Targeting Tools: Anti-Tac and Anti-Tac-SAP

Advanced Targeting Systems announces the release of two reagents for immunological studies:

• Anti-Tac (Cat. # AB-18) – a monoclonal antibody to human CD25, the interleukin-2 receptor, and
• Anti-Tac-SAP (Cat. # IT-24) – the immunotoxin made by conjugation of anti-Tac to saporin.

These reagents add to the growing list of ATS products for use in studies of the hematopoietic systems. Other products include the anti-human and mouse macrophage immunotoxin (Mac-1-SAP, Cat. # IT-06) and the anti-rat and mouse T lymphocyte immunotoxin OX7- SAP (Cat. # IT-02).

The interleukin 2 receptor (IL-2r) is expressed on activated T lymphocytes and is important for the proliferation of T lymphocytes in response to antigen. The IL-2r is not detected on resting cells.1 Anti-Tac is able to prevent activation of T lymphocytes by antigen; apparently by binding to a newly available receptor and blocking IL-2 binding.2 It is reactive with activated and functionally mature human T cells.3 Figure 1 shows FACS analysis of the antibody bound to SR cells. This cell line is derived from the peripheral blood of a patient with mycosis fungoides. The cells express CD25 and respond to IL-2.

Immunotoxins made with an antibody to the IL-2r have been suggested for clinical use in the treatment of T cell leukemias and lymphomas.4 We at ATS believe that, as a research tool, this reagent is an important part of the toolbox. Anti-Tac immunotoxins have been shown to remove activated T lymphocytes in culture,5 and can be used to understand the role of this population in its various processes in the immune system. Figure 2 shows this immunotoxin against SR cells that express CD25. The immunotoxin is more than 100-fold more effective than saporin alone. Later this year we will introduce an anti-rat CD25 immunotoxin that will be useful for in vivo studies in animal models.