Human immunoglobulin G2 (IgG2) and IgG4, but not IgG1 or IgG3, protect mice against Cryptococcus neoformans infection

Monoclonal antibodies: From magic bullet to precision weapon

Monoclonal antibodies (mAbs) are used to prevent, detect, and treat a broad spectrum of non-communicable and communicable diseases. Over the past few years, the market for mAbs has grown exponentially with an expected compound annual growth rate (CAGR) of 11.07% from 2024 (237.64 billion USD estimated at the end of 2023) to 2033 (679.03 billion USD expected by the end of 2033). Ever since the advent of hybridoma technology introduced in 1975, antibody-based therapeutics were realized using murine antibodies which further progressed into humanized and fully human antibodies, reducing the risk of immunogenicity. Some benefits of using mAbs over conventional drugs include a drastic reduction in the chances of adverse reactions, interactions between drugs, and targeting specific proteins. While antibodies are very efficient, their higher production costs impede the process of commercialization. However, their cost factor has been improved by developing biosimilar antibodies as affordable versions of therapeutic antibodies. Along with the recent advancements and innovations in antibody engineering have helped and will furtherly help to design bio-better antibodies with improved efficacy than the conventional ones. These novel mAb-based therapeutics are set to revolutionize existing drug therapies targeting a wide spectrum of diseases, thereby meeting several unmet medical needs. This review provides comprehensive insights into the current fundamental landscape of mAbs development and applications and the key factors influencing the future projections, advancement, and incorporation of such promising immunotherapeutic candidates as a confrontation approach against a wide list of diseases, with a rationalistic mentioning of any limitations facing this field.

Shared and unique antibody and B cell profiles in HIV-positive and HIV-negative individuals with cryptococcal meningoencephalitis

Host non-T cell markers to aid in the diagnosis of cryptococcal meningoencephalitis (CM) have not been identified. In this case-control study, we characterized antibody and B cell profiles in HIV-negative and HIV-positive Vietnamese individuals of the Kinh ethnicity recently diagnosed with CM and controls. The study included 60 HIV-negative with no known immunocompromising condition and 60 HIV-positive individuals, with 30 CM cases and 30 controls in each group. Participants were matched by age, sex, HIV serostatus, and CD4 count in the HIV-positive group. Plasma immunoglobulin (Ig) levels, including IgG1, IgG2, IgM, and IgA, Cryptococcus spp. glucuronoxylomannan (GXM)- and laminarin (branched ${\rm{\beta }}$-[1-3]-glucan)-binding IgG, IgM, IgA levels, and peripheral blood B cell subsets were measured. Logistic regression, principal component, and mediation analyses were conducted to assess associations between antibody, B cell levels, and CM. The results showed that GXM-IgG levels were higher and IgG1 and IgG2 were lower in CM cases than controls, regardless of HIV status. In HIV-negative individuals, IgG2 mediated an inverse association between CD19+CD27+CD43+CD5- (B-1b-like) cells and CM. In HIV-positive individuals, lower levels of IgA, laminarin-IgA, and CD19+CD27+IgM+IgD- (IgM+ memory B) cells were each associated with CM. The shared and distinct antibody and B cell profiles identified in HIV-negative and HIV-positive CM cases may inform the identification of non-T-cell markers of CM risk or unsuspected disease, particularly in HIV-negative individuals.

Hinge influences in murine IgG binding to Cryptococcus neoformans capsule

Decades of studies on antibody structure led to the tenet that the V region binds antigens while the C region interacts with immune effectors. In some antibodies, however, the C region affects affinity and/or specificity for the antigen. One example is the 3E5 monoclonal murine IgG family, in which the mIgG3 isotype has different fine specificity to the Cryptococcus neoformans capsule polysaccharide than the other mIgG isotypes despite their identical variable sequences. Our group serendipitously found another pair of mIgG1/mIgG3 antibodies based on the 2H1 hybridoma to the C. neoformans capsule that recapitulated the differences observed with 3E5. In this work, we report the molecular basis of the constant domain effects on antigen binding using recombinant antibodies. As with 3E5, immunofluorescence experiments show a punctate pattern for 2H1-mIgG3 and an annular pattern for 2H1-mIgG1; these binding patterns have been associated with protective efficacy in murine cryptococcosis. Also as observed with 3E5, 2H1-mIgG3 bound on ELISA to both acetylated and non-acetylated capsular polysaccharide, whereas 2H1-mIgG1 only bound well to the acetylated form, consistent with differences in fine specificity. In engineering hybrid mIgG1/mIgG3 antibodies, we found that switching the 2H1-mIgG3 hinge for its mIgG1 counterpart changed the immunofluorescence pattern to annular, but a 2H1-mIgG1 antibody with an mIgG3 hinge still had an annular pattern. The hinge is thus necessary but not sufficient for these changes in binding to the antigen. This important role for the constant region in antigen binding could affect antibody biology and engineering.

Capsular glycan recognition provides antibody-mediated immunity against tuberculosis

A better understanding of all immune components involved in protecting against Mycobacterium tuberculosis infection is urgently needed to inform strategies for novel immunotherapy and tuberculosis (TB) vaccine development. Although cell-mediated immunity is critical, increasing evidence supports that antibodies also have a protective role against TB. Yet knowledge of protective antigens is limited. Analyzing sera from 97 US immigrants at various stages of M. tuberculosis infection, we showed protective in vitro and in vivo efficacy of polyclonal IgG against the M. tuberculosis capsular polysaccharide arabinomannan (AM). Using recently developed glycan arrays, we established that anti-AM IgG induced in natural infection is highly heterogeneous in its binding specificity and differs in both its reactivity to oligosaccharide motifs within AM and its functions in bacillus Calmette-Guérin vaccination and/or in controlled (latent) versus uncontrolled (TB) M. tuberculosis infection. We showed that anti-AM IgG from asymptomatic but not from diseased individuals was protective and provided data suggesting a potential role of IgG2 and specific AM oligosaccharides. Filling a gap in the current knowledge of protective antigens in humans, our data support the key role of the M. tuberculosis surface glycan AM and suggest the importance of targeting specific glycan epitopes within AM in antibody-mediated immunity against TB.

Sagacity in antibody humanization for therapeutics, diagnostics and research purposes: considerations of antibody elements and their roles

The humanization of antibodies for therapeutics is a critical process that can determine the success of antibody drug development. However, the science underpinning this process remains elusive with different laboratories having very different methods. Well-funded laboratories can afford automated high-throughput screening methods to derive their best binder utilizing a very expensive initial set of equipment affordable only to a few. Often within these high-throughput processes, only standard key parameters, such as production, binding and aggregation are analyzed. Given the lack of suitable animal models, it is only at clinical trials that immunogenicity and allergy adverse effects are detected through anti-human antibodies as per FDA guidelines. While some occurrences that slip through can be mitigated by additional desensitization protocols, such adverse reactions to grafted humanized antibodies can be prevented at the humanization step. Considerations such as better antibody localization, avoidance of unspecific interactions to superantigens and the tailoring of antibody dependent triggering of immune responses, the antibody persistence on cells, can all be preemptively considered through a holistic sagacious approach, allowing for better outcomes in therapy and for research and diagnostic purposes.

