Immunotoxins containing saporin linked to different CD2 monoclonal antibodies: in vitro evaluation

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Abstract
In this study we describe immunotoxins prepared with different CD2 monoclonal antibodies (mAbs) and a ribosome‐inactivating protein, saporin. The CD2 immunotoxins were tested on different models. Anti‐CD2–saporin conjugates inhibited protein synthesis by a neoplastic CD2+ cell line (SKW‐3) and by an interleukin 2 dependent polyclonal CD2+ lymphoid cell culture (T lymphoblasts), with IC50s ranging from 10‐13m to 10‐11m (as saporin). Similar results were obtained with proliferation inhibition tests (3H‐thymidine incorporation) on phytohaemagglutinin (PHA) driven lymphoid cultures and on mixed lymphocyte culture activated lymphocytes. Moreover a CD2–ricin A chain conjugate was less effective than an analogous immunotoxin containing the same CD2 mAb and saporin in inhibiting lymphocyte proliferation induced by PHA (IC50 approximately 10‐9m as ricin A chain versus 10‐12m as saporin). The conjugates were not toxic on bone marrow stem cells. These results suggest that CD2–saporin immunotoxins could represent an effective tool for CD2+ lymphomas or leukaemias, and for T‐dependent immune disorders, such as transplanted organ rejection and graft‐versus‐host disease.

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