Immunotherapy of CMV infections

Recombinant TLR5 agonist CBLB502 promotes NK cell-mediated anti-CMV immunity in mice

Prior work using allogeneic bone marrow transplantation (allo-BMT) models showed that peritransplant administration of flagellin, a toll-like receptor 5 (TLR5) agonist protected murine allo-BMT recipients from CMV infection while limiting graft-vs-host disease (GvHD). However, the mechanism by which flagellin-TLR5 interaction promotes anti-CMV immunity was not defined. Here, we investigated the anti-CMV immunity of NK cells in C57BL/6 (B6) mice treated with a highly purified cGMP grade recombinant flagellin variant CBLB502 (rflagellin) followed by murine CMV (mCMV) infection. A single dose of rflagellin administered to mice between 48 to 72 hours prior to MCMV infection resulted in optimal protection from mCMV lethality. Anti-mCMV immunity in rflagellin-treated mice correlated with a significantly reduced liver viral load and increased numbers of Ly49H+ and Ly49D+ activated cytotoxic NK cells. Additionally, the increased anti-mCMV immunity of NK cells was directly correlated with increased numbers of IFN-γ, granzyme B- and CD107a producing NK cells following mCMV infection. rFlagellin-induced anti-mCMV immunity was TLR5-dependent as rflagellin-treated TLR5 KO mice had ∼10-fold increased liver viral load compared with rflagellin-treated WT B6 mice. However, the increased anti-mCMV immunity of NK cells in rflagellin-treated mice is regulated indirectly as mouse NK cells do not express TLR5. Collectively, these data suggest that rflagellin treatment indirectly leads to activation of NK cells, which may be an important adjunct benefit of administering rflagellin in allo-BMT recipients.

Passive immunization

Passive immunization employs preformed antibodies provided to an individual that can prevent or treat infectious diseases. There are several situations in which passive immunization can be used: for persons with congenital or acquired immunodeficiency, prophylactic administration when there is a likelihood of exposure to a particular infection, or treatment of a disease state already acquired by the individual. Passive immunization is limited by short duration (typically weeks to months), variable response, and adverse reactions. This article focuses on specific immunoglobulins for preventing or treating infectious diseases, as these are the most likely scenarios one might encounter in primary care practice.

Antibody-based therapies as anti-infective agents

Antibody-based therapies are effective against a wide variety of pathogens. Historically, antibody-based therapies were largely abandoned with the advent of antimicrobial chemotherapy, due to the toxicity associated with the administration of heterologous immune sera. As a class, antibody-based therapies have significant advantages and disadvantages relative to conventional antimicrobial chemotherapy. Advantages include versatility, specificity, and antimicrobial activities not available in antibiotic drugs, such as toxin and viral neutralisation, opsonisation, complement activation and the enhancement of host immune function. Disadvantages include expense, the necessity for early and accurate diagnosis prior to use, and the complex logistics necessary for therapeutic use. Advances in antibody technology have minimised some of the disadvantages associated with antibody therapy. In recent years, the therapy of infectious diseases has been complicated by the emergence of new pathogens, the spread of antibiotic-resistant strains and the relative inefficacy of antimicrobial chemotherapy in immunocompromised hosts. This has led to renewed interest in the utilisation of antibody-based therapies as anti-infectives. Many opportunities for developing antibody-based drugs now exist in areas where the available antimicrobial therapies are inadequate.

Herpesviral Fcgamma receptors: culprits attenuating antiviral IgG?

Production of IgG in response to virus infection is central to antiviral immune effector functions and a hallmark of B cell memory. Antiviral antibodies (Abs) recognising viral glycoproteins or protein antigen displayed on the surface of virions or virus-infected cells are crucial in rendering the virus noninfectious and in eliminating viruses or infected cells, either acting alone or in conjunction with complement. In many instances, passive transfer of Abs is sufficient to protect from viral infection. Herpesviruses (HV) are equipped with a large array of immunomodulatory functions which increase the efficiency of infection by dampening the antiviral immunity. Members of the α- and β-subfamily of the Herpesviridae are distinct in encoding transmembrane glycoproteins which selectively bind IgG via its Fc domain. The Fc-binding proteins constitute viral Fcγ receptors (vFcγRs) which are expressed on the cell surface of infected cells. Moreover, vFcγRs are abundantly incorporated into the envelope of virions. Despite their molecular and structural heterogeneity, the vFcγRs generally interfere with IgG-mediated effector functions like antibody (Ab)-dependent cellular cytolysis, complement activation and neutralisation of infectivity of virions. vFcγRs may thus contribute to the limited therapeutic potency of antiherpesviral IgG in clinical settings. A detailed molecular understanding of vFcγRs opens up the possibility to design recombinant IgG molecules resisting vFcγRs. Engineering IgG with a better antiviral efficiency represents a new therapeutic option against herpesviral diseases.

Cytomegalovirus infection in solid organ transplantation: economic implications

Cytomegalovirus (CMV) is a pathogen, commonly encountered in the recipients of solid organ transplantation and is an important cause of morbidity and mortality in these patients. CMV infection and disease have been shown to increase the cost of care in transplant recipients and several different strategies of prevention have been shown to be effective in clinical trials. A systematic review of published information on the economic impact of CMV in solid organ transplantation was performed; both clinical- and decision-analysis-based studies were reviewed. Clinical studies have shown that CMV infection and disease is associated with increased length of hospital stay and overall costs. Decision-analysis-based studies suggest that in general, antiviral chemoprophylaxis against CMV in transplant recipients is a cost-effective intervention compared with other established healthcare interventions such as strategies for colorectal cancer screening. Prophylaxis with oral or parenteral ganciclovir is probably the most cost-effective strategy; however, restricting prophylaxis to high-risk groups (such as donor seropositive/recipient seronegative status and the use of an antilymphocyte antibody) or chemoprophylaxis for an extended period does not improve cost effectiveness. Pre-emptive therapy is an evolving strategy for prevention of CMV disease in transplant recipients and is rapidly gaining in popularity. Well-designed trials incorporating prospective cost data and comparing pre-emptive therapy versus conventional antiviral prophylaxis are needed to establish the superiority of one strategy over the other.