Monoclonal Antibodies as Tools to Combat Fungal Infections

Antibodies represent an important element in the adaptive immune response and a major tool to eliminate microbial pathogens. For many bacterial and viral infections, efficient vaccines exist, but not for fungal pathogens. For a long time, antibodies have been assumed to be of minor importance for a successful clearance of fungal infections; however this perception has been challenged by a large number of studies over the last three decades. In this review, we focus on the potential therapeutic and prophylactic use of monoclonal antibodies. Since systemic mycoses normally occur in severely immunocompromised patients, a passive immunization using monoclonal antibodies is a promising approach to directly attack the fungal pathogen and/or to activate and strengthen the residual antifungal immune response in these patients.

Antibody Responses in HIV-Infected Patients With Advanced Immunosuppression and Asymptomatic Cryptococcal Antigenemia

Background

There are no host biomarkers of risk for HIV-associated cryptococcal meningitis (CM) except CD4+ T-cell deficiency. At present, serum cryptococcal antigen (CrAg) screening of those with CD4 <100 cells/µL is used to identify persons at risk for HIV-associated CM. We determined if plasma antibody profiles could discriminate CrAg+ from CrAg- patients.

Methods

We performed serological analyses of 237 HIV-infected asymptomatic Zimbabwean patients with CD4 <100 cells/µL; 125 CrAg- and CrAg+ but cerebrospinal fluid CrAg- by CrAg lateral flow assay. We measured plasma immunoglobulin M (IgM), immunoglobulin G (IgG) 1, and IgG2 concentrations by Luminex, and titers of Cryptococcus neoformans (Cn) glucuronoxylomannan (GXM) polysaccharide and naturally occurring Laminarin (natural Lam, a β-(1–3)-glucan linked polysaccharide)-binding IgM and IgG by enzyme-linked immunosorbent assay.

Results

GXM-IgG, -IgM, and -IgG2 levels were significantly higher in CrAg+ patients, whereas natural Lam-IgM and Lam-IgG were higher in CrAg- patients before and after adjustment for age, sex, and CD4 T-cell count, despite overlap of values. To address this variability and better discriminate the groups, we used Akaike Information Criteria to select variables that independently predicted CrAg+ status and included them in a receiver operating characteristic curve to predict CrAg status. By inclusion of CD4, GXM-IgG, GXM-IgM, and Lam-IgG, -IgG2, and -IgM, this model had an 80.4% probability (95% confidence interval, 0.75–0.86) of predicting CrAg+ status.

Conclusions

Statistical models that include multiple serological variables may improve the identification of patients at risk for CM and inform new directions in research on the complex role that antibodies may play in resistance and susceptibility to CM.

Human Anti-Als3p Antibodies Are Surrogate Markers of NDV-3A Vaccine Efficacy Against Recurrent Vulvovaginal Candidiasis

A Phase 1b/2a clinical trial of NDV-3A vaccine containing a Candida albicans recombinant Als3 protein formulated with alum protected women <40 years old from recurrent vulvovaginal candidiasis (RVVC). We investigated the potential use of anti-Als3p sera as surrogate marker of NDV-3A efficacy. Pre- and post-vaccination sera from subjects who experienced recurrence of vulvovaginal candidiasis (R) vs. those who were recurrence-free [non-recurrent (NR)] were evaluated. Anti-Als3p antisera obtained were evaluated for (1) titer and subclass profile and (2) their ability to influence C. albicans virulence traits including hyphal elongation, adherence to plastic, invasion of vaginal epithelial cells, biofilm formation on plastic and catheter material, and susceptibility to neutrophil killing in vitro. Serum IgG titers in NR patients were consistently higher than in R patients, particularly for anti-Als3 subclass IgG2. Sera from vaccinated NR patients reduced hyphal elongation, adhesion to plastic, invasion of vaginal epithelial cells, and biofilm formation significantly more than pre-immune sera, or sera from R- or placebo-group subjects. Pre-adsorption of sera with C. albicans germ tubes eliminated these effects, while heat inactivation did not. Finally, sera from NR subjects enhanced neutrophil-mediated killing of C. albicans relative to pre-immune sera or sera from R patients. Our results suggest that higher Als3p antibody titers are associated with protection from RVVC, attenuate C. albicans virulence, and augment immune clearance of the fungus in vitro. Thus, Als3p serum IgG antibodies are likely useful markers of efficacy in RVVC patients vaccinated with NDV-3A.

Efficacy and Mechanism of Antitumor Activity of an Antibody Targeting Transferrin Receptor 1 in Mouse Models of Human Multiple Myeloma

The transferrin receptor 1 (TfR1) is an attractive target for Ab-mediated cancer therapy. We previously developed a mouse/human chimeric IgG3 Ab (ch128.1) targeting human TfR1, which exhibits direct in vitro cytotoxicity against certain human malignant B cells through TfR1 degradation and iron deprivation. ch128.1 also demonstrates exceptional antitumor activity against the B cell malignancy multiple myeloma (MM) in xenograft models of SCID-Beige mice bearing either disseminated ARH-77 or KMS-11 cells in an early disease setting. Interestingly, this activity is observed even against KMS-11 cells, which show no sensitivity to the direct cytotoxic activity of ch128.1 in vitro. To understand the contributions of the Fc fragment, we generated a ch128.1 mutant with impaired binding to FcγRs and to the complement component C1q, which retains binding to the neonatal Fc receptor. We now report that this mutant Ab does not show antitumor activity in these two MM models, indicating a crucial role of the Fc fragment in the antitumor activity of ch128.1, which can be attributed to effector functions (Ab-dependent cell-mediated cytotoxicity, Ab-dependent cell-mediated phagocytosis, and/or complement-dependent cytotoxicity). Interestingly, in the KMS-11 model, complement depletion does not affect protection, whereas macrophage depletion does. Consistent with this observation, we found that ch128.1 induces Ab-dependent cell-mediated cytotoxicity and Ab-dependent cell-mediated phagocytosis against KMS-11 cells in the presence of murine bone marrow-derived macrophages. Finally, we found that ch128.1 therapy effectively increases survival in a late MM disease setting. Our results suggest that macrophages play a major role in ch128.1-mediated antitumor protection in our models and that ch128.1 can be effective against human B cell malignancies such as MM.

The effects of Antibody Engineering CH and CL in Trastuzumab and Pertuzumab recombinant models: Impact on antibody production and antigen-binding

Current therapeutic antibodies such as Trastuzumab, are typically of the blood circulatory IgG1 class (Cκ/ CHγ1). Due to the binding to Her2 also present on normal cell surfaces, side effects such as cardiac failure can sometimes be associated with such targeted therapy. Using antibody isotype swapping, it may be possible to reduce systemic circulation through increased tissue localization, thereby minimising unwanted side effects. However, the effects of such modifications have yet to be fully characterized, particularly with regards to their biophysical properties in antigen binding. To do this, we produced all light and heavy chain human isotypes/subtypes recombinant versions of Trastuzumab and Pertuzumab, and studied them with respect to recombinant production and Her2 binding. Our findings show that while the light chain constant region changes have no major effects on production or Her2 binding, some heavy chain isotypes, in particularly, IgM and IgD isotypes, can modulate antigen binding. This study thus provides the groundwork for such isotype modifications to be performed in the future to yield therapeutics of higher efficacy and efficiency.

