Administration of a nondepleting anti-CD25 monoclonal antibody reduces disease severity in mice infected with Trypanosoma cruzi

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.

Role of myeloid-derived suppressor cells during Trypanosoma cruzi infection

Chagas disease (CD), caused by the protozoan parasite Trypanosoma cruzi, is the third largest parasitic disease burden globally. Currently, more than 6 million people are infected, mainly in Latin America, but international migration has turned CD into an emerging health problem in many nonendemic countries. Despite intense research, a vaccine is still not available. A complex parasite life cycle, together with numerous immune system manipulation strategies, may account for the lack of a prophylactic or therapeutic vaccine. There is substantial experimental evidence supporting that T. cruzi acute infection generates a strong immunosuppression state that involves numerous immune populations with regulatory/suppressive capacity. Myeloid-derived suppressor cells (MDSCs), Foxp3+ regulatory T cells (Tregs), regulatory dendritic cells and B regulatory cells are some of the regulatory populations that have been involved in the acute immune response elicited by the parasite. The fact that, during acute infection, MDSCs increase notably in several organs, such as spleen, liver and heart, together with the observation that depletion of those cells can decrease mouse survival to 0%, strongly suggests that MDSCs play a major role during acute T. cruzi infection. Accumulating evidence gained in different settings supports the capacity of MDSCs to interact with cells from both the effector and the regulatory arms of the immune system, shaping the outcome of the response in a very wide range of scenarios that include pathological and physiological processes. In this sense, the aim of the present review is to describe the main knowledge about MDSCs acquired so far, including several crosstalk with other immune populations, which could be useful to gain insight into their role during T. cruzi infection.

The Blockade of Interleukin-2 During the Acute Phase of Trypanosoma cruzi Infection Reveals Its Dominant Regulatory Role

Trypanosoma cruzi infection causes Chagas’ disease in humans. The infection activates the innate and adaptative immunity in an orchestrated immune response to control parasite growth, guaranteeing host survival. Despite an effective immune response to the parasite in the acute phase, the infection progresses to a chronic stage. The parasite infects different tissues such as peripheral neurons, the brain, skeletal muscle, and heart muscle, among many others. It is evident now that tissue-specific immune responses may develop along with anti-parasite immunity. Therefore, mechanisms to regulate immunity and to ensure tissue-specific tolerance are operating during the infection. Studying those immunoregulatory mechanisms is fundamental to improve host protection or control inflammatory reactions that may lead to pathology. The role of IL-2 during T. cruzi infection is not established. IL-2 production by T cells is strongly down-modulated early in the disease by unknown mechanisms and remains low during the chronic phase of the disease. IL-2 activates NK cells, CD4, and CD8 T cells and may be necessary to immunity development. Also, the expansion and maintenance of regulatory T cells require IL-2. Thus, IL-2 may be a key cytokine involved in promoting or down-regulating immune responses, probably in a dose-dependent manner. This study blocked IL-2 during the acute T. cruzi infection by using a neutralizing monoclonal antibody. The results show that parasitemia and mortality rate was lower in animals treated with anti-IL-2. The percentages and total numbers of CD4⁺CD25⁺Foxp3⁺ T cells diminished within three weeks of infection. The numbers of splenic activated/memory CD4 and CD8 splenic T cells increased during the acute infection. T cells producing IFN-γ, TNF-α and IL-10 also augmented in anti-IL-2-treated infected mice. The IL-2 blockade also increased the numbers of inflammatory cells in the heart and skeletal muscles and the amount of IL-17 produced by heart T cells. These results suggest that IL-2 might be involved in the immune regulatory response during the acute T. cruzi infection, dampening T cell activation through the expansion/maintenance of regulatory T cells and regulating IL-17 production. Therefore, the IL-2 pathway is an attractive target for therapeutic purposes in acute and chronic phases of Chagas’ disease.

Monoclonal Antibodies for Protozoan Infections: A Future Reality or a Utopic Idea?

