High-Dose Sirolimus and Immune-Selective Pentostatin plus Cyclophosphamide Conditioning Yields Stable Mixed Chimerism and Insufficient Graft-versus-Tumor Responses.

Clinical Cancer Research

PubMedID: 26071480

Fowler DH, Mossoba ME, Halverson DC, Kurlander R, Blacklock Schuver B, Carpenter AE, Hansen B, Steinberg SM, Ali SA, Tageja N, Hakim FT, Gea-Banacloche JC, Sportes C, Hardy NM, Hickstein DD, Pavletic S, Khuu H, Sabatini M, Stroncek DF, Levine B, June CH, Mariotti J, Rixe O, Fojo AT, Bishop MR, Gress RE. High-Dose Sirolimus and Immune-Selective Pentostatin plus Cyclophosphamide Conditioning Yields Stable Mixed Chimerism and Insufficient Graft-versus-Tumor Responses. Clin Cancer Res. 2015;21(19):4312-20.
PURPOSE
We hypothesized that lymphoid-selective host conditioning and subsequent adoptive transfer of sirolimus-resistant allogeneic T cells (T-Rapa), when combined with high-dose sirolimus drug therapy in vivo, would safely achieve antitumor effects while avoiding GVHD.

EXPERIMENTAL DESIGN
Patients (n = 10) with metastatic renal cell carcinoma (RCC) were accrued because this disease is relatively refractory to high-dose conditioning yet may respond to high-dose sirolimus. A 21-day outpatient regimen of weekly pentostatin (P; 4 mg/m(2)/dose) combined with daily, dose-adjusted cyclophosphamide (C; =200 mg/d) was designed to deplete and suppress host T cells. After PC conditioning, patients received matched sibling, T-cell-replete peripheral blood stem cell allografts, and high-dose sirolimus (serum trough target, 20-30 ng/mL). To augment graft-versus-tumor (GVT) effects, multiple T-Rapa donor lymphocyte infusions (DLI) were administered (days 0, 14, and 45 posttransplant), and sirolimus was discontinued early (day 60 posttransplant).

RESULTS
PC conditioning depleted host T cells without neutropenia or infection and facilitated donor engraftment (10 of 10 cases). High-dose sirolimus therapy inhibited multiple T-Rapa DLI, as evidenced by stable mixed donor/host chimerism. No antitumor responses were detected by RECIST criteria and no significant classical acute GVHD was observed.

CONCLUSIONS
Immune-selective PC conditioning represents a new approach to safely achieve alloengraftment without neutropenia. However, allogeneic T cells generated ex vivo in sirolimus are not resistant to the tolerance-inducing effects of in vivo sirolimus drug therapy, thereby cautioning against use of this intervention in patients with refractory cancer. Clin Cancer Res; 21(19); 4312-20. ©2015 AACR.