Low immunosuppressive burden after HLA-matched related or unrelated BMT using posttransplantation cyclophosphamide

Standard graft-versus-host disease (GVHD) prophylaxis after allogeneic blood or marrow transplantation (alloBMT) consists of short-course methotrexate (MTX) followed by 3 to 6 months of a calcineurin inhibitor (CNI).¹  However, most patients require more intensive and prolonged immunosuppressive therapy to treat GVHD when it occurs. In 1 study, 89% of patients treated with CNI-based GVHD prophylaxis after myeloablative conditioning (MAC) for HLA-matched alloBMT required corticosteroids, with the majority continually requiring corticosteroids and at least 1 other immunosuppressive agent throughout the first posttransplant year.²  Few patients receiving MAC were able to discontinue immunosuppression within the first 20 months.²  The intensity and duration of this immunosuppression puts patients at substantial risk for potentially life-threatening infections,^3-5  can have significant end-organ toxicity, may increase the risk of relapse,⁶  and obstructs the implementation of emerging immunotherapeutic strategies to prevent or treat relapse. Thus, it has been proposed that the primary measure of success for GVHD prevention studies should be the need for systemic immunosuppression for GVHD treatment.⁷ 

Posttransplantation cyclophosphamide (PTCy) is a promising therapy for reducing GVHD incidence and immunosuppression use.⁸  When used after MAC and HLA-matched bone marrow allografting, PTCy is effective as single-agent GVHD prophylaxis^9-12 ; no immunosuppression is routinely administered after posttransplant day +4 in patients not experiencing GVHD. In this study, utilizing immunosuppression data from 339 patients treated with this transplantation platform, we tested the hypothesis that the global immunosuppressive burden experienced by PTCy-treated patients would compare favorably with published data using CNI-based GVHD prophylaxis.

All patients received PTCy as single-agent GVHD prophylaxis after MAC and HLA-matched related (MRD) or HLA-matched unrelated (MUD) donor T-cell–replete bone marrow transplantation. Details of the treatment regimens are included in the supplemental Methods (see supplemental Data, available on the Blood Web site). The first cohort included all 247 patients treated from 2004 to 2011 at Johns Hopkins Hospital with busulfan/cyclophosphamide (BuCy) MAC (supplemental Table 1)^9,10 ; data were collected retrospectively after institutional review board (IRB) approval. The second cohort included all 92 patients treated from 2009 to 2011 on an IRB-approved, multi-institutional study using busulfan/fludarabine (BuFlu) MAC (supplemental Table 1)¹¹ ; data were collected prospectively as immunosuppression use was a predefined secondary end point of the study. Median follow-up was 4.5 and 2.9 years, respectively, based on the reverse Kaplan-Meier method. Given higher GVHD incidences after MUD compared with MRD allografting for this transplantation platform,^10,11  immunosuppression use was stratified by donor type.

To assess the total immunosuppressive burden associated with this transplantation platform, included was any systemic pharmacologic or phototherapeutic agent given posttransplant for any reason other than corticosteroids at physiologic replacement dosing for documented adrenal insufficiency (supplemental Table 2). This assessment encompassed treatment of GVHD or engraftment syndrome, treatment of GVHD after donor lymphocyte infusion (DLI) or second alloBMT, or GVHD prophylaxis for second alloBMT (supplemental Table 3). Thus, the only competing risk for immunosuppression was death. The duration of each immunosuppressive agent was the entire length of time between the day of initiation and the last day received prior to permanent discontinuation. The only exception was for treatment gaps of >3 months in which case the durations of the discontinuous blocks were summed. Topical agents or budesonide were not included in these analyses. Acute and chronic GVHD were diagnosed and graded based on standard criteria.^13,14  Competing risks for GVHD were graft failure, relapse, DLI, and death.

Cumulative incidences were estimated using a competing-risk framework. Multistate models and the Aalen-Johansen estimator were used to estimate the probabilities of existing in 1 of 3 states at any given time: (1) alive, not on immunosuppression, (2) alive, on immunosuppression, or (3) death (absorbing state) (supplemental Figure 1).^15,16  All analyses were performed using R version 3.3.0.

Cumulative incidences are shown for acute and chronic GVHD (Table 1) and initiation of immunosuppression (Figure 1A; Table 1). Ten percent of corticosteroid initiation and 17% of nonsteroidal immunosuppression initiation occurred after DLI or second alloBMT (supplemental Table 3). Approximately 50% of MRD alloBMT patients and 30% of MUD alloBMT patients never required immunosuppression beyond PTCy on days +3 and +4 (Table 1). When immunosuppression was required, it was typically limited to 1 to 2 agents (Figure 1B). Importantly, the median durations of pharmacologic immunosuppression (4.5-5 months for all groups) (Table 1) were shorter than would typically be given prophylactically (6 months) for patients treated with CNI-based GVHD prophylaxis.

