Biological activity of an intravenous preparation of human vaccinia immune globulin in mouse models of vaccinia virus infection

Therapeutic agents for the treatment of human mpox

PURPOSE OF REVIEW

The aim of this study was to summarize the current knowledge of therapeutic options for mpox (formerly known as monkeypox) in the context of recent outbreaks and the ongoing evolution of the virus.

RECENT FINDINGS

Multiple therapeutic agents, including tecovirimat, cidofovir, brincidofovir, and vaccinia immune globulin, have been used during the multicountry outbreak of mpox caused by Clade 2b monkeypox virus that began in 2022. Tecovirimat has been most extensively used, based on efficacy against mpox lethal challenge in animal models, and human safety data. Real-world observational evidence has further supported safety with minimal adverse events in large cohorts and mixed reports of reductions in time to lesion resolution. Several prospective randomized controlled trials using tecovirimat are underway with headline results from a study in the Democratic Republic of the Congo showing no difference in lesion resolution compared to placebo. Other studies including in outpatient settings are underway in Europe and the Americas. Cidofovir and brincidofovir, limited by adverse event profiles, have been less extensively studied. Vaccinia immune globulin has been used predominantly in salvage therapy for severe mpox, with no large observational series available.

SUMMARY

The 2022 multicountry outbreak of mpox marked a public health emergency. Agents approved for smallpox management were widely used for mpox, supported by animal and in-vitro evidence, and human safety data. The large number of human cases has allowed retrospective observational study of these agents and facilitated recruitment in prospective trials. The ongoing evolution of the virus may pose challenges for therapeutic interventions, necessitating rigorous randomized controlled trials to guide clinical use.

Paediatric, maternal, and congenital mpox: a systematic review and meta-analysis

BACKGROUND

Although mpox has been detected in paediatric populations in central and west Africa for decades, evidence synthesis on paediatric, maternal, and congenital mpox, and the use of vaccines and therapeutics in these groups, is lacking. A systematic review is therefore indicated to set the research agenda.

METHODS

We conducted a systematic review and meta-analysis, searching articles in Embase, Global Health, MEDLINE, CINAHL, Web of Science, Scopus, SciELO, and WHO databases from inception to April 17, 2023. We included studies reporting primary data on at least one case of confirmed, suspected, or probable paediatric, maternal, or congenital mpox in humans or the use of third-generation smallpox or mpox vaccines, targeted antivirals, or immune therapies in at least one case in our population of interest. We included clinical trials and observational studies in humans and excluded reviews, commentaries, and grey literature. A pooled estimate of the paediatric case fatality ratio was obtained using random-effects meta-analysis. This study is registered with PROSPERO (CRD420223336648).

FINDINGS

Of the 61 studies, 53 reported paediatric outcomes (n=2123 cases), seven reported maternal or congenital outcomes (n=32 cases), two reported vaccine safety (n=28 recipients), and three reported transmission during breastfeeding (n=4 cases). While a subset of seven observational studies (21 children and 12 pregnant individuals) reported uneventful treatment with tecovirimat, there were no randomised trials reporting safety or efficacy for any therapeutic agent. Among children, the commonest clinical features included rash (86 [100%] of 86), fever (63 [73%] of 86), and lymphadenopathy (40 [47%] of 86). Among pregnant individuals, rash was reported in 23 (100%) of 23; fever and lymphadenopathy were less common (six [26%] and three [13%] of 23, respectively). Most paediatric complications (12 [60%] of 20) arose from secondary bacterial infections. The pooled paediatric case fatality ratio was 11% (95% CI 4-20), I2=75%. Data from 12 pregnancies showed half resulted in fetal death. Research on vaccine and immune globulin safety remains scarce for children and absent for pregnant individuals.

INTERPRETATION

Our review highlights critical knowledge gaps in the epidemiology, prevention, and treatment of mpox in children and pregnant individuals, especially those residing in endemic countries. Increased funding, international collaboration, and equitable research is needed to inform mpox control strategies tailored for at-risk communities in endemic countries.

FUNDING

None.

TRANSLATIONS

For the French, Spanish and Portuguese translations of the abstract see Supplementary Materials section.

