Nanofiltration of growth media supplemented with human platelet lysates for pathogen-safe xeno-free expansion of mesenchymal stromal cells

Background aims

Human platelet lysate can replace fetal bovine serum (FBS) for xeno-free ex vivo expansion of mesenchymal stromal cells (MSCs), but pooling of platelet concentrates (PCs) increases risks of pathogen transmission. We evaluated the feasibility of performing nanofiltration of platelet lysates and determined the impact on expansion of bone marrow–derived MSCs.

Methods

Platelet lysates were prepared by freeze-thawing of pathogen-reduced (Intercept) PCs suspended in 65% storage solution (SPP+) and 35% plasma, and by serum-conversion of PCs suspended in 100% plasma. Lysates were added to the MSC growth media at 10% (v/v), filtered and subjected to cascade nanofiltration on 35- and 19-nm Planova filters. Media supplemented with 10% starting platelet lysates or FBS were used as the controls. Impacts of nanofiltration on the growth media composition, removal of platelet extracellular vesicles (PEVs) and MSC expansion were evaluated.

Results

Nanofiltration did not detrimentally affect contents of total protein and growth factors or the biochemical composition. The clearance factor of PEVs was >3 log values. Expansion, proliferation, membrane markers, differentiation potential and immunosuppressive properties of cells in nanofiltered media were consistently better than those expanded in FBS-supplemented media. Compared with FBS, chondrogenesis and osteogenesis genes were expressed more in nanofiltered media, and there were fewer senescent cells over six passages.

Conclusions

Nanofiltration of growth media supplemented with two types of platelet lysates, including one prepared from pathogen-reduced PCs, is technically feasible. These data support the possibility of developing pathogen-reduced xeno-free growth media for clinical-grade propagation of human cells.

A double-virally-inactivated (Intercept-solvent/detergent) human platelet lysate for in vitro expansion of human mesenchymal stromal cells

BACKGROUND

Pooled human platelet lysate (HPL) can replace fetal bovine serum (FBS) as xeno-free supplement for ex vivo expansion of mesenchymal stromal cells (MSCs). We evaluate here whether a double-virally-inactivated HPL (DVI-HPL) prepared from expired Intercept-treated platelet concentrates (PCs) and treated by solvent/detergent (S/D) can be used for MSC expansion.

STUDY DESIGN AND METHODS

Expired Intercept-treated PCs in 65% platelet (PLT) additive solution were pooled and subjected to a 1% tri-n-butyl phosphate/1% Triton X-45 treatment followed by soybean oil, hydrophobic interaction chromatography purification, and sterile filtration. Bone marrow-derived MSCs (BM-MSCs) were expanded for four passages in growth medium containing 10% DVI-HPL, I-HPL (from Intercept-PC only), untreated HPL, and FBS. MSC morphology, doubling time, immunophenotype, immunosuppressive activity, and differentiation capacity were compared.

RESULTS

Expanded cells had typical spindle morphology and showed higher viability in all HPL conditions than in FBS. The DVI-HPL and FBS-expanded cells were morphologically larger than in I-HPL and HPL supplements. The cumulative population doubling was lower using DVI-HPL than with HPL and I-HPL, but significantly higher than using FBS. Immunophenotype was not affected by the supplements used. Immunosuppressive activity was maintained with all supplements. Differentiation capacity into chondrocytes and osteocytes was more effective in DVI-HPL but less toward adipocytes compared to other supplements.

CONCLUSIONS

Human PLT lysate made from Intercept-PCs subjected to S/D treatment may be an alternative to untreated HPL and to I-HPL for BM-MSC expansion. This finding reinforces the potential of HPL as a virally safe alternative to FBS for clinical grade MSC expansion protocols.