Immunotherapy of Fungal Infections

Fungal organisms are ubiquitous in the environment. Pathogenic fungi, although relatively few in the whole gamut of microbial pathogens, are able to cause disease with varying degrees of severity in individuals with normal or impaired immunity. The disease state is an outcome of the fungal pathogen's interactions with the host immunity, and therefore, it stands to reason that deep/invasive fungal diseases be amenable to immunotherapy. Therefore, antifungal immunotherapy continues to be attractive as an adjunct to the currently available antifungal chemotherapy options for a number of reasons, including the fact that existing antifungal drugs, albeit largely effective, are not without limitations, and that morbidity and mortality associated with invasive mycoses are still unacceptably high. For several decades, intense basic research efforts have been directed at development of fungal immunotherapies. Nevertheless, this approach suffers from a severe bench-bedside disconnect owing to several reasons: the chemical and biological peculiarities of the fungal antigens, the complexities of host-pathogen interactions, an under-appreciation of the fungal disease landscape, the requirement of considerable financial investment to bring these therapies to clinical use, as well as practical problems associated with immunizations. In this general, non-exhaustive review, we summarize the features of ongoing research efforts directed towards devising safe and effective immunotherapeutic options for mycotic diseases, encompassing work on antifungal vaccines, adoptive cell transfers, cytokines, antimicrobial peptides (AMPs), monoclonal antibodies (mAbs), and other agents.

Contribution of murine IgG Fc regions to antibody binding to the capsule of Burkholderia pseudomallei

Immunoglobulin G3 (IgG3) is the predominant IgG subclass elicited in response to polysaccharide antigens in mice. This specific subclass has been shown to crosslink its fragment crystallizable (Fc) regions following binding to multivalent polysaccharides. Crosslinking leads to increased affinity through avidity, which theoretically should lead to more effective protection against bacteria and yeast displaying capsular polysaccharides on their surface. To investigate this further we have analyzed the binding characteristics of 2 IgG monoclonal antibody (mAb) subclass families that bind to the capsular polysaccharide (CPS) of Burkholderia pseudomallei. The first subclass family originated from an IgG3 hybridoma cell line (3C5); the second family was generated from an IgG1 cell line (2A5). When the Fc region of the 3C5 IgG3 is removed by proteolytic cleavage, the resulting F(ab')2 fragments exhibit decreased affinity compared to the full-length mAb. Similarly, when the parent IgG3 mAb is subclass-switched to IgG1, IgG2b, and IgG2a, all of these subclasses exhibit decreased affinity. This decrease in affinity is not seen when the 2A5 IgG1 mAb is switched to an IgG2b or IgG2a, strongly suggesting the drop in affinity is related to the IgG3 Fc region.

An Fc engineering approach that modulates antibody-dependent cytokine release without altering cell-killing functions

Cytotoxic therapeutic monoclonal antibodies (mAbs) often mediate target cell-killing by eliciting immune effector functions via Fc region interactions with cellular and humoral components of the immune system. Key functions include antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). However, there has been increased appreciation that along with cell-killing functions, the induction of antibody-dependent cytokine release (ADCR) can also influence disease microenvironments and therapeutic outcomes. Historically, most Fc engineering approaches have been aimed toward modulating ADCC, ADCP, or CDC. In the present study, we describe an Fc engineering approach that, while not resulting in impaired ADCC or ADCP, profoundly affects ADCR. As such, when peripheral blood mononuclear cells are used as effector cells against mAb-opsonized tumor cells, the described mAb variants elicit a similar profile and quantity of cytokines as IgG1. In contrast, although the variants elicit similar levels of tumor cell-killing as IgG1 with macrophage effector cells, the variants do not elicit macrophage-mediated ADCR against mAb-opsonized tumor cells. This study demonstrates that Fc engineering approaches can be employed to uncouple macrophage-mediated phagocytic and subsequent cell-killing functions from cytokine release.

B cells and antibodies in the defense against Mycobacterium tuberculosis infection

Better understanding of the immunological components and their interactions necessary to prevent or control Mycobacterium tuberculosis (Mtb) infection in humans is critical for tuberculosis (TB) vaccine development strategies. Although the contributory role of humoral immunity in the protection against Mtb infection and disease is less defined than the role of T cells, it has been well-established for many other intracellular pathogens. Here we update and discuss the increasing evidence and the mechanisms of B cells and antibodies in the defense against Mtb infection. We posit that B cells and antibodies have a variety of potential protective roles at each stage of Mtb infection and postulate that such roles should be considered in the development strategies for TB vaccines and other immune-based interventions.

Influence of IgG Subclass on Human Antimannan Antibody-Mediated Resistance to Hematogenously Disseminated Candidiasis in Mice

Candida albicans is a yeast-like pathogen and can cause life-threatening systemic candidiasis. Its cell surface is enriched with mannan that is resistant to complement activation. Previously, we developed the recombinant human IgG1 antimannan antibody M1g1. M1g1 was found to promote complement activation and phagocytosis and protect mice from systemic candidiasis. Here, we evaluate the influence of IgG subclass on antimannan antibody-mediated protection. Three IgG subclass variants of M1g1 were constructed: M1g2, M1g3, and M1g4. The IgG subclass identity for each variant was confirmed with DNA sequence and subclass-specific antibodies. These variants contain identical M1 Fabs and exhibited similar binding affinities for C. albicans yeast and purified mannan. Yeast cells and hyphae recovered from the kidney of antibody-treated mice with systemic candidiasis showed uniform binding of each variant, indicating constitutive expression of the M1 epitope and antibody opsonization in the kidney. All variants promoted deposition of both murine and human C3 onto the yeast cell surface, with M1g4 showing delayed activation, as determined by flow cytometry and immunofluorescence microscopy. M1g4-mediated complement activation was found to be associated with its M1 Fab that activates the alternative pathway in an Fc-independent manner. Treatment with each subclass variant extended the survival of mice with systemic candidiasis (P < 0.001). However, treatment with M1g1, M1g3, or M1g4, but not with M1g2, also reduced the kidney fungal burden (P < 0.001). Thus, the role of human antimannan antibody in host resistance to systemic candidiasis is influenced by its IgG subclass.

High-throughput sequencing of human immunoglobulin variable regions with subtype identification

The humoral immune response plays a critical role in controlling infection, and the rapid adaptation to a broad range of pathogens depends on a highly diverse antibody repertoire. The advent of high-throughput sequencing technologies in the past decade has enabled insights into this immense diversity. However, not only the variable, but also the constant region of antibodies determines their in vivo activity. Antibody isotypes differ in effector functions and are thought to play a defining role in elicitation of immune responses, both in natural infection and in vaccination. We have developed an Illumina MiSeq high-throughput sequencing protocol that allows determination of the human IgG subtype alongside sequencing full-length antibody variable heavy chain regions. We thereby took advantage of the Illumina procedure containing two additional short reads as identifiers. By performing paired-end sequencing of the variable regions and customizing one of the identifier sequences to distinguish IgG subtypes, IgG transcripts with linked information of variable regions and IgG subtype can be retrieved. We applied our new method to the analysis of the IgG variable region repertoire from PBMC of an HIV-1 infected individual confirmed to have serum antibody reactivity to the Membrane Proximal External Region (MPER) of gp41. We found that IgG3 subtype frequencies in the memory B cell compartment increased after halted treatment and coincided with increased plasma antibody reactivity against the MPER domain. The sequencing strategy we developed is not restricted to analysis of IgG. It can be adopted for any Ig subtyping and beyond that for any research question where phasing of distant regions on the same amplicon is needed.