Multistate modeling was used to assess the longitudinal immunosuppressive burden. In all groups, >40% to 50% of patients were alive and off immunosuppression throughout follow-up. Not unexpectedly, the immunosuppressive burden was greatest within the first posttransplant year. After that point, few patients remained on immunosuppression (Figure 1C; Table 1).

Our study included 2 cohorts, including 1 in which data were collected prospectively. Despite differences in conditioning and timing of data collection, we observed very similar results across cohorts in the percentages of patients who never required additional immunosuppression and the patterns of immunosuppression use in those who did. The major difference was that the durations of steroids and phototherapeutic agents, but not nonsteroidal pharmacologic agents, were higher for BuFlu MUD compared with BuCy MUD patients. This higher immunosuppressive burden likely is due in part to slightly higher rates of grade III-IV acute GVHD and chronic GVHD in that group, which may in part be attributable to higher rates of female-into-male-donor allografting (23% vs 9%; supplemental Table 1).^17,18  These results also may have been skewed by the protracted use of extracorporeal photopheresis in a limited number of BuFlu patients.

Our results only apply to patients receiving bone marrow allografts. PTCy may be insufficient as single-agent GVHD prophylaxis for HLA-matched peripheral blood stem cell transplantation due to high rates of grade III-IV acute GVHD,^19,20  although adding a CNI or sirolimus to PTCy appears effective.^21,22 

Despite low incidence of chronic GVHD, relapse rates in our patients are acceptable (supplemental Figure 2). Indeed, they appear similar to relapse rates reported in other recent studies (supplemental Figure 2; Table 3 of Kanakry et al¹⁰ ).

The global immunosuppressive burden in our patients compares favorably with CNI-based GVHD prophylaxis with or without antithymocyte globulin (ATG). In a randomized phase 3 study of myeloablative MUD alloBMT using cyclosporine/MTX ± ATG-Fresenius,²³  the 3-year probabilities of being alive and immunosuppression-free were 53% for ATG-Fresenius–treated patients and 17% for patients not receiving ATG-Fresenius.²³  Our results are similar to the ATG-Fresenius–treated patients. Results for ATG were not as encouraging in a randomized phase 3 study using a different formulation (thymoglobulin).²⁴  Although the primary end point of freedom from immunosuppression at 1-year posttransplant statistically favored the thymoglobulin group (37% vs 16%), these absolute probabilities were markedly lower than the ATG-Fresenius–treated patients or our own patients. Additionally, the benefit of thymoglobulin was not seen in patients receiving bone marrow allografts.²⁴  In the randomized phase 3 study of MRD alloBMT using CNI-based GVHD prophylaxis ± ATG-Fresenius, rates of cyclosporine discontinuation by 1 year were 91% and 39%, respectively.²⁵  This result for the ATG-Fresenius group is very similar to our MRD patients. However, given that half of our MRD patients required no additional immunosuppression after day +4, the immunosuppressive burden during the first posttransplant year favors PTCy. Overall, these results provide sufficient clinical equipoise to support a study comparing PTCy vs ATG for minimizing GVHD and the posttransplant immunosuppressive burden after HLA-matched alloBMT. These data also furnish benchmarks against which to compare results from the ongoing BMT Clinical Trials Network 1301 study comparing PTCy vs ex vivo T-cell depletion for HLA-matched alloBMT.

This work was supported by a PO1 grant from the National Institutes of Health, National Cancer Institute (CA 015396).

Contribution: C.G.K. and L.L. designed the study; J.B.-M., Y.L.K., M. Mielcarek, K.R.C., R.F.A., E.J.F., P.V.O., and R.J.J. contributed to the study design; C.G.K., J.B.-M., N.D., T.F., and M. Medeot collected data; Y.L.K., I.G., B.D.S., and J.A.K. performed blinded assessments of the remission status of patients at transplant; C.G.K. assembled data; C.G.K., J.B.-M., Y.L.K., T.F., M. Mielcarek, I.G., B.D.S., J.A.K., I.M.B., R.A.B., D.E.G., C.A.H., W.H.M., L.J.S., R.F.A., E.J.F., M.J.d.L., B.S.A., P.V.O., R.J.J., and L.L. provided clinical care of patients; M.Z. and R.V. performed statistical analyses; C.G.K., M.Z., and R.V. prepared figures; C.G.K. and L.L. wrote the manuscript; and all authors edited the manuscript.

Conflict-of-interest disclosure: The authors declare no competing financial interests.

Correspondence: Leo Luznik, Johns Hopkins University School of Medicine, Cancer Research Building I, Room 2M88, 1650 Orleans St, Baltimore, MD 21287; e-mail: luznile@jhmi.edu.