HIGH-DOSE CALCINEURIN INHIBITOR BLOCKS THE GENERATION OF REGULATORY CELLS, WHEREAS LOW-DOSE PROMOTES THEIR DEVELOPMENT.

Abstract

O181* Aims: Regulatory cells (RC) are increasingly recognized as playing a major role in non-deletional forms of tolerance and seem to depend upon IL2-signaling. For safety reasons, clinical trials of tolerance induction (transfusion of donor-specific hematopoietic cells, stem cells etc.) include immunosuppressive (IS) drugs in the early postTx period. It is therefore essential that IS protocols do not block RC generation. The effects of calcineurin inhibitors (dose/timing) on RC generation is not elucidated yet. Methods: We developed a model of RC-based tolerance to cardiac allografts via preTx donor-specific blood transfusion (DSBT) in a fully mismatched RA-to-PVG rat combination. Results: Adoptive transfer from tolerant-to-naïve recipients demonstrated that donor-specific RC operate in this model. We then exposed DSBT-treated rats to high (50mg/kg) and low (10mg/kg) dose of Cyclosporine A (CsA) and we found that high-dose CsA given at the time of DSBT abrogated the development of RC and caused rejection. High-dose CsA at the time of Tx did reduce - but did not abrogate - the tolerogenic effect of DSBT. In stark contrast with high-dose, low-dose CsA did not affect DSBT-induced tolerance. On the contrary, low-dose CsA alone given postTx (day 0-11) in DSBT-untreated rats induced tolerance and allowed the development of RC that could adoptively transfer tolerance in second set naïve recipients. Finally, DSBT given the day of Tx did not promote tolerance in this model, unless recipients received a delayed and subtherapeutic course of low-dose CsA (day 5-9) (n=6 in each experiment, p<.01=significant). Conclusions: High-dose calcineurin inhibitor abrogates RC generation whereas low-dose (alone or in synergy with DSBT) promotes their development. These data have important implications with regard to a more judicious use of calcineurin inhibitors in the clinic, particularly when immunomodulatory strategies based upon RC generation are applied. Sustained and profound (but not delayed and mild) inhibition of IL2-signaling prevents RC generation.