Persistence of residual tumour cells after cytokine-mediated ex vivo expansion of mobilized CD34+ blood cells in multiple myeloma

Molecular purging of multiple myeloma cells by ex-vivo culture and retroviral transduction of mobilized-blood CD34+ cells

Background

Tumor cell contamination of the apheresis in multiple myeloma is likely to affect disease-free and overall survival after autografting.

Objective

To purge myeloma aphereses from tumor contaminants with a novel culture-based purging method.

Methods

We cultured myeloma-positive CD34⁺ PB samples in conditions that retained multipotency of hematopoietic stem cells, but were unfavourable to survival of plasma cells. Moreover, we exploited the resistance of myeloma plasma cells to retroviral transduction by targeting the hematopoietic CD34⁺ cell population with a retroviral vector carrying a selectable marker (the truncated form of the human receptor for nerve growth factor, ΔNGFR). We performed therefore a further myeloma purging step by selecting the transduced cells at the end of the culture.

Results

Overall recovery of CD34⁺ cells after culture was 128.5%; ΔNGFR transduction rate was 28.8% for CD34⁺ cells and 0% for CD138-selected primary myeloma cells, respectively. Recovery of CD34⁺ cells after ΔNGFR selection was 22.3%. By patient-specific Ig-gene rearrangements, we assessed a decrease of 0.7–1.4 logs in tumor load after the CD34⁺ cell selection, and up to 2.3 logs after culture and ΔNGFR selection.

Conclusion

We conclude that ex-vivo culture and retroviral-mediated transduction of myeloma leukaphereses provide an efficient tumor cell purging.

Experimental culture conditions are critical for ex vivo expansion of hematopoietic cells

The ex vivo expansion of hematopoietic stem cells (HSC) for clinical use is now recognized to be a feasible and very promising approach for hematotherapy. Expansion of specific HSC subsets is required for different clinical applications, for example, to increase the number of mature cells, to produce specific cells for adoptive therapy, or to increase the number of primitive stem cells available for engraftment. Although hematopoietic growth factors can play an important role in this setting, in this review we emphasize that other variables affect the outcome of stem and progenitor cell expansion. These variables include the serum supplement, the purity of CD34(+) cells, the initial cell concentration, and the duration of culture. It is also essential to define standard culture conditions for normal stem cells and to limit or prevent expansion of residual tumor cells. In clinical applications, determination of the hematopoietic value of the expanded population is mandatory. Thus, we have to demonstrate the expansion of primitive hematopoietic progenitor and stem cells, with maintenance of their hematopoietic potential as assessed by in vitro or in vivo assays. We draw attention to the challenges in the clinical application of ex vivo expansion. These include the establishment of well-defined experimental conditions and the determination of the hematopoietic value of the expanded grafts, whatever the graft source: bone marrow, mobilized peripheral blood, or cord blood. Future studies hopefully will optimize these procedures and allow not only expansion but engineering of defined cellular functions as HSCs grow under defined conditions.

Ex vivo expansion of CD34-positive peripheral blood progenitor cells from patients with non-Hodgkin's lymphoma: no evidence of concomitant expansion of contaminating bcl2/JH-positive lymphoma cells

