Polysaccharide conjugate vaccine responses in bone marrow transplant patients

Vaccination of stem cell transplant recipients: recommendations of the Infectious Diseases Working Party of the EBMT

Over the last 25 years, the numbers of hematopoietic stem cell transplant (SCT) patients have increased rapidly. Infections have been major obstacles for successful transplantation. Thus, infection prevention is very important in transplant recipients. As the results of transplantation have improved, the number of long-term survivors has increased. Vaccination is a potentially important strategy for reducing the risk for vaccine-preventable infections after SCT. The EBMT produced recommendations for vaccination of SCT recipients published in Bone Marrow Transplantation in 1995. This paper updates the previous recommendations based on current knowledge.

Rationale for the development of immunotherapy regimens against enterococcal infections

Enterococci are the third most common pathogen isolated in bloodstream infections. Increasing resistance against multiple antimicrobial agents has left few treatment options for enterococcal infections, and alternative therapeutic approaches are needed. Although a variety of virulence factors have been described for Enterococcus faecalis, only aggregation substance (AS) and a teichoic acid-like capsular polysaccharide have been evaluated for their potential for vaccine development. Antibodies raised against purified capsular polysaccharide are highly opsonic and protect mice against bacteremia after active and passive immunization. Since E. faecalis expresses only a limited number of capsular serotypes, this antigen may be an attractive candidate for development of a conjugate vaccine.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and pneumonia with consolidation on x-ray in children under two years of age

BACKGROUND

Pneumonia, most commonly caused by Streptococcus pneumoniae (Pnc), is a major cause of morbidity and mortality among young children especially in developing countries. Recently, the prevalence of antibiotic-resistant Pnc has increased worldwide such that the effectiveness of preventive strategies, like the new pneumococcal conjugate vaccines (PCV) on rates of invasive pneumococcal disease (IPD) and pneumonia, needs to be evaluated.

OBJECTIVES

To determine the efficacy of PCV in reducing the incidence of IPD due to vaccine serotypes (VT) and x-ray confirmed pneumonia with consolidation of unspecified etiology in children who received PCV before 12 months of age.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2004), MEDLINE (1990 to March 2004) and EMBASE (1990 to December 2003). Reference list of articles, and books of abstracts of relevant symposia, were hand searched. Researchers in the field were also contacted.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing PCV with placebo, or another vaccine, among children below two years with IPD and clinical/radiographic pneumonia as outcomes.

DATA COLLECTION AND ANALYSIS

Two reviewers independently identified eligible studies, assessed trial quality, and extracted data. Differences were resolved by discussion. The inverse variance method was used to pool effect sizes.

MAIN RESULTS

We identified four trials assessing the efficacy of PCV in reducing the incidence of IPD, two on x-ray confirmed pneumonia as outcome, and one on clinical pneumonia, with or without x-ray confirmation. Results from pooling HIV-1 negative children from the South African study with the other studies were as follows: the pooled vaccine efficacy (VE) for vaccine-type IPD was 88% (95% confidence interval (CI) 73% to 94%; fixed effect and random effects models), the effect measure was statistically significant (p <0.00001) and there was no heterogeneity (p = 0.77I2 0%); the pooled VE for all-serotype IPD was 66% (95% CI 46% to 79%; fixed effect model), the effect measure was statistically significant (p <0.00001) and there was no statistical heterogeneity (p = 0.09, I2 51%); the pooled VE for x-ray confirmed pneumonia was 22% (95% CI 11% to 31%; both fixed effect and random effects models) and there was no statistical heterogeneity (p = 0.80, I2 0%). Analyses that included all the children in the South African study (HIV-1 negative and HIV-1 positive children) and pooled with data from the other studies gave very similar results.

REVIEWERS' CONCLUSIONS

PCV is effective in reducing the incidence of IPD from all serotypes but exerts a greater effect in reducing VT IPD. Although PCV is also effective in reducing the incidence of x-ray confirmed pneumonia, there are still uncertainties about the definition of this outcome. Additional randomised controlled trials are currently in progress.