Fungal vaccines and immunotherapeutics

Concomitant with the increased prevalence of immunocompromised persons, invasive fungal infections have become considerably more frequent in the last 50 years. High mortality rates caused by invasive mycoses and high morbidity because of intractable mucosal infections have created an unmet need for innovative prophylactic and therapeutic strategies against fungal pathogens. Several immunotherapeutics and vaccines are in development to address this need, although one has yet to reach the clinic. This review focuses on past and current immunotherapeutic and vaccine strategies being tested to either prevent or treat fungal infections, as well as the challenges associated with their development.

Cryptococcus antigens and immune responses: implications for a vaccine

Cryptococcosis is a fungal disease primarily occurring in immunocompromised individuals, such as AIDS patients, and is associated with high morbidity and mortality. However, cryptococcosis can occur within immunocompetent populations as observed during an outbreak in Vancouver Island, British Columbia, Canada, the Pacific Northwest and other regions of the USA and in Mediterranean Europe. Mortality rates due to cryptococcosis have significantly declined in economically developed countries since the widespread implementation of highly active antiretroviral therapy. However, the incidence and mortality of this disease remains high in economically undeveloped areas in Africa and Asia where HIV infections are high and availability of HAART is limited. The continuing AIDS epidemic coupled with the increased usage of immunosuppressive drugs to prevent organ transplant rejection or to treat autoimmune diseases has resulted in an increase in individuals at risk for developing cryptococcosis. The purpose of this review is to discuss the need, challenges and potential for developing vaccines against cryptococcosis.

Elucidating the immunological function of the Cryptococcus neoformans capsule

The encapsulated fungal pathogen Cryptococcus neoformans represents a significant agent of life-threatening infections in immunocompromised subjects. A unique characteristic of Cryptococcus species is the presence of a polysaccharide capsule, which is essential for virulence and endows Cryptococcus with potent immunoregulatory properties. This review provides an overview of the immunological properties of the principal components of C. neoformans capsule.

The Role of Complement in Antibody Therapy for Infectious Diseases

The complement system is part of the innate immune system, eliciting central immunoregulatory functions. Detection of foreign surfaces is either achieved through complement-specific patternrecognition molecules or mediated by antigen recognition of antibodies. Immunoglobulin A (IgA), IgG, and IgM all have the potential to initiate a complement response, with the efficiency and response development closely related to the antibody isotype, multimeric state, and degree of glycosylation. A group of serum proteins constitutes the central effector functions of complement, thus allowing direct cell lysis, opsonization, and inflammation. These effector functions can be used in antibody therapies, especially against infectious diseases, as the target membranes lack complement regulatory proteins. The relative contribution of each function and the interplay with direct antibody-mediated clearance is not fully exploited, thus suggesting an option for further rational optimization of antibody therapies.

Antibody Engineering

Advanced molecular biology techniques developed during the past few decades have allowed the industry to exploit and commercialize the natural defense mechanisms that antibodies provide. This review discusses the latest advances in antibody-engineering technologies to enhance clinical efficacy and outcomes. For the constant regions, the choice of the antibody class and isotype has to be made carefully to suit the therapeutic applications. Engineering of the Fc region, either by direct targeted mutagenesis or by modifying the nature of its N -glycan, has played an important role in recent years in increasing half-life or controlling effector functions. The variable regions of the antibody are responsible for binding affinity and exquisite specificity to the target molecule, which together with the Fc determine the drug's efficacy and influence the drug dose required to obtain the desired effectiveness. A key requirement during antibody development is therefore to affinity mature the variable regions when necessary, so that they bind the therapeutic target with sufficiently high affinity to guarantee effective occupancy over prolonged periods. If the antibody was obtained from a non-human source, such as rodents, a humanization process has to be applied to minimize immunogenicity while maintaining the desired binding affinity and selectivity. Finally, we discuss the next next-generation antibodies, such as antibody-drug conjugates, bispecific antibodies, and immunocytokines, which are being developed to meet future challenges.

Fc gamma receptor 3A polymorphism and risk for HIV-associated cryptococcal disease

Cryptococcus neoformans is one of the most common causes of fungal disease in HIV-infected persons, but not all of those who are infected develop cryptococcal disease (CD). Although CD4⁺ T cell deficiency is a risk factor for HIV-associated CD, polymorphisms of phagocytic Fc gamma receptors (FCGRs) have been linked to CD risk in HIV-uninfected persons. To investigate associations between FCGR2A 131 H/R and FCGR3A 158 F/V polymorphisms and CD risk in HIV-infected persons, we performed PCR-based genotyping on banked samples from 164 men enrolled in the Multicenter AIDS Cohort Study (MACS): 55 who were HIV infected and developed CD and a matched control group of 54 who were HIV infected and 55 who were HIV uninfected. Using additive and allelic statistical models for analysis, the high-affinity FCGR3A 158V allele was significantly associated with CD status after adjusting for race/ethnicity (odds ratio [OR], 2.1; P = 0.005), as was the FCGR3A 158 VV homozygous genotype after adjusting for race/ethnicity, rate of CD4⁺ T cell decline, and nadir CD4⁺ T cell count (OR, 21; P = 0.005). No associations between CD and FCGR2A 131 H/R polymorphism were identified. In binding studies, human IgG (hIgG)-C. neoformans complexes exhibited more binding to CHO-K1 cells expressing FCGR3A 158V than to those expressing FCGR3A 158F, and in cytotoxicity assays, natural killer (NK) cells expressing FCGR3A 158V induced more C. neoformans-infected monocyte cytotoxicity than those expressing FCGR3A 158F. Together, these results show an association between the FCGR3A 158V allele and risk for HIV-associated CD and suggest that this polymorphism could promote C. neoformans pathogenesis via increased binding of C. neoformans immune complexes, resulting in increased phagocyte cargo and/or immune activation.

HIV-associated CD4⁺ T cell deficiency is a sine qua non for HIV-associated cryptococcal disease (CD), but not all patients with CD4⁺ T cell deficiency develop CD despite serological evidence of previous infection. At present, there are no biomarkers that predict HIV-associated CD risk. The goal of our study was to understand whether Fc gamma receptor (FCGR) polymorphisms that have been shown to portend CD risk in HIV-uninfected people are associated with CD risk in HIV-infected people. Such biomarkers could identify those who would benefit most from targeted prophylaxis and/or earlier treatment, particularly in sub-Saharan Africa, where there are nearly a million cases of HIV-associated CD annually. A biomarker of risk could also identify potential candidates for immunization, should there be a vaccine for Cryptococcus neoformans.

Constant domains influence binding of mouse-human chimeric antibodies to the capsular polypeptide of Bacillus anthracis

Our laboratory previously described the binding characteristics of the murine IgG3 monoclonal antibody (MuAb) F26G3. This antibody binds the poly-glutamic acid capsule (PGA) of Bacillus anthracis, an essential virulence factor in the progression of anthrax. F26G3 IgG3 MuAb binds PGA with a relatively high functional affinity (10 nM), produces a distinct "rim" quellung reaction, and is protective in a murine model of pulmonary anthrax. This study engineered an IgG subclass family of F26G3 mouse-human chimeric antibodies (ChAb). The F26G3 ChAbs displayed 9- to 20-fold decreases in functional affinity, as compared with the parent IgG3 MuAb. Additionally, the quellung reactions that were produced by the ChAbs all differed from the parent IgG3 MuAb in that they appeared "puffy" in nature. This study demonstrates that human constant domains may influence multiple facets of antibody binding to microbial capsular antigens despite their spatial separation from the traditional antigen-binding site.

