|Home | About | Journals | Submit | Contact Us | Français|
There are limited studies assessing the live attenuated varicella vaccine following alloHCT. Due to the morbidity of varicella acquired after childhood, we immunized and retrospectively analyzed the safety and immunogenicity of this vaccine in 46 VZV seronegative patients <20 years old at HCT who achieved a CD4 cell count ≥200/ul, were off immunosuppression, and responded to ≥1 post HCT vaccines. Two vaccinated patients lacking follow-up titers were excluded from analysis. Stem cells were derived from an HLA-matched sibling (n=18) or an alternative (HLA MM related or unrelated) donor (n=26). Median time to vaccination was 4 years. Sixty-four percent of patients seroconverted following one immunization. There was no significant difference in response between recipients of a matched related or alternative donor graft (p=0.2) or between those given a TCD or T-replete alternative donor graft (p=0.27). Three of 44 patients developed a self-limited varicella-like rash within 2.5 weeks of immunization. With a median follow-up of 29.1 (range: 6.9-167.1 ) months, there were no subsequent cases of varicella-like rashes. No patient developed shingles. This study suggests that this vaccine is safe and immunogenic when given according to pre-set clinical and immunologic milestones, warranting larger prospective studies in patients ≥24 months following HCT as outlined in current post HCT vaccine guidelines.
Although varicella in childhood is generally a mild disease, immunocompetent individuals who develop chickenpox later in life develop a more serious infection, associated with an increased risk of visceral disease and need for hospitalization (1,2). In individuals >20 years of age, fatal varicella is 13 times higher than that observed in children (2). Studies have documented the safety and efficacy of the live attenuated varicella vaccine in healthy children (3) and patients with a history of impaired cellular or humoral immunity (4,5), such as children with acute lymphoblastic leukemia on maintenance therapy (6), pediatric solid organ transplant recipients on chronic immunosuppressive therapy (7,8), and treated children with HIV (9-11). In view of this, our center has chosen to vaccinate VZV seronegative children and adolescents after allogeneic HCT upon acquisition of preset immune milestones. Although both the 2005 European Group for Blood & Marrow Transplantation (12) and 2009 (13) Center for International Blood and Marrow Transplant Research (CIBMTR) vaccine guidelines permit the use of a live attenuated varicella vaccine in select patient groups, there is minimal data on the immunogenicity of this vaccine post HCT (14-16), particularly in recipients of cord blood, unrelated HCT derived from any source, and children transplanted for primary immunodeficiency disease. In view this, this retrospective study analyzed the safety and immunogenicity of this vaccine in allogeneic transplant recipients. The effect of age at transplant and vaccination, diagnosis, time from HCT to vaccination, donor type and stem cell source, history of graft versus host disease and/or the use of T cell depletion, on vaccine responses was assessed.
A waiver of authorization to conduct this study was approved by the Memorial Sloan Kettering Cancer Center Institutional Review Board. The medical records of all patients less than 20 years old at HCT who were disease-free for >10 months following an allogeneic transplant performed from 1/1/1995 through 12/1/08 were reviewed for receipt of the live attenuated varicella vaccine. At this center, VZV seronegative patients were eligible for vaccination if they were ≥24 months following transplant, were off all immunosuppressive therapy, and had no evidence of ongoing chronic GVHD. To increase vaccine safety, patients were required to have a circulating CD4 cell count (>200 cells/ul), a T cell proliferative response against Phytohemagglutinin (PHA) within the lower limit of normal, and a specific antibody response to ≥1 vaccines administered post HCT. Four patients were immunized by their local physicians less than 2 years post HCT despite our recommendations to delay immunization until ≥24 months. Dates of vaccination and pre and post vaccine titers were obtained from a prospectively maintained database and confirmed by retrospective chart review. Pre and post titers were available on 44 patients; two vaccinated patients without follow-up titers were excluded from analysis. All patients were evaluated at MSKCC before and after completing vaccinations, including assessment of acute and chronic GVHD using established criteria (17, 18). Ninety percent of patients were vaccinated at Memorial Sloan-Kettering Cancer Center.