In vitro antiviral and antibacterial activity of commercial intravenous immunoglobulin preparations--a potential role for adjuvant intravenous immunoglobulin therapy in infectious diseases

The identification of specific antimicrobial activity of intravenous immunoglobulin (IVIG) preparations against particular microbial pathogens can assist in determining their therapeutic potential for specific infectious diseases. We analysed five different commercial IVIG preparations for the presence of antibodies directed against a large panel of viral, bacterial, fungal and parasitic pathogens. All IVIG batches contained high activity against herpesviruses types 1, 2, 6 and 7, as well as against varicella zoster virus, Epstein-Barr virus (EBV), measles, mumps, rubella and parvovirus B19. Some IVIG batches also had a significant activity against adenovirus and Saint Louis encephalitis virus. The IVIGs held high activity against several bacterial pathogens, including Mycoplasma pneumonia, Chlamydia pneumonia, Helicobacter pylori and tetanus. No activity was found against various parasitic and fungal pathogens. Our findings may provide further support for the use of IVIG for the prevention and treatment of infections caused by specific viral and bacterial pathogens.

Passive immunity in prevention and treatment of infectious diseases

Antibodies have been used for over a century in the prevention and treatment of infectious disease. They are used most commonly for the prevention of measles, hepatitis A, hepatitis B, tetanus, varicella, rabies, and vaccinia. Although their use in the treatment of bacterial infection has largely been supplanted by antibiotics, antibodies remain a critical component of the treatment of diptheria, tetanus, and botulism. High-dose intravenous immunoglobulin can be used to treat certain viral infections in immunocompromised patients (e.g., cytomegalovirus, parvovirus B19, and enterovirus infections). Antibodies may also be of value in toxic shock syndrome, Ebola virus, and refractory staphylococcal infections. Palivizumab, the first monoclonal antibody licensed (in 1998) for an infectious disease, can prevent respiratory syncytial virus infection in high-risk infants. The development and use of additional monoclonal antibodies to key epitopes of microbial pathogens may further define protective humoral responses and lead to new approaches for the prevention and treatment of infectious diseases.

Passive immunity in prevention and treatment of infectious diseases

Antibodies have been used for over a century in the prevention and treatment of infectious disease. They are used most commonly for the prevention of measles, hepatitis A, hepatitis B, tetanus, varicella, rabies, and vaccinia. Although their use in the treatment of bacterial infection has largely been supplanted by antibiotics, antibodies remain a critical component of the treatment of diptheria, tetanus, and botulism. High-dose intravenous immunoglobulin can be used to treat certain viral infections in immunocompromised patients (e.g., cytomegalovirus, parvovirus B19, and enterovirus infections). Antibodies may also be of value in toxic shock syndrome, Ebola virus, and refractory staphylococcal infections. Palivizumab, the first monoclonal antibody licensed (in 1998) for an infectious disease, can prevent respiratory syncytial virus infection in high-risk infants. The development and use of additional monoclonal antibodies to key epitopes of microbial pathogens may further define protective humoral responses and lead to new approaches for the prevention and treatment of infectious diseases.

Antibodies for the prevention and treatment of viral diseases

This paper reviews current use and evolving role of polyclonal and monoclonal antibody products for the prevention and treatment of viral diseases. Antibodies continue to be indicated for prophylaxis either prior to an anticipated exposure especially in situations of travel, or more commonly following an exposure. The predominant indication for use of antibody products is to prevent infection. With the availability of vaccines for the prevention of chickenpox, hepatitis A, hepatitis B, measles, rabies and smallpox, the role of passive immunization is reserved for susceptible individuals and those at high risk for complications of infection. Risks of transmission of infections associated with use of human plasma-derived products have been reduced by improvements in donor screening and virus removal and inactivation procedures. An additional safety concern has been addressed by the removal of thimerosal as a preservative. Within the last 5 years, two antibodies have been licensed for a viral indication, RespiGam and Synagis both for prevention of respiratory syncytial virus infection. RespiGam is a human plasma derived antibody and Synagis is a humanized monoclonal antibody, the first such antibody to be licensed for an infectious disease indication. CytoGam for prevention of cytomegalovirus infection in kidney transplant patients has recently been granted an expanded indication to include use in lung, liver, pancreas and heart transplant patients. As the use of therapeutics becomes more sophisticated, researchers may find better ways of using antibody products.

New strategies for prevention and therapy of cytomegalovirus infection and disease in solid-organ transplant recipients

In the past three decades since the inception of human organ transplantation, cytomegalovirus (CMV) has gained increasing clinical import because it is a common pathogen in the immunocompromised transplant recipient. Patients may suffer from severe manifestations of this infection along with the threat of potential fatality. Additionally, the dynamic evolution of immunosuppressive and antiviral agents has brought forth changes in the natural history of CMV infection and disease. Transplant physicians now face the daunting task of recognizing and managing the changing spectrum of CMV infection and its consequences in the organ recipient. For the microbiology laboratory, the emphasis has been geared toward the development of more sophisticated detection assays, including methods to detect emerging antiviral resistance. The discovery of novel antiviral chemotherapy is an important theme of clinical research. Investigations have also focused on preventative measures for CMV disease in the solid-organ transplant population. In all, while much has been achieved in the overall management of CMV infection, the current understanding of CMV pathogenesis and therapy still leaves much to be learned before success can be claimed.