Short-term combination therapy with an anti-TcR alpha/beta monoclonal antibody (clone R73) and 15-deoxyspergualine (DOS) was tested in inducing long-term survival of composite tissue allografts. Materials and Methods: Hindlimbs were transplanted from Brown Norway to Lewis rats. Six groups were entered (5 rats each): Group A was a no-treatment control group. Group B received R73 at 500 mcg/Kg i.p on the day of surgery. Group C received R73 (250 mcg/Kg i.p.) on the day of surgery and DOS (2.0 mg/Kg i.p.) for 15 days starting on the day of surgery. Group D received R73 (500 mcg, day of surgery) and DOS (4.0 mg/Kg i.p) for 20 days. Group E and F received a sham operation (limb amputation and replant) respectively with or without a 15-day treatment with DOS, to record weight loss, drug-related toxicity and nerve regeneration. Onset of rejection was assessed clinically. Tissues were harvested for examination and blood for assessment of chimerism with flow citometry after labelling with appropriate monoclonal antibodies. Main results: Rejection became evident for groups A-C as follows: Group A=6-8 days, Group B=12-13 days, Group C=22-25 days, while all the limbs in Group D survived over 50 days. Weigh loss during the treatment period peeked over 20% of preoperative weight, without histological signs of Graft versus Host Disease. The level of chimerism varied throughout the duration of the study and between the groups. Conclusions: Combined therapy with R73/DOS showed to reliably prevent rejection in all the animals during the treatment period. Only treatment extended to 20 days was able to reliably prolong survival well beyond withdrawal, probably because DOS needs to be administered long enough to prevent antigen presentation to the T-cell population while it recovers after the T-cell inhibitory effect of R73, lasting up to 16 days, has subsided.
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