Efficacy of donor vaccination before hematopoietic cell transplantation and recipient vaccination both before and early after transplantation

Allogeneic hematopoietic cell transplantation is followed by humoral immunodeficiency. We evaluated whether antibody levels can be improved by recipient vaccination on day -1 and 50 and whether the levels can be further improved by donor vaccination on day -20. A total of 85 patients were randomized or assigned to one of the following strategies of immunization with Streptococcus pneumoniae polysaccharides, Haemophilus influenzae polysaccharide-protein conjugate, tetanus toxoid (protein recall antigen) and hepatitis B surface antigen (protein neo-antigen): (1) donor on day -20, recipient on days -1, +50 and +365 (D(-20)R(-1,50,365)); (2) donor nil, recipient on days -1, +50 and +365 (D(N)R(-1,50,365)); or (3) donor nil, recipient on day +365 (D(N)R(365)). For H. influenzae and tetanus, IgG levels after grafting were the highest in the D(-20)R(-1,50,365) patients, intermediate in the D(N)R(-1,50,365) patients and the lowest in the D(N)R(365) patients. For S. pneumoniae and hepatitis B, antibody levels appeared to be similar in all three patient groups. The results suggest that for polysaccharide-protein conjugate antigens or protein recall antigens, recipient immunization on days -1 and 50 improves antibody levels and that donor vaccination on day -20 further improves the levels. In contrast, neither recipient immunization on days -1 and 50 nor donor immunization on day -20 appears to be efficacious for polysaccharide antigens and poorly immunogenic protein neo-antigens.

An idiopathic skin eruption resembling a butterfly rash in a septic patient with disseminated intravascular coagulation following bone marrow transplantation

A 31-year-old man who underwent chemotherapy and bone marrow transplantation to treat acute myeloblastic leukemia was admitted to our department complaining of high fever and hypotension. His physical examination revealed warm shock state, eruptions resembling that seen in systemic lupus erythematosus on his face and cyanosis in his fingers. We diagnosed septic shock and idiopathic skin eruption on his face. Following treatment with blood transfusion, anticoagulant, antibiotics, respirator and continuous arteriovenous hemofiltration and dialysis, the patient's condition gradually improved. The eruptions on his face first observed at admission progressed with a worsening of his disseminated intravascular coagulation (DIC), and subsided with an improvement in his DIC. A biopsy of the eruption was taken and pathological findings of the eruption revealed multiple micro-fibrin depositions of the dermis. The skin necrosis in purpura fulminans often begins in the distal extremities. But our patient developed this uncommon skin eruption on his face. Patients with an idiopathic skin eruption resembling a butterfly rash in a septic patient should be considered to complicate DIC as in the present case.

Recommendations for immunizations in stem cell transplantation

Investigations over the past decade have documented that there is a decline in immunity to vaccine preventable diseases in many SCT recipients. The majority of immunization studies conducted in SCT recipients to date support the use of multi-dose regimens for most protein and polysaccharide-conjugate vaccine antigens. The consensus immunization schedule recommended by ACIP/IDSA/ASBMT provides guidance for centers to utilize available vaccines in their SCT populations. With the exception of pneumococcal disease, a schedule beginning at 12 months after SCT is reasonable given the low incidence of disease in HSCT recipients for most of the recommended vaccines and improved immune reconstitution in most recipients by one year post transplant. SCT recipients respond poorly to unconjugated pneumococcal polysaccharide vaccine and the development of polysaccharide-protein conjugate vaccines against S. pneumoniae holds promise to impact potentially on clinical disease in this population. In addition, the strategy of donor immunization may also be effective in eliciting early protective immune responses to vaccine antigens. Future challenges will be the development of safe and effective vaccines against the viral pathogens responsible for considerable morbidity and mortality after SCT.

