Ex vivo expansion of frozen/thawed CD34+ cells isolated from frozen human apheresis products

Chemoprotection by transfer of resistance genes

Dose-limiting toxicity of chemotherapeutic agents, i.e., myelosuppression, can limit their effectiveness. The transfer and expression of drug-resistance genes might decrease the risks associated with acute hematopoietic toxicity. Protection of hematopoietic stem/progenitor cells by transfer of drug-resistance genes provides the possibility of intensification or escalation of antitumor drug doses and consequently an improved therapeutic index. This chapter reviews drug-resistance gene transfer strategies for either myeloprotection or therapeutic gene selection. Selecting candidate drug-resistance gene(s), gene transfer methodology, evaluating the safety and the efficiency of the treatment strategy, relevant in vivo models, and oncoretroviral transduction of human hematopoietic stem/progenitor cells under clinically applicable conditions are described.

Genetic modification of human hematopoietic cells: preclinical optimization of oncoretroviral-mediated gene transfer for clinical trials

This chapter provides information about the oncoretroviral transduction of human hematopoietic stem/ progenitor cells under clinically applicable conditions. We describe in detail a short -60 h transduction protocol which consistently yields transduction efficiencies in the range of 30-50% with five different oncoretroviral vectors. We discuss a number of parameters that affect transduction efficiency, including the oncoretroviral vector characteristics, the vector stock collection, the source of CD34+ cells and transduction conditions.

Heteroclitic CD33 peptide with enhanced anti-acute myeloid leukemic immunogenicity

The goal of these studies was to engineer a synthetic CD33 peptide with enhanced immunogenicity for the induction of acute myeloid leukemia (AML)-specific CTLs. Eight modified CD33 peptides YLISGDSPV, YIGSGDSPV, YIIIGDSPV, YIILGDSPV, YIISGISPV, YIISGDLPV, YIISGDSWV and YIISGDSPL were designed for increased HLA-A2.1 or T cell receptor affinity and compared with the native CD33(65-73) peptide, AIISGDSPV, for enhanced immunogenicity. The YLISGDSPV peptide was found to be the most immunogenic epitope producing highly cytolytic CTLs against AML target cells. The CTLs generated withYLISGDSPV peptide showed CD33 peptide-specificity through targeting of both native (AIISGDSPV) and modified (YLISGDSPV) peptide presenting EBV-BLCL. The CTL cultures displayed a distinct phenotype consisting of a high percentage of activated memory (CD69(+)/CD45RO(+))-CD8(+)and a low percentage of naive (CD45RA(+)/CCR7(+))-CD8(+)cells. In addition, T-cell clones specific to the YLISGDSPV peptide were isolated and characterized to target AML cells. The clones exhibited both HLA-A2.1-restricted and AML cell-specific cytotoxicity that was mediated through a granule-dependent pathway. More importantly, the CTL clones did not lyse or inhibit the proliferation of normal CD34(+) progenitor cells. In conclusion, we report on the identification of a highly immunogenic heteroclitic YLISGDSPV CD33 epitope that is a promising candidate for immunotherapy targeting AML.

Analysis of the relationship between Scl transcription factor complex protein expression patterns and the effects of LiCl on ATRA-induced differentiation in blast cells from patients with acute myeloid leukemia

Exogenous expression of the transcription factor Scl (Tal1) in WEHI-3B D+ myelomonocytic leukemia cells interferes with their capacity to respond to all-trans retinoic acid (ATRA) induced differentiation; combination of ATRA with LiCl, however, circumvents the inhibition of differentiation produced by Scl. To gain information on the possible involvement of this transcription factor in the non-responsiveness of acute myelocytic leukemia (AML) patients to ATRA, we compared the endogenous expression levels of Scl and its transcription complex partners [i.e., Rbtn1 (LMO1), Rbtn2 (LMO2), Ldb1, and GATA family proteins] in leukemic blast cells from patients with AML and acute promyelocytic leukemia (APL), and determined the effects of lithium chloride alone or in combination with ATRA on the capacity of blast cells to differentiate during short-term ex vivo culture. Levels of Scl, Rbtn2, GATA1, and Ldb1 expression were comparable in AML and APL blasts, while the levels of expression of Rbtn1, GATA2, and GATA3 were absent or markedly lower in APL cells. Differentiation markers (cell surface myeloid antigens CD11b, CD15, CD14, and CD33) were also analyzed in blast cells. ATRA produced changes in at least one surface antigen differentiation marker in 89% of patient blasts, while LiCl caused such changes in 72% of the leukemic cells of patients. The combination of LiCl and ATRA induced the differentiation of leukemic blasts from 94% of patients. Although the expression of the transcription factors did not act as individual predictors of responsiveness or non-responsiveness to the inducers of differentiation, ATRA or ATRA plus LiCl, the addition of LiCl to ATRA increased the differentiation response over that of ATRA alone in a number of leukemic samples. These findings suggest that the combination of LiCl and ATRA may produce some clinical benefit in the treatment of the myeloid leukemias.

