rearrangement excision circle (TREC) levels of 2000 or more copies/mug DNA. In addition, overall survival was significantly higher in patients who displayed thymic regeneration and attainment of TREC levels of 2000 or more copies/mug DNA (P = .005). These results indicate that reconstitution of thymopoiesis is critical for long-term clinical outcome in adult recipients of umbilical cord blood transplant. The trial was prospectively registered at http://www.clinicaltrials.gov (NCT00133367).

Figure 1

Reconstitution of various cell populations after double UCB transplantation. (A) T-cell, B-cell, and NK cell reconstitution. The bar graph in the right panel indicates the normal range for each of the lymphocyte subsets. (B) CD4⁺ T-cell subsets. (C) CD8⁺ T-cell subsets. (D) Monocytes. The 25th and 75th percentiles are denoted by the error bars; solid symbols (■, ♦, ▲, ●) denote median values.

Figure 2

Reconstitution of TREC values at various time points after transplantation. The line connects the median values for each of the individual time points. Each dark circle represents the TREC value from 1 patient. TREC concentrations were determined from DNA isolated from total PBLs. The limit of detection of the TREC assay was 10 copies/μg DNA.

Figure 3

Development of CMV-specific T effector cells is detected in patients with or without detectable CMV viremia. Total PBLs were collected at the indicated time points after transplantation and were assessed for the presence of IFN-γ–producing effectors in response to CMV, as described in “IFN-γ ELISpot assay.” Cultures incubated with CMV lysates were scored as positive if the number of resulting spots was 3 standard deviations above the control. (A) Representative patient with detectable CMV effectors and CMV viremia. (B) Representative patient with detectable CMV effectors without detectable viremia.

Figure 4

The proportion of patients with CMV viremia declines, whereas the proportion of patients without CMV viremia increases after transplantation. Patients at risk for CMV (n = 21) were analyzed at various time intervals after transplantation. This patient population included 16 patients who had positive anti-CMV antibody titers before transplantation and 5 patients who were negative for anti-CMV antibody titers but developed CMV viremia after transplantation. The proportion of patients with and without viremia among the tested population at risk is shown for each indicated time interval.