Allogeneic hematopoietic cell transplantation (HCT) is a therapy for which City of Hope is a world leader and is effective for a range of life-threatening hematologic malignancies. However, one of the most difficult-to-treat complications can occur during the first 100 days post-HCT, which is infection with the highly prevalent beta-herpes virus known as human cytomegalovirus (HCMV). HCMV rarely causes disease in healthy individuals, but can be life-threatening in HCT patients as a result of immunosuppression associated with treatment strategies aimed at preventing rejection or graft-versus-host disease (GVHD). To improve outcomes for HCT recipients, the Department of Experimental Therapeutics (ET) aims to substitute toxic antivirals with a vaccine that induces long-lasting, memory immune responses to HCMV, since antivirals are unable to generate adaptive immunity capable of preventing HCMV infection and disease.
In allogeneic HCT, hematopoietic cells are obtained from suitable HLA matched related or unrelated volunteer donors (URD). Pretransplant patients are treated with chemotherapy, with or without radiation therapy, to eradicate cancerous cells, and for suppressing the patient’s immune system to prevent it from attacking donor hematopoietic cells. As a result, patients are vulnerable to pathogens and herpes virus infections, including CMV, as a result of immunosuppression associated with treatment strategies aimed at preventing rejection or graft-versus-host disease (GVHD). Despite advances in development of antiviral therapy, the use of antivirals does not address the major risks of late-onset CMV disease, including reactivation and failure to reconstitute CMV-specific immunity. Substituting toxic antivirals with a vaccine that harnesses the abundant native immune response to CMV may improve outcomes for HCT recipients.
Our first generation vaccine approach relied on a non-living synthetic portion of the virus called a peptide that has cleared its safety hurdle after a successful clinical trial in healthy volunteers. The vaccine peptides were named PADRE-CMV and Tet-CMV, respectively, and were developed with support of the National Cancer Institute sponsored Rapid Access to Interventional Development (NCI-RAID, currently called NCI-NExT) program. After obtaining approval from the FDA, PADRE-CMV and Tet-CMV, with or without PF-03512676 adjuvant (a synthetic single stranded DNA containing bacterial CpG DNA motifs with immunostimulatory activity, produced by Pfizer, Inc.), were clinically evaluated for safety and immunogenicity in a Phase Ib dose-escalation clinical trial. The achievement of the central goal of our phase Ib study in healthy adults supports further evaluation of Tet-CMV combined with PF-03512676 (renamed CMVPepVax) in the HCT setting. A summary of the results of the trial was published in 2012. These promising results are the basis for CMVPepVax as a therapeutic vaccine, to improve outcomes of HCT recipients with uncontrolled CMV viremia. The phase Ib pilot trial was powered to evaluate safety of administering CMVPepVax to HLA matched allogeneic (MRD or URD) patients at risk for CMV complications. To capitalize on the success of the pilot Phase Ib trial, NCI approved a fresh lot of vaccine to support a large multi-center Phase II study jointly with the University of Minnesota Comprehensive Cancer Center. The goal of this Phase II clinical trial is to assess efficacy of CMVPepVax, in protecting against CMV reactivation and disease (Project 1).
As a viral vector that can incorporate foreign antigens and protect against a challenge pathogen, modified vaccinia Ankara (MVA) virus is hypothesized to act as a powerful immunotherapeutic tool against multiple strains of CMV regardless of an individual’s HLA type (Projects 2 and 4). The potential value of MVA for the clinic stems from its ability to elicit strong humoral and T cell responses against diverse antigens. Studies in rodents and macaques affirm the safety of MVA, including protection against more virulent forms of poxviruses. There are over 150 active clinical studies using MVA that are documented on the USPHS website. Recent trials have shown MVA is well tolerated and immunogenic when administered to HCT recipients, indicating minimal human toxicity in either short term or long term studies. Currently, there is no vaccine strategy against CMV applicable to HCT recipients that use a recombinant MVA incorporating multiple cellular response antigens. Three CMV gene products, UL83 (pp65), UL122 (IE2), and UL123 (IE1) have been selected as targets for cell mediated immune response. We have termed this vaccine as CMV-MVA Triplex, which was manufactured and is currently being tested at the City of Hope. This study will compare the immune response of CMV-MVA Triplex vaccine used in persons with no prior CMV immunity and in those with prior CMV immunity. The primary goal of this first in humans clinical trial is to establish the safety of the CMV-MVA Triplex vaccine given to healthy volunteers (Project 2). A current multicenter study is investigating the safety and protective function of the vaccine in the HCT population. Additional studies are envisioned in the solid organ transplant setting.
Fetal infection by HCMV during and after pregnancy poses a serious health risk to the developing child. Thus, a vaccine that confers protective immunity against congenital CMV infection is another significant focus of the Department. Previous studies have shown that neutralizing antibodies (NAb) are crucial in the host immune response to control or prevent the infection with HCMV. Promising progress in the development of an HCMV vaccine has been made by a strategy based on a recombinant form of the envelope glycoprotein B (gB), a dominant NAb target in HCMV-positive individuals. Based on these findings, scientists in the Department have developed a bacterial artificial chromosome (BAC)-derived Modified Vaccinia Ankara (MVA) vaccine vector co-expressing all 5 subunits of the gH/gL-PC (MVA-gH/gL-PC), which is considered as the major target of NAb that block the infection of epithelial and endothelial cells (EC). Focus of current work involves the characterization and isolation of the gH/gL-PC, and identification of gH/gL-PC-specific NAb responses and their epitope targets. Generation of a multi-antigenic BAC-derived MVA vaccine vector that incorporates the gH/gL-PC in combination with other dominant NAb targets (gB, gH/gL, gH/gL/gO, gM, gN) and major targets of the cell-mediated arm of immunity such as pp65 and IE1 are also major efforts (Project 4).