Biological and molecular characterization of PNH-like lymphocytes emerging after Campath-1H therapy

Mutations in PIGA cause a CD52-/GPI-anchor-deficient phenotype complicating alemtuzumab treatment in T-cell prolymphocytic leukemia

OBJECTIVE

Infusional alemtuzumab followed by consolidating allogeneic hematopoietic stem cell transplantation in eligible patients is considered a standard of care in T-cell prolymphocytic leukemia (T-PLL). Antibody selection against CD52 has been associated with the development of CD52-negative leukemic T cells at time of relapse. Clinical implications and molecular mechanisms underlying this phenotypic switch are unknown.

METHODS

We performed flow cytometry and real-time-PCR for CD52-expression and next generation sequencing for PIGA mutational analyses.

RESULTS

We identified loss of CD52 expression after alemtuzumab treatment in two of 21 T-PLL patients resulting from loss of GPI-anchor expression caused by inactivating mutations of the PIGA gene. One patient with relapsed T-PLL exhibited a single PIGA mutation, causing a CD52-negative escape variant of the initial leukemic cell clone, preventing alemtuzumab-retreatment. The second patient with continued complete remission after alemtuzumab treatment harbored three different PIGA mutations that affected either the non-neoplastic T cell or the mononuclear cell compartment and resulted in symptomatic paroxysmal nocturnal hemoglobinuria. Next generation sequencing of T-PLL cells collected before the initiation of treatment revealed PIGA wild-type sequence reads in all 16 patients with samples available for testing.

CONCLUSION

These data indicate that PIGA mutations were acquired during or after completion of alemtuzumab treatment.

Immunoregulatory cytokines gene polymorphisms in Egyptian patients affected with acquired aplastic anemia

The immune system is thought to play an important role in aplastic anemia (AA) in light of recent findings of hematologic reconstitution after immunosuppressive therapy. T cell activation, apoptosis, and the cytokines interferon- and TNF-α are suspected to play a role in the suppression of growth of progenitor cells and induced apoptosis in CD34 target cells, TGFβ is a multifunctional peptide, usually produced in latent form and requiring activation to produce a biological response. Also, TGF-β1 has been described as an important negative regulator of haemopoiesis. Over production of IL-6 is described in AA but is of unknown pathophysiological significance. To investigate the role of cytokine gene polymorphisms (IL-6/-174, TNF-α/-308, IFN-γ/+874, and TGFβ1/-509) in patients with acquired AA to assess if genotypes associated with higher or lower production were more prevalent than in established control population and to study the possible association of these genotypes with the disease severity. Fifty AA patients were included in this study. Polymerase chain reaction-amplification refractory mutation system (PCR-ARMS) technique was used to detect INF-γ single nucleotide polymorphism -874A/T, and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to assess IL-6-174 C/G, TNF-α-308G/A, and TGFb1-509C/T gene polymorphisms. Genotypes associated with high production of TNF-α, TGF-β and IFN-γ, and IL-6 were more frequent in patients than in control; no association was found between the presence of hypersecretory genotypes and the disease severity.

Therapeutic implications of variable expression of CD52 on clonal cytotoxic T cells in CD8+ large granular lymphocyte leukemia

BACKGROUND

T-cell large granular lymphocytic leukemia is a clonal proliferation of cytotoxic T-lymphocytes which often results in severe cytopenia. Current treatment options favor chronic immunosuppression. Alemtuzumab, a humanized monoclonal antibody against glycophosphatidylinositol-anchored CD52, is approved for patients refractory to therapy in other lymphoid malignancies.

DESIGN AND METHODS

We retrospectively examined treatment outcomes in 59 patients with CD8+ T-cell large granular lymphocytic leukemia, 41 of whom required therapy. Eight patients with severe refractory cytopenia despite multiple treatment regimens had been treated with subcutaneous alemtuzumab as salvage therapy. Flow cytometry was used to monitor expression of glycophosphatidylinositol-anchored CD52, CD55, and CD59 as well as to characterize T-cell clonal expansions by T-cell receptor variable beta-chain (Vbeta) repertoire.

RESULTS

Analysis of the effects of alemtuzumab revealed remissions with restoration of platelets in one of one patient, red blood cell transfusion independence in three of five patients and improvement of neutropenia in one of three, resulting in an overall response rate of 50% (4/8 patients). Clonal large granular lymphocytes exhibited decreased CD52 expression post-therapy in patients refractory to treatment. Samples of large granular lymphocytes collected prior to therapy also unexpectedly had a significant proportion of CD52-negative cells while a healthy control population had no such CD52 deficiency (p=0.026).

CONCLUSIONS

While alemtuzumab may be highly effective in large granular lymphocytic leukemia, prospective serial monitoring for the presence of CD52-deficient clonal cytotoxic T-lymphocytes should be a component of clinical trials investigating the efficacy of this drug. CD52 deficiency may explain lack of response to alemtuzumab, and such therapy may confer a survival advantage to glycophosphatidylinositol-negative clonal cytotoxic T-lymphocytes.

