Human Peripheral Blood Mononuclear Cells Exhibit Heterogeneous CD52 Expression Levels and Show Differential Sensitivity to Alemtuzumab Mediated Cytolysis

Abstract

Alemtuzumab is a monoclonal antibody that targets cell surface CD52 and is effective in depleting lymphocytes by cytolytic effects in vivo. Although the cytolytic effects of alemtuzumab are dependent on the density of CD52 antigen on cells, there is scant information regarding the expression levels of CD52 on different cell types. In this study, CD52 expression was assessed on phenotypically distinct subsets of lymphoid and myeloid cells in peripheral blood mononuclear cells (PBMCs) from normal donors. Results demonstrate that subsets of PBMCs express differing levels of CD52. Quantitative analysis showed that memory B cells and myeloid dendritic cells (mDCs) display the highest number while natural killer (NK) cells, plasmacytoid dendritic cells (pDCs) and basophils have the lowest number of CD52 molecules per cell amongst lymphoid and myeloid cell populations respectively. Results of complement dependent cytolysis (CDC) studies indicated that alemtuzumab mediated profound cytolytic effects on B and T cells with minimal effect on NK cells, basophils and pDCs, correlating with the density of CD52 on these cells. Interestingly, despite high CD52 levels, mDCs and monocytes were less susceptible to alemtuzumab-mediated CDC indicating that antigen density alone does not define susceptibility. Additional studies indicated that higher expression levels of complement inhibitory proteins (CIPs) on these cells partially contributes to their resistance to alemtuzumab mediated CDC. These results indicate that alemtuzumab is most effective in depleting cells of the adaptive immune system while leaving innate immune cells relatively intact.

Caspase-8 polymorphisms result in reduced Alemtuzumab-induced T-cell apoptosis and worse survival after transplantation

“…In one study, it was reported that the rate of apoptosis was reduced in an allele dose-dependent manner. 4 Although we did not find this to be the case with the donors in our study, there was some suggestion, from the functional studies, that an allele dose effect may be present in some cellular subsets (for example, NKT cells). Additionally, where both the patient and the donor had an 'apoptosis-resistant' genotype the OS was significantly worse, suggesting that assessment for the presence of multiple deletions may be relevant.…”

“…The development of GVHD, and a subsequently increased TRM rate remains a major impediment to transplant success. 1 The anti-CD52 monoclonal Ab Campath-1H (Alemtuzumab) effectively depletes T lymphocytes and Agpresenting cells [2][3][4] and reduces the risk of both acute (aGVHD) and chronic GVHD (cGVHD). 5,6 There are three main pathways that have been established in Alemtuzumab-mediated cell death: complement-dependent cytotoxicity, 7,8 Ab-dependent cell mediated cytotoxicity 9,10 and apoptosis (activation induced cell death, AICD).…”

Differential Reconstitution of T Cell Subsets following Immunodepleting Treatment with Alemtuzumab (Anti-CD52 Monoclonal Antibody) in Patients with Relapsing–Remitting Multiple Sclerosis

“…Anti-CD52 mAb treatment has been studied during the past years as one of the medications with the longest lasting effect against multiple sclerosis (MS) (7). It depletes T and B lymphocytes and, to a lesser extent, monocytes, macrophages, dendritic cells, and NK cells via Ab-dependent cellular cytotoxicity, complement-induced cell lysis (8)(9)(10)(11), and the induction of apoptosis (12). Although effectively depleting all CD52-bearing cells, this immunodepleting therapy does not affect hematopoietic stem cells (13), and thus the potential for an immune response reconstitution is preserved.…”

Treatment advances and prognosis for patients with adult T-cell leukemia-lymphoma

“…54 Since alemtuzumab may strongly deplete the number of T-cells, it has been used to reduce the risk of GVHD in patients undergoing allo-HSCT. In ATL cells, more than 90% of tumor cells strongly express CD52.…”