Following the SARS-CoV-2 pandemic, several clinical trials have been approved for the investigation of the possible use of mAbs, supporting the potential of this technology as a therapeutic approach for infectious diseases. The first monoclonal antibody (mAb), Muromonab CD3, was introduced for the prevention of kidney transplant rejection more than 30 years ago; since then more than 100 mAbs have been approved for therapeutic purposes. Nonetheless, only four mAbs are currently employed for infectious diseases: Palivizumab, for the prevention of respiratory syncytial virus (RSV) infections, Raxibacumab and Obiltoxaximab, for the prophylaxis and treatment against anthrax toxin and Bezlotoxumab, for the prevention of Clostridium difficile recurrence. Protozoan infections are often neglected diseases for which effective and safe chemotherapies are generally missing. In this context, drug resistance and drug toxicity are two crucial problems. The recent advances in bioinformatics, parasite genomics, and biochemistry methodologies are contributing to better understand parasite biology, which is essential to guide the development of new therapies. In this review, we present the efforts that are being made in the evaluation of mAbs for the prevention or treatment of leishmaniasis, Chagas disease, malaria, and toxoplasmosis. Particular emphasis will be placed on the potential strengths and weaknesses of biological treatments in the control of these protozoan diseases that are still affecting hundreds of thousands of people worldwide.

Neutrophil functions can be regulated by IL-35, which is mainly expressed in IL-15Rα+ cells in grass carp (Ctenopharyngodon idella)

IL-35 plays a key role in regulatory T (Treg) and regulatory B (Breg) cell functions in mammals. CD25 has been demonstrated as one of the markers of Treg cells, and CD19⁺CD25^hiCD71^hi cells have been verified as a type of Breg cells in humans. These results indicate that there is a close relationship between IL-35 and CD25⁺ cells. In mammals, CD25 (alias IL-2Rα) has been identified as having high affinity and specificity for IL-2 binding, and is closely linked and structurally related to IL-15Rα, which having high affinity for IL-15 binding. In teleost, IL-15Rα can bind to both IL-2 and IL-15, with higher affinity to IL-15 than IL-2, and has been termed a CD25-like molecule in some research studies. To date, no studies of IL-35 and IL-15Rα have been documented in fish. In this work, five isoforms of IL-15Rα were cloned from grass carp, and a monoclonal antibody to the protein was developed. The results of flow cytometry and quantitative real-time PCR analyses demonstrated that grass carp IL-35 subunit genes EBI3a and IL-12p35 were mainly expressed in IL-15Rα⁺ cells, while the expression levels of IL-10 and TGF-β in IL-15Rα⁺ and IL-15Rα^- cells were insignificant. Recombinant grass carp IL-35 (rgcIL-35) could increase the proportion of IL-15Rα⁺ cells in leukocytes, and a certain proportion of IL-15Rα⁺ cells also appeared in myeloid cell subset II after stimulation with rgcIL-35. Meanwhile, the migration, phagocytic ability, and bactericidal ability of grass carp neutrophils were significantly decreased after stimulation with certain concentrations of rgcIL-35. Moreover, neutrophil apoptosis could be significantly inhibited by rgcIL-35.

Murine T-Cell Transfer Colitis as a Model for Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a group of severe chronic inflammatory conditions of the human gastrointestinal tract. Murine models of colitis have been invaluable tools to improve the understanding of IBD development and pathogenesis. While the disease etiology of IBD is complex and multifactorial, CD4+ T helper cells have been shown to strongly contribute to the disease pathogenesis of IBD. Here, we present a detailed protocol of the preclinical model of T-cell transfer colitis, which can easily be utilized in the laboratory to study T helper cell functions in intestinal inflammation.

Understanding CD8+ T Cell Immunity to Trypanosoma cruzi and How to Improve It

The protozoan Trypanosoma cruzi is the causative agent of Chagas' disease, endemic in Latin America but present worldwide. Research efforts have focused on the examination of immune mechanisms that mediate host protection as well as immunopathology during this parasitic infection. The study of CD8+ T cell immunity emerges as a key aspect given the critical importance of parasite-specific CD8+ T cells for host resistance throughout the infection. In recent years, new research has shed light on novel pathways that modulate the induction, maintenance, and regulation of CD8+ T cell responses to T. cruzi. This new knowledge is setting the ground for future vaccines and/or immunotherapies. Herein, we critically review and analyze the latest results published in the field.

Vaccines and the regulatory arm of the immune system. An overview from the Trypanosoma cruzi infection model