Recent developments in the understanding and management of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) has been recognised as a discrete disease entity since 1882. Approximately a half of patients will eventually die as a result of having PNH. Many of the symptoms of PNH, including recurrent abdominal pain, dysphagia, severe lethargy and erectile dysfunction, result from intravascular haemolysis with absorption of nitric oxide by free haemoglobin from the plasma. These symptoms, as well as the occurrence of thrombosis and aplasia, significantly affect patients' quality of life; thrombosis is the leading cause of premature mortality. The syndrome of haemolytic-anaemia-associated pulmonary hypertension has been further identified in PNH patients. There is currently an air of excitement surrounding therapies for PNH as recent therapeutic developments, particularly the use of the complement inhibitor eculizumab, promise to radically alter the symptomatology and natural history of haemolytic PNH.

CD55 and CD59 Deficiency in Transplant Patient Populations: Possible Association With Paroxysmal Nocturnal Hemoglobinuria–Like Symptoms in Campath-Treated Patients

Campath-1H therapy is directed to CD52, a small mw protein that has a glycosylphosphatidylinositol (GPI) anchor, which has a conventional structure similar to other GPI anchors such as CD55 and CD59. Paroxysmal nocturnal hemoglobinuria (PNH) results when cells have a somatic defect in the synthesis of GPI anchors and lack CD55 and CD59, as well as CD52. Several patients treated with Campath developed PNH-like symptoms with hemolysis and thrombosis. These patients were followed after therapy by measurement of peripheral CD55 and CD59 levels and showed an increased number of cells deficient in the expression of these molecules. Thereafter we instituted a screening program for the presence of CD55/59 levels in all pretransplant patients. Our results show that 17.3% of all pretransplant samples contained abnormal (9.7% of samples) or slightly abnormal (7.6% of samples) levels of granulocytes deficient in CD55 or CD59. This high prevalence of CD55/59 deficiency in Campath-treated patients with PNH-like symptoms suggests that a lack of these molecules (including CD52) could predispose to a complication of this immunosuppressive therapy.

Immunoregulatory cytokine polymorphisms in Italian patients affected by paroxysmal nocturnal haemoglobinuria and aplastic anaemia

We investigated regulatory variants of five cytokine genes [tumour necrosis factor (TNF)-alpha, interferon (IFN)-gamma, transforming growth factor (TGF)-beta, interleukin (IL)-6 and IL-10] in 40 Italian patients affected by paroxysmal nocturnal haemoglobinuria (PNH) and aplastic anaemia (AA). Genotypes associated with high production of TGF-beta and IFN-gamma were more frequent in patients than in controls. Genetic regulation of the immunological pathways involved in the pathogenesis of bone marrow failure is suggested.

Frequent HPRT mutations in paroxysmal nocturnal haemoglobinuria reflect T cell clonal expansion, not genomic instability

Paroxysmal nocturnal haemoglobinuria (PNH) results from acquired mutations in the PIG-A gene of an haematopoietic stem cell, leading to defective biosynthesis of glycosylphosphatidylinositol (GPI) anchors and deficient expression of GPI-anchored proteins on the surface of the cell's progeny. Some laboratory and clinical findings have suggested genomic instability to be intrinsic in PNH; this possibility has been supported by mutation analysis of hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene abnormalities. However, the HPRT assay examines lymphocytes in peripheral blood (PB), and T cells may be related to the pathophysiology of PNH. We analysed the molecular and functional features of HPRT mutants in PB mononuclear cells from eleven PNH patients. CD8 T cells predominated in these samples; approximately half of the CD8 cells lacked GPI-anchored protein expression, while only a small proportion of CD4 cells appeared to derive from the PNH clone. The HPRT mutant frequency (Mf) in T lymphocytes from PNH patients was significantly higher than in healthy controls. The majority of the mutant T lymphocyte clones were of CD4 phenotype, and they had phenotypically normal GPI-anchored protein expression. In PNH patients, the majority of HPRT mutant clones were contained within the Vbeta2 T cell receptor (TCR) subfamily, which was oligoclonal by complementarity-determining region three (CDR3) size analysis. Our results are more consistent with detection of uniform populations of expanded T cell clones, which presumably acquired HPRT mutations during antigen-driven cell proliferation, and not due to an increased Mf in PNH. HPRT mutant analysis does not support underlying genomic instability in PNH.

Mechanism of action and resistance to monoclonal antibody therapy

Monoclonal antibodies (MoAbs) are increasingly used in the treatment of patients with hematological malignancies and autoimmune diseases. The most commonly employed humanized and chimeric MoAbs are rituximab, alemtuzumab (Campath-1H, Ilex Pharmaceuticals, San Antonio, TX), and gemtuzumab-ozogamicin (Mylotarg, Wyeth-Ayerst Laboratories, St Davids, PA). The mechanism of action of these antibodies, and host and cellular factors influencing the response, are not completely known. Induction of apoptosis, antibody-dependent cell cytotoxicity (ADCC), and complement-mediated cell death (CDC) is the proposed mechanism of action of these antibodies. We review the current understanding of the mechanism of action of and resistance to these MoAbs.