Pneumonia Vaccine in Liver Transplant Recipients: a Booster Strategy Using a Conjugate Vaccine

OBJECTIVE: Responses to 23-valent polysaccharide pneumococcal vaccine (PPV23) are poor in organ transplant recipients. We have recently shown that the conjugate pneumococcal vaccine (PCV7) is immunogenic in this population but responses remain suboptimal. This is a clinical study designed to assess the immunogenicity of a novel pneumococcal vaccination strategy in a cohort of adult liver transplant recipients. The trial will compare a group of patients primed with the pneumococcal conjugate vaccine plus polysaccharide boost with a group primed with placebo plus the standard 23-valent polysaccharide vaccine.

Specific objectives of this study are:

• To determine the quantitative antibody response using both vaccine strategies
• To determine the functional antibody response by the opsonophagocytic assay. This assay has the advantage of assessing if patient antibody responses represent truly functional antibodies that display opsonic activity against pneumococcus and is likely better correlated with protective efficacy.
• To determine the durability of response over two years In addition, the safety of the conjugate vaccine and a determination of whether time from transplant affects response to vaccination will be made.

HYPOTHESIS: It is hypothesized that the PCV7 priming will provide an enhanced response in these immunosuppressed individuals who may respond poorly to standard vaccination.

RESEARCH PLAN: We will enroll 130 liver transplant recipients from the out-patient transplant clinics at Toronto General Hospital, Toronto, Ontario. Recipients who have had pneumococcal vaccination in the past 5 years will be excluded. Upon enrolment, patients will be randomized to receive either placebo or PCV7 in a blinded fashion. Eight weeks later, all subjects will receive PPV23. Serum will be obtained at baseline, 8 weeks, 16 weeks, 6, 12, 18, and 24 months. Sera will be used to perform antibody testing to seven pneumococcal serotypes (4, 6B, 9V, 14, 18C, 19F, 23F). The baseline, 8, and 16 week sera will be used for opsonophagocytic assay to the above seven serotypes. A baseline nasopharyngeal swab will also be obtained to look for colonization with Streptococcus pneumoniae. Patient recruitment is expected to take two years and follow-up of all patients should be complete by year 3. An additional 4 months will be needed to complete all laboratory testing. The primary outcome will be anticapsular antibody concentration at 16 weeks. A serotype response will be defined as a 2-fold or greater rise in titer from the 8 week concentration. A vaccine response will be defined as response to at least one serotype of the seven measured.

FUTURE DIRECTIONS: Results of this trial will help to develop a rational and optimal pneumococcal vaccination strategy that would prevent significant morbidity in organ transplant recipients. We are currently studying the impact of pneumococcal disease in transplantation by: (i) a review of invasive pneumococcal disease in transplant recipients in Toronto-Peel region to determine incidence and predominating serotypes; (ii) a Canadian survey of vaccination practices in transplantation; (iii) a 3-year follow-up study to determine the sustainability of immune response to pneumococcal vaccine in renal transplant patients previously enrolled in a vaccine trial. We hope that these studies will form the basis of pneumococcal vaccination recommendations for organ transplant recipients.