CD45 y leucemia linfoide aguda pediátrica / CD45 and childhood acute lymphoblastic leukemia

Introducción: El CD45 se expresa en las células hematopoyéticas, su determinación es indispensable para la clasificación inmunofenotípica de la leucemia linfoide aguda (LLA). Objetivo: Evaluar la expresión del antígeno CD45 en los blastos de pacientes pediátricos con LLA y su relación con las características biológicas, morfológicas y clínicas al inicio de la enfermedad, la respuesta al tratamiento y la supervivencia global (SG) de los enfermos. Métodos: Se estudiaron 160 pacientes con LLA entre diciembre del 2012 y diciembre del 2017, tratados con el protocolo ALL-IC BFM-SG 2009. El inmunofenotipaje celular de la médula ósea se realizó por citometría de flujo. Resultados: El fenotipo B CD45+ predominó en los menores de seis años de edad y en los mayores de diez, el fenotipo T CD45+. Se encontró diferencia significativa entre la ausencia de adenopatías mediastínicas, el fenotipo leucémico y la ausencia de CD45 (p=0.004); entre la respuesta a la prednisona en sangre periférica al día ocho, el fenotipo leucémico y la ausencia de CD45 (p=0.001). Se encontraron diferencias significativas entre la respuesta a la prednisona en sangre periférica el día ocho y la respuesta en médula ósea el día 33, según fenotipo leucémico (p=0.009) y la presencia en los blastos del antígeno CD45 (p=0.02). Se encontró diferencia significativa entre la SG de los enfermos, según fenotipo leucémico y la ausencia del antígeno CD45 (p=0.017). Conclusión: La expresión o ausencia del antígeno de CD45 en los blastos tiene relación con la respuesta al tratamiento y la SG de pacientes pediátricos con LLA(AU)

Introduction: CD45 is expressed in hematopoietic cells, its determination is essential for the immunophenotypic classification of acute lymphoid leukemia (ALL). Objective: To evaluate the expression of the CD45 antigen in the blasts of pediatric patients with ALL and its relationship with the biological, morphological and clinical characteristics at the onset of the disease, the response to treatment and the overall survival (OS) of the patients. Methods: 160 patients with ALL were studied between December 2012 and December 2017, treated with the ALL-IC BFM-SG 2009 protocol. Bone marrow cellular immunophenotyping was performed by flow cytometry. Results: Patients with the CD45 + B phenotype predominated in those under six years of age, while those with a CD45 + T phenotype in those older than ten. A significant difference was found between the absence of mediastinal lymph nodes, the leukemic phenotype and the absence of CD45 (p = 0.004). A significant difference was found between the response to prednisone in peripheral blood at day eight, the leukemic phenotype and the absence of CD45, p = 0.001. Significant differences were found between the response to prednisone in peripheral blood on day eight and the response in bone marrow on day 33, according to leukemic phenotype and the presence in blasts of the CD45 antigen (p = 0.009 and p = 0.02, respectively). A significant difference was found between the OS of patients, according to leukemic phenotype and the absence of the CD45 antigen, p = 0.017. Conclusion: The expression or absence of the CD45 antigen in blasts is related to the response to treatment and OS of pediatric patients with ALL(AU)

The biology of CD45 and its use as a therapeutic target.

All mature hemopoietic lineage cells, with exclusion of platelets and mature erythrocytes, share the surface expression of a transmembrane phosphatase, the CD45 molecule. It is also present on hemopoietic stem cells and most leukemic clones and therefore presents as an appropriate target for immunotherapy with anti-CD45 antibodies. This short review details the biology of CD45 and its recent targeting for both treatment of malignant disorders and tolerance induction. In particular, the question of potential stem cell depletion for induction of central tolerance or depletion of malignant hemopoietic cells is addressed. Mechanisms underlying the effects downstream of CD45 binding to the cell surface are discussed.

Antibody-targeted therapy for myeloid leukemia.

The availability of antibodies reactive with antigens expressed only by hematopoietic cells has provided clinical investigators with new tools for use in developing therapies for acute myeloid leukemia (AML). Studies performed to date have investigated the use of such antibodies in an unmodified state, combined with potent chemicals to form immunotoxins or combined with various radionuclides. Encouraging results have been obtained in all three settings. The CD33 antigen is expressed by most early myeloid cells and by more than 90% of cases of AML but is not present on the hematopoietic stem cell. Initial in vivo studies with an unmodified murine anti-CD33 antibody in patients with AML demonstrated that the antibody quickly bound to leukemia cells and that the antigen-antibody complex rapidly internalized following cell binding. However, when administered to patients with overt leukemia, unmodified antibody resulted in only brief decreases in peripheral blast counts, not in sustained response. A number of CD33-based immunotoxins have also been studied, including a calicheamicin conjugate, CMA-676. In a phase I dose-escalation study of patients with refractory AML, CMA-676 was well tolerated with the only consistent toxicities being the development of fevers and chills several hours after administration and the subsequent development of temporary pancytopenia. A phase III study has been performed involving patients with AML in first relapse. An interim analysis of the first 23 patients found that in 10, treatment with CMA-676 resulted in elimination of blasts from peripheral blood and marrow. This was achieved with far less toxicity than seen with standard chemotherapy. Radiolabeled antibodies have been explored as a stand-alone treatment or in the context of bone marrow transplantation. In an effort to avoid toxicities to normal stem cells residing alongside leukemic cells in the marrow, studies have been performed to explore the use of 231Bi conjugated to an anti-CD33 monoclonal antibody. The short path length of this alpha-emitter could theoretically allow killing of the targeted leukemic cell without damage to normal neighbors. Of 12 patients with recurrent AML who received this drug, eight had reductions in marrow and peripheral blast counts. Complete remissions (CRs) have not been observed to date. Another set of studies focused on the use of radiolabeled antibodies to deliver radiation specifically to sites of leukemia as part of a transplant preparative regimen. In a phase I clinical trial, 131I-labeled anti-CD45 antibody delivered at least threefold more radiotherapy to spleen and marrow than any other organ. In a phase II trial, among 25 AML patients in first remission, 22 are alive and in remission for periods up to 6 years.

Leucocyte depletion of neocyte-rich red blood cell concentrates by use of immunomagnetic beads.

In a series of pilot experiments we depleted neocyte-rich red blood cell concentrates of contaminating leucocytes by use of immunomagnetic beads. The beads were coated with monoclonal antibodies directed against the leucocyte common antigen CD 45. The number of cells isolated depended on the dose of beads which also corresponded to the decrease in leucocytes in the neocyte concentrates. The required ratio of beads to target cells was approximately 25:1, the depletion rate of leucocytes was about 96.0-99.8%.