Factors affecting antibody levels after allogeneic hematopoietic cell transplantation

To obtain insight into the mechanism(s) of posttransplantation humoral immunodeficiency, we evaluated factors affecting serum antibody levels against polio, tetanus, Haemophilus influenzae, and Streptococcus pneumoniae in 87 patients. Patients with hematologic malignancies were randomized to receive marrow versus blood stem cells, which contain approximately 10 times more lymphocytes than marrow. Blood stem cell recipients did not have higher antibody levels than marrow recipients. Recipient pretransplantation antibody levels were correlated with the posttransplantation levels, especially in the first 6 months after transplantation when the correlation coefficients typically exceeded 0.6. Donor pretransplantation antibody levels had less of a correlation with posttransplantation levels in the recipient. Patient or donor age, total body irradiation, and graft-versus-host disease or its treatment appeared to have no effect. In conclusion, antibody levels in the first year after transplantation are affected primarily by pretransplantation antibody levels in the recipient and, to a lesser degree, in the donor. These findings suggest that immunization of the recipient and the donor before transplantation may be more effective in improving antibody immunity after transplantation than manipulating graft-versus-host disease, changing conditioning, or increasing the number of lymphocytes in the graft.

Donor immunization with pneumococcal conjugate vaccine and early protective antibody responses following allogeneic hematopoietic cell transplantation

Patients undergoing hematopoietic cell transplantation (HCT) are at increased risk for infections with Streptococcus pneumoniae and have long-lasting, impaired antibody responses to pneumococcal polysaccharide vaccines. We examined whether donor immunization with a heptavalent pneumococcal conjugate vaccine (PCV7) would elicit protective antibody responses to additional doses of vaccine administered early after transplantation. Ninety-six patients scheduled to receive an allogeneic hematopoietic cell transplant were randomized with their donors to receive either a dose of PCV7 vaccine or no vaccine before transplantation. All patients received PCV7 at 3 months, 6 months, and 12 months following transplantation, and serotype-specific antibody concentrations were determined after each dose. Following HCT, geometric mean antibody concentrations of patients in the immunized donor group were significantly higher for 5 of the 7 vaccine serotypes after one dose (P <.05) and for 4 of the 7 serotypes after 2 doses of vaccine (P <.03). Sixty-seven percent of patients in the immunized donor group had presumed protective IgG concentrations more than or equal to 0.50 microg/mL to all 7 serotypes following the first dose of vaccine compared to 36% in the unimmunized donor group (P =.05). After the third dose of vaccine, both groups had more than 60% of patients with concentrations at least 0.50 microg/mL to all vaccine serotypes. Donor immunization enhances early antibody responses of patients undergoing HCT to pneumococcal conjugate vaccine. A 3-dose schedule of PCV7 vaccine at 3, 6, and 12 months is immunogenic in these patients regardless of donor immunization.

[Post-transplantation vaccination of bone-marrow transplant recipients]

BACKGROUND

Patients subject to bone marrow transplantation (BMT) and other blood stem cell transplantations are severely immunocompromised after transplantation. Some studies have suggested that post-transplantation loss of acquired immunity may play a role. The objective of this study was to determine the susceptibility to vaccine-preventable diseases in people subject to BMT and the serologic response after vaccination.

PATIENTS AND METHOD

Study population was people subject to transplantation at least 6 months before initiating vaccination and without immunosuppressive treatment at that time. A prevaccination serologic analysis was carried out, and the hepatitis B, the adult tetanus-diphtheria (Td), the IPV, the influenza and the pneumococccal vaccines were administered in accordance with standard guidelines Depending on the immune status of the patient according to the serologic analysis, the MMR vaccine was administered no sooner than 18 months after transplantation. After vaccination, a serologic analysis was carried out to determine the response.

