Murine and humanized constructs of monoclonal antibody m195 (anti-cd33) for the therapy of acute myelogenous leukemia

Abstract

Long‐term survival rates of patients with acute myelogenous leukemia treated with intensive chemotherapy are 15–20%, despite efforts to develop new treatment strategies. Murine M195 (131I‐M195), an anti‐CD33, immunoglobulin (Ig) G2a monoclonal antibody has reactivity restricted to early myeloid cells and myeloid leukemic blasts but not hematopoietic progenitors. Previous trials in patients with relapsed or refractory myeloid leukemia showed that 131I‐M195 rapidly targeted to the bone marrow and internalized into target cells. This article describes a therapeutic dose escalation study in which 24 patients received from 50 mCi/m2 to 210 mCi/m2 of 131I‐M195 in divided doses. Cytoreduction of peripheral cell counts and bone marrow blasts occurred without nonhematopoietic toxicity. Doses of 131I‐M195 greater than 135 mCi/m2 were associated with marrow cytoreduction sufficient to necessitate bone marrow transplant. However, 37% of the patients developed human anti‐mouse antibody, preventing retreatment. To decrease immunogenicity and improve effector function, chimeric IgG1 and IgG3, and complementarity‐determining region‐grafted, humanized IgG1 and IgG3 versions of mouse M195 were developed by genetic engineering techniques. The new versions maintained specificity and biologic function, and they were superior to the mouse M195 in their ability to perform antibody‐dependent cellular cytotoxicity against leukemia cells. Humanized M195, but not chimeric M195, showed a 4–8.6 times higher avidity than its mouse counterpart. Because effector function of IgG depends to a large extent on Fc clustering, a homodimeric HuG1 also was developed. Homodimeric HuG1 showed an ability to cause additional dramatic improvements in effector functions, as well as an ability to internalize and retain radioisotope in target leukemia cells. Monomeric and dimeric forms of humanized M195 may be advantageous in the therapy of acute myelogenous leukemia. Cancer 1994; 73:1049–56.

Gemtuzumab ozogamicin (Mylotarg) monotherapy for relapsed AML after hematopoietic stem cell transplant: efficacy and incidence of hepatic veno-occlusive disease

“…8,26 Neither VOD nor significant hepatotoxicity have been described with other anti-CD33 monoclonal antibodies, either unlabeled or radiolabeled, used in human studies. [27][28][29] It therefore seems unlikely that direct targeting of CD33 + cells is responsible for the hepatotoxic effect.…”

Engagement of p75/AIRM1 or CD33 inhibits the proliferation of normal or leukemic myeloid cells

“…For example, cells expressing CD34 include the pluripotent hemopoietic stem cells whereas CD33 is absent from these stem cells but appears on myelomonocytic precursors and continues to be expressed in both the myeloid and monocytic lineages while it is lost by mature granulocytes (3)(4)(5). Although CD33 represents a useful marker to distinguish myeloid from lymphoid leukemias, little is known of its function (6,7). Being a member of the sialoadhesin family, it has been proposed to mediate cell-to-cell adhesion but it is unclear whether it actually plays any role in the process of myeloid cell differentiation (6).…”

Allogeneic hematopoietic cell transplantation in patients with AML not achieving remission: potentially curative therapy

“…41 Investigators at the Memorial Sloan Kettering Cancer Center used a slightly different 131 I-labeled murine monoclonal antibody against CD33, designated as M195. 46,47 Early-phase trials testing a humanized version of this antibody in a 17 patient cohort comprised of patients with primary refractory disease or untreated or refractory relapse. Allogeneic HCT used grafts from HLAidentical or one antigen mismatched related donors.…”