Highlights
Third-line therapy for steroid- and ruxolitinib-refractory acute graft-versus-host disease with gastrointestinal involvement demonstrates limited effectiveness, with only 36% overall response rate at Day 28. More than half of responding patients lost their response within 90 days, highlighting significant durability concerns. The median overall survival was 86 days, though responders showed substantially better outcomes with median OS of 186 days compared to 45 days in non-responders. Infectious complications and aGvHD progression remained the leading causes of mortality, affecting over half of the patient population within three months.
Background
Acute graft-versus-host disease represents one of the most significant complications following allogeneic hematopoietic stem cell transplantation, affecting approximately 30-50% of recipients despite prophylactic immunosuppressive regimens. The gastrointestinal tract emerges as a particularly vulnerable target organ, with GI involvement accounting for substantial morbidity and mortality in this patient population. When aGvHD develops despite standard prophylaxis and initial therapy with corticosteroids, clinicians face a formidable therapeutic challenge that has driven intense research into salvage treatment strategies.
The introduction of ruxolitinib as a second-line agent following steroid failure marked a meaningful advancement in the management of steroid-refractory aGvHD, supported by data from the REACH2 trial. However, a substantial proportion of patients either fail to respond to ruxolitinib or experience disease progression after an initial response, creating an unmet medical need for effective third-line therapeutic options. The heterogeneity of salvage approaches, including extracorporeal photopheresis, mesenchymal stromal cells, anti-thymocyte globulin, and various investigational agents, underscores the lack of standardized management algorithms for this relapsed or refractory population.
The CHRONOS study was specifically designed to address this evidence gap by systematically evaluating clinical outcomes associated with third-line therapy initiation in this highly treatment-refractory patient subset with predominant gastrointestinal involvement.
Study Design
The CHRONOS investigation employed a multicenter, retrospective cohort study design across 16 participating sites throughout Europe. Adult patients diagnosed with acute graft-versus-host disease presenting with gastrointestinal symptoms who had failed both corticosteroid therapy and ruxolitinib treatment were eligible for inclusion. Patients were required to have initiated third-line therapeutic intervention between May 30, 2019, and September 30, 2024, allowing for a contemporary assessment of current treatment patterns and outcomes in this indication.
The primary efficacy endpoints focused on response assessment at approximately 28 days following third-line therapy initiation. These included the all-organ overall response rate, defined as the proportion of patients achieving complete or partial response across any organ involvement, and the gastrointestinal-specific overall response rate, which specifically evaluated response within the GI tract as the primary site of disease activity. Response assessments followed established international consensus criteria for aGvHD grading and response evaluation.
Secondary endpoints expanded the outcome characterization to include duration of response, measured as the time from initial response achievement to documented disease progression or loss of response. Real-world progression-free survival of the underlying malignancy and overall survival were captured as key long-term outcome measures. Safety evaluations included the incidence and severity of infectious complications and hematologic toxicities, with particular attention to Grade 2 or higher infectious events and Grade 3-4 thrombocytopenia and neutropenia occurring within the first three months of therapy.
Study Population
A total of 59 patients meeting all eligibility criteria were included in the final analysis, representing a relatively modest cohort that reflects the clinical challenge of treating this heavily pretreated population. The multicenter European design ensured broader generalizability across different transplant programs and national healthcare systems while acknowledging the inherent limitations of retrospective data collection in this rare treatment scenario.
Key Findings
The primary efficacy analysis revealed a 28-day overall response rate of 36% with a 95% confidence interval of 24-49%, indicating that approximately one in three patients achieved meaningful disease control with third-line therapy. The gastrointestinal-specific response rate paralleled this finding at 37% (95% CI: 25-51%), demonstrating that responses observed in the GI tract largely drove the all-organ response outcomes. These response rates underscore the modest but meaningful activity of available salvage therapies in this refractory population.
Response durability emerged as a critical concern throughout the study period. Among patients who achieved an initial response, 29% experienced loss of response within the first 30 days following treatment initiation, with this proportion increasing to 52% by Day 90. These findings highlight the substantial challenge of maintaining disease control in steroid- and ruxolitinib-refractory aGvHD, suggesting that even patients who achieve initial response face a high risk of subsequent disease progression.
Survival outcomes demonstrated the severe prognosis associated with failure of both first- and second-line therapy. The median real-world progression-free survival of the underlying malignancy and median overall survival both reached 86 days (95% CI: 54-128 days), indicating that most patients experienced either disease progression or death within approximately three months of third-line therapy initiation. However, substantial differentiation emerged when analyzing outcomes by response status: responders achieved a median overall survival of 186 days compared to only 45 days in non-responders, representing a clinically meaningful survival advantage of approximately four months.