RESULTS

The mean time SD between transplant and the initiation of vaccination was 3.2 2.9 years. Of the 122 recipients of BMT (average age 35.8 13 years; 54.2% male), 51.7% received an allogenic and 48.3% an autologous transplant. Before vaccination, the susceptibility was 48.2% for tetanus, 66.7% for diphtheria, 74.1% for pertussis, 85.9% for hepatitis B, 13.4% for measles, 36.7% for rubella and 9.2% for mumps. The rates of seroconversion with protective titers after vaccination for tetanus, diphtheria and hepatitis B were 94%, 67% and 75% respectively. The response to the MMR vaccine was greater than 70%, with a second dose of the vaccine being needed in 26% of patients.

CONCLUSIONS

Susceptibility to vaccine-preventable diseases in transplanted patients is high. The acceptable response to vaccination justifies the development of specific programs. Given the special characteristics of this group of patients, vaccination programs must be simple and flexible.

Structure-function relationships for human antibodies to pneumococcal capsular polysaccharide from transgenic mice with human immunoglobulin Loci

To investigate the influence of antibody structure and specificity on antibody efficacy against Streptococcus pneumoniae, human monospecific antibodies (MAbs) to serotype 3 pneumococcal capsular polysaccharide (PPS-3) were generated from transgenic mice reconstituted with human immunoglobulin loci (XenoMouse mice) vaccinated with a PPS-3-tetanus toxoid conjugate and their molecular genetic structures, epitope specificities, and protective efficacies in normal and complement-deficient mice were determined. Nucleic acid sequence analysis of three MAbs (A7, 1A2, and 7C5) revealed that they use two different V(H)3 genes (A7 and 1A2 both use V3-15) and three different V(kappa) gene segments. The MAbs were found to have similar affinities for PPS-3 but different epitope specificities and CDR3 regions. Both A7 and 7C5 had a lysine at the V(H)-D junction, whereas 1A2 had a threonine. Challenge experiments with serotype 3 S. pneumoniae in BALB/c mice revealed that both 10- and 1- micro g doses of A7 and 7C5 were protective, while only a 10- micro g dose of 1A2 was protective. Both A7 and 7C5 were also protective in mice lacking either an intact alternative (FB(-/-)) or classical (C4(-/-)) complement pathway, but 1A2 was not protective in either strain. Our data suggest that PPS-3 consists of epitopes that can elicit both highly protective and less protective antibodies and that the superior efficacies of certain antibodies may be a function of their structures and/or specificities. Further investigation of relationships between structure, specificity, and efficacy for defined MAbs to PPS may identify antibody features that might be useful surrogates for antibody (and vaccine) efficacy.

Use of an inactivated varicella vaccine in recipients of hematopoietic-cell transplants

BACKGROUND

The reactivation of varicella-zoster virus from latency causes zoster and is common among recipients of hematopoietic-cell transplants.

METHODS

We randomly assigned patients who were scheduled to undergo autologous hematopoietic-cell transplantation for non-Hodgkin's or Hodgkin's lymphoma to receive varicella vaccine or no vaccine. Heat-inactivated, live attenuated varicella vaccine was given within 30 days before transplantation and 30, 60, and 90 days after transplantation. The patients were monitored for zoster and for immunity against varicella-zoster virus for 12 months.

RESULTS

Of the 119 patients enrolled, 111 received a transplant. Zoster developed in 7 of 53 vaccinated patients (13 percent) and in 19 of 58 unvaccinated patients (33 percent) (P=0.01). After two patients in whom zoster developed before transplantation were excluded, the respective rates were 13 percent and 30 percent (P=0.02). In vitro CD4 T-cell proliferation in response to varicella-zoster virus (expressed as the mean stimulation index) was greater in patients who received the vaccine than in those who did not at 90 days, after three doses (P=0.04); at 120 days, after all four doses (P<0.001); at 6 months (P=0.004); and at 12 months (P=0.02). The risk of zoster was reduced for each unit increase in the stimulation index above 1.6; a stimulation index above 5.0 correlated with greater than 93 percent protection. Induration, erythema, or local pain at the injection site was observed in association with 10 percent of the doses.

