Targeting Latent Human Cytomegalovirus (CMV) with a Novel Fusion Toxin Protein during Ex Vivo Lung Perfusion

Purpose Donor to recipient CMV mismatch leads to high incidence of CMV infection post lung transplant leading to inferior long-term patient outcomes. CMV latently infected cells ubiquitously express a surface marker, US28. We aimed to evaluate the therapeutic effects of a novel fusion toxin protein (F49A-FTP) that targets US28 in human lungs during EVLP, with the ultimate goal of minimizing or preventing CMV reactivation post transplantation. Methods Human lungs rejected for transplantation were randomly placed on EVLP alone or EVLP+1mg/L of F49A-FTP (n=6 each) for 6 hours. Biopsies were collected to evaluate viral reactivation using an in vitro assay that induces latent CMV to reactivate to an infectious phase. Since US28 has 38% homology to the human CX3CR1 chemokine receptor, potential off-target effects of the toxin were studied using flow cytometry for cell death assessment of CD34+ and CD14+ cells. Lung function on EVLP was evaluated as a safety endpoint. Results F49A-FTP was delivered through the PA on EVLP with no acute toxic events based on physiological parameters (Figure 1A). We performed an in vitro assay using tissue samples obtained after EVLP to stimulate CMV to reactivate in order to assess efficacy of the drug. After primary culture from lung tissue samples, relative reactivation events (assessed with IFF staining for IE protein of lytic CMV, Figure 1B) occurred in 100% of controls vs. only 0.04±0.02% of treated lungs. For off-target analysis, we performed flow cytometry and calculated the ratio of post:pre perfusion CD34+ and CD14+ cells (Figure 1C). There were no changes in number of cells for both groups: CD34+ ratio 0.8±0.5 vs. 0.6±0.5 (control and F49A-FTP, respectively, p=0.4974); CD14+ ratio 1.54±0.74 vs. 1.66±1.13 (control and F49A-FTP, respectively, p=0.8660). Conclusion Our study demonstrates that ex vivo F49A-FTP treatment of human lungs on EVLP markedly attenuates CMV reactivation. Ongoing ex vivo and in vivo reactivation experiments will confirm these findings.