Combinatorial immunotherapies for infectious diseases

Natural products and synthetic compounds as immunomodulators

Research on immunomodulation by natural products or synthetic derivatives is of key interest for anti-infective therapy for a number of reasons. Many plant remedies well-known in traditional medicine or refined natural products in clinical use exert their anti-infective effects not only (if at all) by directly affecting the pathogen. At least part of their effect is indirect, by stimulating natural and adaptive defense mechanisms of the host. These findings have now given many empirical therapies a rationale, scientific basis and thereby a means for 'intelligent' improvement. In discovering the molecular mechanisms by which known remedies exert their effects, chosen elements further down the 'chain of command' might be synthesized and applied directly for more rapid and selective cure, omitting unwanted side effects. The direct use of recombinant cytokines, often in combination with antibiotics, is one consequence of this rationale.

Low Dose Oral Combination Chemoprophylaxis with Oseltamivir and Amantadine for Influenza a Virus Infections in Mice

In the present study, the effect of combining anti-influenza drugs active at different steps of the influenza virus replication cycle, oseltamivir as a neuraminidase (NA) inhibitor and amantadine targeting M2 protein, was investigated in vivo by oral administration in a mouse model of aerosol influenza virus infection and in vitro in MDCK cells. In mice, doses of oseltamivir and amantadine providing 50-60% survival against A/Hongkong/1/68 (H3N2) or A/PR/8/34 (H1N1) were capable of conferring complete protection when used simultaneously, suggesting that increased inhibition of influenza virus replication by combining oseltamivir and amantadine in vitro translates into protection from lethal infection of mice. The combination of amantadine with oseltamivir required 15-fold less oseltamivir than monotherapy to confer complete protection against lethal aerosol influenza virus infection. Remarkably, amantadine-based combination chemoprophylaxis was even effective against amantadine-resistant A/PR/8/34 influenza virus. Thus, combination chemotherapy may be more efficacious than monotherapy against newly emerging Influenza A subtypes.

Overview of biologic response modifiers in infectious disease

The conventional treatment of infectious agents is increasingly encountering antimicrobial resistance. This resistance has led to an intense search for novel treatment modalities for infectious diseases. Elucidation of the mechanisms underlying the inhibitory activity of chemokines has been instrumental in the rational design of anti-human immunodeficiency virus chemokine drugs. The immune-based therapies, in combination with antimicrobial drugs, for viral hepatitis have attracted much attention. Recognition of toll-like receptors by synthetic immunomodulators is used for certain viral infections. New methodologies have the potential to identify novel targets and foster the development of individually tailored immunomodulatory drug treatments.

C7 Anti-infective activity of immunomodulators

Infectious diseases continue to impact human morbidity and mortality. Every individual is vulnerable to microbial infections regardless of socioeconomic status, gender, age group or ethnic background. There has been an explosion of international air travel with an estimated 2 billion passengers travelling on commercial airlines every year. The rapid expansion of globalization and mass tourism has facilitated the spread of disease-causing pathogens from one continent to another at unprecedented rates.

Francisella tularensis infection-derived monoclonal antibodies provide detection, protection, and therapy

Francisella tularensis is the causative agent of tularemia and a potential agent of biowarfare. As an easily transmissible infectious agent, rapid detection and treatment are necessary to provide a positive clinical outcome. As an agent of biowarfare, there is an additional need to prevent infection. We made monoclonal antibodies to the F. tularensis subsp. holarctica live vaccine strain (F. tularensis LVS) by infecting mice with a sublethal dose of bacteria and, following recovery, by boosting the mice with sonicated organisms. The response to the initial and primary infection was restricted to immunoglobulin M antibody directed solely against lipopolysaccharide (LPS). After boosting with sonicated organisms, the specificity repertoire broadened against protein antigens, including DnaK, LpnA, FopA, bacterioferritin, the 50S ribosomal protein L7/L12, and metabolic enzymes. These monoclonal antibodies detect F. tularensis LVS by routine immunoassays, including enzyme-linked immunosorbent assay, Western blot analysis, and immunofluorescence. The ability of the antibodies to protect mice from intradermal infection, both prophylactically and therapeutically, was examined. An antibody to LPS which provides complete protection from infection with F. tularensis LVS and partial protection from infection with F. tularensis subsp. tularensis strain SchuS4 was identified. There was no bacteremia and reduced organ burden within the first 24 h when mice were protected from F. tularensis LVS infection with the anti-LPS antibody. No antibody that provided complete protection when administered therapeutically was identified; however, passive transfer of antibodies against LPS, FopA, and LpnA resulted in 40 to 50% survival of mice infected with F. tularensis LVS.