The aim of the present study was to evaluate the capacity to expand of hematopoietic stem cell (HSC) samples from eight patients with NHL, and to follow in parallel the fate of tumor cells in four of eight samples still containing bcl2/JH+ tumor cells after CD34+ or CD19-/20-/34+ cell selection. The presence of bcl2/JH+ cells was also investigated after expansion in four of eight samples, two of which were bcl2/JH at harvesting and two which were initially bcl2/JH+ but became bcl2/JH (below the level of PCR detection) after cell selection, to assess a possible reappearance of occult tumor cells after expansion culture. We used culture conditions that we previously had established to allow high level expansion of normal precursors, progenitors and LTC-ICs. In this study, particular attention was given to the role of Flt3-ligand, known to favor the growth of B cells. The expansion conditions were: 1.5 x 10(3) cells/ml in serum-free medium containing stem cell factor (SCF), interleukin-3 (IL-3), IL-6, granulocyte-stimulating factor (G-CSF), erythropoietin (Epo) +/- Flt3-ligand (Flt3-L) for 10 days. After culture, total cells, CFU-GMs, BFU-Es and LTC-ICs were expanded to a mean of 833-, 6.6-, 4.6-, and 1.8-fold, respectively with the cocktail of cytokines not including Flt3-L. When Flt3-L was added, the mean expansion values were 1095-, 31-, 15- and three-fold, respectively. Residual bcl2/JH+ cells present in four of eight samples before expansion were not detected after expansion. Similarly, no tumor cells reappeared after expansion of the two samples which had become negative after selection, as well as in the two samples which were bcl2/JH- at harvesting. These results suggest first that ex vivo expansion of hematopoietic stem cells in patients with non-Hodgkin's lymphoma is feasible without incurring the parallel risk of amplifying tumor cells; second, that Flt3-L did not stimulate the growth of tumor cells while it clearly favored the growth of normal progenitors.

CD34+ selection of autologous peripheral blood stem cells for transplantation following sequential cycles of high-dose therapy and mobilization in multiple myeloma

A potential problem of autologous transplantation in the treatment of multiple myeloma (MM) is the infusion of tumor cells. CD34+ selection has been used to purge autografts in MM and it is also possible to reduce tumour cell contamination of autografts by cytotoxic drug therapy prior to peripheral blood stem cell (PBSC) collection. To evaluate the effectiveness of a protocol combining multiple cycles of high-dose therapy and CD34+ selection to reduce tumour contamination of PBSC autografts, 34 MM patients were entered on a treatment schedule comprising two sequential cycles of mobilisation, CD34+ selection, and transplantation following high-dose therapy. In the second cycle of mobilisation there was a five-fold reduction in tumour contamination of the stem cell harvest (0.5 x 106/kg) compared with the first cycle (2.5 x 106/kg). In the 97 CD34+ selection procedures performed a median of 185 x 108 mononuclear cells (MNC) were processed yielding a median of 0.98 x 108 CD34+-enriched cells. CD34+ cells were enriched 68-fold from 1. 3% to 88.6%. The median yield of CD34+ cells was 42.2%. Following CD34+ selection the tumour cell contamination of the leukapheresis product was reduced by a median of 2.7 logs. This study demonstrates that in multiple myeloma a significant reduction in the malignant contamination of stem cell autografts can be achieved by combining the in vivo purging effect of cytotoxic therapy with in vitro purging by CD34+ selection.

Effects of flt-3 ligand in combination with TPO on the expansion of megakaryocytic progenitors

As an early acting growth factor, flt-3 ligand (FL) promotes the ex vivo expansion of hematopoietic stem and progenitor cells. The effect and mechanism of FL on the development of the megakaryocytic lineage remain unclear. In this study, we compared the effects of FL and stem cell factor (SCF) in combination with other megakaryocyte-promoting cytokines on the differentiation and proliferation of megakaryocytic progenitors and investigated the expression of flt-3 receptors on megakaryocytic cell lines. In liquid cultures of enriched CD34+ cells from human umbilical cord blood for 14 days, FL plus thrombopoietin (TPO), interleukin-3 (IL-3), and IL-6 promoted the expansion of nucleated cells, CD34+ cells, CD34+ CD38- cells, and megakaryocyte colony-forming units (CFU-MK) by 300 +/- 115-, 23.8 +/- 11.3-, 33.9 +/- 28.6-, and 584 +/- 220-fold, respectively. Replacing FL with SCF significantly decreased the yield of all cell types. Using murine bone marrow (BM) cells, we demonstrated that FL at a range of 0-100 ng/ml had no significant mitogenic effect on CFU-MK formation. TPO increased CFU-MK (p < 0.001) but the effect was not significantly modified by FL. While one human acute lymphoblastic leukemia sample expressed high levels of flt-3 receptor, the four megakaryocytic cell lines (Meg-01, CHRF-288-11, M-07e, and Dami) did not show any positive expression. Our data suggest that the present cytokine combination and expansion conditions provide an effective and potentially useful system for the clinical expansion of cord blood for bone marrow transplantation (BMT). FL alone did not stimulate megakaryocytopoiesis, possibly due to the lack of receptor expression on megakaryocytes. The effect of FL in augmenting the expansion of CFU-MK in liquid culture might be due to the early action of FL at the pluripotent stem cell stage.