Complementary MS methods assist conformational characterization of antibodies with altered S-S bonding networks

As therapeutic monoclonal antibodies (mAbs) become a major focus in biotechnology and a source of the next-generation drugs, new analytical methods or combination methods are needed for monitoring changes in higher order structure and effects of post-translational modifications. The complexity of these molecules and their vulnerability to structural change provide a serious challenge. We describe here the use of complementary mass spectrometry methods that not only characterize mutant mAbs but also may provide a general framework for characterizing higher order structure of other protein therapeutics and biosimilars. To frame the challenge, we selected members of the IgG2 subclass that have distinct disulfide isomeric structures as a model to evaluate an overall approach that uses ion mobility, top-down MS sequencing, and protein footprinting in the form of fast photochemical oxidation of proteins (FPOP). These three methods are rapid, sensitive, respond to subtle changes in conformation of Cys → Ser mutants of an IgG2, each representing a single disulfide isoform, and may be used in series to probe higher order structure. The outcome suggests that this approach of using various methods in combination can assist the development and quality control of protein therapeutics.

Releasable layer-by-layer assembly of stabilized lipid nanocapsules on microneedles for enhanced transcutaneous vaccine delivery

Here we introduce a new approach for transcutaneous drug delivery, using microneedles coated with stabilized lipid nanocapsules, for delivery of a model vaccine formulation. Poly(lactide-co-glycolide) microneedle arrays were coated with multilayer films via layer-by-layer assembly of a biodegradable cationic poly(β-amino ester) (PBAE) and negatively charged interbilayer-cross-linked multilamellar lipid vesicles (ICMVs). To test the potential of these nanocapsule-coated microneedles for vaccine delivery, we loaded ICMVs with a protein antigen and the molecular adjuvant monophosphoryl lipid A. Following application of microneedle arrays to the skin of mice for 5 min, (PBAE/ICMV) films were rapidly transferred from microneedle surfaces into the cutaneous tissue and remained in the skin following removal of the microneedle arrays. Multilayer films implanted in the skin dispersed ICMV cargos in the treated tissue over the course of 24 h in vivo, allowing for uptake of the lipid nanocapsules by antigen presenting cells in the local tissue and triggering their activation in situ. Microneedle-mediated transcutaneous vaccination with ICMV-carrying multilayers promoted robust antigen-specific humoral immune responses with a balanced generation of multiple IgG isotypes, whereas bolus delivery of soluble or vesicle-loaded antigen via intradermal injection or transcutaneous vaccination with microneedles encapsulating soluble protein elicited weak, IgG(1)-biased humoral immune responses. These results highlight the potential of lipid nanocapsules delivered by microneedles as a promising platform for noninvasive vaccine delivery applications.

Immunoglobulins in defense, pathogenesis, and therapy of fungal diseases

Only two decades ago antibodies to fungi were thought to have little or no role in protection against fungal diseases. However, subsequent research has provided convincing evidence that certain antibodies can modify the course of fungal infection to the benefit or detriment of the host. Hybridoma technology was the breakthrough that enabled the characterization of antibodies to fungi, illuminating some of the requirements for antibody efficacy. As discussed in this review, fungal-specific antibodies mediate protection through direct actions on fungal cells and through classical mechanisms such as phagocytosis and complement activation. Although mechanisms of antibody-mediated protection are often species-specific, numerous fungal antigens can be targeted to generate vaccines and therapeutic immunoglobulins. Furthermore, the study of antibody function against medically important fungi has provided fresh immunological insights into the complexity of humoral immunity that are likely to apply to other pathogens.

Vaccine and immunotherapeutic approaches for the prevention of cryptococcosis: lessons learned from animal models

Cryptococcus neoformans and C. gattii, the predominant etiological agents of cryptococcosis, can cause life-threatening infections of the central nervous system in immunocompromised and immunocompetent individuals. Cryptococcal meningoencephalitis is the most common disseminated fungal infection in AIDS patients, and C. neoformans remains the third most common invasive fungal infection among organ transplant recipients. Current anti-fungal drug therapies are oftentimes rendered ineffective due to drug toxicity, the emergence of drug resistant organisms, and/or the inability of the host's immune defenses to assist in eradication of the yeast. Therefore, there remains an urgent need for the development of immune-based therapies and/or vaccines to combat cryptococcosis. Studies in animal models have demonstrated the efficacy of various vaccination strategies and immune therapies to induce protection against cryptococcosis. This review will summarize the lessons learned from animal models supporting the feasibility of developing immunotherapeutics and vaccines to prevent cryptococcosis.

Host defense pathways against fungi: the basis for vaccines and immunotherapy

Fungal vaccines have long been a goal in the fields of immunology and microbiology to counter the high mortality and morbidity rates owing to fungal diseases, particularly in immunocompromised patients. However, the design of effective vaccination formulations for durable protection to the different fungi has lagged behind due to the important differences among fungi and their biology and our limited understanding of the complex host–pathogen interactions and immune responses. Overcoming these challenges is expected to contribute to improved vaccination strategies aimed at personalized efficacy across distinct target patient populations. This likely requires the integration of multifaceted approaches encompassing advanced immunology, systems biology, immunogenetics, and bioinformatics in the fields of fungal and host biology and their reciprocal interactions.

Immunotherapy of Cryptococcus infections

Despite appropriate antifungal treatment, the management of cryptococcal disease remains challenging, especially in immunocompromised patients, such as human immunodeficiency virus-infected individuals and solid organ transplant recipients. During the past two decades, our knowledge of host immune responses against Cryptococcus spp. has been greatly advanced, and the role of immunomodulation in augmenting the response to infection has been investigated. In particular, the role of 'protective' Th1 (tumour necrosis factor-α, interferon (IFN)-γ, interleukin (IL)-12, and IL-18) and Th17 (IL-23 and IL-17) and 'non-protective' Th2 (IL-4, IL-10, and IL-13) cytokines has been extensively studied in vitro and in animal models of cryptococcal infection. Immunomodulation with monoclonal antibodies against the capsular polysaccharide glucuronoxylomannan, glucosylceramides, melanin and β-glucan and, lately, with radioimmunotherapy has also yielded promising results in animal models. As a balance between sufficiently protective Th1 responses and excessive inflammation is important for optimal outcome, the effect of immunotherapy may range from beneficial to deleterious, depending on factors related to the host, the infecting organism, and the immunomodulatory regimen. Clinical evidence supporting immunomodulation in patients with cryptococcal infection remains too limited to allow firm recommendations. Limited human data suggest a role for IFN-γ. Identification of surrogate markers characterizing patients' immunological status could possibly suggest candidate patients for immunotherapy and the type of immunomodulation to be administered.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Antibodies in infectious diseases: polyclonals, monoclonals and niche biotechnology

