Successful transplantation and engraftment of peripheral blood stem cells after cryopreservation, positive and negative purging procedures, and a second cryopreservation cycle

CD34(+) hematopoietic progenitor cell selection of bone marrow grafts for autologous transplantation in pediatric patients

CD34(+)-selection of hematopoietic grafts for patients undergoing autologous hematopoietic stem cell transplantation (HSCT) is frequently used to obtain a tumor-free graft. The majority of published experience is with peripheral blood stem cell (PBSC) products; only scant information has been published on bone marrow (BM) grafts. We reviewed our experience using CD34(+) selection of BM grafts in children undergoing autologous BM transplantation. After obtaining institutional approval, we performed a retrospective review of the medical records of patients who underwent autologous stem cell collection at St. Jude. From January 1, 1999, to December 31, 2003, 373 patients underwent autologous HSCT; 131 received marrow grafts, 237 received PBSC grafts, and 5 received a combination. Seventeen patients underwent BM harvests for CD34(+) selection of their stem cell grafts. Sixteen patients received 19 CD34 purified grafts processed on the Isolex 300i Magnetic Cell Selection System device. Four patients were not included in the engraftment analysis as 1 did not receive the collected product, 1 received a tandem product, and 2 received products that were composed of 2 or 3 combined purified products. Following selection, marrow grafts contained a median of 1.4 x 10(6) CD34(+) cells/kg (range: 0.09-8.3 x 10(6)/kg) and a median of 0.014 x10(8) total nucleated cell cells/kg (range: 0.001-0.09 x 10(8)/kg). The median CD34% recovery was 30.9% (range: 9.3%-57.1%), with the median CD34 purity being 95.5% (range: 62.2%-98.8%). All patients engrafted. The median time to absolute neutrophil count > or = 500/mm(3) was 19 days (range: 12-35 days), and to platelet recovery was 28 days (range 18-37 days). No patient died from transplant-related complications. Our study demonstrates that CD34(+)-selection of marrow grafts is feasible, and these grafts are able to successfully reconstitute hematopoiesis in patients undergoing autologous BMT.

Purging of leukemia-contaminated bone marrow grafts using suicide adenoviral vectors: an in vivo murine experimental model

Autologous bone marrow transplantation is an alternative therapeutic option for acute myeloid leukemia patients lacking a compatible donor. However, bone marrow from these patients may contain residual leukemic cells that should be ideally eliminated prior to the infusion of the graft. With the aim of developing more efficient protocols of graft purging, adenoviral-mediated gene transfer protocols have been conducted. We studied whether suicide adenoviral vectors expressing the cytosine deaminase gene (AdCD) could be used for selectively killing leukemic WEHI-3B cells. The AdCD transduction followed by the 5-fluorocytosine exposure abrogated the growth of WEHI-3B cells in vitro, with a minimal effect on normal hematopietic progenitors. To test the efficacy of the purging protocol in vivo, bone marrow cells were mixed with syngenic WEHI-3B cells and this chimeric cell population was transduced with AdCD vectors. Infected cells were injected into myeloablated Balb-c mice, which then received a 5-fluorocytosine treatment for 4 days. All mice transplanted with unpurged bone marrow developed leukemia and died. However, 90% of recipients receiving the purging treatment were healthy up to 9 months post-transplantation and had a perfectly re-established hematopoietic system, without any signal of leukemic cell presence. In conclusion, suicide adenoviral vectors are proposed as a tool for the purging of Adenoviral-susceptible myeloid leukemia cells contaminating autologous bone marrow grafts.

Cryopreservation and mycophenolate therapy are detrimental to hematopoietic progenitor cells

BACKGROUND

The aim of the present study was to determine whether certain components of nonmyeloablative regimens for hematopoietic cell transplantation might compromise the growth of hematopoietic progenitors.

METHODS

Porcine peripheral blood progenitor cells (PBPC) were cytokine-mobilized, collected by leukapheresis, and cryopreserved using 5% dimethyl sulfoxide and 6% hydroxyethyl starch. The influence of cryopreservation on PBPC was tested in vitro by enumeration of colony-forming units (CFUs) in methylcellulose and cobblestone area-forming cell (CAFC) subsets in stromal-associated long-term cultures on fresh and frozen PBPC. The effects of mycophenolate mofetil (MMF) on porcine PBPC and baboon and human bone marrow (BM) were tested in vitro by adding varying doses of MMF to the CFU assays. One baboon was treated with increasing doses of MMF (100-500 mg/kg per day continuously intravenous), and sequential BM aspirations were tested for CFU content.

RESULTS

Fresh cytokine-mobilized PBPC had similar frequencies of progenitor cells when compared with porcine BM. Freezing-thawing of PBPC had no effect on porcine CFUs but reduced the recovery of CAFCs by more than 90%. In vitro, MMF completely inhibited the development of porcine and human CFUs at a concentration of 1 microg/mL and of baboon CFUs at levels between 10 and 100 microg/mL. Plasma-free mycophenolic acid levels of 10 to 30 microg/mL were associated with decreased CFUs in the BM.

CONCLUSIONS

Cryopreservation and MMF potentially prevent engraftment of porcine PBPC by reducing the content or development of progenitor cells. These results indicate that the use of fresh PBPC might improve the induction of mixed hematopoietic chimerism and raise the possibility that use of high doses of MMF in the poststem cell transplant may compromise engraftment.