Critical Appraisal of Immunization Strategies for Prevention of Infection in the Compromised Host

Immunization and Organ Transplantation

With the rapid pace of immunologic research, it is more important than ever for readers to understand rational immunodiagnosis, immunopro-phylaxis, and immunotherapy. This column is intended to help you ensure proper immunologic drug use in your practice.

Targeting Vaccines to Specific Clusters of People

With the rapid pace of immunologic research, it is more important than ever for readers to understand rational immunodiagnosis, immunopro-phylaxis, and immunotherapy. This column is intended to help you ensure proper immunologic drug use in your practice.

Exposure to nicotine adversely affects the dendritic cell system and compromises host response to vaccination

The magnitude of Th1 cells response to vaccination is a critical factor in determining protection from clinical disease. Our previous in vitro studies suggested that exposure to the nicotine component of cigarette smoke skews the differentiation of both human and mouse dendritic cell (DC) precursors into atypical DCs (DCs differentiated ex vivo in the presence of nicotine) lacking parameters essential for the development of Th1-mediated immunity. In this study, we determined the causal relationship between nicotine-induced DC alterations and host response to vaccines. We show that animals exposed to nicotine failed to develop and maintain Ag-specific effector memory Th1 cells and Ab production to protein-based vaccine formulated with Th1 adjuvants. Accordingly, both prophylactic and therapeutic vaccines failed to protect and cure the nicotine-exposed mice from disease. More importantly, we demonstrate the nicotine-induced defects in the biological activities of in vivo DCs as an underlying mechanism. Indeed, i.v. administration of DCs differentiated in the presence of nicotine preferentially promoted the development of Ag-specific IL-4-producing effector cells in the challenged mice. In addition, DC subsets isolated from mice exposed to nicotine produced significantly less cytokines in response to Th1 adjuvants and inadequately supported the development of Ag-specific Th1 cells. Collectively, our studies suggest that nicotine-induced defects in the DC system compromises vaccine efficacy in smokers.

High susceptibility to severe infectious complications at reinduction chemotherapy in patients who relapse after stem cell transplantation

Patients who relapse after stem cell transplantation (SCT) usually appear to be liable to severe infectious complications at reinduction chemotherapy compared to patients at the first induction therapy, though this is not statistically substantiated. The aim of this study was to analyze episodes of infectious complications during reinduction chemotherapy among patients who relapsed after SCT compared with those at the first induction chemotherapy. Between February 1988 and March 2004, 145 children received SCT, and 17 (12 with hematologic malignancies and 5 with solid tumors) were enrolled as eligible subjects for this study. Positive blood cultures (sepsis) were present in six patients exclusively at the reinduction therapy but none at the first induction (P = .009). Three of the six patients progressed to septic shock. Moreover, all patients positive for blood cultures were those with hematologic malignancy (P = .007), and every patient with septic shock had received allogenic transplantation. Our results showed that reinduction chemotherapy needs attention for severe infectious complications, particularly among patients with hematologic malignancies receiving allogenic transplantations. Possible immaturity of the reconstructed systemic immune system and/or insufficient recovery of mucosal protective functions in the patients after SCT are discussed in view of their high susceptibility to severe infectious complications.

Response to booster hepatitis B vaccines in liver-transplanted children primarily vaccinated in infancy

BACKGROUND

A hepatitis B virus (HBV) universal vaccination program for infants was implemented for 24 years in Taiwan. Most of the children who received organ transplantation were primarily vaccinated before transplantation. This study investigated the efficacy of HBV vaccination and booster responses in children after liver transplantation (LT).

METHODS

Totally 31 children were enrolled. They were clinically stable for more than 1 year after LT. Twenty of them kept a titer of antibody to hepatitis B surface antigen (anti-HBs) more than 10 mIU/mL and received no booster, while 11 received one booster because their anti-HBs titers were less than 10 mIU/mL. Cellular immunity was checked by enzyme-linked immunospot assay with interferon-gamma surrogated for T-helper 1 cells and interleukin-5 for T-helper 2 before and after booster vaccine.

RESULTS

One of the non-boosters had de novo HBV infection after LT and recovered to be anti-HBs positive. The first booster restored an adequate titer in 64% (7/11) of those with anti-HBs titer less than 10 mIU/mL after LT. The four patients who failed the first booster responded well to the second dose. After the booster, the mononuclear cells of all 11 had more than one spot-forming cell for interferon-gamma or interleukin-5. Transplanted girls maintained a higher antibody titer than boys.

CONCLUSION

Primary HBV vaccination or the booster dose(s) of HBV vaccine could provide adequate humoral and cellular immunity in children with LT.

