Virusvaccin kan bli skydd mot typ 1-diabetes
Uppskattningsvis 50 000 svenskar lever med typ 1-diabetes, som ibland kallas för barndiabetes. Det är inte känt vad som orsakar sjukdomen. Vissa gener har stor betydelse, men det krävs också en miljöpåverkan för att sjukdomen ska utvecklas. En miljöfaktor som tros vara viktig i sammanhanget är infektioner orsakade av vissa typer av enterovirus, som är mycket vanliga virus. Den aktuella undergruppen kallas Coxsackie B och dessa virus består i sin tur av sex stammar, som bland annat kan leda till förkylning. Men Coxsackie B, CVB, kan också orsaka allvarligare infektioner, som hjärtmuskelinflammation (myokardit) och hjärnhinneinflammation (meningit).
Enligt en forskarhypotes antas CVB också spela en roll vid utvecklandet av diabetes typ 1. Sjukdomen kännetecknas av ett autoimmunt angrepp på de insulinproducerande betacellerna i bukspottskörteln och eventuellt kan virusinfektionen på något sätt påverka immunförsvaret i denna riktning. Epidemiologiska studier, där barn med genetisk riskprofil för typ 1-diabetes har följts via blodprov under många år, pekar mot att CVB kan ha en roll vid insjuknandet. Det finns också obduktionsfynd, som talar för att CVB kan ha betydelse för utvecklande av diabetes typ 1. Något säkert samband är dock inte påvisat, utan det rör sig om teorier, som dock är väl etablerade bland diabetesforskare.
Skyddar hos djur
Nu har forskare vid Karolinska Institutet tillsammans med kollegor vid Tampere University och University of Jyväskylä i Finland tagit fram ett vaccin som skyddar mot samtliga sex kända stammar av CVB. Vaccinet testades i djurmodeller och visade sig då skydda möss som infekterats med CVB från att utveckla diabetes typ 1.
Forskarna har sedan gått vidare och prövat vaccinet på rhesusapor, vars immunförsvar är mycket likt människans. De försöken har visat att vaccinet har en skyddande effekt mot dessa virusinfektioner, då apor som vaccinerats också har utvecklat antikroppar mot CVB.
– Resultaten ger stöd åt ett pågående kliniskt program som syftar till att testa ett liknande kommersiellt vaccin i människor, säger Heikki Hyöty, professor vid Tampere University som deltar i de kliniska prövningarna. Prövningarna görs av ett amerikanskt läkemedelsbolag i samarbete med ett finskt bioteknikbolag.
Ska provas på barn
Planen är att i nästa steg pröva det på barn som har en genetisk riskprofil för att utveckla diabetes typ 1. Om det på lång sikt visar sig att få eller inga av dessa barn utvecklar diabetes typ 1, då kan tesen om CVB som en utlösande miljöfaktor vara bekräftad, skriver forskarna i sin artikel.
– Förhoppningen är att vaccinet ska visa sig ge ett skydd mot typ 1-diabetes och att det i så fall skulle bli möjligt att ge till barn. Det vore fantastiskt om de fall som vi idag misstänker orsakas av Coxsackievirus i så fall skulle kunna förhindras, även om det är svårt att uppskatta hur många diabetespatienter som skulle kunna påverkas. Samtidigt skulle vaccinet ge ett skydd mot hjärtmuskelinflammation, som kan ha ett allvarligt förlopp hos både barn och vuxna, och mot många förkylningar, som skapar stora bortfall i skola och arbetsliv, säger Malin Flodström-Tullberg, professor i typ 1-diabetes vid institutionen för medicin, Huddinge, Karolinska Institutet, och studiens korresponderande författare.
A hexavalent Coxsackievirus B vaccine is highly immunogenic and has a strong protective capacity in mice and non-human primates. (V. M. Stone, M. M. Hankaniemi, O. H. Laitinen, A. B. Sioofy-Khojine, A. Lin, I. Diaz Lozano, M. A. Mazur, V. Marjomäki, K. Loré, H. Hyöty, V. P. Hytönen, M. Flodström-Tullberg) Science Advances, online 6 maj 2020.