Mpox (formerly monkeypox): pathogenesis, prevention, and treatment

In 2022, a global outbreak of Mpox (formerly monkeypox) occurred in various countries across Europe and America and rapidly spread to more than 100 countries and regions. The World Health Organization declared the outbreak to be a public health emergency of international concern due to the rapid spread of the Mpox virus. Consequently, nations intensified their efforts to explore treatment strategies aimed at combating the infection and its dissemination. Nevertheless, the available therapeutic options for Mpox virus infection remain limited. So far, only a few numbers of antiviral compounds have been approved by regulatory authorities. Given the high mutability of the Mpox virus, certain mutant strains have shown resistance to existing pharmaceutical interventions. This highlights the urgent need to develop novel antiviral drugs that can combat both drug resistance and the potential threat of bioterrorism. Currently, there is a lack of comprehensive literature on the pathophysiology and treatment of Mpox. To address this issue, we conducted a review covering the physiological and pathological processes of Mpox infection, summarizing the latest progress of anti-Mpox drugs. Our analysis encompasses approved drugs currently employed in clinical settings, as well as newly identified small-molecule compounds and antibody drugs displaying potential antiviral efficacy against Mpox. Furthermore, we have gained valuable insights from the process of Mpox drug development, including strategies for repurposing drugs, the discovery of drug targets driven by artificial intelligence, and preclinical drug development. The purpose of this review is to provide readers with a comprehensive overview of the current knowledge on Mpox.

Therapeutics for treating mpox in humans

BACKGROUND

Mpox was declared a Public Health Emergency of International Concern (PHEIC) by the World Health Organization (WHO) on 23 July 2022, following the identification of thousands of cases in several non-endemic countries in previous months. There are currently no licenced therapeutics for treating mpox; however, some medications may be authorized for use in an outbreak. The efficacy and safety of possible therapeutic options has not been studied in humans with mpox. There is a need to investigate the evidence on safety and effectiveness of treatments for mpox in humans; should any therapeutic option be efficacious and safe, it may be approved for use around the world.

OBJECTIVES

There are two parts to this Cochrane Review: a review of evidence from randomized controlled trials (RCTs), and a narrative review of safety data from non-randomized studies. Randomized controlled trials review To systematically review the existing evidence on the effectiveness of therapeutics for mpox infection in humans compared to: a) another different therapeutic for mpox, or b) placebo, or c) supportive care, defined as the treatment of physical and psychological symptoms arising from the disease. Non-randomized studies review To assess the safety of therapeutics for mpox infection from non-randomized studies (NRS).

SEARCH METHODS

Randomized controlled trials review We searched the following databases up to 25 January 2023: MEDLINE (OVID), Embase (OVID), Biosis previews (Web of Science), CAB Abstracts (Web of science), and Cochrane CENTRAL (Issue 1 2023). We conducted a search of trial registries (Clinicaltrials.gov and International Clinical Trials Registry Platform (ICTRP)) on 25 January 2023. There were no date or language limits placed on the search. We undertook a call to experts in the field for relevant studies or ongoing trials to be considered for inclusion in the review. Non-randomized studies review We searched the following databases on 22 September 2022: Cochrane Central Register of Controlled Trials (CENTRAL; Issue 9 of 12, 2022), published in the Cochrane Library; MEDLINE (Ovid); Embase (Ovid); and Scopus (Elsevier). We also searched the WHO International Clinical Trials Registry Platform and ClinicalTrials.gov for trials in progress.

SELECTION CRITERIA

For the RCT review and the narrative review, any therapeutic for the treatment of mpox in humans was eligible for inclusion, including tecovirimat, brincidofovir, cidofovir, NIOCH-14, immunomodulators, and vaccine immune globulin. Randomized controlled trials review Studies were eligible for the main review if they were of randomized controlled design and investigated the effectiveness or safety of therapeutics in human mpox infection. Non-randomized studies review Studies were eligible for inclusion in the review of non-randomized studies if they were of non-randomized design and contained data concerning the safety of any therapeutic in human mpox infection.

DATA COLLECTION AND ANALYSIS

Randomized controlled trials review Two review authors independently applied study inclusion criteria to identify eligible studies. If we had identified any eligible studies, we planned to assess the risk of bias, and report results with 95% confidence intervals (CI). The critical outcomes were serious adverse events, development of disease-related complications, admission to hospital for non-hospitalized participants, pain as judged by any visual or numerical pain scale, level of virus detected in clinical samples, time to healing of all skin lesions, and mortality. We planned to perform subgroup analysis to explore whether the effect of the therapeutic on the planned outcomes was modified by disease severity and days from symptom onset to therapeutic administration. We also intended to explore the following subgroups of absolute effects: immunosuppression, age, and pre-existing skin disease. Non-randomized studies review One review author applied study inclusion criteria to identify eligible studies and extracted data. Studies of a non-randomized design containing data on the safety of therapeutics could not be meta-analyzed due to the absence of a comparator; we summarized these data narratively in an appendix.