CONCLUSIONS

Inactivated varicella vaccine given before hematopoietic-cell transplantation and during the first 90 days thereafter reduces the risk of zoster. The protection correlates with reconstitution of CD4 T-cell immunity against varicella-zoster virus.

Immunity of patients surviving 20 to 30 years after allogeneic or syngeneic bone marrow transplantation

The duration of immunodeficiency following marrow transplantation is not known. Questionnaires were used to study the infection rates in 72 patients surviving 20 to 30 years after marrow grafting. Furthermore, in 33 of the 72 patients and in 16 donors (siblings who originally donated the marrow) leukocyte subsets were assessed by flow cytometry. T-cell receptor excision circles (TRECs), markers of T cells generated de novo, were quantitated by real-time polymerase chain reaction. Immunoglobulin G(2) (IgG(2)) and antigen-specific IgG levels were determined by enzyme-linked immunosorbent assay. Infections diagnosed more than [corrected] 15 years after transplantation occurred rarely. The average rate was 0.07 infections per patient-year (one infection every 14 years), excluding respiratory tract infections, gastroenteritis, lip sores, and hepatitis C. The counts of circulating monocytes, natural killer cells, B cells, CD4 T cells, and CD8 T cells in the patients were not lower than in the donors. The counts of TREC(+) CD4 T cells in transplant recipients younger than age 18 years (at the time of transplantation) were not different from the counts in their donors. In contrast, the counts of TREC(+) CD4 T cells were lower in transplant recipients age 18 years or older, even in those with no history of clinical extensive chronic graft-versus-host disease, compared with their donors. The levels of total IgG(2) and specific IgG against Haemophilus influenzae and Streptococcus pneumoniae were similar in patients and donors. Overall, the immunity of patients surviving 20 to 30 years after transplantation is normal or near normal. Patients who received transplants in adulthood have a clinically insignificant deficiency of de novo-generated CD4 T cells, suggesting that in these patients the posttransplantation thymic insufficiency may not be fully reversible.

Effects of alum adjuvant or a booster dose on immunogenicity during clinical trials of group B streptococcal type III conjugate vaccines

Phase 1 and 2 clinical trials of group B streptococcal (GBS) capsular polysaccharide (CPS)-protein conjugate vaccines in healthy adults have demonstrated their safety and improved immunogenicity compared with uncoupled CPSs. Two recent trials sought to determine (i) whether adsorption of conjugate vaccine to aluminum hydroxide would improve immunogenicity and (ii) whether the CPS-specific immunoglobulin G (IgG) response could be boosted by administration of a second dose. Adsorption of GBS type III CPS-tetanus toxoid (III-TT) conjugate vaccine to alum did not improve the immune response to a 12.5-microg dose in healthy adult recipients. Four weeks after vaccination, the geometric mean antibody concentrations (GMCs) for the 15 recipients of III-TT with or without alum were 3.3 and 3.6 microg/ml, respectively. In the second trial, 36 healthy adults vaccinated previously with GBS III-TT conjugate were given a second 12.5-microg dose 21 months later. At 4 weeks after the second dose, the GMCs of type III CPS-specific IgG were similar to those measured 4 weeks after the primary vaccination, suggesting a lack of a booster response. However, 8 (22%) of the 36 participants who had undetectable III CPS-specific IgG (<0.05 microg/ml) before the first dose of III-TT conjugate exhibited a booster response to the second dose, with a fourfold-greater GMC of type III CPS-specific IgG than after the initial immunization. These results suggest that prior natural exposure to type III GBS or a related antigen may be responsible for the brisk IgG response to CPS noted in most adults after vaccination. However, a second dose of GBS III-TT conjugate vaccine may be required for adults whose initial CPS-specific IgG concentrations are very low and would also restore the initial peak-specific III CPS-IgG in responders to previous vaccination.