Over the 12-month follow-up period, 41 of the 59 enrolled patients died, yielding a mortality rate approaching 70%. The leading cause of death was aGvHD progression, accounting for 25 deaths, followed by infectious complications, which contributed to 9 deaths. This mortality pattern emphasizes the dual challenge of controlling underlying immune-mediated tissue damage while managing the infectious complications arising from intensified immunosuppressive therapy.
Safety analyses revealed substantial treatment-related toxicity in this heavily pretreated population. Within the first three months of therapy initiation, Grade 2 or higher infectious events occurred in 51% of patients, reflecting the immunosuppressive burden of multiple lines of therapy and underlying transplant-related immune dysfunction. Hematologic toxicity was particularly pronounced, with Grade 3-4 thrombocytopenia developing in 64% of patients and Grade 3-4 neutropenia observed in 32% of the cohort.
Expert Commentary
The CHRONOS findings illuminate the critical unmet need in managing steroid- and ruxolitinib-refractory aGvHD, a population for whom evidence-based guidance remains extremely limited. The modest 36% response rate, combined with the concerning durability data showing that over half of responders lost their benefit within 90 days, underscores the urgency for novel therapeutic approaches in this indication. Current salvage options appear to provide temporary disease control for a subset of patients, but sustained remission remains an elusive goal for the majority.
The substantial survival differential between responders and non-responders, while not unexpected, carries important implications for clinical trial design and patient counseling. Achieving response to third-line therapy translated into approximately a four-month survival advantage, suggesting that early identification of effective salvage strategies could meaningfully impact patient outcomes. However, the inability to reliably predict which patients will respond to specific therapeutic agents remains a significant barrier to optimizing treatment selection.
The safety profile documented in this cohort demands careful consideration in clinical decision-making. The high incidence of infectious complications and hematologic toxicities suggests that the risk-benefit calculus for third-line intervention must be carefully evaluated, particularly in patients with poor performance status or significant comorbidities. The finding that infectious complications represented the second leading cause of death highlights the delicate balance between controlling GVHD activity and preserving immune function against opportunistic pathogens.
Several limitations merit acknowledgment in interpreting these findings. The retrospective design introduces potential selection biases and variability in response assessment across participating centers. The relatively small sample size of 59 patients limits statistical power for subgroup analyses and prevents robust identification of predictive factors for treatment response. The absence of standardized third-line treatment protocols across sites reflects the lack of consensus in this area but complicates interpretation of aggregate outcomes. Additionally, the study period spanning from 2019 to 2024 may have included variability in supportive care practices and evolving approaches to infectious prophylaxis.
The generalizability of these findings to non-European populations and to patients with predominantly non-GI aGvHD manifestations remains uncertain. Future prospective studies with standardized treatment protocols, centralized response adjudication, and longer follow-up durations will be essential for advancing evidence-based management in this challenging clinical scenario.
Conclusion
The CHRONOS study provides valuable real-world evidence regarding the outcomes of third-line therapy in steroid- and ruxolitinib-refractory aGvHD with gastrointestinal involvement. The modest response rates and limited response durability observed in this European cohort underscore the substantial therapeutic challenges in this population, while the marked survival advantage in responders validates the clinical importance of achieving disease control when possible. The substantial infectious and hematologic toxicity burden highlights the need for careful patient selection and vigilant supportive care in the third-line setting.
These findings reinforce the critical importance of developing novel therapeutic agents with improved efficacy and safety profiles for this unmet medical need. Ongoing clinical trials evaluating bispecific antibodies, cytokine-targeted therapies, and cellular therapeutics offer promising avenues for improving outcomes in steroid- and ruxolitinib-refractory aGvHD. Until more effective options become available, clinicians should engage in careful risk-benefit discussions with patients and families regarding the limited but potentially meaningful benefits of third-line intervention in this heavily pretreated population.
References
Clausen J, Pérez Simón JA, Carré M, Castilla-Llorente C, Michonneau D, Schauwvlieghe A, Asensi Cantó P, François S, Gabellier L, Corral LL, Benzaquén A, Labussière-Wallet H, Cornillon J, Devillier R, Huynh A, Turlure P, Bauhofer A, Jullien de Pommerol H, Bruelle M, Faghmous I, Masouleh BK, Plantamura E, Malard F, Mohty M. Clinical outcomes of third-line therapy for aGvHD with gastrointestinal involvement after steroids and ruxolitinib failure. Bone Marrow Transplantation. 2026 Mar 28. PMID: 41904242.