MAIN RESULTS

Randomized controlled trials review We did not identify any completed RCTs investigating the effectiveness of therapeutics for treating mpox for the main review. We identified five ongoing trials that plan to assess the effectiveness of one therapeutic option, tecovirimat, for treating mpox in adults and children. One of these ongoing trials intends to include populations with, or at greater risk of, severe disease, which will allow an assessment of safety in more vulnerable populations. Non-randomized studies review Three non-randomized studies met the inclusion criteria for the narrative review, concerning data on the safety of therapeutics in mpox. Very low-certainty evidence from non-randomized studies of small numbers of people indicates no serious safety signals emerging for the use of tecovirimat in people with mpox infection, but a possible safety signal for brincidofovir. All three participants who received brincidofovir had raised alanine aminotransferase (ALT), but not bilirubin, suggesting mild liver injury. No study reported severe drug-induced liver injury with brincidofovir.

AUTHORS' CONCLUSIONS

Randomized controlled trials review This review found no evidence from randomized controlled trials concerning the efficacy and safety of therapeutics in humans with mpox. Non-randomized studies review Very low-certainty evidence from non-randomized studies indicates no serious safety signals emerging for the use of tecovirimat in people with mpox infection. In contrast, very low-certainty evidence raises a safety signal that brincidofovir may cause liver injury. This is also suggested by indirect evidence from brincidofovir use in smallpox. This warrants further investigation and monitoring. This Cochrane Review will be updated as new evidence becomes available to assist policymakers, health professionals, and consumers in making appropriate decisions for the treatment of mpox.

African Swine Fever Vaccinology: The Biological Challenges from Immunological Perspectives

African swine fever virus (ASFV), a nucleocytoplasmic large DNA virus (NCLDV), causes African swine fever (ASF), an acute hemorrhagic disease with mortality rates up to 100% in domestic pigs. ASF is currently epidemic or endemic in many countries and threatening the global swine industry. Extensive ASF vaccine research has been conducted since the 1920s. Like inactivated viruses of other NCLDVs, such as vaccinia virus, inactivated ASFV vaccine candidates did not induce protective immunity. However, inactivated lumpy skin disease virus (poxvirus) vaccines are protective in cattle. Unlike some experimental poxvirus subunit vaccines that induced protection, ASF subunit vaccine candidates implemented with various platforms containing several ASFV structural genes or proteins failed to protect pigs effectively. Only some live attenuated viruses (LAVs) are able to protect pigs with high degrees of efficacy. There are currently several LAV ASF vaccine candidates. Only one commercial LAV vaccine is approved for use in Vietnam. LAVs, as ASF vaccines, have not yet been widely tested. Reports thus far show that the onset and duration of protection induced by the LAVs are late and short, respectively, compared to LAV vaccines for other diseases. In this review, the biological challenges in the development of ASF vaccines, especially subunit platforms, are discussed from immunological perspectives based on several unusual ASFV characteristics shared with HIV and poxviruses. These characteristics, including multiple distinct infectious virions, extremely high glycosylation and low antigen surface density of envelope proteins, immune evasion, and possible apoptotic mimicry, could pose enormous challenges to the development of ASF vaccines, especially subunit platforms designed to induce humoral immunity.

The prophylactic effects of human IgG derived from sera containing high anti-PcrV titers against pneumonia-causing Pseudomonas aeruginosa

The PcrV cap structure of the type III secretory apparatus of Pseudomonas aeruginosa is a vaccine target. Human immunoglobulin G (IgG) molecules extracted from sera containing high or low anti-PcrV titers were tested for their effects against P. aeruginosa pneumonia in a mouse model. Among 198 volunteers, we selected the top 10 high anti-PcrV titer sera and the bottom 10 low anti-PcrV titer sera and extracted the IgG fraction from each serum sample. First, we examined the effects of the IgG against virulent P. aeruginosa. A lethal dose of P. aeruginosa premixed with saline, low titer human IgG, high titer human IgG, or rabbit-derived polyclonal anti-PcrV IgG was intratracheally administered into the lungs of mice, and their survival and lung inflammation were evaluated for 24 h. The high anti-PcrV titer human IgG had a prophylactic effect. Next, the prophylactic effects of intravenous administration of extracted and pooled high or low anti-PcrV titer human IgG were examined. Here, prophylactic intravenous administration of pooled high anti-PcrV titer human IgG, which showed binding capacity to P. aeruginosa PcrV, was more effective than the administration of its low titer pooled equivalent, and the measured physiological and inflammatory parameters correlated with the anti-PcrV titer levels. This result indirectly implies that high anti-PcrV titers in blood can help to protect against virulent P. aeruginosa infections. In addition, the IgG fractions from such high titer sera have potential to be a source of specific intravenous immunoglobulin products for passive vaccination against virulent P. aeruginosa infections.