Antibody testing. Varicella antibody was measured in the Clinical Microbiology Laboratory of Memorial Sloan-Kettering Cancer Center using a two step enzyme immunoassay sandwich method with a final fluorescent detection (BIOMERIEUX, Durham, NC). The result is indicated by test value calculated by the computer based on the ratio from the relative fluorescent value of the sample to that of the standards which are run for each test. A test value >0.9 is considered positive.
Four color Immunofluorescence and T cell proliferative responses. Circulating lymphoid populations were analyzed by 4 color immunofluorescence within three months of initiating vaccination using methods as previously described (19). In vitro T cell proliferative responses to Phytohemagglutinin (PHA-P) and varicella virus were performed as follows: 50,000 isolated peripheral blood mononuclear cells were re-suspended in RPMI, supplemented with 10% pooled human serum, penicillin/streptomycin, and L-glutamine and plated in round bottom microtiter wells in a volume of 175 ul/well. Cells were stimulated with PHA-P (DIFCO) at optimal final concentrations of 42.9, 21.4, and 10.7 mcg/ml of culture and Varicella Zoster CF antigen (1:10, 1:20, 1:40, 1:80 dilution) (BioWhittaker, Walkersville, MD). Cultures were pulse labeled with 1.0 uCi/well 3H-thymidine for the last 24 hr of the 120 hour incubation for PHA and 168 hours for varicella, harvested onto glass-fiber filter paper, and counted in a liquid scintillation counter. The absolute proliferative response was calculated as the median counts per minute (cpm) of triplicate wells minus the unstimulated medium control. Each day all assays performed on patients were run in parallel with a normal control and compared to values derived from 60 normal controls evaluated every 2 years.
Fisher's exact test and the Wilcoxon rank sum test was used to examine covariate differences between responders and non-responders. The statistical packages SAS (9.2) was used to generate the test statistics. Only p values less than <0.05 were considered statistically significant.
Patient and donor characteristics are shown in Table 1. The majority of patients were transplanted for a hematologic malignancy (57%) or primary immunodeficiency disease (23%). The stem cell donor was an HLA-A, B, DRβ1 identical sibling, a haplo-identical family member, or an unrelated donor in 41%, 14%, and 45% of cases, respectively. Seventy percent of patients received an unmodified HCT. Of the remaining thirteen patients, 8 received a bone marrow transplant T cell depleted by either soybean lectin agglutination followed by rosetting with sheep erythrocytes (n=6) (20) or treatment with the T10B9 monoclonal antibody plus complement, n=2 (21) and 5 received a a peripheral blood stem cell graft T cell depleted by CD34 positive selection followed by rosetting with sheep erythrocytes (22). Eight-nine percent of patients received myeloablative cytoreduction which contained either hyperfractionated total body irradiation (n=15) or >8 mg/kg busulfan (n=24). Three patients received non-myeloablative conditioning [(melphalan, fludarabine, anti-CD52 (n=2) or cyclophosphamide and anti-thymocyte globulin (n=1)]. Two patients with severe combined immunodeficiency disease (SCID) received an HLA matched sibling BMT without prior cytoreduction. Three patients received post transplant rituximab at 25, 49, and 50 months prior to vaccination for the treatment of a severe auto-immune hemolytic anemia following an unmodified unrelated BMT (n=1) or to prevent an Epstein Barr virus lymphoproliferative disorder following a T cell depleted unrelated peripheral blood stem cell transplant (n=2). Six patients had a history of grade II-III acute GVHD and 3 patients developed chronic GVHD, which had resolved in all patients prior to vaccination.
Prior to receipt of the LAVV, all patients were VZV seronegative and 42 of 44 patients lacked a T cell proliferative response against varicella antigen. The median age at vaccination was 9 years. The median time from transplant to vaccination was 4 years with a range of 0.92-14.04 years. The wide range between HCT and immunization was due to the time it took patients to discontinue immunosuppression, reach immunologic milestones, and/or physician comfort administering the LAVV. There was no significant difference in time to vaccine in recipients of T cell depleted or T-replete transplant. The median time to first LAVV was 3.9 (range: 0.92- 14.04) years following a T cell depleted HCT and 4.1(range: 1.67-9.13) years post unmodified HCT, p=0.64.