The prevention of pneumococcal disease by vaccines: promises and challenges

This article reviews the epidemiology of pneumococcal disease and the current data on pneumococcal vaccine efficacy, discusses promising new data regarding development of new protein-conjugate pneumococcal vaccines, and addresses controversies surrounding the widespread population use of these vaccines. Armed with these data, physicians, nurses, third party payers, and health care systems should develop systems and eliminate unintentional barriers so as to achieve widespread use of these life-saving vaccines. As history has demonstrated to us, control of pneumococcal disease is highly unlikely to occur from heavy investments in newer and ever more expensive antibiotics, as opposed to better methods of preventing disease through the rational and widespread population use of vaccines.

Vaccines for transplant recipients

Immune dysregulation and immunosuppression regimens impact on the ability of transplant recipients to respond to immunizations. The distinct challenges of immunizations to benefit stem cell transplant recipients and solid organ transplant recipients are discussed separately. Recommended vaccines for stem cell transplant recipients and solid organ transplant candidates are suggested. New approaches to consider to enhance immune responses of transplant recipients are discussed.

Opsonophagocytic activity against Streptococcus pneumoniae type 19F in allogeneic BMT recipients before and after vaccination with pneumococcal polysaccharide vaccine

Opsonophagocytic activity (OPA) of pneumococcal polysaccharide (Pnc PS) antibodies in vitro, a measure of antibody functional activity, usually correlates with specific IgG antibody concentrations measured by an EIA method. In order to investigate the functional activity of specific Pnc PS antibodies, we determined IgG antibodies to Pnc PS type 19F by an EIA method and OPA against Pnc type 19F by a killing assay in a randomized study, where 23 adult allogeneic BMT recipients were vaccinated with Pnc PS vaccine at 8 months (early group) and 21 recipients at 20 months (late group) after transplantation. Serum samples drawn before BMT, before vaccination, and at 1 and 16 months after vaccination were available from 27, 35, 34 and 30 patients, respectively. The geometric mean anti-Pnc 19F concentrations were 4.3, 1.3, 1.6 and 1.3 microg/ml in the early group and 3.8, 0.9, 0.6 and 0.6 microg/ml in the late group before transplantation, before vaccination, and at 1 and 16 months after vaccination, respectively. OPA (titre > or = 8) was found in 10/27, 5/35, 5/34 and 6/30 patients before BMT, before vaccination, and at 1 and 16 months after vaccination, respectively. The specific IgG antibody concentration and OPA correlated with each other before BMT, and in the early group patients before and at 1 month after vaccination. The results demonstrate that after Pnc PS vaccination allogeneic BMT recipients have antibodies with low functional activity to a Pnc PS antigen associated with low specific IgG responses. There is a need to study new Pnc conjugate vaccines in multi-dose schedules for their capacity to elicit higher specific antibody concentrations with high OPA in BMT recipients.

Tetravalent meningococcal polysaccharide vaccine is immunogenic in adult allogeneic BMT recipients

Forty-four adult BMT recipients transplanted from an HLA-identical sibling donor were randomized to receive meningococcal polysaccharide (Men PS) vaccine either 8 (early group; 22 patients) or 20 (late group; 22 patients) months after BMT. The geometric mean concentrations (GMC) of antibodies to serogroup A Neisseria meningitidis (Men A) and serogroup C Neisseria meningitidis (Men C), determined by an EIA method, decreased during the first 6 months after BMT but remained at a stable level thereafter. Before vaccination the GMCs of anti-Men A were 1.53 microg/ml and 1.61 microg/ml, but 1 month after vaccination they were significantly higher, 3.46 microg/ml and 6.39 microg/ml, in the early and late groups. The GMCs of anti-Men C increased from 0.37 microg/ml and 0.44 microg/ml before vaccination to 3.31 microg/ml and 4.62 microg/ml at 1 month after vaccination in the early and late groups, respectively. By 6 months after vaccination the GMCs of Men antibodies had decreased to levels of about 50% of those measured at 1 month after vaccination. Two-fold responses to Men A PS were seen in 52% and 74% and to Men C PS in 76% and 89% of the BMT recipients in the early and late groups, respectively. Chronic GVHD had no influence on the vaccination response. In the present study, Men PS vaccine induced good and equal antibody responses to Men A and Men C PSs in allogeneic BMT recipients regardless of timing after BMT. Vaccination against Neisseria meningitidis should be considered, especially in the event of travelling or military service > or = 8 months after BMT.