Enhanced efficacy of cidofovir combined with vaccinia immune globulin in treating progressive cutaneous vaccinia virus infections in immunosuppressed hairless mice

The treatment of progressive vaccinia in individuals has involved antiviral drugs, such as cidofovir (CDV), brincidofovir, and/or tecovirimat, combined with vaccinia immune globulin (VIG). VIG is costly, and its supply is limited, so sparing the use of VIG during treatment is an important objective. VIG sparing was modeled in immunosuppressed mice by maximizing the treatment benefits of CDV combined with VIG to determine the effective treatments that delayed the time to death, reduced cutaneous lesion severity, and/or decreased tissue viral titers. SKH-1 hairless mice immunosuppressed with cyclophosphamide and hairless SCID mice (SHO strain) were infected cutaneously with vaccinia virus. Monotherapy, dual combinations (CDV plus VIG), or triple therapy (topical CDV, parenteral CDV, and VIG) were initiated 2 days postinfection and were given every 3 to 4 days through day 11. The efficacy assessment included survival rate, cutaneous lesion severity, and viral titers. Delays in the time to death and the reduction in lesion severity occurred in the following order of efficacy: triple therapy had greater efficacy than double combinations (CDV plus VIG or topical plus parenteral CDV), which had greater efficacy than VIG alone. Parenteral administration of CDV or VIG was necessary to suppress virus titers in internal organs (liver, lung, and spleen). The skin viral titers were significantly reduced by triple therapy only. The greatest efficacy was achieved by triple therapy. In humans, this regimen should translate to a faster cure rate, thus sparing the amount of VIG used for treatment.

Protection of rabbits and immunodeficient mice against lethal poxvirus infections by human monoclonal antibodies

Smallpox (variola virus) is a bioweapon concern. Monkeypox is a growing zoonotic poxvirus threat. These problems have resulted in extensive efforts to develop potential therapeutics that can prevent or treat potentially lethal poxvirus infections in humans. Monoclonal antibodies (mAbs) against smallpox are a conservative approach to this problem, as the licensed human smallpox vaccine (vaccinia virus, VACV) primarily works on the basis of protective antibody responses against smallpox. Fully human mAbs (hmAbs) against vaccinia H3 (H3L) and B5 (B5R), targeting both the mature virion (MV) and extracellular enveloped virion (EV) forms, have been developed as potential therapeutics for use in humans. Post-exposure prophylaxis was assessed in both murine and rabbit animal models. Therapeutic efficacy of the mAbs was assessed in three good laboratory practices (GLP) studies examining severe combined immunodeficiency mice (SCID) given a lethal VACV infection. Pre-exposure combination hmAb therapy provided significantly better protection against disease and death than either single hmAb or vaccinia immune globulin (VIG). Post-exposure combination mAb therapy provided significant protection against disease and death, and appeared to fully cure the VACV infection in ≥50% of SCID mice. Therapeutic efficacy was then assessed in two rabbit studies examining post-exposure hmAb prophylaxis against rabbitpox (RPXV). In the first study, rabbits were infected with RPVX and then provided hmAbs at 48 hrs post-infection, or 1 hr and 72 hrs post-infection. Rabbits in both groups receiving hmAbs were 100% protected from death. In the second rabbitpox study, 100% of animal treated with combination hmAb therapy and 100% of animals treated with anti-B5 hmAb were protected. These findings suggest that combination hmAb treatment may be effective at controlling smallpox disease in immunocompetent or immunodeficient humans.

Development of the small-molecule antiviral ST-246 as a smallpox therapeutic

Naturally occurring smallpox has been eradicated, yet it remains as one of the highest priority pathogens due to its potential as a biological weapon. The majority of the US population would be vulnerable in a smallpox outbreak. SIGA Technologies, Inc. has responded to the call of the US government to develop and supply to the Strategic National Stockpile a smallpox antiviral to be deployed in the event of a smallpox outbreak. ST-246(®) (tecovirimat) was initially identified via a high-throughput screen in 2002, and in the ensuing years, our drug-development activities have spanned in vitro analysis, preclinical safety, pharmacokinetics and efficacy testing (all according to the 'animal rule'). Additionally, SIGA has conducted Phase I and II clinical trials to evaluate the safety, tolerability and pharmacokinetics of ST-246, bringing us to our current late stage of clinical development. This article reviews the need for a smallpox therapeutic and our experience in developing ST-246, and provides perspective on the role of a smallpox antiviral during a smallpox public health emergency.

