Allogeneic transplantation using peripheral blood stem cells

Granulocyte Colony Stimulating Factor-Mobilized Peripheral Blood Mononuclear Cells: An Alternative Cellular Source for Chimeric Antigen Receptor Therapy

Lymphocyte collection by apheresis for CAR-T production usually does not include blood mobilized using granulocyte colony stimulating factor (G-CSF) due to the widespread knowledge that it causes a decrease in the number and functionality of lymphocytes. However, it is used for stem cell transplant, which is a common treatment for hematological malignancies. The growing demand for CAR therapies (CAR-T and NK-CAR), both in research and clinics, makes it necessary to evaluate whether mobilized PBSC products may be potential candidates for use in such therapies. This review collects recent works that experimentally verify the role and functionality of T and NK lymphocytes and the generation of CAR-T from apheresis after G-CSF mobilization. As discussed, T cells do not vary significantly in their phenotype, the ratio of CD4+ and CD8+ remains constant, and the different sub-populations remain stable. In addition, the expansion and proliferation rates are invariant regardless of mobilization with G-CSF as well as the secretion of proinflammatory cytokines and the cytotoxic ability. Therefore, cells mobilized before apheresis are postulated as a new alternative source of T cells for adoptive therapies that will serve to alleviate high demand, increase availability, and take advantage of the substantial number of existing cryopreserved products.

Variant rs1801157 in the 3'UTR of SDF-1ß does not explain variability of healthy-donor G-CSF responsiveness

The genetics responsible for the inter-individually variable G-CSF responsiveness remain elusive. A single nucleotide polymorphism (SNP) in the 3’UTR of CXCL12, rs1801157, was implicated in X4-tropic HiV susceptibility and later, in two small studies, in G-CSR responsiveness in patients and donors. The position of the SNP in the 3’UTR together with in-silico predictions suggested differential binding of micro-RNA941 as an underlying mechanism. In a cohort of 515 healthy stem cell donors we attempted to reproduce the correlation of the CXCL12 3’UTR SNP and mobilization responses and tested the role of miR941 in this context. The SNP was distributed with the expected frequency. Mobilization efficiency for CD34+ cells in WT, heterozygous and homozygous SNP individuals was indistinguishable, even after controlling for gender. miR941 expression in non-hematopoietic bone marrow cells was undetectable and miR941 did not interact with the 3’ UTR of CXCL12. Proposed effects of the SNP rs1801157 on G-CSF responsiveness cannot be confirmed in a larger cohort.

An MHC-defined primate model reveals significant rejection of bone marrow after mixed chimerism induction despite full MHC matching

In murine models, mixed hematopoietic chimerism induction leads to robust immune tolerance. However, translation to primates and to patients has been difficult. In this study, we used a novel MHC-defined rhesus macaque model to examine the impact of MHC matching on the stability of costimulation blockade-/sirolimus-mediated chimerism, and to probe possible mechanisms of bone marrow rejection after nonmyeloablative transplant. Using busulfan-based pretransplant preparation and maintenance immunosuppression with sirolimus, as well as CD28 and CD154 blockade, all recipients demonstrated donor engraftment after transplant. However, the mixed chimerism that resulted was compartmentalized, with recipients demonstrating significantly higher whole blood chimerism compared to T cell chimerism. Thus, the vast majority of T cells presenting posttransplant were recipient-rather than donor-derived. Surprisingly, even in MHC-matched transplants, rejection of donor hematopoiesis predominated after immunosuppression withdrawal. Weaning of immunosuppression was associated with a surge of antigen-experienced T cells, and transplant rejection was associated with the acquisition of donor-directed T cell alloreactivity. These results suggest that a reservoir of alloreactive cells was present despite prior costimulation blockade and sirolimus, and that the post-immunosuppression lymphocytic rebound may have lead to a phenotypic shift in these recipient T cells towards an activated, antigen-experienced phenotype, and ultimately, to transplant rejection.

The human-sheep chimeras as a model for human stem cell mobilization and evaluation of hematopoietic grafts' potential

OBJECTIVE

To investigate whether the sheep xenograft model of human hematopoiesis can be used to mimic mobilization of human hematopoietic stem cells in vivo.

