Non-viral GM-CSF Gene Therapy is an Effective Treatment in a Novel Murine Model of Autoimmune PAP

Autoimmune pulmonary alveolar proteinosis (aPAP) is a rare lung disease, characterised by the accumulation of surfactant in the alveoli due to anti-GM-CSF autoantibodies. We have previously shown correction of the underlying defect using non-viral gene transfer in a GM-CSF knock-out mouse model (PAP mice). This model however, does not carry anti-GM-CSF autoantibodies present in humans. To progress clinical translation, we assessed whether efficacy may be altered in the presence of anti-GM-CSF autoantibodies. We utilised passive immunisation of PAP mice with murine anti-mGM-CSF antibodies as a novel option.

The antibody pair utilised (B2.6 and A7.39) effectively neutralises GM-CSF activity in vitro. Through a dose escalation in mice, we defined an antibody dose required to reach comparable levels to those seen in aPAP patients.

Here, we assessed efficacy of non-viral GM-CSF gene transfer in the presence of anti-GM-CSF antibodies. Lungs of PAP mice were transfected with phCEFI-mGM-CSF complexed to the cationic lipid GL67A (single dose or 5 weekly doses of 80 µg pDNA/mouse) (n=4-5/group). Treated mice also received 8 weekly doses of 20 µg/mice of anti mGM-CSF antibody pair at the same time and 3-weeks post therapy. PAP biomarkers (bronchoalveolar lavage fluid turbidity and surfactant deposition) were significantly (p<0.05) reduced 1 month after transfection in comparison to irrelevant vector treated mice. The anti-mGM-CSF antibody level in epithelial lining fluid (ELF) was in the range compared to the levels found in aPAP patients (median 100-400 µg/ml ELF).

These data suggests that non-viral based GM-CSF gene therapy may be suitable for clinical translation to treat aPAP.