Expansion of donor-derived hematopoietic stem cells with PIGA mutation associated with late graft failure after allogeneic stem cell transplantation

Development of hemolytic paroxysmal nocturnal hemoglobinuria without graft loss following hematopoietic stem cell transplantation for acquired aplastic anemia

PNH is the most common clonal hematopoietic disorder arising in patients with aAA. PNH is caused by mutations in PIGA, a gene that encodes the catalytic subunit of an enzyme involved in the biosynthesis of GPI anchors, transmembrane glycolipids required for cell surface expression of many proteins. PNH clones likely arise as immune escape mechanisms in aAA by preventing CD1D-restricted T-cell recognition of GPI anchors and GPI-linked autoantigens. Though many patients with aAA treated with IST will develop subclinical PNH clones, only a subset will develop PNH disease, characterized by increased thrombosis, intravascular hemolysis, and potential for severe organ dysfunction. In contrast to IST, allogeneic HSCT for patients with aAA is thought to cure bone marrow aplasia and prevent hematopoietic clonal evolution to PNH. Herein, we present a phenomenon of host-derived PNH disease arising in a patient with aAA many years following MSD-BMT, highlighting the importance of monitoring for this clonal disease in aAA patients with stable mixed donor/recipient chimerism after HSCT. We also provide a literature review for similar occurrences of PNH arising after HSCT.

Paroxysmal Nocturnal Hemoglobinuria with a Distinct Molecular Signature Diagnosed Ten Years after Allogenic Bone Marrow Transplantation for Acute Myeloid Leukemia

Paroxysmal nocturnal hemoglobinurea (PNH) is a rare disorder of complement regulation due to somatic mutation of PIGA (phosphatidylinositol glycan anchor) gene. We herewith report a case who developed a symptomatic PNH long after an allogenic marrow transplant. Some reasonable arguments concerning the origin of PNH clone have been discussed. The molecular studies revealed presence of JAK2 and TET2 mutations without a BCOR mutation. The literature review has been performed to probe into the complex interplay of autoimmunity and clonal selection and expansion of PNH cells, which occurs early in hematopoietic differentiation. The consequent events such as hypoplastic and/or hemato-oncologic features could further be explained on the basis of next-generation sequencing (NGS) studies. Paroxysmal nocturnal hemoglobinuria (PNH) is a rare clonal disorder of hematopoietic stem cells, characterized by a somatic mutation of the phosphatidylinositol glycan-class A (PIGA). The PIGA gene products are crucial for biosynthesis of glycosylphosphatidylinositol (GPI) anchors, which attaches a number of proteins to the plasma membrane of the cell. Amongst these proteins, the CD55 and CD59 are complement regulatory proteins. The CD55 inhibits C3 convertase whereas the CD59 blocks the membrane attack complex (MAC) by inhibiting the incorporation of C9 to MAC. The loss of complement regulatory protein renders the red cell susceptible to complement-mediated lysis leading to intravascular and extravascular hemolysis. The intravascular hemolysis explains most of the morbid clinical manifestations of the disease. The clinical features of syndrome of PNH are recurrent hemolytic episodes, thrombosis, smooth muscle dystonia, and bone marrow failure; other important complications include renal failure, myelodysplastic syndrome (MDS), and acute myeloid leukemia (AML). The most used therapies were blood transfusions, immunosuppressive, and steroid. Allogeneic stem cell transplantation was also practiced. At present, the therapy of choice is eculizumab (Soliris, Alexion Pharmaceuticals), a humanized monoclonal antibody that blocks activation of the terminal complement at C5. The limiting factor for this therapy is breakthrough hemolysis and the frequent dosing schedule. Ravulizumab (ALXN1210) is the second generation terminal compliment inhibitor which seems to provide a sustained control of hemolysis without breakthrough hemolysis and with a longer dosing interval.