MATERIAL AND METHODS

Sheep transplanted with 3.6 x 10(6) CD34+ from human adult bone marrow were mobilized 1.5 years posttransplantation with human granulocyte colony-stimulating factor for 5 days. At day 3 and 4 of mobilization, human cells were harvested from peripheral blood (PB) and bone marrow (BM) and were injected into secondary sheep recipients (n = 6) and these animals were analyzed for the presence of human cells in their BM and PB, starting at 3.5 months posttransplantation.

RESULTS

Maximum mobilization of human cells in PB occurred at day 3, with a 21-fold increase in total numbers of human cells, and a recovery of 5.5 x 10(4)/mL CD34+. In the BM, maximal numbers of human cells were achieved at day 4, with a 6.3-fold increase and a recovery of 1.5 x 10(4)/mL CD34+ cells. PB and BM mobilized human cells were then transplanted into new sheep recipients, and analysis at 3.5 months posttransplantation demonstrated that levels of human cell engraftment in BM of the group transplanted with mobilized PB were significantly lower than those transplanted with BM cells (0.6% +/- 0.1% vs 8.0% +/- 1.8%). Furthermore, in sheep transplanted with mobilized PB, the levels of human cells in circulation remained 2.5-fold higher than the levels of human cells found in their BM.

CONCLUSION

Mobilization of human cells in the sheep model parallels human PB and BM hematopoietic stem cells (HSC) mobilization in healthy human donors in their ability to engraft, differentiate, and repopulate secondary hosts. Thus, this model can become a useful tool to study mobilization regimens, mechanisms, and quality of products obtained.

Fewer relapses and increased chronic GVHD in patients transplanted with blood stem cells: a 5-year follow-up in a single centre study

A total of 61 consecutive adult patients with haematological malignancies with an HLA-identical or one antigen-mismatched haploidentical family donor were randomised to allogeneic transplantation with blood stem cells (BSC) or bone marrow (BM). The median observation time was 5 years. Apart from engraftment parameters and acute graft-versus-host disease (GVHD), transplant-related mortality (TRM), incidence and severity of chronic GVHD, relapse, leukaemia-free survival (LFS) and overall survival (OS) were recorded. In the BSC and BM group, respectively, TRM was 8/30 and 4/30 (P=0.405), the incidence of chronic GVHD was 15/26 and 11/30 (P=0.138), extensive chronic GVHD was 10/26 and 4/30 (P=0.034), and relapse one and 10 patients (P=0.007). In log-rank test restricted to the cases allografted from HLA-identical donors, the difference remained significant with regard to relapse incidence (P=0.039), but not extensive chronic GVHD (P=0.072). No difference in LFS and OS was observed. In conclusion, our study strongly indicates an enhanced graft-versus-leukaemia effect in BSC recipients, which is not expressed in increased survival. The increased chronic GVHD in these patients may contribute, but the relation is complex and not yet understood.

A case of chronic graft-versus-host-disease following allogeneic peripheral blood stem cell rescue for poor graft function after bone marrow transplantation

To overcome poor graft function after allogeneic bone marrow transplantation (BMT), the use of peripheral blood stem cells (PBSC) instead of bone marrow is gaining more popularity because of its advantages. There may, however, be an increased risk of graft-versus-host-disease (GVHD) because of the large number of lymphocytes present in a leukapheresis product. An 18-year-old man with severe aplastic anemia underwent an allogeneic BMT using his HLA-identical sister. After initial excellent graft take for 8 months, his blood counts gradually decreased to 2.8 x 10(9)/L of white cells and 28 x 10(9)/L of platelets with marrow cellularity of < 10%. After allogeneic granulocyte-colony stimulating factor mobilized PBSC rescue, the patient's blood counts recovered satisfactorily. Around 1 year after the boost, he developed chronic GVHD that responded to prednisolone and cyclosporin A. He is now well on low-dose steroids at day +1055 after PBSC rescue. The present case is the first experience of a long-term follow-up who underwent allogeneic PBSC rescue in Korea.