Antibody preparations have a long history of providing protection from infectious diseases. Although antibodies remain the only natural host-derived defense mechanism capable of completely preventing infection, as products, they compete against inexpensive therapeutics such as antibiotics, small molecule inhibitors and active vaccines. The continued discovery in the monoclonal antibody (mAb) field of leads with broadened cross neutralization of viruses and demonstrable synergy of antibody with antibiotics for bacterial diseases, clearly show that innovation remains. The commercial success of mAbs in chronic disease has not been paralleled in infectious diseases for several reasons. Infectious disease immunotherapeutics are limited in scope as endemic diseases necessitate active vaccine development. Also, the complexity of these small markets draws the interest of niche companies rather than big pharmaceutical corporations. Lastly, the cost of goods for mAb therapeutics is inherently high for infectious agents due to the need for antibody cocktails, which better mimic polyclonal immunoglobulin preparations and prevent antigenic escape. In cases where vaccine or convalescent populations are available, current polyclonal hyperimmune immunoglobulin preparations (pIgG), with modern and highly efficient purification technology and standardized assays for potency, can make economic sense. Recent innovations to broaden the potency of mAb therapies, while reducing cost of production, are discussed herein. On the basis of centuries of effective use of Ab treatments, and with growing immunocompromised populations, the question is not whether antibodies have a bright future for infectious agents, but rather what formats are cost effective and generate safe and efficacious treatments to satisfy regulatory approval.

Plant production of anti-β-glucan antibodies for immunotherapy of fungal infections in humans

There is an increasing interest in the development of therapeutic antibodies (Ab) to improve the control of fungal pathogens, but none of these reagents is available for clinical use. We previously described a murine monoclonal antibody (mAb 2G8) targeting β-glucan, a cell wall polysaccharide common to most pathogenic fungi, which conferred significant protection against Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans in animal models. Transfer of this wide-spectrum, antifungal mAb into the clinical setting would allow the control of most frequent fungal infections in many different categories of patients. To this aim, two chimeric mouse-human Ab derivatives from mAb 2G8, in the format of complete IgG or scFv-Fc, were generated, transiently expressed in Nicotiana benthamiana plants and purified from leaves with high yields (approximately 50 mg Ab/kg of plant tissues). Both recombinant Abs fully retained the β-glucan-binding specificity and the antifungal activities of the cognate murine mAb against C. albicans. In fact, they recognized preferentially β1,3-linked glucan molecules present at the fungal cell surface and directly inhibited the growth of C. albicans and its adhesion to human epithelial cells in vitro. In addition, both the IgG and the scFv-Fc promoted C. albicans killing by isolated, human polymorphonuclear neutrophils in ex vivo assays and conferred significant antifungal protection in animal models of systemic or vulvovaginal C. albicans infection. These recombinant Abs represent valuable molecules for developing novel, plant-derived immunotherapeutics against candidiasis and, possibly, other fungal diseases.

Rapid and refined separation of human IgG2 disulfide isomers using superficially porous particles

A rapid reversed-phase HPLC separation of recombinant human immunoglobulin gamma 2 (IgG2) disulfide isomers using columns packed with superficially porous particles is reported. Under optimal conditions, a separation of monoclonal IgG2 disulfide isomers was achieved in 10 min using a Poroshell™ 300SB-C8 column via a combination of high column temperature (85°C), mobile phases with high eluotropic strength (e.g. isopropanol) and high flow rate (1.5 mL/min). Thermodynamic stability analyses of chromatographically enriched IgG2 disulfide isomers revealed differences in their individual denaturation temperatures, which correlate with the observed temperature-dependent refinement of peak profiles by reversed-phase HPLC. This reversed-phase HPLC method in conjunction with other orthogonal analytical techniques (e.g. capillary gel electrophoresis, peptide mapping, ion exchange chromatography, etc.) is being used to characterize disulfide isomers in the development of therapeutic IgG2 antibodies.

Monoclonal antibodies against peptidorhamnomannans of Scedosporium apiospermum enhance the pathogenicity of the fungus

Scedosporium apiospermum is part of the Pseudallescheria-Scedosporium complex. Peptidorhamnomannans (PRMs) are cell wall glycopeptides present in some fungi, and their structures have been characterized in S. apiospermum, S. prolificans and Sporothrix schenckii. Prior work shows that PRMs can interact with host cells and that the glycopeptides are antigenic. In the present study, three monoclonal antibodies (mAbs, IgG1) to S. apiospermum derived PRM were generated and their effects on S. apiospermum were examined in vitro and in vivo. The mAbs recognized a carbohydrate epitope on PRM. In culture, addition of the PRM mAbs increased S. apiospermum conidia germination and reduced conidial phagocytosis by J774.16 macrophages. In a murine infection model, mice treated with antibodies to PRM died prior to control animals. Thus, PRM is involved in morphogenesis and the binding of this glycopeptide by mAbs enhanced the virulence of the fungus. Further insights into the effects of these glycopeptides on the pathobiology of S. apiospermum may lead to new avenues for preventing and treating scedosporiosis.

The incidence of fungal infections has increased dramatically over the last 50 years, largely because of the increasing size of the population at risk, which especially includes immunocompromised hosts. Scedosporium apiospermum is a filamentous fungus that causes a variety of infections, ranging from localized disease to life-threatening disseminated infections. Glycoproteins are molecules present in the fungal surface and are comprised of carbohydrate and protein components. They are involved in different important functions in the fungal cell. Monoclonal antibodies can be used as therapeutic agents for infectious disease, but some factors involved in their efficacy are often not well understood. We found that monoclonal antibodies to glycoproteins present in fungal surface can be nonprotective and can even enhance the disease. The administration of these antibodies can affect functions of the fungal cell and the immune cells, resulting in a survival advantage for the fungus during interactions with the host.

Vaccine-induced IgG2 anti-HIV p24 is associated with control of HIV in patients with a 'high-affinity' FcgammaRIIa genotype

OBJECTIVES

We have previously shown that vaccination with a recombinant fowlpox virus carrying the genes for HIV Gag-Pol and interferon-gamma (IFN-gamma) was associated with partial control of HIV replication after antiretroviral therapy (ART) was ceased but not with increased anti-HIV T-cell responses. Because IFN-gamma enhances IgG2 production, and IgG2 antibodies to HIV antigens and the 'high-affinity' polymorphism of FcgammaRIIa (the major Fc receptor for IgG2) have been associated with a favourable outcome of HIV infection, we examined the association of IgG2 antibodies to HIV p24 and 'high-affinity' polymorphisms of FcgammaRIIa with control of HIV replication in these patients.

METHODS

Plasma from weeks 0 (cessation of ART 1 week after the last vaccination), 9 and 20 was available from patients who had received the full construct vaccine, a partial construct (without IFN-gamma) or placebo. IgG2 and IgG1 anti-p24 and anti-gp41 were assayed and all patients were genotyped for the FcgammaRIIa 131 R/H polymorphism that affects IgG2 binding.

RESULTS

At week 0, IgG2 anti-p24 was present in five of nine full construct patients but none of 14 partial construct or placebo patients and was associated with a smaller increase in plasma HIV RNA over 20 weeks. Patients with IgG2 anti-p24 and the 'high-affinity' polymorphism of FcgammaRIIa exhibited lower HIV replication than other patients at week 20.

CONCLUSION

The role of IgG2 anti-HIV antibodies and FcgammaRIIa in the control of HIV replication should be investigated further. Inclusion of an IFN-gamma gene in DNA vaccine constructs might be a means of enhancing IgG2 antibody production.

