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

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 IC 50 s ranging from 10 ‐13 m to 10 ‐11 m (as saporin). Similar results were obtained with proliferation inhibition tests ( 3 H‐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 (IC 50 approximately 10 ‐9 m as ricin A chain versus 10 ‐12 m 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.