Immunizations for children with cancer

Children with malignant diseases are at risk of severe outcomes from vaccine preventable infections. Vaccination of these children presents challenges due to efficacy and safety concerns. There is a paucity of data on several aspects of vaccination in this group of children. Consequently, for the most part, data are extrapolated from healthy populations and combined with experts' opinions. This article reviews the use of vaccines in infants and children with cancer. In this context, an all-encompassing review is not the goal. Key principles are reviewed to provide a framework to guide the use of vaccines in children with malignant diseases.

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.

Vaccinations for adult solid-organ transplant recipients: current recommendations and protocols

Recipients of solid-organ transplantation are at risk of severe infections due to their life-long immunosuppression. Despite emerging evidence that vaccinations are safe and effective among immunosuppressed patients, most vaccines are still underutilized in these patients. The efficacy, safety, and protocols of several vaccines in this patient population are poorly understood. Timing of vaccination appears to be critical because response to vaccinations is decreased in patients with end-stage organ disease and in the first 6 months after transplantation. For these reasons, the primary immunizations should be given before transplantation, as early as possible during the course of disease. Vaccination strategy should include vaccination of household contacts and health care workers at transplant centers unless contraindicated. No conclusive data are available on the use of immunoadjuvants and screening for protective titers. Most vaccines appear to be safe in solid-organ transplantation recipients, but live vaccines should be avoided until further studies are available. The risk of rejection appears minimal. Recommended vaccines include pneumovax, hepatitis A and B, influenza, and tetanus-diphtheria. We outline specific protocols and recommendations in this particular patient population. Specific contraindications exist for other vaccines, such as yellow fever, oral polio vaccine, bacillus Calmette-Guerin, and vaccinia. We conclude that solid-organ recipients will benefit from consistent immunization practices. Further studies are recommended to improve established protocols in this patient population.

Effects of multidose combination chemotherapy on the humoral immune system

Patients receiving multidose combination chemotherapy are at risk for severe, life-threatening infections, caused by among others encapsulated bacteria like Streptococcus pneumoniae. The splenic marginal zone is essential in the initiation of immune responses to S. pneumoniae. We analyzed effects of multidose combination chemotherapy on B-cell subpopulations. Immune response capacity was evaluated by using Pneumovax (PPS) or Tetavax (TT) as antigenic challenge. Three days after finishing therapy, all B-cell subpopulations in bone marrow and spleen were severely reduced, including the mature marginal zone B-cell population. When analyzing the anti-PPS immune response capacity at 3 days after finishing therapy, we found that the IgM antibody levels did not differ significantly from control immunized rats. The IgG antibody levels were significantly lower compared to control immunized rats but still significantly higher compared to unimmunized rats. The depletion of marginal zone B cells by multidose combination chemotherapy most likely contributes to the prolonged period that patients are at risk for developing severe infections after chemotherapy, despite the capacity to generate sufficient antibody levels. It is conceivable that the local (temporary) loss of immunological memory, together with the supposed inability to generate a humoral response in a short time frame, plays an important role in this vulnerability.

[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.

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.

Association between cancer chemotherapy and canine distemper virus, canine parvovirus, and rabies virus antibody titers in tumor-bearing dogs

OBJECTIVE

To determine the association between cancer chemotherapy and serum canine distemper virus (CDV), canine parvovirus (CPV), and rabies virus antibody titers in tumor-bearing dogs.

DESIGN

Prospective study.

ANIMALS

21 client-owned dogs with various malignancies and 16 client-owned dogs with lymphoma.

PROCEDURE

In study A, serum antibody titers were measured by use of hemagglutination inhibition (CPV titers) or serum neutralization (CDV titers) before and at least 1 month after initiation of chemotherapy. Baseline values were compared with values obtained from a control population of 122 healthy dogs seen for routine revaccination. Titers were considered protective at > or = 1:96 for CDV and > or = 1:80 for CPV. In study B, serum IgG titers were measured by use of immunofluorescent assay (CDV and CPV titers) and rapid fluorescent focus inhibition test (RFFIT, rabies titers) at baseline and again at weeks 5, 8, and 24 of a standard chemotherapy protocol for treatment of lymphoma. An IgG titer of > or = 1:50 was considered protective for CPV and CDV. An RFFIT titer of > or = 0.5 U/ml was considered protective for rabies virus.

RESULTS

Significant changes were not detected in CDV, CPV, and rabies virus titers following chemotherapy in tumor-bearing dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that established immunity to CDV, CPV, and rabies virus from previous vaccination is not significantly compromised by standard chemotherapy used to treat tumor-bearing dogs.

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.

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.