Preventing opportunistic infections after hematopoietic stem cell transplantation: the Centers for Disease Control and Prevention, Infectious Diseases Society of America, and American Society for Blood and Marrow Transplantation Practice Guidelines and beyond

This review presents evidence-based guidelines for the prevention of infection after blood and marrow transplantation. Recommendations apply to all myeloablative transplants regardless of recipient (adult or child), type (allogeneic or autologous) or source (peripheral blood, marrow or cord blood) of transplant. In Section I, Dr. Dykewicz describes the methods used to rate the strength and quality of published evidence supporting these recommendations and details the two dozen scholarly societies and federal agencies involved in the genesis and review of the guidelines. In Section II, Dr. Longworth presents recommendations for hospital infection control. Hand hygiene, room ventilation, health care worker and visitor policies are detailed along with guidelines for control of specific nosocomial and community-acquired pathogens. In Section III, Dr. Boeckh details effective practices to prevent viral diseases. Leukocyte-depleted blood is recommended for cytomegalovirus (CMV) seronegative allografts, while ganciclovir given as prophylaxis or preemptive therapy based on pp65 antigenemia or DNA assays is advised for individuals at risk for CMV. Guidelines for preventing varicella-zoster virus (VZV), herpes simplex virus (HSV) and community respiratory virus infections are also presented. In Section IV, Drs. Baden and Rubin review means to prevent invasive fungal infections. Hospital design and policy can reduce exposure to air contaminated with fungal spores and fluconazole prophylaxis at 400 mg/day reduces invasive yeast infection. In Section V, Dr. Sepkowitz details effective clinical practices to reduce or prevent bacterial or protozoal disease after transplantation. In Section VI, Dr. Sullivan reviews vaccine-preventable infections and guidelines for active and passive immunizations for stem cell transplant recipients, family members and health care workers.

Clinical and immunological risk factors associated with Haemophilus influenzae type b conjugate vaccine failure in childhood

Haemophilus influenzae type b (Hib) conjugate vaccines have proved extremely efficacious in healthy children. True Hib vaccine failures are rare. Hib conjugate vaccines were introduced for routine immunization in the United Kingdom and the Republic of Ireland in 1992. Coincident with this, active prospective and national surveillance via pediatricians, microbiologists, and public health physicians was commenced to assess the clinical and immunological factors associated with vaccine failure. During the 6 years of the study, 115 children with true vaccine failure were reported. Of the children who were vaccinated before 12 months of age, a clinical risk factor was detected in 20%, an immunological deficiency was detected in 30%, and one or both were detected in 44%. Children who were vaccinated after 12 months of age were more likely to have one or both factors (67%). Thirty percent (33 of 105) of children with true vaccine failure had a low Hib antibody response (concentration, <1.0 microg/mL) after disease, but the majority then responded to a further dose of Hib vaccine. Children who develop Hib disease despite vaccination deserve further clinical and immunological evaluation.

