The significance of minimal residual disease in stem cell grafts and the role of purging: is it better to purge in vivo or in vitro?

Establishment of a cell processing laboratory to support hematopoietic stem cell transplantation and chimeric antigen receptor (CAR)-T cell therapy

Cell processing laboratories are an important part of cancer treatment centers. Cell processing laboratories began by supporting hematopoietic stem cell (HSC) transplantation programs. These laboratories adapted closed bag systems, centrifuges, sterile connecting devices and other equipment used in transfusion services/blood banks to remove red blood cells and plasma from marrow and peripheral blood stem cells products. The success of cellular cancer immunotherapies such as Chimeric Antigen Receptor (CAR) T-cells has increased the importance of cell processing laboratories. Since many of the diseases successfully treated by CAR T-cell therapy are also treated by HSC transplantation and since HSC transplantation teams are well suited to manage patients treated with CAR T-cells, many cell processing laboratories have begun to produce CAR T-cells. The methods that have been used to process HSCs have been modified for T-cell enrichment, culture, stimulation, transduction and expansion for CAR T-cell production. While processing laboratories are well suited to manufacture CAR T-cells and other cellular therapies, producing these therapies is challenging. The manufacture of cellular therapies requires specialized facilities which are costly to build and maintain. The supplies and reagents, especially vectors, can also be expensive. Finally, highly skilled staff are required. The use of automated equipment for cell production may reduce labor requirements and the cost of facilities. The steps used to produce CAR T-cells are reviewed, as well as various strategies for establishing a laboratory to manufacture these cells.

The Combination of Rituximab and Bendamustine as First-Line Treatment Is Highly Effective in the Eradicating Minimal Residual Disease in Follicular Lymphoma: An Italian Retrospective Study

R-Bendamustine is an effective treatment for follicular lymphoma (FL). Previous large trials demonstrated the prognostic role of the molecular minimal residual disease (MRD) during the most frequently adopted chemotherapeutic regimens, but there are not yet conclusive data about the effect of combination of rituximab (R) and bendamustine in terms of MRD clearance. Thus, the aim of this retrospective study was to assess if and in what extent the combination of rituximab and bendamustine would exert a significant reduction of the molecular disease in 48 previously untreated FL patients. The molecular marker at baseline was found in the 62.5% of cases; no significant differences were observed between patients with or without the molecular marker in respect of the main clinical features. Moreover, the quantization of the baseline molecular tumor burden showed a great variability: the median value was 1.4 × 10-2 copies, ranging from 3 × 10-5 to 4 × 104. The initial molecular tumor burden did not correlate with clinical features and did not impact on the subsequent quality of response. After treatment, 93% of cases became MRD-negative; the median reduction of the BCL2/JH load was 4 logs. The 2-years PFS was 85%; it was significantly longer for patients in complete than for those in partial response (91 vs. 57%; p = 0.002), and for cases with lower FLIPI-2 score (88 vs. 60%; p = 0.004). On the contrary, PFS did not differ between patients with or without the molecular marker at baseline; a molecular tumor burden 15 times higher was observed in the relapsed subgroup in comparison to the relapse-free one, but this difference did not change the PFS length. The 2-years OS was 93.6%; the only variable that significantly impacted on it was the FLIPI-2 score; the presence of the molecular marker at baseline or its behavior after treatment did not impact on survival. This study, even if retrospective and conducted on a small series of patients, would represent a proof of concept that R-bendamustine is able to so efficaciously eradicate MRD that it could be able to by-pass the prognostic significance of MRD already demonstrated for other chemotherapeutic regimens in FL.

