Xenopax from a real-world and economic perspective: The future of second-line treatment and prophylaxis for SR-aGVHD

Abstract

Steroid-refractory acute graft-versus-host disease (SR-aGVHD) remains a major therapeutic challenge after allogeneic hematopoietic stem cell transplantation. Although ruxolitinib and basiliximab are widely used, their limitations highlight the need for safer, more effective, and scalable biologic strategies. Xenopax, a humanized anti-CD25 monoclonal antibody, has demonstrated encouraging results across real-world and clinical studies. The multicenter RELAX study reported a 28-day overall response rate of 64.5% and a 2-year overall survival of 68.0%, with reduced corticosteroid exposure and infection rates compared with historical basiliximab cohorts. Importantly, RELAX incorporated an economic assessment, showing a lower incremental cost per responder and reinforcing xenopax as a cost-efficient option for SR-aGVHD. Beyond salvage therapy, xenopax is gaining momentum in prophylactic settings, including as a potential replacement for methotrexate in haploidentical transplantation. Looking ahead, integration with autonomous decision-support systems—most notably daGOAT, the first AI platform validated to prescribe risk-adapted GVHD prophylaxis—may further strengthen CD25-targeted approaches. Together, these developments position xenopax as a versatile biologic with the potential to reshape both treatment and prevention paradigms in GVHD management.

The management of steroid-refractory acute graft-versus-host disease (SR-aGVHD) remains one of the most urgent challenges after allogeneic hematopoietic stem cell transplantation (allo-HSCT) ¹ . For decades, available second-line options have remained limited. Ruxolitinib, approved on the basis of the REACH2 trial, achieved a 28-day overall response rate (ORR) of 62.3% ² , but complete response rates remained below 35%, highlighting the unmet need for more effective therapies^2,3. Basiliximab, widely used in China, carries risks of infections and immunogenicity^4,5. More effective and safer alternatives are urgently needed.

Against this background, the multicenter real-world RELAX study provided timely and compelling evidence for xenopax, a humanized anti-CD25 monoclonal antibody ⁶ . The study included 172 patients across 17 centers and demonstrated a 28-day overall response rate of 64.5% and a two-year overall survival of 68.0%. Infections occurred in 37.8% of patients, lower than expected compared with historical basiliximab cohorts ⁴ , and no infusion-related reactions were observed. Importantly, more than half of patients achieved a 50% reduction in corticosteroid exposure within 28 days, underscoring xenopax’s capacity to serve as a steroid-sparing therapy.

Beyond efficacy and safety, RELAX uniquely incorporated a cost-effectiveness analysis, demonstrating a lower incremental cost per responder compared with basiliximab and favorable long-term utility projections ⁷ . Considering the substantial healthcare burden associated with SR-aGVHD—including prolonged hospitalization, infection management, and high-dose immunosuppression—these findings highlight xenopax’s potential to reduce not only clinical burden but also overall healthcare expenditure. This additional economic dimension aligns the study with the title of this commentary and supports xenopax’s value for future guideline and reimbursement decisions.

While RELAX has consolidated xenopax’s role in salvage therapy, emerging evidence highlights its potential to move earlier in the treatment paradigm. A pivotal study led by Xia and colleagues recently reported that xenopax could replace methotrexate as part of frontline prophylaxis in haploidentical HSCT ⁸ . This regimen not only reduced the incidence of severe (grade III–IV) aGVHD but also mitigated the rates of oral mucositis and infections, complications often associated with methotrexate ⁹ . These results suggest that xenopax has the capacity not only to improve GVHD prevention but also to reduce transplant-related morbidity, representing a major advance in frontline management. In addition, a prospective trial has been registered in China (NCT06473909) to evaluate the combination of xenopax and corticosteroids as first-line therapy for newly diagnosed aGVHD. This trial is designed to assess both efficacy and safety, marking an important step toward redefining the role of xenopax beyond salvage therapy and into the frontline treatment setting.

Prevention strategies for aGVHD are increasingly moving toward individualized, risk-adapted approaches. At the Chinese Academy of Medical Sciences and Peking Union Medical College, a clinical trial (NCT06880419) is integrating xenopax with an artificial intelligence–based platform, daGOAT, designed for dynamic risk stratification of GVHD. This platform enables early identification of high-risk patients and delivers tailored prophylactic interventions ¹⁰ . Notably, daGOAT has been prospectively validated as the first autonomous AI capable of prescribing medication in clinical practice ¹¹ . In this phase 2 trial involving 110 HLA-haploidentical transplant recipients, daGOAT automatically stratified patients between days +17 and +23 post-transplant and initiated risk-adapted ruxolitinib, achieving 98% compliance and reducing the incidence of severe (grade III–IV) aGVHD from 16% in matched controls to 5.5% in the AI-guided group, without excess toxicity. Building on this foundation, daGOAT is now being extended to guide intensified prophylaxis strategies that incorporate xenopax and other CD25-targeting approaches. The combination of a validated digital prescribing agent with a novel biologic thus represents a paradigm shift—offering precision, adaptability, and enhanced protection against severe GVHD.

Taken together, these developments suggest that xenopax is evolving from a second-line treatment option into a versatile agent that may reshape GVHD management across the full spectrum, extending from salvage therapy to frontline use and individualized prevention.