Anti-HIV activity mediated by natural killer and CD8+ cells after toll-like receptor 7/8 triggering

We previously found that triggering TLR7/8 either by single stranded HIV RNA or synthetic compounds induced changes in the lymphoid microenvironment unfavorable to HIV. In this study, we used selective TLR7 and 8 agonists to dissect their contribution to the anti-HIV effects. While triggering TLR7 inhibited efficiently HIV replication in lymphoid suspension cells from tonsillar origin, its effect was inconsistent in peripheral blood mononuclear cells (PBMC). In contrast, triggering TLR8 showed a very prominent and overall very consistent effect in PBMC and tonsillar lymphoid suspension cells. Depletion of dendritic cells (DC), Natural killer cells (NK) and CD8+ T-cells from PBMC resulted in the reversal of TLR8 induced anti-HIV effects. Especially noteworthy, depletion of either NK or CD8+ T-cells alone was only partially effective. We interpret these findings that DC are the initiator of complex changes in the microenvironment that culminates in the anti-HIV active NK and CD8+ effector cells. The near lack of NK and the low number of CD8+ T-cells in tonsillar lymphoid suspension cells may explain the lower TLR8 agonist's anti-HIV effects in that tissue. However, additional cell-type specific differences must exist since the TLR7 agonists had a very strong inhibitory effect in tonsillar lymphoid suspension cells. Separation of effector from the CD4+ target cells did not abolish the anti-HIV effects pointing to the critical role of soluble factors. Triggering TLR7 or 8 were accompanied by major changes in the cytokine milieu; however, it appeared that not a single soluble factor could be assigned for the potent effects.

These results delineate the complex effects of triggering TLR7/8 for an efficient antiviral defense. While the ultimate mechanism(s) remains unknown, the potent effects described may have therapeutic value for treating chronic viral diseases. Notably, HIV replication is blocked by TLR triggering before HIV integrates into the host chromosome which would prevent the establishment or maintenance of the latent reservoir.

Fungal heat-shock proteins in human disease

Heat-shock proteins (hsps) have been identified as molecular chaperones conserved between microbes and man and grouped by their molecular mass and high degree of amino acid homology. This article reviews the major hsps of Saccharomyces cerevisiae, their interactions with trehalose, the effect of fermentation and the role of the heat-shock factor. Information derived from this model, as well as from Neurospora crassa and Achlya ambisexualis, helps in understanding the importance of hsps in the pathogenic fungi, Candida albicans, Cryptococcus neoformans, Aspergillus spp., Histoplasma capsulatum, Paracoccidioides brasiliensis, Trichophyton rubrum, Phycomyces blakesleeanus, Fusarium oxysporum, Coccidioides immitis and Pneumocystis jiroveci. This has been matched with proteomic and genomic information examining hsp expression in response to noxious stimuli. Fungal hsp90 has been identified as a target for immunotherapy by a genetically recombinant antibody. The concept of combining this antibody fragment with an antifungal drug for treating life-threatening fungal infection and the potential interactions with human and microbial hsp90 and nitric oxide is discussed.

Risk factors associated with development of poxvirus lesions in hospitalized California sea lions

OBJECTIVE

To identify risk factors that may predispose California sea lions (Zalophus californianus) to development of cutaneous poxvirus nodules during hospitalization in a rehabilitation center.

DESIGN

Retrospective case-control study.

ANIMALS

90 California sea lions admitted to a rehabilitation center.

PROCEDURE

Hospital records of 275 stranded California sea lions admitted to the rehabilitation center between January 1 and December 31, 2002, were reviewed. All California sea lions (n = 18) that developed > or = 1 cutaneous poxvirus nodule during hospitalization were classified as cases. Seventy-two California sea lions that did not develop poxvirus lesions during hospitalization were randomly selected (control group). The frequencies of various exposure factors prior to admission, at admission, and during hospitalization for cases and control sea lions were compared by use of logistic regression.

RESULTS

California sea lions that had previously been admitted to the rehabilitation center were 43 times as likely to develop poxvirus lesions as sea lions admitted for the first time; those with high band neutrophil counts (> 0.69 X 10(3) bands/microL) at admission were 20 times less likely to develop poxvirus lesions than sea lions with counts within reference limits.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that sea lions with a history of prior hospitalization or band neutrophil counts within reference limits at admission were more likely to develop poxvirus lesions during hospitalization. Sea lions with histories of hospitalization should be kept in quarantine and infection control measures implemented to help prevent disease transmission to attending personnel and other hospitalized animals.