The knowledge that the immune system is composed of a regulatory/suppressor arm added a new point of view to better understand the nature of several pathologies including cancer, transplants, infections and autoimmune diseases. The striking discoveries concerning molecules and cells involved in this kind of regulation were followed by the elucidation of equally notable mechanisms used by several pathogens to manipulate the host immune system. Vaccines against pathogens are an invaluable tool developed to help the immune system cope with a potential infection or prevent disease pathology. Nowadays, there is accumulated evidence indicating that the powerful stimulation capacity of vaccines influences not only the effector arm of the immune system but also cells with regulatory/suppressor capacity, such as myeloid derived suppressor cells (MDSCs) and Foxp3+ regulatory T cells (Tregs). Trypanosoma cruzi (T. cruzi) is a protozoan parasite with a complex life cycle that has evolved several strategies to influence the regulatory immune response. Although diverse vaccine formulations have been able to stimulate the effector response, achieving non-sterilizing protection against T. cruzi, the influence of the vaccine candidates on the regulatory machinery has scarcely been assessed. This fact may not only reveal important information concerning how vaccines may influence cells with regulatory/suppressor capacity but also open the possibility to analyze whether vaccines are able to disrupt the mechanisms used by some pathogens to manipulate the host regulatory circuits. The aim of this review is to summarize and discuss available data related to the role of cellular components, like MDSCs and Foxp3+ Tregs, during T. cruzi infection, and the potential utility of those populations as additional targets for the rational design of vaccines.

TCR signal strength controls the differentiation of CD4+ effector and memory T cells

CD4⁺ T cell responses are composed of heterogeneous T cell receptor (TCR) signals that influence the acquisition of effector and memory characteristics. We sought to define early TCR-dependent activation events that control T cell differentiation. A polyclonal panel of TCRs specific for the same viral antigen demonstrated substantial variability in TCR signal strength, expression of CD25, and activation of nuclear factor of activated T cells and nuclear factor κB. After viral infection, strong TCR signals corresponded to T helper cell (T_H1) differentiation, whereas T follicular helper cell and memory T cell differentiation were most efficient when TCR signals were comparatively lower. We observed substantial heterogeneity in TCR-dependent CD25 expression in vivo, and the vast majority of CD4⁺ memory T cells were derived from CD25^lo effector cells that displayed decreased TCR signaling in vivo. Nevertheless, memory T cells derived from either CD25^lo or CD25^hi effector cells responded vigorously to rechallenge, indicating that, although early clonal differences in CD25 expression predicted memory T cell numbers, they did not predict memory T cell function on a per cell basis. Gene transcription analysis demonstrated expression clustering based on CD25 expression and enrichment of transcripts associated with enhanced T follicular helper cell and memory development within CD25^lo effector cells. Direct enhancement of TCR signaling via knockdown of Src homology region 2 domain-containing phosphatase 1, a tyrosine phosphatase that suppresses early TCR signaling events, favored the differentiation of T_H1 effector and memory cells. We conclude that strong TCR signals during early T cell activation favor terminal T_H1 differentiation over long-term T_H1 and T follicular helper cell memory responses.

Pathology and Pathogenesis of Chagas Heart Disease

Chagas heart disease is an inflammatory cardiomyopathy that develops in approximately one-third of people infected with the protozoan parasite Trypanosoma cruzi. One way T. cruzi is transmitted to people is through contact with infected kissing bugs, which are found in much of the Western Hemisphere, including in vast areas of the United States. The epidemiology of T. cruzi and Chagas heart disease and the varied mechanisms leading to myocyte destruction, mononuclear cell infiltration, fibrosis, and edema in the heart have been extensively studied by hundreds of scientists for more than 100 years. Despite this wealth of knowledge, it is still impossible to predict what will happen in an individual infected with T. cruzi because of the tremendous variability in clonal parasite virulence and human susceptibility to infection and the lack of definitive molecular predictors of outcome from either side of the host-parasite equation. Further, while several distinct mechanisms of pathogenesis have been studied in isolation, it is certain that multiple coincident mechanisms combine to determine the ultimate outcome. For these reasons, Chagas disease is best considered a collection of related but distinct illnesses. This review highlights the pathology and pathogenesis of the most common adverse sequela of T. cruzi infection-Chagas heart disease-and concludes with a discussion of key unanswered questions and a view to the future.

Regulatory Lymphoid and Myeloid Cells Determine the Cardiac Immunopathogenesis of Trypanosoma cruzi Infection

