Highlights
- The incidence of tuberculosis (TB) in Allo-HSCT recipients in a low-incidence country (France) is approximately 60 per 100,000 patient-years, significantly higher than the general population.
- The most potent independent risk factor is being born in a high-TB-incidence country (OR = 19.4), emphasizing the role of reactivation of latent TB infection (LTBI).
- Extrapulmonary TB is the dominant presentation (82% of cases), often complicating diagnosis and requiring prolonged multi-drug therapy.
- Management is hindered by severe adverse drug reactions (25%) and TB-attributable mortality (9%), necessitating rigorous pre-transplant screening protocols.
Background
Allogeneic hematopoietic stem cell transplantation (Allo-HSCT) is a curative modality for various hematologic malignancies and bone marrow failure syndromes. However, the procedure involves profound and prolonged immunosuppression, primarily affecting T-cell mediated immunity, which is essential for the containment of *Mycobacterium tuberculosis*. While the risk of TB post-transplant is well-documented in endemic regions, data from low-incidence countries remains scarce. In these settings, TB is often an overlooked complication, leading to diagnostic delays and significant morbidity. This review synthesizes recent nationwide data to clarify the epidemiology and clinical impact of TB in the modern era of Allo-HSCT.
Key Content
Epidemiology and Incidence in Low-Incidence Countries
Recent data from the Société Francophone de Greffe de Moelle et de Thérapie Cellulaire (SFGM-TC) database, spanning a decade (2012–2023), provides a comprehensive look at TB in the French Allo-HSCT population. The study identified an incidence rate of 60 per 100,000 patient-years. While this confirms that TB remains a rare event in absolute terms within low-incidence countries, it represents a substantial increase relative to the general population (where incidence is typically <10 per 100,000). This elevated risk highlights the extreme vulnerability of the transplant recipient's immune system, regardless of the surrounding environment's disease burden.
Risk Factor Analysis: The Burden of Origin
In a multivariate case-control analysis, the single most significant predictor for developing TB post-Allo-HSCT was being born in a high-incidence country (OR = 19.4, p < 0.001). This finding strongly suggests that post-transplant TB in low-incidence settings is primarily a result of the reactivation of latent TB infection (LTBI) rather than recent transmission. Other factors often associated with opportunistic infections, such as the type of conditioning regimen or the presence of Graft-versus-Host Disease (GVHD), did not emerge as independent risk factors in this specific cohort, although they likely contribute to the overall state of immunosuppression that allows reactivation to occur.
Clinical Presentation and Diagnostic Timelines
One of the most striking features of TB in this population is the timing and nature of its manifestation. The median time from Allo-HSCT to TB diagnosis is approximately 147 days (range 30–7244 days). This early onset—often within the first six months—corresponds to the period of maximal immunosuppression and T-cell reconstitution lag.
Clinically, 82% of patients presented with extrapulmonary involvement. This high rate of disseminated or non-pulmonary disease is characteristic of patients with profound T-cell deficiencies, where the body fails to form organized granulomas to sequester the bacilli. Presentation may be protean, involving the central nervous system, lymph nodes, or bone, which often mimics other transplant complications or malignancies, thereby complicating the clinical pathway.
Therapeutic Challenges and Outcomes
Treatment of TB in Allo-HSCT recipients is fraught with pharmacological complexities. The median duration of anti-tuberculous therapy is approximately 273 days. The study noted that 25% of patients experienced severe adverse reactions to anti-TB drugs, particularly hepatotoxicity.
Furthermore, the use of rifamycins presents a major hurdle due to their role as potent inducers of the cytochrome P450 system. This leads to significant drug-drug interactions with essential post-transplant medications, including calcineurin inhibitors (cyclosporine, tacrolimus) and certain antifungal agents (voriconazole, posaconazole). Inadequate management of these interactions can result in subtherapeutic levels of immunosuppressants, triggering GVHD, or subtherapeutic levels of anti-TB drugs, leading to treatment failure or relapse (observed in 6% of cases). The TB-attributable mortality rate of 9% underscores the severity of this infection in the transplant setting.
Expert Commentary
The findings from the SFGM-TC study provide a critical mandate for transplant centers in low-incidence countries. The overwhelming association between TB and birth in endemic regions suggests that current screening practices for LTBI are insufficient. Many centers traditionally rely on Tuberculin Skin Tests (TST), which have poor sensitivity in patients with hematologic malignancies due to anergy.
There is a strong clinical rationale for moving toward mandatory Interferon-Gamma Release Assays (IGRA) for all transplant candidates, particularly those from high-risk backgrounds. Prophylactic treatment for LTBI, if identified prior to transplant, could significantly reduce the incidence of post-transplant reactivation. However, clinicians must balance the timing of LTBI treatment with the urgency of the transplant, as many anti-TB drugs are myelosuppressive or hepatotoxic. Pre-emptive monitoring and a high index of suspicion for extrapulmonary symptoms in foreign-born recipients remain essential components of post-transplant care.
Conclusion
Tuberculosis post-Allo-HSCT, while rare in low-incidence countries like France, is a high-severity condition characterized by early onset and frequent extrapulmonary dissemination. The reactivation of latent infection is the primary driver, specifically among patients born in endemic areas. Improving outcomes will require standardized LTBI screening protocols, careful management of drug-drug interactions, and heightened awareness among clinicians regarding non-respiratory TB presentations. Future research should focus on the safety and efficacy of shorter, less toxic LTBI treatment regimens in the pre-transplant setting to mitigate the risk of reactivation without delaying curative HSCT.
References
- Imbert de Trémiolles G, Nguyen S, Lebeaux D, et al. Tuberculosis after allogeneic hematopoietic stem cell transplantation: a decade nationwide case-control retrospective study in low-incidence country. Bone Marrow Transplant. 2026. PMID: 41807605.
- Cordonnier C, et al. Vaccination of haemopoietic stem cell transplant recipients: guidelines of the 4th European Conference on Infections in Leukaemia (ECIL-4). Lancet Infect Dis. 2013.
- Lortholary O, et al. Guidelines for the management of Mycobacterium tuberculosis infection and disease in patients with hematological malignancies. Chemotherapy. 2008.
