Hematopoietic stem cell transplantation for adults with acute lymphoblastic leukemia

The clinical outcomes of B-cell Acute Lymphoblastic Leukemia Patients Treated with Haploidentical Stem Cells Combined with Umbilical Cord Blood Transplantation

BACKGROUND

Clinical outcomes of the transplantation strategy combined with a haploidentical stem cell graft and an unrelated umbilical cord blood unit (haplo-cord HSCT) for the treatment of B-cell acute lymphoblastic leukemia (B-ALL) remain unclear.

OBJECTIVE

To explore the clinical outcomes of haplo-cord HSCT in B-ALL patients.

STUDY DESIGN

A total of 112 B-ALL patients who received haplo-cord HSCT and 64 patients who received haploidentical hematopoietic stem cell transplantation (haplo-HSCT) in our center from 2010 to 2020 were retrospectively included in this study, and clinical outcomes and prognostic factors were further analyzed.

RESULTS

A total of 94.6% (106/112) of the haplo-cord patients achieved complete haploidentical chimerism, while 5.4% (6/112) of patients had mixed cord blood chimerism. No differences were observed in neutrophil and platelet recovery or the incidences of GVHD, CMV/EBV viremia, bloodstream infection or hemorrhagic cystitis between the haplo-cord HSCT and haplo-HSCT groups. Compared to haplo-HSCT group, the haplo-cord HSCT group had a higher absolute number of CD3⁺ cells (P=0.029) and a lower ratio of CD3⁺CD4⁺ /CD3⁺CD8⁺ cells (P=0.049) at 1 month after transplantation. Moreover, Haplo-cord HSCT patients showed lower minimal residual disease (MRD) levels at 1 month (P=0.020) and 100 days (P=0.038) after transplantation and better 3-year prognoses than the haplo-HSCT group (OS: P=0.016; DFS: P=0.041; cumulative incidence of relapse (CIR): P=0.016). The CIRs in patients with adverse genomic features (P=0.040) or flow cytometry-based minimal residual disease (FCM-MRD)≥1 × 10^-4 (P=0.033) were improved by haplo-cord HSCT. By multivariate analysis, we found that haplo-cord HSCT could independently improve the 3-year OS, DFS and CIR of B-ALL patients (OS: P=0.029; DFS: P=0.024; CIR: P=0.024). Additionally, allo-HSCT at CR1 was an independent parameter associated with 3-year OS for B-ALL patients (P=0.014). FCM-MRD≥1 × 10^-4 pre-HSCT could independently predict unfavorable 3-year DFS and CIR (DFS: P=0.020; CIR: P=0.036) in B-ALL patients.

CONCLUSION

Haplo-cord HSCT could independently improve survival in B-ALL patients.

Dissecting the mechanisms involved in anti-human T-lymphocyte immunoglobulin (ATG)-induced tolerance in the setting of allogeneic stem cell transplantation - potential implications for graft versus host disease

Polyclonal anti-human thymocyte globulins (ATG) have been recently shown to significantly reduce the incidence of graft versus host disease (GVHD) post allogeneic stem cell transplantation (HSCT) from both sibling and unrelated donors. Induction of regulatory T cells has been suggested as one of the possible mechanisms. The aim of current study was to further characterize the T cell populations induced by ATG treatment and to delineate the mechanisms involved in ATG-induced tolerance. Phenotypic characterization revealed a significant increase in the expression of FoxP3, GITR, CD95, PD-1 and ICOS as well as the complement inhibitory molecules CD55, CD58 and CD59 on CD4+CD25+ T cells upon ATG treatment. Addition of ATG-treated cells to autologous and allogeneic peripheral blood mononuclear cells (PBMCs) stimulated with anti-CD3/anti-CD28 antibodies resulted in significant inhibition of proliferation. Moreover, T-cell activation and IFNγ secretion were reduced in the presence of ATG-induced Treg cells. The CD4+CD25+CD127-low Treg fraction sorted from ATG-treated culture demonstrated greater suppressive potency than negative fraction. Conditioned medium produced by ATG-treated but not IgG-treated cells contained TGFβ and suppressed T cell proliferation and activation in a TGFβ receptor-dependent manner. TGFβ receptor kinase inhibitor SB431542 interfered with the suppressive activity of ATG-primed cells, enabling partial rescue of proliferation and IFNγ secretion. Moreover, SB431542 prevented Treg phenotype induction upon ATG treatment. Altogether, our data reveal the role of TGFβ signaling in ATG-mediated immunosuppression and further support the use of ATG, a potent inducer of regulatory T cells, for prevention of GVHD post HSCT and potentially other therapeutic applications.

NKT cells, Treg, and their interactions in bone marrow transplantation

Bone marrow transplantation (BMT) is a potentially curative treatment for patients with leukemia and lymphoma. Tumor eradication is promoted by the anti-tumor activity of donor T cells contained in the transplant; however, donor T cells also mediate the serious side effect of graft-versus-host disease (GVHD). Separation of GVHD from graft anti-tumor activity is an important goal of research in improving transplant outcome. One approach is to take advantage of the immunomodulatory activity of regulatory NKT cells and CD4(+)CD25(+) Treg of host and/or donor origin. Both host and donor NKT cells and donor Treg are able to prevent GVHD in murine models. In this review, we summarize the mechanisms of NKT cell- and Treg-mediated protection against GVHD in mice while maintaining graft anti-tumor activity. In addition, we also examine the interactions between NKT cells and Treg in the context of BMT, and integrate the data from murine experimental models with the observations made in humans.

Functional screening identifies CRLF2 in precursor B-cell acute lymphoblastic leukemia

The prognosis for adults with precursor B-cell acute lymphoblastic leukemia (B-ALL) remains poor, in part from a lack of therapeutic targets. We identified the type I cytokine receptor subunit CRLF2 in a functional screen for B-ALL-derived mRNA transcripts that can substitute for IL3 signaling. We demonstrate that CRLF2 is overexpressed in approximately 15% of adult and high-risk pediatric B-ALL that lack MLL, TCF3, TEL, and BCR/ABL rearrangements, but not in B-ALL with these rearrangements or other lymphoid malignancies. CRLF2 overexpression can result from translocation with the IGH locus or intrachromosomal deletion and is associated with poor outcome. CRLF2 overexpressing B-ALLs share a transcriptional signature that significantly overlaps with a BCR/ABL signature, and is enriched for genes involved in cytokine receptor and JAK-STAT signaling. In a subset of cases, CRLF2 harbors a Phe232Cys gain-of-function mutation that promotes constitutive dimerization and cytokine independent growth. A mutually exclusive subset harbors activating mutations in JAK2. In fact, all 22 B-ALLs with mutant JAK2 that we analyzed overexpress CRLF2, distinguishing CRLF2 as the key scaffold for mutant JAK2 signaling in B-ALL. Expression of WT CRLF2 with mutant JAK2 also promotes cytokine independent growth that, unlike CRLF2 Phe232Cys or ligand-induced signaling by WT CRLF2, is accompanied by JAK2 phosphorylation. Finally, cells dependent on CRLF2 signaling are sensitive to small molecule inhibitors of either JAKs or protein kinase C family kinases. Together, these findings implicate CRLF2 as an important factor in B-ALL with diagnostic, prognostic, and therapeutic implications.