Immunization with Haemophilus influenzae type b conjugate vaccine in children given bone marrow transplantation: comparison with healthy age-matched controls

Forty-seven patients (age range, 7 months-18 years) with malignant (38 cases) and nonmalignant (9 cases) disorders given an allogeneic or an autologous bone marrow transplantation (BMT) were immunized with Haemophilus influenzae type b (Hib) polysaccharide-diphtheria toxoid conjugate vaccine administered in a single dose at different time points after transplantation. Results were compared with those of 13 healthy children matched for age and sex who received the same immunization schedule. Serum and saliva samples for measurement of total IgG subclass and specific antibody levels were obtained from patients and healthy controls before and 3 weeks after vaccination. Twenty-five of the 47 patients (53%) had a specific anti-Hib IgG response, while an effective IgA and IgM response was mounted by 23 (49%) and 11 (23%) children, respectively. In the control group, 13 of 13 subjects mounted a specific IgG antibody production (P < 0.005 in comparison to the patients' response rate), while an IgA and IgM response was demonstrated in 12 (92%; P < 0.01 compared to transplanted patients) and 7 (54%; P < 0.05 in comparison to BMT recipients) children, respectively. Lapse of time from BMT to immunization was the most important factor predicting antibody response, as proved by an effective increase in prevaccination specific IgG levels in the majority of patients vaccinated after 2 years from transplant. Our data demonstrate that BMT recipients have a reduced capacity to mount an antibody response to polysaccharide antigens compared to normal controls, even when a protein-conjugated vaccine is employed. Since time after transplant is the major factor influencing the recovery of immune reactivity to polysaccharide antigens, the ontogeny of the B cell repertoire seems to follow a predetermined sequential program of development.

Use of licensed vaccines for active immunization of the immunocompromised host

The latter part of the 20th century has witnessed an unprecedented rise in the number of individuals with impaired immunity. This is primarily attributable to the increased development and use of antineoplastic therapy for malignancies, organ and bone marrow transplantation, and the AIDS epidemic. Individuals with impaired immunity are often at increased risk for infections, and they can experience more severe and complicated courses of infection. The lack of therapy for a variety of viruses and the rise in antimicrobial resistance of many pathogens have focused attention on vaccination to prevent infectious diseases. The efficacy of most licensed vaccines has been established in immunocompetent hosts. However, there is also considerable experience with most vaccines in those with impaired immunity. We reviewed the use of licensed live, inactivated, and polysaccharide vaccines in this group, and several themes emerged: (i) most vaccines are less immunogenic in those with impaired immunity than in normal individuals; (ii) live vaccines are generally contraindicated in this group; and (iii) the efficacy of many commonly used vaccines has not been established in people with impaired immunity. This review suggests that for most vaccines there are little or no efficacy data in those with impaired immunity but their use in this patient group is generally safe.

Antibody response to pneumococcal vaccine in children receiving bone marrow transplantation

Fifty-three pediatric patients given an allogeneic or an autologous bone marrow transplantation (BMT) were immunized with a polyvalent pneumococcal capsular polysaccharide vaccine (Pneumovax II). Vaccine was administered six months or more after BMT and the pneumococcal IgM, total IgG, and IgG subclasses levels were evaluated before and three weeks after immunization. Immunization promoted a significant rise in antibody serum levels (P < 0.000001), and all children vaccinated more than two years after transplantation responded to pneumococcal polysaccharides, whereas only 20-30% and 50% of patients given BMT between six months and one year and one and two years, respectively, mounted an effective antibody production (P < 0.0001). In univariate analysis, lapse of time from BMT to vaccination, chronic graft-versus-host disease occurrence, and female sex influenced the response rate. However, in multivariate analysis, only time between marrow transplant and immunization was a powerful predictor of response. Interestingly, four of 11 patients with IgG2 deficiency before immunization normalized serum levels of this IgG subclass after the pneumococcal antigenic challenge. Our study suggests that time after transplant is the major factor influencing the recovery of immune reactivity to polysaccharide antigens. This seems to confirm the hypothesis that ontogeny of the B-cell repertoire follows a predetermined sequential program in which polysaccharide antigens are some of the last to evoke an antibody response.