Understanding the Immune Response to Two Different Meningitis Vaccines
Understanding the Immune Response to Two Different Meningitis Vaccines
The bacterium (germ) Neisseria meningitidis causes meningitis and blood poisoning. N
 meningitidis is classified into different serogroups (types), based on its outer
 polysaccharide (carbohydrate) capsule. Serogroups A,B,C,W & Y are responsible for the vast
 majority of meningococcal disease worldwide.

 Older vaccines against types A,C,W & Y contain part of the polysaccharide capsule of the
 germ. However, these polysaccharide vaccines do not provide long-term protection against
 disease and are less effective in young children, the group most at risk of meningococcal
 disease. Newer "conjugate" ACWY vaccines attach a polysaccharide to a protein carrier - these
 provoke a good response in young children and can provide long-term protection.

 White blood cells called B cells produce antibodies, which are the main components of
 protection against meningococcal disease. Although many studies have investigated the immune
 response to these vaccines in different age groups by measuring specific antibodies, there is
 limited information about the B cells underlying such an immune response. Several different
 subsets (populations) of B cells exist in the blood. Previous studies by the investigators
 group suggest that different numbers of B cells are produced in response to each vaccine
 type. However, little is understood about which subset of B cell is important for antibody
 production in response to these polysaccharide or conjugate vaccines.

 This study aims to provide detailed information on the immune response to meningococcal
 vaccines by investigating the appearance of B cells and their subsets in the blood after
 vaccination with the polysaccharide and conjugate vaccines. These observations will help us
 understand how polysaccharide and conjugate vaccines stimulate the immune system in different
 ways. This knowledge will help in the development of new vaccines that are effective across
 all age groups.

 The investigators aim to recruit 20 adults aged 30-70 from Oxfordshire. The study will be
 funded by the Oxford Vaccine Group.
EPIDEMIOLOGY

 Neisseria meningitidis is a globally important cause of meningitis and septicaemia. The
 polysaccharide capsule is an important virulence factor in causing invasive disease. The
 serogroup of a meningococcal strain is determined by the biochemical composition of the
 polysaccharide capsule. There are 13 diverse polysaccharide capsules but only A, B, C, W and
 Y commonly cause invasive infections. In particular serogroups A,C,W, & Y account for >70% of
 meningococcal disease in North America, serogroups B & C are responsible for the vast
 majority of disease in Europe and Serogroup A causes cyclical meningitis epidemics in the
 African meningitis belt, including the recent outbreak in 2009/2010.

 Given the rapid progression and serious sequelae of meningococcal disease, primary prevention
 is vital and this is most effectively achieved by vaccination. In the absence of a serogroup
 B vaccine, quadrivalent vaccines against serogroups ACW & Y represent the broadest mechanism
 of control of meningococcal disease worldwide. Protection induced by these vaccines relies on
 anti-capsular polysaccharide antibodies.

 MENINGOCOCCAL POLYSACCHARIDE AND CONJUGATE VACCINES

 Polysaccharide ACWY vaccines consist of pure capsular polysaccharide from each of the four
 serogroups and have been in widespread use since the late 1970's. However, in common with
 polysaccharide vaccines against other encapsulated bacteria, meningococcal polysaccharide
 vaccines are poorly immunogenic in young children, do not provoke long lasting immune
 responses[5] and may not reduce nasopharyngeal carriage. Newer conjugate vaccines consist of
 capsular oligosaccharides chemically linked to a protein carrier. Conjugation of a
 polysaccharide to a protein carrier allows the recruitment of cognate T cell help with
 subsequent exposure to antigen provoking a potentiated antibody response and immunological
 memory.

 This study aims to investigate novel aspects of the B cell immune responses to meningococcal
 polysaccharide and conjugate vaccines. To achieve this, we will administer a quadrivalent
 ACWY polysaccharide vaccine (MenACWY-PS), and a quadrivalent ACWY conjugate vaccine
 (MenACWY-CRM) containing capsular oligosaccharides of serogroups A, C, W-135 & Y conjugated
 to a CRM197 mutant diphtheria toxoid carrier to adult volunteers. Each of these vaccines
 contains different amounts of capsular antigen (see Table 1). The polysaccharide vaccine has
 50µg of polysaccharide from each of the 4 serogroups, while the conjugate has 10µg of A and
 5µg of each of C, W & Y.

 A recent trial using MenACWY-PS and MenACWY-CRM conducted by the Oxford Vaccine Group
 (Understanding the Immune Response to Meningitis Vaccines, OXREC 09/H0606/20, Eudract
 2007-001349-17) showed preliminary evidence of a difference in B cell responses to
 polysaccharide and conjugate meningococcal vaccines. However, a confounding factor in
 interpreting the data from this trial has been the difference in the amount of capsular
 antigen contained in each of the two types of vaccine used in the study.