Effects of cryopreservation on lymphocyte immunophenotype and function

Cryopreservation of isolated peripheral blood mononuclear cells (PBMCs) for phenotypic and functional analyses is considered a standard procedure in order to minimize operator-dependent inter-assay variability and to optimize the use of available resources. However, only few and somewhat conflicting data are presently available on the effects of cryopreservation on PBMCs, especially in samples from HIV-infected patients in which assessment of lymphocyte phenotype and function is of the outmost importance. In this study, we compared fresh versus frozen/thawed (F/T) samples isolated from 19 healthy individuals and 21 HIV-infected patients, showing that cryopreservation induces: (i) a profound decrease of CD62L expression, with a consequent significant decline of the calculated proportions of "naïve" (CD45RA+CD62L+) and "central memory" (CD45RO+CD62L+) T cells; (ii) an increase of the calculated proportions of "effector" CD8+ T cells (CD45RA+CD62L- and CD45RO+CD62L-) in the healthy subjects, while no changes were observed in the HIV-infected group; (iii) a significant decline of CC chemokine receptor 5 (CCR5) expression; (iv) a loss of proliferative responses to some HIV antigens (i.e. p24) and recall antigens [cytomegalovirus (CMV) and Influenza] in HIV-infected patients. We thus conclude that cryopreservation induces a consistent set of changes in PBMCs from both healthy and HIV-infected individuals, and that certain immunological studies of HIV-infected patients (i.e. studies of immune reconstitution following antiretroviral therapy in HIV-infected patients or studies of HIV-infectivity in vitro using CCR5-tropic strains) should be performed on fresh samples.

Large scale purification of human blood CD34+ cells from cryopreserved peripheral blood stem cells, using a nylon-fiber syringe system and immunomagnetic microspheres

Isolation of large numbers of human peripheral blood CD34+ cells could lead to therapeutic applications, including purging of malignant cells from blood cell transplantations, purging of T cells from allogeneic bone marrow, and even blood cell transplantation. This procedure has limitations if there are not sufficient numbers of progenitor cells in the leukapheresis concentrates available for selection after detection of tumor cells in apheresis products. Use of frozen/thawed peripheral blood mononuclear cell (PBMC) samples would make feasible pooling of two or even more stem cell harvests collected at different time points and the total number of CD34+ progenitor cells available would increase. We established an efficient method for purification of CD34+ cells from cryopreserved apheresis products, using a nylon-fiber syringe system and immunomagnetic microspheres. We compared purity, recovery rate and clonogenicity of CD34+ cells purified from fresh (n = 22) and cryopreserved apheresis products (n = 14), using a nylon-fiber syringe system and immunomagnetic microspheres. The purity of CD34+ cells from cryopreserved products was less than that from fresh products (85.9 +/- 14.4% vs 94.6 +/- 10.0%), but the recovery rate of CD34+ cells and colony-forming cells was comparable between fresh and cryopreserved products. One patient underwent grafting with peripheral blood CD34+ cells selected after freezing, with good success. Therefore, these cells are capable of rapidly reconstituting hematopoiesis after high-dose chemotherapy. Bone Marrow Transplantation (2000) 26, 787-793.

Effective ex vivo generation of granulopoietic postprogenitor cells from mobilized peripheral blood CD34(+) cells

OBJECTIVE

Neutropenia following high-dose chemotherapy and peripheral blood progenitor cell (PBPC) transplantation might be abrogated by an additional transplantation of ex vivo generated granulopoietic postprogenitor cells (GPPC). Therefore, the ex vivo expansion of CD34(+) PBPC was systematically studied aiming for optimum GPPC production.

MATERIALS AND METHODS

CD34(+) PBPC were cultured in serum-free medium comparing different (n = 32) combinations of stem cell factor (S), interleukin 1 (1), interleukin 3 (IL-3) (3), interleukin-6 (6), erythropoietin (E), granulocyte colony-stimulating factor (G), granulate-macrophage colony-stimulating factor (GM), daniplestim (D, a novel IL-3 receptor agonist), and Flt3 ligand (FL) under various culture conditions. Ex vivo generated cells were assessed by flow cytometry, morphology, and progenitor cell assays.

RESULTS

Addition of G +/- GM but not GM alone to cultures stimulated with S163E effectively induced the generation of GPPC. GPPC production was maximum after 12 to 14 days. Best expansion rates were observed when cells were cultured at 1.5x10(4)/mL in 21% O(2). Modifications of culture conditions were either less or equally effective (i.e., modification of starting cell concentrations, low oxygen, addition of serum albumin or autologous plasma, repetitive feeding). Comparison of different cytokine combinations revealed that the optimum GPPC expansion cocktail consisted of S6GD+FL (day 12: 130-fold cellular expansion, 32% myeloblasts/promyelocytes, 49.4% myelocytes/metamyelocytes, 12.4% bands/segmented), which furthermore expanded CD34(+) cells (3.4-fold) and clonogenic progenitors (13.4-fold).

CONCLUSION

Using the S6DG+FL expansion cocktail, GPPC could be effectively produced ex vivo starting from positively selected CD34 PBPC, possibly enabling amelioration or even abrogation of posttransplant neutropenia.