Production of an ideal cord blood graft


Background
Hematopoietic stem cell (HSC) transplantation can cure many hematologic diseases and malignancies. These HSCs are usually obtained from a related or unrelated donor’s bone marrow or peripheral blood. Unfortunately, 40% of patients lack the required HLA-matched donor and the majority of patients will need to find an alternative stem cell source, such as cord blood (CB) cells.

The immaturity of a CB immune system permits for multiple HLA mismatches. This permissiveness increases access to HSC transplantation. Moreover, CB transplants are associated with less chronic graft versus host disease (GVHD) and possibly with less relapse of the underlying malignancy when compared to other grafts1.

Problems with CB
The low cell dose of CB results in delay or absence of engraftment, increasing early mortality. Therefore only 5% of stored CBs are suitable for adults. It is by expending the cord and thus increasing cell dose that survival could increase. This explains the great interest in molecules that expand HSC/progenitors (HSPCs). In addition, CB transplants suffer delayed T cell and platelet reconstitution.

Our vision
The ideal graft source would be a CB, simultaneously expanded for HSPCs, T cells and megakaryocyte progenitors. Expansion of anti-leukemia natural killer (NK) cells would also represent an important added benefit 2. We propose 4 activities to improve the outcome of CB transplantation:

1. Optimizing HSC production
2. Optimizing production of CB-derived platelets
3. Optimizing T cell and NK cell precursor production
4. Integrating molecules for the design of optimal CB grafts

1. Optimizing HSC production


Our lab recently identified the small molecule UM729 and its optimized version UM171, which enhances self-renewal (expansion) of human HSCs3-4. UM171 should generate extensive clinical benefits such as:
          • abrogating the prolonged aplasia and consequent infections
          • allowing the use of smaller better-matched CB
          • decreasing the risk of transplant mortality.
To further improve HSC production, newly discovered molecules which synergize with UM171 to expand human HSCs will be optimized. If successful, this will lead to faster neutrophil recovery after transplantation. It will also reduce the volume and duration of our cultures, two major issues for generation of clinically-relevant culture protocols.

2. Optimizing production of CB-derived platelets


Platelets are a blood component necessary for normal blood clotting. Their production is ensured by megakaryocytes (picture), a large bone marrow cell derived from HSCs.

The in vitro production of megakaryocyte precursors and their addition to the graft would reduce the need for transfusion and the risk of bleeding after transplantation.

Our team found a unique compound which massively induces platelet production from UM171-expanded CB HSCs. This molecule which demonstrates a selective activity on CB-derived megakaryocyte progenitors will be optimized and tested in vivo in mice and monkeys for eventual clinical applications.

3. Optimizing T cell and NK cell precursor production


T and NK cells are lymphocytes, also called white blood cell. They play an important role in the immune system.

Before HSC transplantation, the recipient's immune system is usually destroyed with radiation or chemotherapy. As a consequence, the recipient will suffer from prolonged immunodeficiency after transplantation, leaving him very vulnerable to infections.

Further optimization of CB grafts will be obtained by identifying new compounds to produce large amounts of natural killer and T cell precursors. Their addition to the graft would possibly help to reduce cancer recurrence and incidence of life threatening viral infections.

4. Integrating molecules for the design of optimal CB grafts


Once all the small molecules will have been identified and optimized, we will determine the best culture conditions for each of them (duration, growth factors, etc.). The small molecules will then be combined with a bioreactor device required for the generation of clinically ideal CB grafts.

If successful, the integration of our small molecules will lead to the in vitro production of all the important blood elements needed for a successful transplantation.

The strong translational pipeline supported by a group of clinician scientists and bioengineers supports our belief that several paradigm-changing findings will occur from this research. For example, we foresee a noticeable reduction of neutrophil recovery and hence mortality, infectious complications and malignancy relapse with marked improvement in quality of life of CB transplants. Most importantly, the ideal CB graft could extend the indication of CB transplantation to non-malignant diseases (e.g., auto-immune, inflammatory), and make CB the most popular graft source.



References

  1. Brunstein CG, Gutman JA, Weisdorf DJ, Woolfrey AE, Defor TE, Gooley TA, Verneris MR, Appelbaum FR, Wagner JE, Delaney C. (2010). Allogeneic hematopoietic cell transplantation for hematologic malignancy: relative risks and benefits of double umbilical cord blood. Blood, 116(22): 4693-9.

  2. Klingemann, H. (2015). Challenges of cancer therapy with natural killer cells. Cytotherapy, 17(3): 245-9.

  3. Fares I, Chagraoui J, Gareau Y, Gingras S, Ruel R, Mayotte N, Csaszar E, Knapp DJHF, Miller P, Ngom M, Imren S, Roy DC, Watts KL, Kiem HP, Herrington R, Iscove N, Humphries RK, Eaves C, Cohen S, Marinier A, Zandstra PW, Sauvageau G. (2014). Cord blood expansion. Pyrimidoindole derivatives are agonists of human hematopoietic stem cell self-renewal. Science 345(6203):1509-12.

  4. Pabst C, Krosl J, Fares I, Boucher G, Ruel R, Marinier A, Lemieux S, Hébert J, Sauvageau G. (2014). Identification of small molecules that support human leukemia stem cell activity ex vivo. Nature Methods. 11(4): 436-42.