Pulmonary Complications Due to Iduronidase Deficiency (Hurler Syndrome) Linked to Active Pro-Inflammatory Status.

Mucopolysaccharidosis type IH (Hurler syndrome) is caused by alpha-L-iduronidase (IDUA) enzyme deficiency resulting in the accumulation of glycosaminoglycans (GAGs). This affects the function of many vital organs, causes mental retardation and early death. Although BMT can reduce many of these manifestations, pulmonary complications have limited the success of allogeneic BMT for Hurler patients. In our BMT population, non-infectious post-BMT lung complications were seen in 52% of MPS (n=23) vs 8% of patients with other metabolic storage diseases (n=25) (p<0.01). These complications adversely affected 5-yr survival rates, with the survival of females inferior to males (p<0.02).

To understand how IDUA deficiency affects lung function pre- and post-BMT, we examined the lungs of IDUA^−/− mice (C57BL/6 background) and compared them to C57BL/6 wild type controls (WT). Alcian blue staining of lung cryosections prepared from 7–10 mo old IDUA^−/− mice showed large areas of GAG deposition. These areas were associated with large perivascular and peribronchiolar infiltrates composed of predominantly CD4⁺ T cells with CD8⁺ T cells, CD11b⁺ cells and high numbers of MHC class II⁺ cells. Since GAGS have been shown in vitro to stimulate cells of the immune system, the co-localization of T cells, macrophages and accumulated GAGS sets the stage for the lung being a target injured by immune-mediated mechanisms. Pro-inflammatory cytokines (TNFα, IL-1β, IL-6, IL-12p70) were elevated (p<0.05) in the serum and bronchoalveolar lavage fluid (BALF) of the majority of IDUA^−/− as compared to WT controls. In addition, GM-CSF, IL-13 and MCP-1 (CCL2) were elevated in IDUA^−/− mice, indicative of an overall activated immune system, especially the macrophage component since these cytokines are typically macrophage products. Female IDUA^−/− mice tended to have much higher levels of these cytokines compared to their male counterparts (p<0.05). Consistent with these high cytokine levels, flow cytometry demonstrated that IDUA^−/− alveolar macrophages had significantly (p<0.05) higher expression levels of costimulatory ligands (CD40; CD80) and adhesion molecules (CD54) that we have shown are associated with acute post-BMT lung injury. Pulmonary function tests showed that, as compared to WT controls, 7–10 mo old IDUA^−/− mice had increased lung compliance (0.434 ± 0.003 vs 0.280 ± 0.006 1/cm H2O; p < 0.003) and tissue hysteresivity (measurement of lung resistance over elastance: 0.188 ± 0.02 vs 0.158 ± 0.03, p = 0.04). Together, these data indicate that lung injury in non-treated IDUA^−/− mice is associated with a pre-existing pro-inflammatory state that may be a significant contributing factor to the mortality we have observed in such mice undergoing allo-BMT. Lethally irradiated (8 Gy) IDUA^−/− recipients of 20x10⁶ T-cell-depleted allogeneic B10.BR (H2^k) BM had only 20% survival at 4 mo post-BMT vs 100 % survival of WT, p=0.009. The presence of accumulated GAGS at perivascular sites may explain the severity of post-BMT lung injury in the Hurler setting since these areas are the “ports of entry” of the donor cells into the lungs. Since immune-mediated lung injury is a major source of morbidity and mortality in allo-BMT patients, these findings may have important clinical implications for higher risk BMT patients such as those with Hurler syndrome.