Expansion of granulocyte colony-stimulating factor/chemotherapy-mobilized CD34+ hematopoietic progenitors: role of granulocyte-macrophage colony-stimulating factor/erythropoietin hybrid protein (MEN11303) and interleukin-15

Ex vivo stroma-free static liquid cultures of granulocyte colony-stimulating factor (G-CSF)/chemotherapy-mobilized CD34+ cells were established from patients with epithelial solid tumors. Different culture conditions were generated by adding G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CSF), Flt3 ligand (Flt3), megakaryocyte growth and development factor (Peg-rHuMGDF), GM-CSF/erythropoietin (EPO) hybrid protein (MEN11303), and interleukin-15 (IL-15) to the basic stem cell factor (SCF) + interleukin-3 (IL-3) + EPO combination. This study showed that, among the nine different combinations tested in our 5% autologous plasma-containing cultures, only those containing IL-3/SCF/Flt3/MEN11303 and IL-3/SCF/Flt3/MEN11303/IL-15 significantly expanded colony-forming unit granulocyte-macrophage (CFU-GM), burst-forming unit erythroid (BFU-E), long-term culture-initiating cells (LTC-IC), CD34+, and CD34+/CD38- cells after 14 days of culture. Particularly, the addition of IL-15 to IL-3/SCF/Flt3/MEN11303 combination produced a significant increase of LTC-IC, with an average 26-fold amplification as compared to input cells, without any detrimental effect on CFU-GM and BFU-E expansion. This combination also produced a statistically significant 3.6-fold expansion of primitive CD34+/CD38- cells. Moreover, this study confirms the previously described erythropoietic effect of MEN11303, which, in our experience, was the only factor capable of expanding BFU-E. Compared to equimolar concentrations of GM-CSF and EPO, MEN11303 hybrid protein showed a significantly higher capacity of expanding CFU-GM, BFU-E, LTC-IC, CD34+, and CD34+/CD38- cells when these cytokines were tested in combination with IL-3/SCF/Flt3. These cultures indicated that Peg-rHuMGDF addition to IL-3/SCF/EPO/Flt3 does not affect CFU-GM and BFU-E expansion but, unlike G-CSF or GM-CSF, it does not decrease the ability of Flt3 to expand primitive LTC-IC. These studies indicate that, starting from G-CSF/chemotherapy-mobilized CD34+ cells, concomitant expansion of primitive LTC-IC, CFU-GM, BFU-E, CD34+, and CD34+/CD38- cells is feasible in simple stroma-free static liquid cultures, provided IL-3/SCF/Flt3/MEN11303/IL-15 combination is used as expanding cocktail in the presence of 5% autologous plasma.

Clinical utility of immunoglobulin heavy chain gene rearrangement identification for tumour cell detection in multiple myeloma

In an attempt to define the clinical utility of immunoglobulin heavy chain (IgH) gene rearrangement identification for tumour cell detection in multiple myeloma, we investigated 36 consecutive newly diagnosed patients intended for high-dose chemotherapy in a study protocol. After identification of the IgH rearrangement, an allele specific oligonucleotide (ASO) was constructed and used in a semiquantative PCR for minimal residual disease (MRD) evaluation. The myeloma-specific IgH gene rearrangement could be identified and an ASO primer constructed in 24 (67%) of the patients. All of these patients underwent transplantation; 22 were autologous, of whom three had PCR-negative stem cell harvests, and two were allogeneic. 10 patients achieved a clinical complete response (CR) and five were PCR negative in sequential bone marrow analyses. In patients not achieving CR, PCR negativity was occasionally found, but in general the PCR results reflected the clinical status of the patients. No consistent relationship between the bone marrow MRD status and the clinical course was found, and early relapses occurred also in PCR-negative patients.