Virus . Immunosuppression . Transplantation . Antibody . T-cells . Antivirals

Transplantation and Clinical Virology

Translational Research in Clinical Virology: From Bedside to Bench and Back to the Patients

“Transplantation and Clinical Virology” is interested in translational research of virus infections to improve clinical diagnosis, prevention, and treatment. This includes
– Respiratory viruses (RV);
– Human herpesviruses; and
– Human polyomaviruses in vulnerable populations (e. g. HIV/AIDS; transplantation;autoimmunity; inherited immunodeficiency).
We aim at characterizing 1) key determinants of virus pathology; 2) potential targets of antiviral intervention; 3) adaptive immune responses; 4) modifiable and non-modifiable risk factors in patients.
The focus on human polyomaviruses (HPyVs) serves as example: In the last decade,12 new HPyVs have been identified by molecular methods in addition to BKPyV and JCPyV known since 1971. Currently, at least 5 HPyVs have been convincingly linked to diseases, all in immuncompromized patients. Importantly, no specific antivirals are available for the treatment of HPyV disease making immune reconstitution the main stay of any therapeutic approach today.
The polyomavirus non-coding control region (NCCR) harbors the origin of viralDNA genome replication and promoter/enhancers controlling the sequential bi-directional expression of PyV early and late gene expression. We reported that kidney transplant patients with persistent BKPyV viremia showed the emergence of viral variants with rearranged NCCR. We demonstrated that the emerging rr-NCCR caused an activated early viral gene expression, higher viral loads, and replication rates (replication capacity) in vitro, and more advanced disease in patients.A similar dynamic change of the NCCR was seen in JCPyV of HIV patients with PML linking activated early viral gene expression to replication and pathology. Importantly,non-rearranged JCPyV NCCR is activated by HIV1 explaining the high number of PML among HIV/AIDS patients.
We conducted extensive point mutation analyses of the archetype BKPyV NCCR identifying 3 phenotypic groups whereby Sp1 affinity and orientation governed bidirectional BKPyV early and late gene expression (Fig. 1). The pathologic relevance of the point mutations was supported by their identification in clinical isolates from patients with nephropathy and hemorrhagic cystitis. Thus, similar to HIV/tat in JCPyV, BKPyV (re-)activation does not only result from failure of immune control,but also from activation from the NCCR.
Based on clinical studies, BKPyV viremia and nephropathy has been associated with tacrolimus as main calcineurin inhibitor. We observed that cyclosporine A inhibited/slowed BKPyV replication, whereas tacrolimus activated/accelerated BKPyV replication in vitro. Importantly, viral activation by tacrolimus was antagonized by sirolimus competing the intracellular binding protein FKBP-12 (Fig. 2). The data strengthen the theme that activation of virus replication plus failure of adaptive immune control synergize in the emergence of opportunist viral infections in immuno compromised hosts. This knowledge could be taken back to the clinical management of BKPyV not only by reducing immunosuppression, but by switching tolow-dose cyclosporine plus mTOR inhibitor combinations.
Characterizing BKPyV T-cell responses through IGRAs to 15mers, we observed that BKPyV Vp1 responses were generally stronger and involved mostly CD4 Tcells, whereas LTag responses were weaker, but contained a larger fraction of specificCD8 T-cells in peripheral blood. Since CD8 T-cells are the main cytotoxic effectors, and since LTag are rate limiting for BKPyV replication in vitro and in vivo (see NCCR mutant variants), we hypothesized that LTag-specific CD8 T-cells are key effectors of antiviral immunity. We identified 39 of 90 predicted immunodominant 9mers responses that will be developed for T-cell vaccines (Fig. 3), and for clinical assays to guide immosuppression reduction.

Fig. 1: The host cell factors Sp1, TATA- and downstream core promoter elements form imperfect symmetry underlying bidirectional expression of the early and late viral gene region of BKPyV (see Bethge et al. 2016 J. Virol 90: 10083–10101).

Fig. 2: Effects of calcineurin inhibitors and mTOR inhibitors on BKPyV replication (see Hirsch et al. 2016 Am J Transplant 16: 821–832).

Fig. 3: Characterization BKPyV-specific CD8 T-cell responses identifying immune-dominant 9mers epitopes (see Cioni et al. 2016 Am J Transplant 16: 1193–1206). CD8+ T cell proliferation (CSFE dye) and cytotoxic degranulation (CD107a) of HLA-9mer-streptamer CD8 T-cells (blue).