CMV peptide vaccine clinical trial
The crucial element in a peptide vaccine approach is the ability of the cytotoxic T-lymphocyte (CTL) epitope to bind to MHC molecules that are expressed in a major proportion of the population. CMV pp65495-503 CTL epitope is largely recognized among CMV+ HLA-A*0201 individuals. Linking the pan-DR epitope peptide (PADRE) or one of several tetanus TH epitopes to the immunodominant pp65495-503 CTL epitope induces robust cytotoxic cellular immune responses in HLA-A*0201 transgenic mice. CpG-containing single-stranded DNA added to the fusion peptides dramatically up regulates immune recognition. TH-CTL epitope fusion peptides in combination with CpG ss-ODN is the innovative strategy that we have developed for delivery of a safe CMV immunogen. Our approach is to amplify the CMV-pp65-specific memory CTL response in a transplant donor, by administering the CMV fusion peptides with or without CpG adjuvant.
The vaccines have been produced in collaboration with the National Cancer Institute according to federal c-GMP regulations and the phase I clinical dose-escalation trial has started in the fall of 2006, at our General Clinic Research Center. The trial focuses on demonstrating safety and immunogenicity of PADRE-CMV and Tetanus-CMV vaccines in healthy adults. We have enrolled so far 30% of the volunteers needed to fill the study cohorts, and vaccinated 18 of them. The fusion peptides are safe and well tolerated, and at 2.5 mg of the vaccine dose the levels of CMV-specific CD8+ T-cell producing IFN-gappear to transiently rise. While these encouraging results need to be confirmed on additional volunteers, increased frequencies of these CMV-specific T cell subsets may characterize a successful vaccine response, and be indicative of protection from disease or viremia.
Immunological evaluation of CMV-MVA recombinant vectors
The highly attenuated modified vaccinia Ankara (MVA) engineered with recombinant genes is being increasingly evaluated as a clinical vaccine for infectious disease and cancer. The attractiveness of MVA for clinical use stems from its efficacy records and pronounced safety, even under conditions of immunosuppression. We have developed recombinant MVA incorporating immunogenic targets of CMV. CMV-MVA vectors stimulate vigorous expansion of CMV-specific CD8+ and CD4+ T cells in CMV+ PBMC, which show minimal alloreactivity and high levels of HLA tetramer binding, cytokine production, and cytotoxicity. Transgenic mice, immunized with CMV-MVA, produce a robust CMV-specific response. The specificity of the vigorous immunologic response to CMV-MVA makes them candidates for clinical evaluation in the context of adoptive immunotherapy or donor vaccination. We have completed a stabilization analysis of a markedly immunogenic MVA candidate vaccine, co-expressing CMV pp65, IE1, IE2 immunodominant antigens. This construct has been selected for a Phase I/II evaluation, and clinical trial batches are going to be soon c-GMP manufactured.
Immunologic correlates of late CMV disease in high-risk liver transplant recipients
Since there is a critical lack of prognostic tools for early detection of post-transplant CMV disease, the goal of this project is to develop predictive immunological assays to target preventive strategies against symptomatic CMV infection. Our investigation focuses on CMV- recipients (R-) receiving a solid organ transplant from CMV+ donors (D+), who are at the highest risk for life-threatening CMV disease. This study is in collaboration with University of Washington Medical Center. We have found that CMV-specific cell lytic function and IFN-g production are not predictive of CMV disease or viraemia in D+/R- recipients. In contrast, increased expression levels of the pro-apoptotic marker PD-1 are temporally and quantitatively associated with incipient and overt CMV disease, and viraemia in the same patients. PD-1 could be developed as a prognostic tool to predict CMV disease and guide therapeutic interventions. Supported by our novel findings, we are planning to perform a broader longitudinal study with the aim of identifying correlates of protection, which will be instrumental in managing at risk D+/R- patients.