Immune-Mediated Hematopoietic Failure after Allogeneic Hematopoietic Stem Cell Transplantation: A Common Cause of Late Graft Failure in Patients with Complete Donor Chimerism

Late graft failure (LGF) without evidence of residual recipient cells is a serious complication after allogeneic hematopoietic stem cell transplantation (allo-SCT) and often requires stem cell infusion from the same donor when the patient fails to respond to conventional therapies. We screened the peripheral blood (PB) of 14 patients who developed donor-type LGF at 2 to 132 months after allo-SCT for the presence of the markers for immune-mediated bone marrow (BM) failure. Increased glycosylphosphatidyl inositol-anchored protein-deficient (GPI-AP^-) leukocytes, which accounted for .009% to 0.147% of the total granulocytes, were detected in 5 patients (severe aplastic anemia, n = 2; follicular lymphoma, n = 1; acute lymphoblastic leukemia, n = 1; myelodysplastic syndromes; n = 1) and 4.7% to 81.2% HLA-allele-lacking leukocytes (HLA-LLs) were detected in 2 patients (acute myelogenous leukemia, n = 1; and myelodysplastic syndromes, n = 1). Three of the 5 patients with increased GPI-AP^- leukocytes were treated with antithymocyte globulin (ATG), and 2 patients achieved transfusion independence. These results suggest that immune mechanisms that are similar to acquired aplastic anemia underlie condition of approximately one-half of the patients with donor-type LGF, and that in patients with increased GPI-AP^- cells, donor-derived hematopoiesis may be restored by ATG therapy alone without donor stem cell infusion.

GPI-anchored protein-deficient T cells in patients with aplastic anemia and low-risk myelodysplastic syndrome: implications for the immunopathophysiology of bone marrow failure

Glycosylphosphatidylinositol-anchored protein-deficient (GPI-AP(-) ) T cells can be detected in some patients with bone marrow failure (BMF), but the link between these cells and BMF pathophysiology remains to be elucidated. To clarify the significance of GPI-AP(-) T cells in BMF, peripheral blood from 562 patients was examined for the presence of CD48(-) CD59(-) CD3(+) cells using high-resolution flow cytometry (FCM), and the GPI-AP(-) T cells were characterized with regard to their phenotype and sensitivity to inhibitory molecules, including herpesvirus entry mediator (HVEM) and a myelosuppressive cytokine, TGF-β. A multi-lineage FCM analysis detected CD48(-) CD59(-) CD3(+) T cells in 72 (12.8%) of the patients, together with GPI-AP(-) myeloid cells. Unexpectedly, 12 patients (10 with aplastic anemia and 2 with myelodysplastic syndrome-refractory anemia, 2.1%), who showed clinical features similar to those of other BMF patients with GPI-AP(-) myeloid cells, such as a good response to immunosuppressive therapy, displayed 0.01-0.3% GPI-AP(-) cells exclusively in T cells. The CD48(-) CD59(-) T cells consisted of predominantly effector memory (EM) and terminal effector cells, while CD48(-) CD59(-) T cells from non-BMF patients who had received anti-CD52 antibody only showed EM and central memory phenotypes. TGF-β and HVEM capable of inhibiting T-cell proliferation via its GPI-AP CD160 ligation suppressed the in vitro proliferation of GPI-AP(+) T cells more potently than that of GPI-AP(-) T cells from the same patients. The presence of GPI-AP(-) T cells, as well as GPI-AP(-) myeloid cells, may therefore reflect the immunopathophysiology of BMF in which cytokine-mediated suppression of hematopoietic stem cells via GPI-AP-type receptors takes place.

Ex vivo expansion and long-term hematopoietic reconstitution ability of sorted CD34+CD59+ cells from patients with paroxysmal nocturnal hemoglobinuria

Autologous bone marrow transplantation (ABMT) for paroxysmal nocturnal hemoglobinuria (PNH) remains difficult so far. To expand residual normal CD34(+)CD59(+) cells isolated from patients with PNH and observe the long-term hematopoietic reconstruction ability of the expanded cells both ex vivo and in vivo, CD34(+)CD59(+) cells from 13 PNH patients and CD34(+) cells from 11 normal controls were separated from bone marrow mononuclear cells first by immunomagnetic microbeads and then by flow cytometry autoclone sorting. The cells were then cultivated under different conditions. The long-term hematopoietic supporting ability of expanded CD34(+)CD59(+) cells was evaluated by long-term culture in semi-solid medium in vitro and long-term engraftment in irradiated severe combined immunodeficiency (SCID) mice in vivo. The best combination of hematopoietic growth factors for ex vivo expansion was SCF + IL-3 + IL-6 + FL + Tpo + Epo. The most suitable time for harvest was on day 7. CD34(+)CD59(+) PNH cells retained strong colony-forming capacity even after expansion. The survival rate, complete blood cell count recovery on day 90, and human CD45 expression in different organs were similar between the irradiated SCID mice transplanted with expanded CD34(+)CD59(+) PNH cells and those with normal CD34(+) cells (P > 0.05) both in primary and secondary transplantation. These data provided a new potential way of managing PNH with ABMT.