The median time to measure antibody levels following the initial vaccine was 108 days (range: 29-395 days). Overall, 64% (28/44) of patients seroconverted following one vaccine. There was no significant different in the proportion of responders in patients evaluated < or > 108 days post immunization (14/23 vs 15/22). Response was observed in 50% (7/14), 68% (13/19), and 73% (8/11) of patients immunized between 0.92 and 3, 3 and 5, and >5 years post HCT. There was no significant difference in B cell response on the basis of age at HCT, age at vaccination, patient diagnosis, or history of resolved acute or chronic GVHD (data not shown). Eight of 10 patients transplanted for a primary immunodeficiency disease responded to the first LAVV administered at a median (range) of 3.3 (1.6-4.9) years post HCT. There was no significant difference in response in recipients of a HLA matched related compared to an alternative donor HCT (9/18 versus 19/26), respectively (p=0.2). Ten of 12 and 9 of 14 recipients of a T cell depleted or T-replete alternative donor HCT seroconverted after one LAVV, respectively, (p=0.27). Three of 5 patients who received a cord blood transplant seroconverted following their first vaccine administered at a median (range) of 3.76 (2.76-5.89) months post HCT.
Fourteen patients who did not respond to the first LAVV received a second immunization at a median of 7.2 (range: 2.7-14.6) months following the primary LAVV. Seven of 8 recipients of an unmodified HLA matched sibling HCT and 3 of 6 recipients of an unrelated HCT (p=0.16) seroconverted following the second vaccine (Figure 1).
Following the initial LAVV, in vitro T cell proliferative response against VZV was assessed in 17 patients who seroconverted and 14 patients who did not. Of the 17 patients who mounted a B cell response, 13 developed a VZV specific T cell proliferative response. Despite failure to seroconvert, 7 of 14 patients developed a specific in vitro T cell response against varicella.
No patient suffered a serious adverse reaction attributable to vaccination. Three unrelated transplant recipients (cord blood, n=1, unmodified PBSCT, n=1, T10B9 + complement TCD BMT, n=1), developed a mild (<25 vesicles) disseminated rash within 2.5 weeks of vaccination. The rash resolved in all 3 patients within 7 days of onset without treatment. Currently, 43 of 44 patients are alive, disease-free with a median (range) follow-up of 29.1 (6.9-167.1) months post immunization. There have been no cases of primary varicella or a varicella-like rash > 2.5 weeks post vaccination nor any cases of shingles. No patient has required acyclovir, gammaglobulin, or hyperimmune zoster immune globulin since vaccination.
Reactivation of wild-type varicella is known to cause significant morbidity and occasionally mortality following an allogeneic HCT (23, 24). The risk of shingles in younger patients whose VZV immunity was acquired through vaccination rather than wild type disease is currently unknown. In addition, patients immunized in early childhood who undergo HCT later in life may be at an increased risk of varicella due to the known loss of vaccine immunity even in healthy recipients of a single LAVV (25). In a 10 year study by Chaves et al. of 11,356 healthy vaccinated subjects, 1080 developed breakthrough varicella. The annual rate of breakthrough disease increased significantly with time following immunization, with 1.6 compared to 58.2 cases per 1000 person-years occurring within 1 year and 9 years post LAVV, respectively. The risk of break-though disease was highest in children 8-12 years of age who were five or more years following immunization (26).