Systemic therapy with oncolytic myxoma virus cures established residual multiple myeloma in mice

Multiple myeloma is an incurable malignancy of plasma B-cells. Traditional chemotherapeutic regimes often induce initial tumor regression; however, virtually all patients eventually succumb to relapse caused by either reintroduction of disease during autologous transplant or expansion of chemotherapy resistant minimal residual disease. It has been previously demonstrated that an oncolytic virus known as myxoma can completely prevent myeloma relapse caused by reintroduction of malignant cells during autologous transplant. The ability of this virus to treat established residual disease in vivo, however, remained unknown. Here we demonstrate that intravenous administration of myxoma virus into mice bearing disseminated myeloma results in the elimination of 70–90% of malignant cells within 24 hours. This rapid debulking was dependent on direct contact of myxoma virus with residual myeloma and did not occur through destruction of the hematopoietic bone marrow niche. Importantly, systemic myxoma therapy also induced potent antimyeloma CD8⁺ T cell responses which localized to the bone marrow and were capable of completely eradicating established myeloma in some animals. These results demonstrate that oncolytic myxoma virus is not only effective at preventing relapse caused by reinfusion of tumor cells during stem cell transplant, but is also potentially curative for patients bearing established minimal residual disease.

Higher incidence of relapse with peripheral blood rather than marrow as a source of stem cells in adults with acute myelocytic leukemia autografted during the first remission

PURPOSE

The cell source for autologous stem cell transplantation has shifted from bone marrow (BM) to peripheral blood (PB). In acute myelocytic leukemia (AML), for patients who receive transplants during first complete remission (CR1), no prospective randomized study has compared relapse incidence (RI) to cell source.

PATIENTS AND METHODS

We analyzed 2,165 patients who received autografts (1,607 PB and 558 BM) from 1994 to 2006 and were reported to the European Cooperative Group for Blood and Marrow Transplantation with complete research data. Relative to the time of CR1, PB transplants were performed earlier than BM transplants. Because a poorer outcome was associated with a shorter interval from CR1 to transplantation, patients were divided into three groups: BM, early PB (< or = 80 days after CR1), and late PB (> 80 days after CR1) transplantation.

RESULTS

In a multivariate analysis adjusted for differences between groups and center, RI was higher with both early PB (56% +/- 3%; hazard ratio [HR], 1.45; 95% CI, 1.11 to 1.9; P = .006) and late PB transplantation (46% +/- 2%; HR, 1.3; 95% CI, 1.06 to 1.59; P = .01) as compared with BM transplantation (39% +/- 2%). This translated into a significantly worse leukemia-free survival (LFS) for early PB transplantation (36% +/- 3%; HR, 0.75; 95% CI, 0.58 to 0.96; P = .02) and a trend for a poorer LFS for late PB (46% +/- 2%; HR, 0.84; 95% CI, 0.7 to 1.01; P = .06) as compared with BM (52% +/- 2%).

CONCLUSION

For patients with AML in CR1, risk of relapse is greater with PB transplantation rather than BM, independent of the interval from CR1 to transplantation.

Flow electroporation with pulsed electric fields for purging tumor cells

Electroporation has been used in biological laboratories for many years to transiently porate cell membranes and permit plasmid or protein transfection. It has been shown that the application of pulsed electric fields (PEFs) of defined strength will kill off larger cells and select for viable small cells, in samples containing heterogeneous cells. This permits the selective killing of several blood and bone marrow-resident tumor cells. PEF technology is being applied to tumor purging of progenitor-cell transfusions, in support of high-dose chemotherapy, for the treatment of cancers such as lymphoma and multiple myeloma. Autologous stem-cell transplantation, in the setting of hematologic malignancies such as lymphoma, improves disease-free survival if the graft has undergone tumor purging. Progenitor cells are preserved or enriched. To overcome issues of electrical resistance, purging fidelity, and large sample volume, a flowing chamber PEF apparatus was designed and constructed for large-scale purging of clinical quantities of progenitor-cell transfusions. The specifics of this technique are described here. Treatment of greater than 10(9) cells is achieved in 30 min, under optimized flow conditions designed to overcome surface area or resistance issues and to optimize exposure of cells to electric fields. Efficient, large volume tumor purging of greater than 3 logs, for mixtures of tumor cells and mononuclear cells, is routinely achieved under defined conditions.