Single Unit Cord Blood Transplant Supported by Third Party Highly Purified Mobilized Hematopoietic Stem Cells: Immune Reconstitution Studies.

Background and Objectives: Following cord blood transplants (CBT) there is a period of severe and often prolonged immune deficiency that results in long term susceptibility to infections. Immune reconstitution is an important factor for long term survival. We analyzed the immune reconstitution of adult recipients of a single unit CBTs supported by a low number of third party donor highly purified mobilized hematopoietic stem cells (dual CB/TPD transplants), as previously described (

Patients and Methods: Data were obtained from 19 patients between July 2004 and July 2006. Data collection was initiated at different intervals (from day −7 to +720, quartiles Q₁=35, Q₂=90 and Q₃=210). Samples were obtained on days +15, +35, +55, +90 and monthly thereafter up to two years. By four-color flow cytometric immunophenotyping we analyzed the subsets of peripheral blood lymphocytes: CD3+/CD4+ (T helper/inducer), CD3+/CD8+ (T suppressor/cytotoxic), NK cells (CD3−/CD56+/CD16+) and B cells, as well as cells with naïve, memory and effector T-cell immunophenotypes. TREC bearing cells were analyzed by quantitative PCR in sorted CD4+ and CD8+ T cells collected from 3 months post-transplant onwards.

Results: CD56+ cells recovered early after transplantation, with median absolute number counts (ANC) of 69 (range 18–307), 170 (0–366) and 159 (32–531) cells/uL in days +15, +35 and +55 samples [normal controls 153 (71–438)], representing the largest subset within the first two months (decreasing proportions of 60%, 50% and 40%, respectively). ANC of CD4 and CD8 T cells remained low for several months, progressively increasing to reach normal ranges at different intervals. Naïve CD4 and CD8 cells (CD45RO−/CD27+) start to be detected by immunophenotyping after three months post-transplantation with median ANC of 17 (12–79) and 12 (5–103) cells/uL respectively and increasing thereafter [normal controls 860 (552–1072) and 331 (227–521)]. By the end of the first year values of T cell subsets were: CD4+, 823 (16–1123) cells/uL [normal controls 872 (470–1093)]; CD8 934 (56–1174) [normal controls 371 (208–808)], with persisting predominance of the naive phenotypes and proportions of memory phenotypes slowly increasing. B cells became detectable around day +90 with median ANC of 249 (0–1934) cells/uL, rapidly reaching values within the normal range [275 (133–684)]. Transient acute GVHD was developed by six of the 19 patients. All showed a transient drop in absolute numbers of NK, T and B cells. Chimerism analysis showed initial transient double chimerism of CB and TPD cells. Complete CB chimerism was achieved between days +15 and +94 (median, +35). Results of chimerism of lymphocyte subsets and TREC are not yet available.

Conclusions: Following dual CB/TPD transplants we have observed early recovery of NK and B-cells and slow development of T cells subsets and of non-naive immunophenotypes.