Although both the 2005 EBMT (12) and 2009 CIBMTR (13) guidelines permit the use of the live varicella vaccine in select patient groups starting at 24 months post HCT, only two published studies have assessed safety and/or response in allogeneic HCT recipients. Sauerbrei and colleagues (14) vaccinated 15 pediatric patients, 8 of whom received an allogeneic HCT. Patients were vaccinated at a median of 18 (range:12-23) months post HCT. Immunologic criteria for vaccination included a circulating lymphocyte count of >1000 cells/ul, serum IgG >500 mg/dL, and a positive skin test to a recall antigen. Of the four VZV seronegative allogeneic patients immunized, three of 4 seroconverted at 6 weeks post immunization. Kussmaul and colleagues (15) evaluated the safety of the LAVV in 18 autologous and 50 allogeneic HCT recipient, 25 of whom were evaluable for response. Eligibility for vaccination included a circulating CD4 count of ≥ 200 cells/ul, a PHA response at least 50% of the lower limit of normal, a humoral response to the inactivated polio vaccine, and specific T and B cell response to tetanus toxoid. The median time to the first LAVV was 32 months post HCT (range: 16-144 months). There were no serious vaccine related events. Although the study by Kussmaul et al did not stipulate the proportion of responders who received an autologous versus an allogeneic HCT, of the 25 patients clearly evaluable for response, seroconversion occurred in 40%, 8%, and 4% of patients after one, two, or three vaccines, respectively (16).
Our study, although retrospective, represents the largest series analyzing the response of VZV seronegative patients following HCT vaccinated with LAVV. Although an ELISA was used to assess response, the seroconversion rate following the LAVV in our study is not markedly different than the 74% conversion rate observed in healthy children when measured by the highly sensitive fluorescent antibody to membrane antigen (FAMA) (27). The latter assay requires viral propagation in tissue culture, is not commercially available, and requires considerable operator expertise. In view of this several studies ((7-9, 14,16), including ours have used an ELISA based method to measure response to the LAVV .
The risk of shingles following the LAVV has been one of the main concerns surrounding immunization of children against chickenpox particularly those with a history of or ongoing immunodeficiency (27,28) . This risk has been evaluated in children with a history of leukemia (29), pediatric recipients of solid organ transplants (7,8), and HIV infected children on retroviral therapy (9-11). Studies in these populations have not shown an increased risk of VZV . In 1989, Lawrence et al. compared the risk of shingles in children with ALL in remission who were immunized versus those with a history of natural infection (29). Of the 346 immunized children, the incidence of zoster was 0.552 cases/100 person-years. In a subset of 82 matched pairs, there was no significant difference in the incidence of shingles in patients who were vaccinated (1.23 cases per 100 person-years) compared to 3.11 cases in children with a history of varicella, respectively (p=NS). In 2009, Civen and colleagues demonstrated immunized children<10 years had a 4 to 12 times lower risk of developing shingles than children with a history of chickenpox (29).
Due to breakthrough cases of varicella in recipients of a single vaccine, the Advisory Committee on Immunization Practices (ACIP) currently recommends a two dose schedule in healthy children at 12-15 months and 4-6 years, a second dose in children, adolescents, and adults previously given only one vaccine, routine immunization of all healthy VZV seronegative individuals 13 years of age or older, and immunization of HIV-infected children and adults with circulating CD4+ T lymphocyte counts > 200 cells/ul (3). Our study supports the use of the live attenuated varicella vaccine in VZV seronegative patients. The dichotomy of T and B cell responses in some of our patients (ie seroconversion in the absence of concurrent T cell response) suggest that kinetics of recovery of lymphoid populations required for a full response may differ from patient to patients. Larger prospective trials assessing the safety, immunogenicity, protection against chickenpox, and subsequent risk of shingles following the live attenuated varicella vaccine in this population are needed. Ideally, trials should be designed to identify biological markers which might allow earlier re-vaccination of patients with the requisite T and B cell populations and prevent premature vaccination and/or risk in patients unable to respond.
T.N.S. designed the study and wrote the manuscript with the help of J.F.C., N.A.K, S.P, E.B.P, A.S. R.K.
J.F.C., T.N.S, G. H. performed the biostatistics.
T.N.S. M.A.K., A.C, C.C. J.T-C., N. C. and J.R. collected the data.
Supported by CA23766 (T.N.S.) and the National Shingles Foundation (T.N.S)
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.