Investigation of the mechanism of action of alemtuzumab in a human CD52 transgenic mouse model

Abstract

Summary Alemtuzumab is a humanized monoclonal antibody against CD52, an antigen found on the surface of normal and malignant lymphocytes. It is approved for the treatment of B‐cell chronic lymphocytic leukaemia and is undergoing Phase III clinical trials for the treatment of multiple sclerosis. The exact mechanism by which alemtuzumab mediates its biological effects in vivo is not clearly defined and mechanism of action studies have been hampered by the lack of cross‐reactivity between human and mouse CD52. To address this issue, a transgenic mouse expressing human CD52 (hCD52) was created. Transgenic mice did not display any phenotypic abnormalities and were able to mount normal immune responses. The tissue distribution of hCD52 and the level of expression by various immune cell populations were comparable to those seen in humans. Treatment with alemtuzumab replicated the transient increase in serum cytokines and depletion of peripheral blood lymphocytes observed in humans. Lymphocyte depletion was not as profound in lymphoid organs, providing a possible explanation for the relatively low incidence of infection in alemtuzumab‐treated patients. Interestingly, both lymphocyte depletion and cytokine induction by alemtuzumab were largely independent of complement and appeared to be mediated by neutrophils and natural killer cells because removal of these populations with antibodies to Gr‐1 or asialo‐GM‐1, respectively, strongly inhibited the activity of alemtuzumab whereas removal of complement by treatment with cobra venom factor had no impact. The hCD52 transgenic mouse appears to be a useful model and has provided evidence for the previously uncharacterized involvement of neutrophils in the activity of alemtuzumab.

Regulation of complement and modulation of its activity in monoclonal antibody therapy of cancer

“…60,61 Similarly, no role was found for complement in alemtuzumab treatment in a CD52 transgenic mouse model. 62 Treatment of liver metastasis in a metastatic melanoma model by the anti-gp75 mAb TA99 was not impaired in neither C1q nor CR3-deficient mice. 63 Evidence for a beneficial role of complement was obtained in several independent animal models.…”

Alemtuzumab Therapy for Multiple Sclerosis

“…Although monocytes carry the CD52 antigen, they are depleted for only a few days. Within minutes of infusing a single dose of alemtuzumab in humans, peripheral lymphocytes are depleted, probably by antibody-dependent, cell-mediated cytotoxicity [13]. Crosslinking of Natural Killer cells causes a rise in serum cytokines, including tumor necrosis factor-α, interleukin-6, and interferon-γ [14], which results in infusion-associated symptoms that are successfully reduced or prevented by pretreatment with corticosteroids and an antihistamine [15].…”

Immunomonitoring Lymphocyte Subpopulations in Multiple Sclerosis Patients

“…As CD52 is a panleucocitary molecule, it promotes a rapid, marked, and sustained depletion of T-lymphocytes and B-lymphocytes, NK cells, monocytes, and some granulocytes. Studies performed in a transgenic mouse model postulated that the mechanism of lymphocyte depletion is predominantly antibody-dependent cytolysis (81). A decrease in the percentage of T-cell subpopulations at day 7 posttreatment with the onset of reconstitution 1 month after treatment has been described (82).…”