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Coxsackievirus B (CVB) enteroviruses are common human pathogens known to cause severe diseases including myocarditis, chronic dilated cardiomyopathy, and aseptic meningitis. CVBs are also hypothesized to be a causal factor in type 1 diabetes. Vaccines against CVBs are not currently available, and here we describe the generation and preclinical testing of a novel hexavalent vaccine targeting the six known CVB serotypes. We show that the vaccine has an excellent safety profile in murine models and nonhuman primates and that it induces strong neutralizing antibody responses to the six serotypes in both species without an adjuvant. We also demonstrate that the vaccine provides immunity against acute CVB infections in mice, including CVB infections known to cause virus-induced myocarditis. In addition, it blocks CVB-induced diabetes in a genetically permissive mouse model. Our preclinical proof-of-concept studies demonstrate the successful generation of a promising hexavalent CVB vaccine with high immunogenicity capable of preventing CVB-induced diseases.
From the article Discussion
Our studies document the excellent immunogenicity of a novel hexavalent CVB1–6 vaccine in several mouse strains and a nonhuman primate model. We also report that this vaccine has the ability, in relevant preclinical models, to protect against acute CVB infections, block CVB infection of the heart, and prevent CVB-induced pancreatitis and diabetes.
Historically, there have been very few attempts to create a polyvalent CVB vaccine. In 1994, See and Tilles (33) described the efficacy of a CVB1–6 vaccine in mice; however, their vaccine did not completely protect against challenge from different CVB serotypes, only one mouse strain was used, and protection against CVB-induced diseases was not explored. In our study, a strong nAB response to all CVB1–6 viruses was induced both in mice and in rhesus macaques. Also, no unwanted side effects were seen in any of the species used. Moreover, several different mouse strains immunized with the hexavalent vaccine were protected from infection with the tested serotypes (CVB1, CVB3, and CVB4) and the vaccine did not affect the expression of genes involved in innate immunity 2 weeks after the final vaccination, suggesting that protection is mediated via the nAB response rather than residual activation of the innate immune system. Collectively, this demonstrates the excellent safety and strong efficacy of this newly developed experimental vaccine.
Our CVB1–6 vaccine shares a number of similarities with the inactivated poliovirus vaccine (IPV) that is being used worldwide (alongside the oral poliovirus vaccine) in an attempt to eradicate poliomyelitis. For instance, both vaccines are produced in Vero cells and are inactivated by formalin treatment. According to the World Health Organization (WHO) Practical Guide to IPV (2014), the preferred delivery of IPV is via the intramuscular route, and two to three basic immunizations are required early in life with a number of boost vaccinations later on for maximum immunity (over 90% of cases immunized after 8 weeks of age have sufficient immunological responses against all three poliovirus serotypes present in the vaccine after two immunizations; WHO Immunological Basis for Immunization Series: Module 6 Poliomyelitis). The results obtained with the CVB1–6 vaccine in rhesus macaques mirror the IPV vaccine, where intramuscular immunization of the CVB1–6 vaccine (with a boost dose after 28 days) resulted in a strong serum immunity against all six CVB serotypes, which lasted up to 10 weeks after the prime dose, when monitoring of the animals finished. These data were further supported by the murine studies, where the vast majority of mice immunized with the CVB1–6 vaccine had high nAB titers at the terminal time point (which varied between studies). In the initial studies using C57BL/6J mice, the CVB4 neutralizing capacity was lost by day 84 after the prime vaccination. This was not, however, a consistent finding, and strong CVB4 nAB titers were seen in both NOD and Balb/c mice. In NOD mice, CVB4 nAB titers were equal to 1:256 up to a period of 70 to 113 days after the prime vaccination (fig. S3).
The coadministration of an adjuvant at the time of immunization was not necessary in either mice or rhesus macaques for strong serum CVB immunity after CVB1–6 vaccination. Based on the strategies used for IPV, the similarities between the two vaccines, and the aforementioned results we have obtained (particularly in the rhesus macaques), it would be reasonable to assume that an immunization strategy with the CVB1–6 vaccine that followed a similar approach to that used for IPV would induce sufficient serum immunity in humans to protect against CVB infections. Although other enterovirus vaccines are also known to provide long-term and effective protection against infection (9), this must of course be established in clinical trials before the ability of the vaccine to prevent CVB-induced diseases can be established. Together, the CVB1–6 vaccine shows excellent promise with regard to the induction of nABs and the duration of the response.