Chagas disease is a multisystemic disorder caused by the protozoan parasite Trypanosoma cruzi, which affects ~8 million people in Latin America, killing 7,000 people annually. Chagas disease is one of the main causes of death in the endemic area and the leading cause of infectious myocarditis in the world. T. cruzi infection induces two phases, acute and chronic, where the infection is initially asymptomatic and the majority of patients will remain clinically indeterminate for life. However, over a period of 10–30 years, ~30% of infected individuals will develop irreversible, potentially fatal cardiac syndromes (chronic chagasic cardiomyopathy [CCC]), and/or dilatation of the gastro-intestinal tract (megacolon or megaesophagus). Myocarditis is the most serious and frequent manifestation of chronic Chagas heart disease and appears in about 30% of infected individuals several years after infection occurs. Myocarditis is characterized by a mononuclear cell infiltrate that includes different types of myeloid and lymphoid cells and it can occur also in the acute phase. T. cruzi infects and replicates in macrophages and cardiomyocytes as well as in other nucleated cells. The pathogenesis of the chronic phase is thought to be dependent on an immune-inflammatory reaction to a low-grade replicative infection. It is known that cytokines produced by type 1 helper CD4+ T cells are able to control infection. However, the role that infiltrating lymphoid and myeloid cells may play in experimental and natural Chagas disease pathogenesis has not been completely elucidated, and several reports indicate that it depends on the mouse genetic background and parasite strain and/or inoculum. Here, we review the role that T cell CD4+ subsets, myeloid subclasses including myeloid-derived suppressor cells may play in the immunopathogenesis of Chagas disease with special focus on myocarditis, by comparing results obtained with different experimental animal models.

Scrutinizing the Biomarkers for the Neglected Chagas Disease: How Remarkable!

Biomarkers or biosignature profiles have become accessible over time in population-based studies for Chagas disease. Thus, the identification of consistent and reliable indicators of the diagnosis and prognosis of patients with heart failure might facilitate the prioritization of therapeutic management to those with the highest chance of contracting this disease. The purpose of this paper is to review the recent state and the upcoming trends in biomarkers for human Chagas disease. As an emerging concept, we propose a classification of biomarkers based on plasmatic-, phenotype-, antigenic-, genetic-, and management-related candidates. The available data revisited here reveal the lessons learned thus far and the existing challenges that still lie ahead to enable biomarkers to be employed consistently in risk evaluation for this disease. There is a strong need for biomarker validation, particularly for biomarkers that are specific to the clinical forms of Chagas disease. The current failure to achieve the eradication of the transmission of this disease has produced determination to solve this validation issue. Finally, it would be strategic to develop a wide variety of biomarkers and to test them in both preclinical and clinical trials.

Immunity and immune modulation in Trypanosoma cruzi infection

Chagas disease is caused by the protozoan Trypanosoma cruzi. The parasite reaches the secondary lymphoid organs, the heart, skeletal muscles, neurons in the intestine and esophagus among other tissues. The disease is characterized by mega syndromes, which may affect the esophagus, the colon and the heart, in about 30% of infected people. The clinical manifestations associated with T. cruzi infection during the chronic phase of the disease are dependent on complex interactions between the parasite and the host tissues, particularly the lymphoid system that may either result in a balanced relationship with no disease or in an unbalanced relationship that follows an inflammatory response to parasite antigens and associated tissues in some of the host organs and/or by an autoimmune response to host antigens. This review discusses the findings that support the notion of an integrated immune response, considering the innate and adaptive arms of the immune system in the control of parasite numbers and also the mechanisms proposed to regulate the immune response in order to tolerate the remaining parasite load, during the chronic phase of infection. This knowledge is fundamental to the understanding of the disease progression and is essential for the development of novel therapies and vaccine strategies.

Depletion of regulatory T cells decreases cardiac parasitosis and inflammation in experimental Chagas disease

Infection with the protozoan parasite Trypanosoma cruzi may lead to a potentially fatal cardiomyopathy known as Chagas heart disease. This disease is characterized by infiltration of the myocardium by mononuclear cells, including CD4+ T cells, together with edema, myofibrillary destruction, and fibrosis. A multifaceted systemic immune response develops that ultimately keeps parasitemia and tissue parasitosis low. T helper 1 and other pro-inflammatory T cell responses are effective at keeping levels of T. cruzi low in tissues and blood, but they may also lead to tissue inflammation when present chronically. The mechanism by which the inflammatory response is regulated in T. cruzi-infected individuals is complex, and the specific roles that Th17 and T regulatory (Treg) cells may play in that regulation are beginning to be elucidated. In this study, we found that depletion of Treg cells in T. cruzi-infected mice leads to reduced cardiac parasitosis and inflammation, accompanied by an augmented Th1 response early in the course of infection. This is followed by a downregulation of the Th1 response and increased Th17 response late in infection. The effect of Treg cell depletion on the Th1 and Th17 cells is not observed in mice immunized with T. cruzi in adjuvant. This suggests that Treg cells specifically regulate Th1 and Th17 cell responses during T. cruzi infection and may also be important for modulating parasite clearance and inflammation in the myocardium of T. cruzi-infected individuals.