Prevention of infection in the immunocompromised host

The Association for Professionals in Infection Control and Epidemiology, Inc, is accredited as a provider of continuing education in nursing by the American Nurses Credentialing Center's Commission on Accreditation. This learner-paced study package is designated for 1.1 contact hours. APIC's California nursing provider number is CEP 7146. This continuing medical laboratory education activity is recognized by the American Society of Clinical Pathologists as meeting the criteria for 1 CMLE credit hour. ASCP CMLE credit hours are acceptable to meet the continuing education requirements for the ASCP Board of Registry Continuing Competence Recognition Program. (See the instructions and examination at the end of the article.)Infectious diseases represent a major cause of morbidity and mortality in immunocompromised patients. Infectious complications are often predictable and may be preventable. This article is an overview of practical considerations in the care of immunocompromised patients. Recognizing the compromised host, identifying and correcting risk factors in advance, and reducing sources of infection all play a role in prevention. Topics were chosen to include the areas of care that differ from the immune competent patient, such as diet, pet therapy, handwashing, immunizations, augmentation of host resistance, prevention of pneumonia, and antibiotic prophylaxis. National practice guidelines are cited when possible; evidence-based literature review and experience are applied to situations lacking consensus statements. Treatment decisions are made in areas for which information is often incomplete. A systematic approach to care of the immunocompromised host, tailored to the individual patient's needs, should reduce the risk of infection.

Immune recovery in children with malignancy after cessation of chemotherapy

PURPOSE

To study longitudinally the extent and recovery of cellular and humoral immune alterations in children with cancer after completion of their therapy.

PATIENTS AND METHODS

Using standard immune assays, cellular and humoral immunity was measured in 43 infants and children with cancer at completion of therapy and every 3 months thereafter for 1 year. There were 17 patients with acute lymphoblastic leukemia, 9 with Hodgkin disease, and 17 with solid nonhematopoietic tumors. All children had received standard childhood immunizations before diagnosis of cancer. Immune assays performed included circulating lymphocyte subpopulations, in vitro antigen-induced responses, and total concentrations of serum immunoglobulin G (IgG), IgM, IgA, and IgG subclasses, and specific antibodies against diphtheria, tetanus, pertussis, and poliovirus types I, II, and III.

RESULTS

At completion of therapy, the majority of patients had low circulating lymphocyte subpopulations and antigen-induced responses. Serum antibody concentrations were low in up to 89% of patients regardless of the underlying malignancy. Although improvement occurred during the year of follow-up, 35 of 43 (81%) patients continued to exhibit one or more immune abnormalities 9 to 12 months after cessation of chemotherapy. Younger patients had more persistent alterations. Other risk factors studied (including gender, duration of therapy, and underlying malignancy) did not correlate with the severity of the immune defects. With the exception of poliovirus antibodies, specific antibody titers against common childhood vaccine antigens were deficient at completion of therapy and 9 to 12 months later in a substantial proportion of patients.

CONCLUSION

Children with malignancy have persistent specific and nonspecific immune alterations 9 to 12 months after cessation of chemotherapy. The clinical implications of these in vitro observations are unclear and require further evaluation.

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.

Reimmunization after allogeneic bone marrow transplantation

Allogeneic bone marrow transplant patients are severely immunocompromised during the immediate posttransplant period, and the risk for common and opportunistic infections may persist for many months. The role of reimmunization for these patients, however, remains unsettled. We briefly review current concepts regarding the recapitulation of immunity from the totipotential hematopoietic stem cells in the donor marrow. The fact that various components of the new immune system mature at different rates can have clinical consequences with regard to specific infections. Most previously immunized patients become antibody seronegative within a few months after allogeneic marrow transplantation. Adoptive transfer of specific antibody-producing cells from the donor to the recipient has been demonstrated in small clinical trials, and is augmented when both donor and recipient are vaccinated. Passive transfer of immunity is more easily achieved to recall antigens than to neoantigens. Primary immunization requires prolonged antigenic stimulation and mature T-cell function or help from natural killer cells. Most healthy patients generate adequate antibody titers to vaccinations that are given 12 months after transplantation, but the presence of chronic graft-versus-host disease can diminish the response. Currently available vaccines have been evaluated in marrow transplant patients. Protein antigens such as tetanus and diphtheria toxoids are more immunogenic than polysaccharide antigens such as pneumococcal vaccine. The new polysaccharide-protein conjugate vaccines, such as the Hemophilus influenzae type b vaccine, also appear more immunogenic. Inactivated poliovirus vaccine has been used successfully. Relatively few data are available about hepatitis B or influenza vaccines. The literature supports the use of standard vaccines in allogeneic bone marrow transplant patients. However, more data on the optimal methods and timing of immunization are needed. We present guidelines for a reimmunization schedule.