Post-transplantation malignancy: a cell autonomous mechanism with implications for therapy.

Malignancy is a dreaded complication following organ transplantation. Immunosuppressive therapy-induced impairment of the host immune system is the prevailing hypothesis for the high incidence and aggressive progression of post-transplant neoplasm. We summarize our observations supporting an autonomous cellular mechanism for cyclosporine and tacrolimus associated metastases. Cyclosporine conferred tumor invasiveness by a direct effect on the tumor cells and promoted metastases in T-, B-, and NK cell deficient SCID- beige mice, and anti-TGF-beta antibodies reduced metastases. Tacrolimus, another calcineurin inhibitor widely used in transplantation, induced TGF-beta secretion by tumor cells and promoted metastases in the SCID- beige mice. The immunosuppressive macrolide rapamycin reversed an invasive phenotype to a non-invasive one, reduced circulating levels of TGF-beta1 and prevented tumor growth and metastases in the immocompetant BALB/c mice and in the SCID-beige mice. Our studies, in addition to demonstrating a cell autonomous mechanism for tumor progression, advance TGF-beta blockade as an anti-tumor strategy.