Accelerated Immunization to Induce Cytomegalovirus Immunity in Stem Cell Donors

Overview

This study will evaluate the safety and effectiveness of a new vaccine, ALVAC-pp65, in boosting immunity to cytomegalovirus (CMV) infection in stem cell transplant donors. CMV is a member of the herpesvirus group, which includes herpes simplex virus types 1 and 2, varicella-zoster virus (which causes chickenpox), and Epstein-Barr virus (which causes infectious mononucleosis). Most adults are infected with CMV, but a healthy immune system keeps the virus in check, so that it does not cause harm. In people with a weakened immune system, such as transplant recipients, the virus can become reactivated. Medications for treating the infection may cause low blood counts and kidney damage, and, in some cases, the virus may cause death. The ALVAC-pp65 vaccine is intended to improve immunity against CMV in stem cell donors and thereby prevent its reactivation in recipients. It is made from a virus that ordinarily infects canaries. The virus is weakened so that it cannot infect the person who receives it, and it is modified to carry a copy of a CMV gene called pp65. This gene instructs cells to make CMV proteins that the vaccine recipient's immune system can produce antibodies to, thus conferring immunity to the disease. Persons 18 years of age or older who are scheduled to donate stem cells for a patient in an NIH protocol and who are not allergic to eggs, egg products, or other vaccines, may be eligible for this study. Candidates are screened with a medical history, physical examination, and blood tests. Participants receive three vaccinations one week apart beginning at least 3 weeks before the scheduled stem cell donation. They are observed for 30 minutes after each vaccination to look for any immediate side effects of the vaccine. Approximately 3 tablespoons of blood are drawn before each vaccination and 1 week after the last vaccination to evaluate vaccine safety. Blood samples are also collected at the screening evaluation, 3 weeks after the start of vaccination, and 3 months after the last vaccination to check for CMV immunity. Participants keep a diary, recording any reactions to the vaccine and any change in medications. They are contacted by telephone for follow-up 3 months after the last vaccination to report any additional symptoms.

Cytomegalovirus (CMV) infection is a major complication following allogeneic stem cell transplantation (SCT). The risk of CMV infection after SCT is inversely related to the number of CMV-specific cytotoxic T-lymphocytes (CTLs) present in the allograft. CMV-specific lymphocytes can be readily detected and quantified in the blood by sensitive in vitro techniques that measure T cell cytokine secretion following antigen stimulation. A previous phase I clinical trial has demonstrated that CMV-specific T cells can be safely generated in normal CMV-seronegative (naive) subjects after immunization with the CMV vaccine, ALVAC-pp65 (vCP260), an attenuated canary pox-based vaccine Sanofi Pasteur (formerly known as Aventis Pasteur, Lyon, France). We propose a clinical trial to evaluate an accelerated immunization schedule with the same vaccine. Study participants will be 1) SCT donors and their matched recipients participating in intramural NIH allogeneic SCT protocols and 2) CMV sero-negative normal volunteers. Donors will receive two or three immunizations prior to allograft collection, and followed for 45 days for the development of CMV immunity. Normal volunteers will receive two or three immunizations and followed similarly to the donors. CMV sero-positive subjects will receive two immunizations; CMV sero-negative subjects will receive three. Transplant (SCT) recipients will be evaluated for incidence of CMV infection and disease. The study is designed as a two-stage phase II trial with stopping rules at each stage. The primary outcome measures are the effectiveness of the vaccine in (a) generating cellular immunity in CMV-seronegative (naive) donors or CMV sero-negative normal volunteers and (b) boosting the cellular immune response in CMV-seropositive (sensitized) donors and healthy volunteers. Secondary outcomes include the clinical safety profile of the vaccine in vaccine recipients and the incidence of CMV infection/disease in transplant recipients. Since the cellular immune response to CMV is a standard model for immune reconstitution post transplant, our study may also provide important information on the feasibility of immunizing stem cell transplant donors with other microbial and tumor vaccines.