Multimodal preclinical imaging of Aspergillus fumigatus invasion and treatment

侵袭性曲霉病(IA)是一种威胁生命的机会性疾病，影响免疫系统受损的患者，其特点是死亡率高达40%以上，社会成本高。由于非特异性症状，这种真菌感染在虚弱的患者中很难诊断，因为非侵入性成像方法(MRI、X射线CT)不能识别特定的特征。这迫使从业者依靠侵入性程序(支气管肺泡灌洗或活检)来建立明确的诊断，而患者负担很高。因此，治疗的管理常常被危险地拖延。迫切需要一种更快、更具体的诊断程序来识别IA。为了解决这一临床需求，我们与几个欧洲研究机构合作，开发了一种新的无创性诊断IA的成像方法。这种新的诊断方法是基于一种针对正在生长的真菌的放射性标记抗体，以及PET和MR的组合，即所谓的“免疫-PET/MR”方法。除了在临床前研究中具有高度的特异性和敏感性外，这种基于抗体的方法在患者中也显示了良好的结果。然而，这些研究也揭示了该方法的明显局限性，因为抗体的长循环时间引起的高背景噪声，使得除非对抗体进行适当的修饰，否则不太可能在临床上广泛应用。虽然通过免疫-PET/MR早期诊断IA将允许更好的治疗选择和更早的治疗，但治疗、真菌负荷变化和放射性示踪剂积累之间的相关性仍不清楚，使得治疗监测变得不可能。鉴于IA在虚弱的患者中进展迅速，在所有感染部位迅速评估治疗效率至关重要，特别是考虑到新出现的耐药真菌菌株和当今抗真菌药物的显著副作用。为了优化用于这些分析的放射性示踪剂，有必要缩短抗体载体的循环时间，以提高方法的信噪比。因此，在本项目中，我们将对现有的抗JF5抗体的Fc部分进行修饰，以极大地缩短其在体内的循环时间。然后，将对修改后的抗体进行放射性标记，并将研究其在活体小鼠模型中更快速、更清晰地检测真菌存在的能力(目标1)。此外，还将研究JF5抗原在抗真菌治疗中的表达情况。在几个与治疗相关的测量点，将建立测量信号与实验动物的实际真菌负荷之间的相关性(目标2)。在最后一步中，我们将研究这种方法如何在小鼠模型中可靠地检测到脑曲霉病(目标3)。

Invasive Aspergillosis (IA) is a life threatening opportunistic disease that affects patients with a compromised immune system and is characterized by a very high mortality rate of over 40% and high societal costs. With non-specific symptoms, this fungal infection is difficult to diagnose in weakened patients as non-invasive imaging methods (MRI, X-ray CT) do not identify specific features. This forces practitioners to rely on invasive procedures (broncho-alveolar lavage or biopsies) with high patient burden to establish a definitive diagnosis. As a result, the administration of treatment is often dangerously delayed. A faster and more specific diagnostic procedure for the identification of IA is desperately needed. To address this clinical need we developed a novel imaging method for the non-invasive diagnosis of IA in a research effort with several European research institutions. This new diagnostic method is based on a radiolabeled antibody specific to the growing fungus and the combination of PET and MR, a so-called “immuno-PET/MR” approach. In parallel to its high specificity and sensitivity in preclinical studies, this antibody-based approach also showed promising results in patients. However, these studies also revealed clear limitations of the approach due to high background noise caused by long circulation times of the antibody, rendering widespread clinical use unlikely baring suitable modifications of the antibody. While early diagnosis of IA enabled by immuno-PET/MR will allow for better therapeutic choices and earlier treatment, the correlation between treatment, changes in fungal burden and radiotracer accumulation remains unclear, making therapy monitoring impossible. Given the swift progression of IA in weakened patients, it is of prime importance to assess the efficiency of treatment rapidly at all infection sites, in particular given the emerging resistant fungal strains and pronounced side effects of present day antifungals. To optimize the radiotracer for these analyses, it is necessary to shorten the circulation times of the antibody vector to increase the signal-to-noise ratio of the approach. In this project, we will therefore modify the existing anti JF5 antibody at its Fc part to greatly reduce the circulation time in vivo. The modified antibody will then be radiolabelled and its ability to detect more rapidly and with clearer signal the presence of the fungus in a mouse model in vivo will be investigated (Aim 1). Furthermore, the expression of the JF5 antigen during antimycotic therapy will be investigated. At several therapeutically relevant measurement points, a correlation of the measurement signal to the actual fungal load in the test animals will be established (Aim 2). In the final step, we will investigate how this method can reliably detect cerebral aspergillosis in a mouse model (objective 3).