Science, ethics and communication remain essential for the success of cell-based therapies

Cell-based therapeutics, such as marrow or peripheral blood stem cell transplantation, are a standard of care for certain malignancies. More recently, a wider variety of cell-based therapeutics including the use of mesenchymal stromal/stem cells, T-cells, and others show great promise in a wider range of diseases. With increased efforts to expand cell-based treatments to several clinical settings, many institutions around the world have developed programs to explore cellular therapy's potential for safe and effective applications. In legitimate investigations, usually conducted through academic centers or biotechnology industry-sponsored efforts, these studies are regulated and peer-reviewed to ensure safety and clear determination of potential efficacy. However, in some cases, the use of cell-based approaches is conducted with insufficient preclinical data, scientific rationale, and/or study plan for the diseases claimed to be treated, with patients being charged for these services without clear evidence of clinical benefit. In this context, patients may not be properly informed regarding the exact treatment they are receiving within a consenting process that may not be completely valid or ethical. Here, the authors emphasize the importance of distinguishing "proven cell-based therapies" from "unproven" and unauthorized cell-based therapies. This publication also addresses the necessity for improved communication between the different stakeholders in the field, patient associations, and advocacy groups in particular, to favor medical innovation and provide legitimate benefits to patients. Considering the progressive growth of cell-based treatments, their increasing therapeutic value and the expectation that society has about these therapies, it is critically important to protect patients and ensure that the risk/benefit ratio is favorable. This paper is a review article. Literature referred to in this paper has been listed in the references section. The datasets supporting the conclusions of this article are available online by searching PubMed. Some original points in this article come from the laboratory practice in our research centers and the authors' experiences.

Cytomegalovirus-specific cellular immune responses and viremia in recipients of allogeneic stem cell transplants

The immune suppression inherent in allogeneic stem cell transplantation (SCT) offers a favorable environment for infection by opportunistic agents, such as human cytomegalovirus (CMV). Despite the application of potent antiviral prophylaxis, patients remain at risk for CMV infection until adequate immunity is restored. CMV-specific CD8(+) T cell counts were monitored, using HLA-A2 tetrameric complexes, to establish the level of immune response to the viral phosphoprotein UL83 in patients after allogeneic SCT. Correlating this with viral replication and clinical status shows that the level of tetramer-positive T cells provides an assessment of CMV immune reconstitution after stem cell transplantation. Most patients with seropositive donors did reconstitute long-term CMV immunity, unless prolonged immunosuppression to control graft-versus-host disease was induced. Together with polymerase chain reaction testing, this technique provides measurable parameters that can be a guide to therapeutic decision making and can form the basis of CMV immunotherapy.

Immunotherapy of AML: future directions

Immunotherapy in the form of allogeneic GvL has been curing AML patients for nearly 30 years but our understanding of the mechanisms has been poor. Our rapidly evolving understanding of the human immune system and the concomitant technical developments in ex vivo cell manipulation, the vision of funding bodies, the dedication of clinical and research staff, and above all the commitment of our patients, promise substantial progress in the treatment of this disease in the year 2000 and beyond.

Selective removal of alloreactive cells from haematopoietic stem cell grafts: graft engineering for GVHD prophylaxis

One of the main goals in allogeneic bone marrow transplantation is the abrogation of graft-versus-host disease with the preservation of antileukaemia and antiviral activity. We have established a novel system for the selective removal of alloreactive lymphocytes from donor grafts while retaining an effective allogeneic response to third-party stimulator cells. Initial feasibility studies were done with unrelated HLA-mismatched pairs and then extended into the matched setting. Mononuclear cells from HLA-matched donors were cocultured with irradiated recipient cells prestimulated with cytokines (gamma-IFN and TNF-alpha) in a modified mixed lymphocyte culture (MLC). Alloreactive donor lymphocytes were identified by expression of CD69, an early activation marker and selectively removed by paramagnetic bead sorting. The remaining 'non-alloreactive' lymphocytes were tested in proliferative assays against the original matched recipient and to a third-party donor. A mean depletion of proliferative capacity to 11.5 +/- 9.9% of the original matched recipient response was achieved while the residual third-party response was largely preserved at 77.8 +/- 20.9% which should translate into improved immune reconstitution and preservation of antiviral activity. The non-alloreactive lymphocytes could also possess functional antileukaemia activity. Moreover, the alloreactive cells are easily recoverable in this selective T cell depletion strategy for cryopreservation and ready for immediate access as therapeutic donor lymphocyte infusions in cases of frank relapse post transplant.