Stem cell enrichment in graft engineering

Background

CD34⁺ cell enrichment with the CliniMACS System results in an enriched stem cell product, which is depleted of non-target cells. The purity of CD34 enriched stem cell product is often higher than 95% and the passive T cell depletion results in a log10 depletion of about 4.5. 

Reagents

There are two product lines available for stem cell enrichment. CliniMACS CD34 enrichment is widely used for enrichment of CD34⁺ cells from hematopoietic stem cell grafts. The use of these products leads to passive T cell depletion. Stem cell enrichment strategies are widely used for graft-versus-host disease (GvHD) prophylaxis in the context of allogeneic stem cell transplantation.

Applications

Stem cell enrichment can be useful in a number of different transplantation scenarios. The following will provide you with details of current clinical applications of graft engineering by stem cell enrichment.

Haploidentical transplantations

The main application studied for CD34 enrichment as graft manipulation is allogeneic, and in particular, haploidentical hematopoietic stem cell transplantation (HSCT). Haploidentical HSCT can be a therapy option for patients suffering from haematologic malignancies or non-malignant diseases, who are eligible for allogeneic transplantation, and do not have a matched related or unrelated donor. A thorough T and B cell depletion is necessary to reduce the risk of severe graft-versus-host disease (GvHD) and post-transplant lymphoproliferative disorders (PTLD). In the haploidentical transplant setting, the transplantation of a high number of highly purified CD34 enriched stem cells as sole GvHD prophylaxis, without any post-transplant immunosuppression, for adult patients with acute leukemia, has been shown to result in excellent long term survival without any chronic GvHD.^2-4 Similar results have been reported for pediatric patients being treated with haploidentical HSCT.⁵

Matched transplantations

Allogeneic hematopoietic stem cell transplantation has been studied as a curative treatment option for a number of malignant and non-malignant diseases.⁴¹ However, a major risk is the development of acute and chronic GvHD. Ex vivo T cell depletion has been shown to be an efficient means to prevent severe GvHD after transplantation. 

Recently the results have been published of a National Heart, Lung, and Blood Institute (NHLBI)-sponsored clinical Phase II multi-center trial for adult patients with acute myeloid leukemia (AML), who had received extensively T cell–depleted grafts from human leukocyte antigen (HLA) identical sibling donors, have been published. The data show that the risk of severe acute and chronic GvHD, as well as of relapse, is low⁶. 

These data were compared to another NHLBI-sponsored trial, which took place at the same time and included a similar patient cohort who had received a non-manipulated graft. The authors of the subsequent report stated that recipients of T cell-depleted grafts experienced lower rates of acute and chronic GvHD, whereas the incidence of relapse, treatment related mortality (TRM), disease-free and overall survival (DFS, OS) were all similar after with two years of follow-up.⁷

Stem cell boost

Poor graft function is a possible complication following allogeneic HSCT. Several groups have reported that poor graft function can be overcome by transfusion of highly enriched CD34⁺ stem cells without further conditioning. It has been demonstrated that, in patients with poor graft function, a boost of enriched CD34⁺ cells can be associated with a high chance of trilineage recovery and a low risk of GVHD.^8-12

Autologous transplantations

Although the main application studied using of CD34 enrichment is the prevention of severe GvHD and post transplant lymphoproliferative disease in allogeneic hematopoietic stem cell transplantation, autologous transplantation with CD34 enrichment is also applied occasionally to eliminate contaminating tumor cells (“purging”) in the treatment of solid childhood cancers, such as high risk neuroblastoma¹⁴, or in Hodgkin’s disease¹³. 

Autologous hematopoietic stem cell transplantation has also been applied to treat patients with severe and therapy-refractive autoimmune diseases. Autologous HSCT is performed for patients with severe forms of multiple sclerosis (MS), systemic sclerosis (SSc), systemic lupus erythematosus (SLE), or Crohn’s disease.⁴¹ 
CD34 enrichment of the autologous graft has been utilized in several centers in order to prevent reinfusion of autoreactive immune cells back into the patient.^15-18

Cord blood transplantation

One of the major drawbacks of cord blood (CB) transplantation is the limited number of total nucleated cells and hematopoietic stem cells, which are about 10-fold lower in CB than in bone marrow (BM) and 50 to 100-fold lower as compared to mobilized peripheral blood. This may result in delayed engraftment and a higher risk of transplant related mortality (TRM). Several strategies are being investigated to enhance engraftment after CB transplantation. 

The support of single CB transplantation by co-infusion of a relatively low number of T cell-depleted mobilized hematopoietic stem cells from a third party donor (TPD) was originally developed by Manuel Fernandez¹⁹. This strategy resulted in:

• early recovery of circulating granulocytes,
• high rates of CB engraftment,
• full CB chimerism.
  

Published data of this approach in combination with a myeloabative^{20, 21} or reduced intensity²² conditioning show promising overall and disease free survival.

References

1. Keever-Taylor et al. (2012) Biol. Blood Marrow Transplant. 18: 690–697.
2. Aversa et al. (2005): J. Clin. Oncol. 23: 3447–3454.
3. Aversa et al.(2008): Blood Cells Mol. Dis. 40: 8–12.
4. Ciceri et al. (2008) Blood 112: 3574–3581.
5. Handgretinger et al. (2001) Bone Marrow Transplant. 27: 777–783.
6. Devine et al. (2011) Biol. Blood Marrow Transplant. 17: 1343–1351.
7. Pasquini et al. (2012) J. Clin. Oncol. 30: 3194-3201.
8. Klyuchnikov et al. (2009) Bone Marrow Transplant. 43: 158.
9. Cho et al. (2007) Blood 110: Abstract 1111.
10. Oyekunle et al. (2006) Cytotherapy 8: 375–380.
11. Larocca et al.(2006) Haematologica 91: 935–940.
12. Lang et al. (2006) Bone Marrow Transplant. 37 (Suppl. 1): 67.
13. Marabelle et al.(2011) Pediatr. Blood Cancer 56: 134–142.
14. Ballova et al. (2008) Neoplasma 55: 428–436.
15. Atkins et al. (2012) Biol. Blood Marrow Transplant. 18 (Suppl. 1): 177–183.
16. Vonk et al.(2008) Ann. Rheum. Dis. 67: 98–104.
17. Alexander et al. (2009) Blood 113: 214–223.

18. Kreisel et al. (2003) Bone Marrow Transplant. 32: 337–340.
19. Fernández (2009): British Journal of Haematology 147: 161–176.
20. Bautista et al. (2009): Bone Marrow Transplant. 43: 365–373.
21. Lindemans et al. (2012) BBMT 18 (Suppl. 2): 214.
22. Liu et al.(2011): Blood 118: 6438–6445.
41. The EBMT Handbook 6th Edition, Haematopoietic Stem Cell Transplantation, 2012, ISBN 978-88-89620-15-