A Shifting Immune Landscape: T-Cell Activation and Food Allergy Susceptibility After Pediatric Liver Transplantation.

Pediatric liver transplant (pLT) recipients have a higher risk of developing de novo food allergy, defined also as liver transplant–associated food allergy (LTFA), when compared with healthy children as well as recipients of other solid organ transplants.1 Among those who develop allergies, eczema and IgE-mediated food allergies are most common.2 Furthermore, although LTFA is rare in adult LT, it has been estimated that LTFA can occur in up to 40% of pLT recipients.1 The exact pathophysiology of LTFA remains unresolved although 3 potential mechanisms have been proposed. The first is based on the concept of passive transfer of donor allergen-specific IgE within the liver allograft, thereby transferring it into recipients at the time of transplant. The second is based on the transfer of allergen-reactive B and T cells from donor to recipient. The third involves immunosuppressant-dependent immune dysregulation that can manifest as a shift from Th1 to Th2 immune responses, persistent T-cell activation, and alterations in cytokine profiles, resulting in allergic or autoimmune diseases.3 In their recent study, “T-cell activation and increased levels of cytokines in children after liver transplantation—A potential association with increased susceptibility to food allergy development,” Käppi et al investigate the relationship between T-and B-cell activation, cytokine profiles, and the development of LTFA.4 By comparing peripheral immune profiles of pLT recipients with LTFA and without (“LT no food allergy”: LTNFA) to nontransplanted allergic children and healthy controls, the study provides the groundwork for future investigations. Among 43 pLT recipients at the Transplantation Unit in Gothenburg, Sweden, transplanted from 2014 to 2017, 8 LTFA and 28 LTNFA patients were identified. Compared with the LTNFA group, blood samples from the LTFA group exhibited a higher proportion of newly activated (CD69+) T cells in both CD4+ and CD8+ subsets, along with intestinal homing B cells (CCR10+β7+). Additionally, LTFA patients showed elevated serum levels of the Th2 cytokine interleukin (IL)-4 and proinflammatory cytokines tumor necrosis factor-alpha and tumor necrosis factor-beta, a pattern not observed in the LTNFA group. When the LTFA group was compared with nontransplanted children with food allergy, in addition to differences in the previous immune profiles, the authors also observed increased proportions of HLA-DR+ and effector memory T cells. These findings suggest a state of heightened immune activation in LTFA pLT recipients, suggesting potential mechanisms linking LT to dysregulated immune responses and allergic susceptibility. Although Käppi et al do not explicitly define the mechanism underlying these findings, their results support current hypotheses described in the literature. The 2 leading explanations center on the paradoxical effects of immunologic tolerance of a transplanted liver and the effects of prolonged, high-dose immunosuppressive therapy. The liver is uniquely immunotolerant, characterized by relatively low expression of major histocompatibility complex molecules on hepatic cells and a tendency to promote anti-inflammatory cytokine signaling, both of which contribute to T-cell inhibition.5 This intrinsic tolerogenic environment may translate into tolerance to dietary allergens. However, when this baseline tolerogenic state is disrupted or subject to prolonged, high-dose immunosuppressive therapy, this can result in impaired protective immunity, driven by excessive T-cell inhibition and dysfunction, alterations in cytokine profiles, and diminished immune surveillance.5,6 Tacrolimus, a commonly used calcineurin inhibitor in pLT, has been particularly associated with these immune shifts. Although tacrolimus is a potent T-cell suppressor and has been shown to broadly inhibit both Th1 and Th2 cytokine production in vitro,6 more recent data suggest a preferential suppression of Th1 pathways, with relative preservation of Th2 responses and disruption of regulatory T-cell function.7 This imbalance may promote a shift toward Th2-mediated immunity, favoring allergic sensitization and IgE-mediated pathways.3 More specifically, the role of IL-5 and its elevation posttransplant is unique in LTFA compared with nontransplanted children with food allergies.8 Interestingly, this shift in IL-5 was not observed in the study by Käppi et al. In fact, IL-5 was among the few cytokines that did not show a significant elevation in children with LTFA compared with either healthy controls or non-LT food-allergic controls. This discrepancy may be partially explained by the widespread use of tacrolimus within the study cohort and the small sample size. Thus, a larger study cohort that accounts for differences in immunosuppressive regimens may help clarify this relationship. These inconsistencies across studies underscore an ongoing need for more focused investigation into the underlying mechanisms of LTFA, with the goal of identifying potential targets for risk stratification and prevention in high-risk patients. In contrast to this study, others have identified several potential risk factors for the development of LTFA, including younger age at transplantation, female sex, atopic family history, and concomitant Epstein-Barr virus infection.9 The mechanisms underlying these associations remain incompletely defined, but several plausible explanations have been proposed. Younger age at transplantation may reflect the relative immaturity of the immune system and a greater susceptibility to immune modulation. Observed sex differences may be related partly to hormonal influences on immune regulation. A family history of atopy likely reflects a well-known underlying genetic predisposition toward allergic disease.9 In addition, viral infections, especially Epstein-Barr virus infection, may contribute to immune dysregulation through their effects on lymphocyte function and cytokine signaling. The findings by Käppi et al underscore the need for further investigation to better define the mechanisms underlying these observed shifts in immune function and associations with LTFA. This is particularly important given that food allergies, depending on severity, can have lasting effects on quality of life and posttransplant nutritional management. As long-term outcomes in pLT continue to gain focus, understanding the interplay between immune modulation and allergic disease will become increasingly important. A clearer definition of these pathways may ultimately inform risk stratification and guide more tailored immunosuppressive strategies for patients at higher risk of developing LTFA. Studies such as these have the potential to reduce posttransplant morbidity and mortality while highlighting the long-term implications of chronic immunosuppression. Although graft survival remains the primary goal, these findings underscore the importance of considering the broader spectrum of comorbidities associated with current treatment approaches. A more comprehensive understanding of these risks may ultimately support more balanced, patient-centered care and improve overall outcomes.