One of the most well-documented diseases caused by CVBs is myocarditis, which can lead to DCM. Approximately 4 to 20% of sudden cardiac deaths in young adults are attributed to myocarditis and it also causes around 9% of DCM cases (4, 5). Moreover, in children, more than 40% of DCMs are estimated to result from myocarditis (34). In the United States alone, it was estimated that cardiomyopathies place a burden on the U.S. health care system of between $4 and $10 billion annually (6). Although CVBs are not associated with every case, they are the most commonly identified cause of the disease in developed countries (4) and are thought to account for around 25% of viral myocarditis cases [approximately 70% of clinical myocarditis and/or pericarditis cases are associated with specific viral infections (5)]. Various studies describe murine models for CVB3 myocarditis, including the initial description by Woodruff and Woodruff (35), and young male Balb/c mice are a commonly used model (4, 35). Here, we show that our hexavalent vaccine prevents acute CVB3 infections and the dissemination of virus to the heart (and pancreas) in Balb/c mice, highlighting the clinical relevance of such a vaccine for use in preventing CVB-induced diseases such as myocarditis in humans.
T1D is another disease associated with enteroviruses, but there is no definitive proof confirming the causal involvement of these viruses, despite a large variety of existing data that implicates enteroviruses, and more specifically CVBs, in the pathogenesis of the disease [as reviewed in (9, 10, 12, 13)]. Here we have demonstrated in a proof-of-concept study that our hexavalent CVB vaccine is capable of protecting SOCS-1-tg mice from virus-induced diabetes that occurs due to the direct infection and destruction of the pancreatic β-cells. Vaccination of children with genetic profiles that increase their T1D disease susceptibility risk and the subsequent monitoring of disease incidence would provide empirical evidence for a possible role of these viruses in T1D. Similar randomized clinical trials, like TRIGR (36) that examined the effects of dietary interventions on T1D, provide an example of such an intervention study performed to explore the causality of T1D-associated exposures. If T1D cases dropped in number in immunized children, the causal role of CVBs in T1D would be proven and the vaccine would provide a viable preventative treatment. This would, however, require immunization early in life or potentially immunity gained via the immunization of expectant mothers.
Further research could look to increase the valency of the vaccine to include, for instance, enterovirus A serotypes such as EV71 and CVA16, which are known to cause HFMD (8), and EV-D68, an enterovirus D serotype, that can result in severe respiratory illness (37) and is associated with acute flaccid paralysis in many studies (38). To this end, a study from 2016 documented the success of a 25-valent rhinovirus vaccine in mice and a 50-valent rhinovirus vaccine in rhesus macaques (39), suggesting the feasibility of such a vaccine. In this study, the vaccines were adjuvanted, which was not required for a strong immune response with our hexavalent vaccine. As such, this could be used if necessary when the valency of the vaccine is increased to include further enteroviruses. Virus-like particles (18, 21) could also be considered as an option, especially in the case of viruses that propagate poorly in cell culture.
A limitation of the study is that we have performed studies to show that the vaccine protects against three, namely, CVB1, CVB3, and CVB4, but not all six CVB serotypes in relevant preclinical murine disease models. Another limitation of the study is that a single strain of each CVB1–6 serotype was used to produce the individual vaccine components of the CVB1–6 hexavalent vaccine. At any given time, different CVB1–6 strains will be in circulation, which poses the challenge of producing a vaccine with the ability to protect against as many different strains as possible. It will be important in the future to properly assess the extent of the CVB strain coverage provided by the vaccine when it is produced for and tested in humans. Further to this, it would be of relevance to perform studies that examine whether and how formalin inactivation alters the antigenicity of the virus particles, as this may modify the ability of the vaccine to elicit protective nABs in humans.
To summarize, we have described the development and preclinical testing of a novel experimental hexavalent CVB vaccine with a high capacity to induce serum nABs in a number of animal models. Moreover, we show in proof-of-concept studies that the vaccine prevents acute CVB infections and CVB infections that can lead to CVB-induced diseases such as myocarditis and potentially T1D. Currently, there are no commercially available preventative measures that provide protection against CVB-induced diseases such as myocarditis, meningitis, and pancreatitis or for elucidating the role of these viruses in diseases like T1D. The vaccine we describe here provides a viable option for tackling CVB infections and associated diseases. As such, it is a prime candidate for human clinical trial and efforts to develop this type of polyvalent CVB vaccine for human use have recently been initiated (14).
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