Carbohydrate vaccines: developing sweet solutions to sticky situations?

Recent technological advances in glycobiology and glycochemistry are paving the way for a new era in carbohydrate vaccine design. This is enabling greater efficiency in the identification, synthesis and evaluation of unique glycan epitopes found on a plethora of pathogens and malignant cells. Here, we review the progress being made in addressing challenges posed by targeting the surface carbohydrates of bacteria, protozoa, helminths, viruses, fungi and cancer cells for vaccine purposes.

A histoplasma capsulatum-specific IgG1 isotype monoclonal antibody, H1C, to a 70-kilodalton cell surface protein is not protective in murine histoplasmosis

Monoclonal antibodies to Histoplasma capsulatum can modify pathogenesis. We now show that monoclonal antibody H1C to a 70-kDa antigen increases intracellular fungal growth and reduces macrophage nitric oxide release but has no effect on fungal burden or survival in murine infection. This further demonstrates the complexities of host-pathogen interactions.

Production and characterization of mouse monoclonal antibodies recognizing multiple subclasses of human IgG

Different IgG subclass profiles are produced in response to different antigenic stimuli in a variety of diseases. IgG subclass levels may reflect disease severity. Quantification of IgG subclasses depends on the availability of specific Monoclonal antibodies (MAbs). In the present study seven hybridoma clones producing MAbs reactive with multiple subclasses of human IgG were established. Splenocytes from Balb/c mice immunized with Fc fractions of human IgG1 or IgG2 myeloma proteins were fused with mouse myeloma cells. Fused cells were selected and cloned by limiting dilution assay. Antibody secreting cells were screened by Enzyme-linked immunosorbent assay (ELISA) and the specificity of secreted MAbs was further analyzed, using a panel of purified human myeloma paraproteins of different IgG subclasses by ELISA and immunoblotting. Cross-reactivity to immunoglobulins (Igs) of other species was studied by indirect ELISA using serum samples collected from 9 animals. The MAbs were found to react with triple IgG subclasses, including IgG1,2,4 (n=4) and IgG1,2,3 (n=3). Immunoblotting studies revealed recognition of linear (n=4) or conformational (n=3) epitopes by these MAbs. The most abundant cross-reactivity (71.4%) was observed with monkey Ig while no cross-reactivity was detected with hen and cat sera. The MAbs mostly displayed a restricted pattern of cross-reactivity and one of them did not bind to any of the animal sera tested. The affinity constant of 3 MAbs was measured by ELISA. Based on the data obtained from this study, mouse MAbs reactive with multiple human IgG subclasses are directed to a variety of immunogenic epitopes, mostly shared with IgG of other species. These MAbs are valuable tools for purification of non-reactive IgG subclasses through negative affinity chromatography. These MAbs could also provide an opportunity for epitope mapping of the Fc region of IgG, as well as serological phylogenetic studies.

Fc-receptors and immunity to malaria: from models to vaccines

The complexity and number of antigens (Ags) seen during an immune response has hampered the development of malaria vaccines. Antibodies (Abs) play an important role in immunity to malaria and their passive administration is effective at controlling the disease. Abs represent approximately 25% of all proteins undergoing clinical trials, and these 'smart biologicals' have undergone a major revival with the realization that Abs lie at the interface between innate and adaptive immunity. At least 18 Abs have FDA approval for clinical use and approximately 150 are in clinical trials, the majority for the treatment of cancer, allograft rejection or autoimmune disease. Despite these triumphs none are in development for malaria, principally because they are perceived as being too expensive for a disease mainly afflicting poor and marginalized populations. Although unlikely, at least in the foreseeable future, that Ab-based prophylaxis will be made available to the millions of people at risk from malaria, they may be incorporated into current vaccine approaches, since Abs act as correlates of protection in studies aimed at defining the best Ags to include in vaccines. Abs may also form the basis for novel vaccination strategies by targeting Ags to appropriate antigen presenting cells. Therefore, to develop the most efficacious vaccines it will be necessary to fully understand which Abs and Fc-receptors (FcRs) are best engaged for a positive outcome.

A proteomic-based approach for the identification of immunodominant Cryptococcus neoformans proteins

Cryptococcus neoformans is an opportunistic fungal pathogen that can cause life-threatening meningoencephalitis in immune compromised patients. Previous, studies in our laboratory have shown that prior exposure to an IFN-gamma-producing C. neoformans strain (H99gamma) elicits protective immunity against a second pulmonary C. neoformans challenge. Here, we characterized the antibody response produced in mice protected against experimental pulmonary C. neoformans infection compared to nonprotected mice. Moreover, we evaluated the efficacy of using serum antibody from protected mice to detect immunodominant C. neoformans proteins. Protected mice were shown to produce significantly more C. neoformans-specific antibodies following a second experimental pulmonary cryptococcal challenge compared to nonprotected mice. Immunoblot analysis of C. neoformans proteins resolved by 2-DE using serum from nonprotected mice failed to show any reactivity. In contrast, serum from protected mice was reactive with several cryptococcal protein spots. Analysis of these spots by capillary HPLC-ESI-MS/MS identified several cryptococcal proteins shown to be associated with the pathogenesis of cryptococcosis. Our studies demonstrate that mice immunized with C. neoformans strain H99gamma produce antibodies that are immune reactive against specific cryptococcal proteins that may provide a basis for the development of immune based therapies that induce protective anticryptococcal immune responses.

Central nervous system involvement in cryptococcal infection in individuals after solid organ transplantation or with AIDS

BACKGROUND

Cryptococcus neoformans is an important pathogen of immunocompromised hosts. Manifestations of cryptococcal infection have not been compared between populations based on the nature of the underlying immune deficiencies.

METHODS

The Prospective Antifungal Therapy Alliance (PATH) is a registry that collects clinical data from patients with invasive fungal infections from medical centers in North America. Univariate analyses and group comparisons were conducted from the PATH registry for cases of infection due to Cryptococcus species occurring between March 2004 and April 2008.

RESULTS

A total 235 cases of proven infection due to Cryptococcus species were documented, all of which were due to C. neoformans (52 in solid organ transplant [SOT] recipients, 107 in patients infected with the human immunodeficiency virus [HIV], and 76 with neither HIV nor organ transplantation). A total of 140 cases manifested as meningitis (25 in SOT recipients, 88 in HIV-positive patients, and 27 in those with neither risk factor). Of individuals with cryptococcal infection, 44.2% of SOT recipients had central nervous system (CNS) disease, while 84.1% of those with HIV infection presented with CNS involvement (P=0.0265). SOT recipients receiving calcineurin inhibitors (CNIs) were less likely to have CNS involvement in cryptococcal infection (40.1% versus 66.7%). Overall, 12-week mortality for patients with cryptococcal infection in the PATH Alliance registry was 22.6% (21.2% for SOT, 15.9% for HIV-infected patients, and 32.9% for patients with risk factors other than HIV infection or organ transplantation).

CONCLUSIONS

In a prospectively assembled cohort of individuals with proven infection due to C. neoformans, CNS involvement was more common in individuals with HIV infection than in SOT recipients. The role of CNIs in the reduction of risk for CNS cryptococcosis remains to be defined. Overall survival of patients with cryptococcal infection in immunocompromised hosts has improved over time. Observed differences in the context of various host immune deficits provide a basis for further investigation of cryptococcosis and other opportunistic infections.

