Acute graft-versus-host disease (aGvHD) of the gastrointestinal tract remains a major complication after allogeneic stem cell transplantation. The outcome of patients who fail first-line therapy with steroids is poor (Martin et al, 1991). No standard therapy for steroid-refractory aGvHD has been established. A promising strategy is the use of pentostatin, an inhibitor of adenosine deaminase (Margolis & Vogelsang, 2000). The capacity of this purine analogue to inhibit proliferation and to induce apoptosis of T-cells in combination with its mild toxicity resulted in the approach to use pentostatin in steroid-refractory aGvHD. Since more than 10 years pentostatin has been used as first line salvage therapy in severe steroid-refractory intestinal aGvHD at Frankfurt University Hospital. Here we describe the results of a retrospective analysis of 23 consecutive patients transplanted between 1999 and 2006 (9 × females, 14 × males, median age 45, range: 25–61 years) with a follow up after pentostatin treatment of at least 3 years by 31 December 2009. Patient′s characteristics are shown in Table I. Patients received disease specific conditioning regimens and a cyclosporine based GvHD-prophylaxis (except one patient). The conditioning regimen was myeloablative in 14 patients and reduced intensity in nine patients. The underlying diseases were AML (n = 17), ALL (n = 3), CML (n = 1), Hodgkin′s disease (n = 1), and multiple myeloma (n = 1). Patients were transplanted with peripheral blood stem cells (except one bone marrow transplantation) from matched related (n = 13), matched unrelated (n = 9) or mismatched donors (n = 1). Patients suffered from histologically confirmed grade III (n = 15) or IV (n = 8) acute intestinal GvHD. GvHD was graded and staged according to the revised Glucksberg criteria (Przepiorka et al, 1995). Steroid-refractory aGvHD was defined as progression or no improvement of diarrhoea despite a treatment with prednisolone (≥ 2 mg/kg/d) or as early relapse under the same dose of steroids. Patients received pentostatin (1 mg/m2/d) intravenously for three consecutive days. Cyclosporine A and prednisolone were continued. After at least a PR was achieved prednisolone was tapered by 20% every 4 d. Criteria for PR or CR were applied as published by Bolanos-Meade et al (2005). Survival curves were prepared using the method of Kaplan and Meier and compared by Mantel-Cox test. Survival time was measured in days from the first dose of pentostatin. Statistical analysis was performed by GraphPad Prism software (release 5.03; GraphPad Prism software, San Diego, CA, USA). Nineteen patients (83%) responded to pentostatin. Sixteen patients (70%) achieved CR, three patients (13%) PR (Table I). Clinical improvement occurred within a median of 13 (range: 8–58) days (Fig 1A). Four patients died before a response to pentostatin occurred (1 × day 8, 1 × day 9, 2 × day 11). All patients with an at least 12 d survival responded. Eight patients reached a CR of aGvHD before day 21. These patients received only one cycle of pentostatin. In 10 patients PR was seen at day 21. Ten of these patients received further cycles of pentostatin every 3 weeks (5 × 2 cycles, 4 × 3 cycles and 1 × 4 cycles). Eight of these patients reached a CR subsequently. Nine patients are still alive (median follow up: 2476, range: 1318–3414 d). Patient No. 709 died 4 years after salvage therapy with pentostatin due to relapse of Hodgkin′s disease. All other 1-year survivors stayed alive. Fourteen patients (61%) died (4 × relapse of malignant disease, 10 × therapy related). Median survival after pentostatin therapy was 85 d. The 2 year survival rate was 43% (10/23), the overall survival at 31 December 2009 was 39% (9/23; Fig 1B). The long term survival rate of patients who reached a CR of aGvHD is 56% (9/16; Fig 1C). The probability of long term survival was significantly higher for patients who achieved CR after one cycle of pentostatin in comparison with PR patients at day 21 (88% vs. 20%, P = 0·013, Fig 1D). Thus, further therapy beyond one cycle of pentostatin has only limited positive impact on survival. Out of the nine living patients three experienced no episode of chronic GvHD (cGvHD). Six patients developed cGvHD (3 × limited, 3 × extensive). Toxicity of pentostatin salvage therapy was moderate. No clinically significant myelosuppression was observed. Four patients experienced a rapid clinical deterioration within 2 weeks after pentostatin due to sepsis. These early deaths are more likely attributable to the progression of aGvHD rather than to toxicity of pentostatin. One patient died due to hemolytic uremic syndrome (HUS). (A) Kaplan–Meier plot for time to response after treatment with pentostatin; (B–D) Kaplan–Meier plots for overall survival (B), survival of patients achieving complete response of acute GvHD (C) and survival of patients with complete versus partial response of aGvHD 21 d after treatment with pentostatin (D). In the critical clinical situation of severe steroid-refractory intestinal aGvHD pentostatin demonstrated high rates of response and overall survival at our institution. The response rates are in line with those of a prospective phase I dose escalation study on pentostatin (64% CR, 26% overall survival) (Bolanos-Meade et al, 2005). In comparison with the existing literature on treatment of steroid-refractory aGvHD the results after pentostatin in terms of complete response and long term survival are encouraging: Several immunosuppressive approaches for steroid-refractory aGvHD such as anti-thymocyte-globulin, OKT3, antagonists of pro-inflammatory cytokines (e.g. daclizumab or etanercept), extracorporeal photopheresis or mesenchymal stem cells have been investigated in clinical trials (Willenbacher et al, 2001; Greinix et al, 2006; Van Lint et al, 2006; Knop et al, 2007; Le Blanc et al, 2008; Levine et al, 2008). These therapies reached response rates of 40–70%. However, in most of these trials either not only patients with grade III/IV aGvHD or patients without GI-tract involvement were included. Despite the high percentage of low grade aGvHD the 2-year or long term overall survival rates after these salvage regimens did hardly exceed 10%. In comparison with other treatment options pentostatin has some favourable characteristics. Its effect is sustainable and the majority of responding patients survived. Costs for pentostatin are relatively low and toxicity is moderate. However, despite salvage therapy with pentostatin mortality in steroid-refractory aGvHD is still high. Since response rate and long term survival with other salvage therapies are even less convincing we suggest the use of pentostatin as salvage therapy in severe steroid-refractory intestinal aGvHD. This work was supported by the Alfred und Angelika Gutermuth-Stiftung.