Evaluation of Mycograb®, amphotericin B, caspofungin, and fluconazole in combination against Cryptococcus neoformans by checkerboard and time-kill methodologies

This article reported the identification of heat shock protein 90 (hsp90) homologues by immunoblot in Cryptococcus neoformans. Mycograb, a genetically recombinant antibody against hsp90, was evaluated against 8 clinical isolates and the National External Quality Assessment Service for Microbiology strain of C. neoformans alone and in combination with amphotericin B, caspofungin, and fluconazole by checkerboard assay. At the end point of an optically clear well, the minimum inhibitory concentration (MIC) 0's ranged from 256 to 1024 microg/mL for Mycograb, from 0.5 to 1 microg/mL for amphotericin B, and from 16 to 32 microg/mL for caspofungin. The combination of Mycograb and amphotericin B produced a fractional inhibitory concentration index from 0.27 to 0.56, indicating a mainly synergistic effect, whereas for caspofungin, it varied from 0.5 to 2. At an end point of > or =50% inhibition, the MIC-2s varied from 16 to 128 microg/mL for Mycograb and from 0.125 to 16 microg/mL for fluconazole. The fractional inhibitory concentration index classified the combination as indifferent for 5 isolates, additive for 3 more isolates, and synergistic in a single isolate. Time-kill analysis on 2 isolates (F/7844 and F/10156), which had synergistic and additive results with amphotericin B, respectively, on checkerboard was performed with 4-16 microg/mL of Mycograb, 2-8 microg/mL of fluconazole, and 0.0625-2 microg/mL of amphotericin B. This demonstrated an increasingly static effect with augmenting concentrations of fluconazole and an initial static effect with amphotericin B at lower concentrations, which became fungicidal as the level of drug increased. The addition of either 4 or 8 microg/mL of Mycograb to 0.5 microg/mL of amphotericin B with C. neoformans F/7844 changed a static effect to a fungicidal effect at 8 h with an increased killing of 1.2 logs at 48 h. With C. neoformans F/10156, the addition of 16 microg/mL of Mycograb to 0.25 microg/mL of amphotericin B produced a difference in killing from 1 logarithm after 4 h to 1.5 logarithms after 48 h. These data suggest that the combination of amphotericin B and Mycograb would be worth exploring in the treatment of infection due to C. neoformans.

Anti-infective activity of immunomodulators

The availability of a vast array of recombinant and synthetic IMMUNOMODULATORS is a significant milestone toward the development of effective therapies for infectious diseases. This is evinced by licensing of several recombinant human CYTOKINES, including COLONY-STIMULATING FACTORS, INTERLEUKINS, INTERFERONS and erythropoietin, for clinical use in patients. Diverse combinations with INTERFERONS and other CYTOKINES for the treatment of various infections have been proposed. Others, including various CHEMOKINES, synthetic CpG oligodeoxynucleotides and glucans, are extensively being investigated in clinical and preclinical studies. Considerable advances have been made on compounds exhibiting CYTOKINE inhibitory properties useful for new treatments of infectious and inflammatory diseases. Many of the major developments and current trends are highlighted in this review. Novel strategies based on the engineering of CYTOKINES and inhibitors are poised to revolutionize therapeutic options contingent upon scientific evidence rather than dictates of discursive empiricism in the coming decades.

Alternative and/or integrative therapies for pneumonia under development

PURPOSE OF REVIEW

Increasing antimicrobial resistance among common respiratory bacteria has created challenges in selecting appropriate therapy for pneumonia. Fortunately, the analysis of genome sequences has allowed us to find novel, nontraditional targets that are involved in disease pathogenesis or in adaptation and growth in infection sites. The advantage of the nonclassical targets is that targeting these sites could ablate infection without inducing resistance. Interfering with bacterial adhesion, inhibiting, neutralizing and clearing endotoxin, and administering cytokines as immunoadjuvants are the most promising alternative or integrative treatments for pneumonia that are under development.

RECENT FINDINGS

Interference with bacterial adhesion is possible using inhibitors of sortase or inactivators of the srtA gene against gram-positive bacteria, inhibitors of the periplasmic chaperone or those of usher function against gram-negative bacteria, novel polysaccharides that are present on echinoderm surfaces, antiadhesin vaccines, or the passive administration of antiadhesin antibodies. Inhibition, neutralization, and clearance of endotoxin possibly interferes in the lipid A biosynthetic pathway or using lipid A analogues with reduced or lack of ability to activate the major endotoxin receptors or proteins such as recombinant Limulus antilipopolysaccharide factor, bactericidal/permeability increasing protein, or lipopolysaccharide binding protein. Tumor necrosis factor 70-80, an adenoviral vector that encodes murine tumor necrosis factor alpha, and recombinant interferon gamma seem to be the most promising cytokines for use as immunoadjuvants for the treatment of pneumonia.

SUMMARY

Ideally, potential treatment of life-threatening bacterial pneumonia will combine immunoadjuvant and conventional antibiotic therapy. Compounds capable of stimulating early host defense and microbial clearance, but not the later phases of inflammatory tissue injury associated with sepsis, may be advantageous.