The capsule of the fungal pathogen Cryptococcus neoformans

The capsule of the fungal pathogen Cryptococcus neoformans has been studied extensively in recent decades and a large body of information is now available to the scientific community. Well-known aspects of the capsule include its structure, antigenic properties and its function as a virulence factor. The capsule is composed primarily of two polysaccharides, glucuronoxylomannan (GXM) and galactoxylomannan (GalXM), in addition to a smaller proportion of mannoproteins (MPs). Most of the studies on the composition of the capsule have focused on GXM, which comprises more than 90% of the capsule's polysaccharide mass. It is GalXM, however, that is of particular scientific interest because of its immunological properties. The molecular structure of these polysaccharides is very complex and has not yet been fully elucidated. Both GXM and GalXM are high molecular mass polymers with the mass of GXM equaling roughly 10 times that of GalXM. Recent findings suggest, however, that the actual molecular weight might be different to what it has traditionally been thought to be. In addition to their structural roles in the polysaccharide capsule, these molecules have been associated with many deleterious effects on the immune response. Capsular components are therefore considered key virulence determinants in C. neoformans, which has motivated their use in vaccines and made them targets for monoclonal antibody treatments. In this review, we will provide an update on the current knowledge of the C. neoformans capsule, covering aspects related to its structure, synthesis and particularly, its role as a virulence factor.

Potential aggregation prone regions in biotherapeutics: A survey of commercial monoclonal antibodies

Aggregation of a biotherapeutic is of significant concern and judicious process and formulation development is required to minimize aggregate levels in the final product. Aggregation of a protein in solution is driven by intrinsic and extrinsic factors. In this work we have focused on aggregation as an intrinsic property of the molecule. We have studied the sequences and Fab structures of commercial and non-commercial antibody sequences for their vulnerability towards aggregation by using sequence based computational tools to identify potential aggregation-prone motifs or regions. The mAbs in our dataset contain 2 to 8 aggregation-prone motifs per heavy and light chain pair. Some of these motifs are located in variable domains, primarily in CDRs. Most aggregation-prone motifs are rich in beta branched aliphatic and aromatic residues. Hydroxyl-containing Ser/Thr residues are also found in several aggregation-prone motifs while charged residues are rare. The motifs found in light chain CDR3 are glutamine (Q)/asparagine (N) rich. These motifs are similar to the reported aggregation promoting regions found in prion and amyloidogenic proteins that are also rich in Q/N, aliphatic and aromatic residues. The implication is that one possible mechanism for aggregation of mAbs may be through formation of cross-beta structures and fibrils. Mapping on the available Fab-receptor/antigen complex structures reveals that these motifs in CDRs might also contribute significantly towards receptor/antigen binding. Our analysis identifies the opportunity and tools for simultaneous optimization of the therapeutic protein sequence for potency and specificity while reducing vulnerability towards aggregation.

Role of complement in protection against Cryptococcus gattii infection

Previous studies have shown that the alternative pathway of complement activation plays an important role in protection against infection with Cryptococcus neoformans. Cryptococcus gattii does not activate the alternative pathway as well as C. neoformans in vitro. The role of complement in C. gattii infection in vivo has not been reported. In this study, we used mice deficient in complement components to investigate the role of complement in protection against a C. gattii isolate from an ongoing outbreak in northwestern North America. While factor B-deficient mice showed an enhanced rate of death, complement component C3-deficient mice died even more rapidly, indicating that the alternative pathway was not the only complement pathway contributing to protection against disease. Both C3- and factor B-deficient mice had increased fungal burdens in comparison to wild-type mice. Histopathology revealed an overwhelming fungal burden in the lungs of these complement-deficient mice, which undoubtedly prevented efficient gas exchange, causing death. Following the fate of radiolabeled organisms showed that both factor B- and C3-deficient mice were less effective than wild-type mice in clearing organisms. However, opsonization of C. gattii with complement components was not sufficient to prolong life in mice deficient in complement. Killing of C. gattii by macrophages in vitro was decreased in the presence of serum from factor B- and C3-deficient versus wild-type mice. In conclusion, we have demonstrated that complement activation is crucial for survival in C. gattii infection. Additionally, we have shown that the alternative pathway of complement activation is not the only complement pathway contributing to protection.

Structural and functional characterization of disulfide isoforms of the human IgG2 subclass

In the accompanying report ( Wypych, J., Li, M., Guo, A., Zhang, Z., Martinez, T., Allen, M. J., Fodor, S., Kelner, D. N., Flynn, G. C., Liu, Y. D., Bondarenko, P. V., Ricci, M. S., Dillon, T. M., and Balland, A. (2008) J. Biol. Chem. 283, 16194-16205 ), we have identified that the human IgG2 subclass exists as an ensemble of distinct isoforms, designated IgG2-A, -B, and -A/B, which differ by the disulfide connectivity at the hinge region. In this report, we studied the structural and functional properties of the IgG2 disulfide isoforms and compared them to IgG1. Human monoclonal IgG1 and IgG2 antibodies were designed with identical antigen binding regions, specific to interleukin-1 cell surface receptor type 1. In vitro biological activity measurements showed an increased activity of the IgG1 relative to the IgG2 in blocking interleukin-1beta ligand from binding to the receptor, suggesting that some of the IgG2 isoforms had lower activity. Under reduction-oxidation conditions, the IgG2 disulfide isoforms converted to IgG2-A when 1 m guanidine was used, whereas IgG2-B was enriched in the absence of guanidine. The relative potency of the antibodies in cell-based assays was: IgG1 > IgG2-A > IgG2 >> IgG2-B. This difference correlated with an increased hydrodynamic radius of IgG2-A relative to IgG2-B, as shown by biophysical characterization. The enrichment of disulfide isoforms and activity studies were extended to additional IgG2 monoclonal antibodies with various antigen targets. All IgG2 antibodies displayed the same disulfide conversion, but only a subset showed activity differences between IgG2-A and IgG2-B. Additionally, the distribution of isoforms was influenced by the light chain type, with IgG2lambda composed mostly of IgG2-A. Based on crystal structure analysis, we propose that IgG2 disulfide exchange is caused by the close proximity of several cysteine residues at the hinge and the reactivity of tandem cysteines within the hinge. Furthermore, the IgG2 isoforms were shown to interconvert in whole blood or a "blood-like" environment, thereby suggesting that the in vivo activity of human IgG2 may be dependent on the distribution of isoforms.

The mold conundrum in chronic rhinosinusitis: where do we stand today?

Chronic rhinosinusitis (CRS) is an inflammatory disorder affecting the nose and paranasal sinuses. Although bacteria have long been implicated as pathogens in most forms of CRS, fungi may be responsible for some forms. Several recent studies demonstrated that, under optimal conditions, fungi can be identified in the nose and paranasal sinuses of nearly every individual (including all CRS patients). An aberrant immune response to these ubiquitous fungi has been suggested to explain the development of CRS in some individuals. Several mechanisms requiring additional research, including adequate controls, have been proposed and are reviewed in this article. Although preliminary trials suggested that CRS signs and symptoms improve upon treatment with topical and oral antifungal agents, several double-blind, placebo-controlled trials demonstrated the contrary. In the absence of convincing immunologic data and evidence of clinical improvement upon therapy with antifungal agents, the case against fungi remains unproven.