Smallpox vaccines: targets of protective immunity

The eradication of smallpox, one of the great triumphs of medicine, was accomplished through the prophylactic administration of live vaccinia virus, a comparatively benign relative of variola virus, the causative agent of smallpox. Nevertheless, recent fears that variola virus may be used as a biological weapon together with the present susceptibility of unimmunized populations have spurred the development of new-generation vaccines that are safer than the original and can be produced by modern methods. Predicting the efficacy of such vaccines in the absence of human smallpox, however, depends on understanding the correlates of protection. This review outlines the biology of poxviruses with particular relevance to vaccine development, describes protein targets of humoral and cellular immunity, compares animal models of orthopoxvirus disease with human smallpox, and considers the status of second- and third-generation smallpox vaccines.

Postexposure prevention of progressive vaccinia in SCID mice treated with vaccinia immune globulin

A recently reported case of progressive vaccinia (PV) in an immunocompromised patient has refocused attention on this condition. Uniformly fatal prior to the licensure of vaccinia immune globulin (VIG) in 1978, PV was still fatal in about half of VIG-treated patients overall, with a greater mortality rate in infants and children. Additional therapies would be needed in the setting of a smallpox bioterror event, since mass vaccination following any variola virus release would inevitably result in exposure of immunocompromised people through vaccination or contact with vaccinees. Well-characterized animal models of disease can support the licensure of new products when human studies are not ethical or feasible, as in the case of PV. We chose vaccinia virus-scarified SCID mice to model PV. As in immunocompromised humans, vaccinia virus-scarified SCID animals develop enlarging primary lesions with minimal or no inflammation, eventual distal virus spread, and lethal outcomes if left untreated. Postexposure treatment with VIG slowed disease progression, caused local lesion regression, and resulted in the healthy survival of most of the mice for more than 120 days. Combination treatment with VIG and topical cidofovir also resulted in long-term disease-free survival of most of the animals, even when initiated 7 days postinfection. These results support the possibility that combination treatments may be effective in humans and support using this SCID model of PV to test new antibody therapies and combination therapies and to provide further insights into the pathogenesis and treatment of PV.

Therapeutic Vaccines and Antibodies for Treatment of Orthopoxvirus Infections

Despite the eradication of smallpox several decades ago, variola and monkeypox viruses still have the potential to become significant threats to public health. The current licensed live vaccinia virus-based smallpox vaccine is extremely effective as a prophylactic vaccine to prevent orthopoxvirus infections, but because of safety issues, it is no longer given as a routine vaccine to the general population. In the event of serious human orthopoxvirus infections, it is important to have treatments available for individual patients as well as their close contacts. The smallpox vaccine and vaccinia immune globulin (VIG) were used in the past as therapeutics for patients exposed to smallpox. VIG was also used in patients who were at high risk of developing complications from smallpox vaccination. Thus post-exposure vaccination and VIG treatments may again become important therapeutic modalities. This paper summarizes some of the historic use of the smallpox vaccine and immunoglobulins in the post-exposure setting in humans and reviews in detail the newer animal studies that address the use of therapeutic vaccines and immunoglobulins in orthopoxvirus infections as well as the development of new therapeutic monoclonal antibodies.

Combination therapy of vaccinia virus infection with human anti-H3 and anti-B5 monoclonal antibodies in a small animal model

BACKGROUND

Treatment of rare severe side effects of vaccinia virus (VACV) immunization in humans is currently very challenging. VACV possesses two immunologically distinct virion forms in vivo - intracellular mature virion (MV, IMV) and extracellular virion (EV, EEV).

METHODS

Antibody-mediated therapeutic efficacy was determined against VACV infection in a small animal model of progressive vaccinia. The model consisted of severe combined immunodeficiency mice infected with VACV New York City Board of Health vaccine strain and treated with monoclonal antibodies (mAbs).

RESULTS

Here, we show that combination therapy with two fully human mAbs against an immunodominant MV antigen, H3 (H3L), and an EV antigen, B5 (B5R), provides significantly better protection against disease and death than either single human monoclonal or human vaccinia immune globulin, the currently licensed therapeutic for side effects of smallpox vaccination.

CONCLUSIONS

The preclinical studies validate that this combination of mAbs against H3 and B5 is a promising approach as a poxvirus infection treatment for use in humans.

Effective post-exposure protection against lethal orthopoxviruses infection by vaccinia immune globulin involves induction of adaptive immune response

The therapeutic potential of human vaccinia immunoglobulin (VIG) in orthopoxvirus infection was examined using two mouse models for human poxvirus, based on Ectromelia virus and Vaccinia Western Reserve (WR) respiratory infections. Despite the relatively fast clearance of human VIG from mice circulation, a single VIG injection protected immune-competent mice against both infections. Full protection against lethal Ectromelia virus infection was achieved by VIG injection up to one day post-exposure, and even injection of VIG two or three days post-infection conferred solid protection (60-80%). Nevertheless, VIG failed to protect VACV-WR challenged immune-deficient mice, even though repeated injections prolonged SCID mice survival. These results suggest the involvement of host immunity in protection. VIG provides the initial protective time-window allowing induction of the adaptive response required to achieve complete protection. Additionally, VIG can be administered in conjunction with active Vaccinia-Lister vaccination. Vaccine efficiency is not impaired, providing a non-prohibitive VIG dose is used. Thus, VIG can be used as a prophylactic measure against post-vaccinal complications but could also serve for post-exposure treatment against smallpox.

Vaccinia virus extracellular enveloped virion neutralization in vitro and protection in vivo depend on complement

Antibody neutralization is an important component of protective immunity against vaccinia virus (VACV). Two distinct virion forms, mature virion and enveloped virion (MV and EV, respectively), possess separate functions and nonoverlapping immunological properties. In this study we examined the mechanics of EV neutralization, focusing on EV protein B5 (also called B5R). We show that neutralization of EV is predominantly complement dependent. From a panel of high-affinity anti-B5 monoclonal antibodies (MAbs), the only potent neutralizer in vitro (90% at 535 ng/ml) was an immunoglobulin G2a (IgG2a), and neutralization was complement mediated. This MAb was the most protective in vivo against lethal intranasal VACV challenge. Further studies demonstrated that in vivo depletion of complement caused a >50% loss of anti-B5 IgG2a protection, directly establishing the importance of complement for protection against the EV form. However, the mechanism of protection is not sterilizing immunity via elimination of the inoculum as the viral inoculum consisted of a purified MV form. The prevention of illness in vivo indicated rapid control of infection. We further demonstrate that antibody-mediated killing of VACV-infected cells expressing surface B5 is a second protective mechanism provided by complement-fixing anti-B5 IgG. Cell killing was very efficient, and this effector function was highly isotype specific. These results indicate that anti-B5 antibody-directed cell lysis via complement is a powerful mechanism for clearance of infected cells, keeping poxvirus-infected cells from being invisible to humoral immune responses. These findings highlight the importance of multiple mechanisms of antibody-mediated protection against VACV and point to key immunobiological differences between MVs and EVs that impact the outcome of infection.

Initiation of primary anti-vaccinia virus immunity in vivo

The primary focus of our work is the initiation of an antiviral immune response. While we employ many experimental systems to address this fundamental issue, much of our work revolves around the use of vaccinia virus. Concerns over the negative effects of vaccination have prevented the return of the smallpox immunization program to the general population and underscored the importance of understanding the primary immune response to vaccinia virus. This response is comprised of a complex symphony of immune system components employing a variety of different mechanisms. In this review, we will both highlight the roles of many of these components and touch on the applications of vaccinia virus in the laboratory and the clinic.

Immunity and immunological memory following smallpox vaccination

The smallpox vaccine consists of live vaccinia virus and is generally considered the gold standard of vaccines, since it is the only one that has led to the complete eradication of an infectious disease from the human population. Renewed fears that smallpox might be deliberately released in an act of bioterrorism have led to resurgence in the study of immunity and immunological memory to vaccinia virus and other poxviruses. Here we review our current understanding of memory T-cell, memory B-cell, and antibody responses to vaccinia and related poxviruses, both in animal models and human subjects. Of particular interest are recent advances in understanding protective immunity to poxviruses, quantifying immunological memory to the smallpox vaccine in humans, and identifying major vaccinia-specific T-cell and B-cell epitopes. In addition, potential mechanisms for maintenance of immunological memory are discussed.