 Full dose MenACWY-PS Polysaccharide vaccine has 50µg each of MenA, MenC,MenW and MenY
 capsular antigen. MenACWY-CRM Conjugate vaccine contains 10µg of MenA capsular antigen and
 5µg each of MenC, MenW and MenY.

 The current study is designed to compare both the full dose MenACWY-PS and a 1/5th dose of
 MenACWY-PS (which contains 10µg of each serogroup) to a full dose of MenACWY-CRM. This will
 differentiate between a polysaccharide dose-dependent response and a true polysaccharide
 vaccine vs. conjugate vaccine response. In particular, we aim to investigate the thymus
 dependent or thymus independent nature of the immune response to polysaccharide and conjugate
 meningococcal vaccines respectively.

 THYMUS INDEPENDENT AND THYMUS DEPENDENT IMMUNE RESPONSES

 Thymus independent (TI) antigens are defined by their ability to induce immune responses in
 T-cell deficient or athymic mice. In common with other high molecular weight molecules with
 repetitive structures, polysaccharide vaccine antigens are further classified as Type 2 TI
 antigens. The repetitive polysaccharide epitopes cross-link the BCR of antigen specific B
 cells, triggering activation signals and stimulating proliferation and differentiation into
 antibody-secreting plasma cells. The absence of T cell help precludes the generation of
 memory B cells.

 TI responses are thought to be largely mediated by marginal zone B cells (MZB), which mature
 in the marginal zone of the spleen. This compartment is poorly developed in children under
 two years of age, which results in an ineffective anti-polysaccharide immune response in this
 age group. Murine studies have revealed an important role for a further subset of mature B
 cells, B1b cells, in adaptive immunity . Unlike the development of conventional B cell
 memory, which requires the formation of germinal centres and T cells, the development of B1b
 cell-mediated long-lasting antibody responses occur independently of T cell- help.

 In contrast, conjugate vaccines act as thymus dependent (TD) antigens. Binding of the
 polysaccharide moiety to antigen specific B cell receptors allows uptake of the
 polysaccharide protein conjugate and processing via the classical MHC class II pathway.
 Peptides derived from the carrier protein are presented to cognate CD4+ T helper cells, which
 provide signals for further B cell differentiation.

 TD responses are mediated by follicular B cells (FOB), with generation of antibody secreting
 plasma cells and memory B cells, capable of responding to further specific antigenic
 challenge[10]. Recent work conducted at the Oxford Vaccine Group suggests that pneumococcal
 polysaccharide and conjugate vaccines induce B1b and FOB cells, respectively. This study will
 investigate whether this also holds true for meningococcal conjugate and polysaccharide
 vaccines. This will be done by analysing the different populations of B cells produced in
 response to the full dose polysaccharide vaccine, 1/5th polysaccharide vaccine and conjugate
 vaccine using novel immunological techniques developed in our laboratories.

 HYPORESPONSIVENESS

 Vaccine-induced hyporesponsiveness is the inability to mount a booster response of at least
 the same magnitude as that produced to the priming dose. Previous vaccination with
 meningococcal polysaccharide vaccine has been shown to impair antibody responses to
 subsequent meningococcal polysaccharide or conjugate vaccines. The design of this study will
 allow investigation of the phenomenon of polysaccharide induced hyporesponsiveness in
 quadrivalent meningococcal vaccines at the level of memory B cell and plasma cell responses.

 SEROGROUP A

 Unlike the sialic acid based polysaccharide capsules of serogroups B, C, W-135 & Y, serogroup
 A meningococcal capsules are composed of N-acetyl mannosamine phosphate. Plain serogroup A
 polysaccharide vaccines show unexpected immunogenicity in young infants.These results suggest
 that perhaps due to its chemical structure, group A polysaccharide may not be handled by the
 immune system as a classic TI antigen. This study will test the hypothesis that follicular B
 cells are produced in response to the serogroup A component of MenACWY-PS, and by contrast,
 marginal zone or B1b cells are produced in response to the serogroup C component of the same
 vaccine. This study will also test the hypothesis that follicular B cells are produced in
 response to serogroups A and C components of MenACWY-CRM.

 ANTIBODY REPERTOIRE

 The human humoral response is anticipatory; potential specific antibody exists prior to
 encountering the extensive collection of antigen encountered over the lifetime of an
 individual. The basis for this diverse repertoire is the multiple gene segments comprising
 the variable region of the antibody molecule. The potential for each V D & J segment to
 combine randomly introduces combinatorial diversity to the repertoire. During rearrangement,
 further nucleotides may be added to or removed from the junction of the gene segments, termed
 junctional diversity. Furthermore, during maturation of the antibody response, somatic
 hypermutation of the variable region occurs during B cell proliferation in the germinal
 centres. This underlies the increase in antibody affinity in secondary responses to antigen.
 These mechanisms help create a potential repertoire of up to 1016 antibody molecules.

 Previous studies have shown that the human humoral response to specific antigens is
 restricted in diversity within the individual and across populations with a limited number of
 antibody encoding variable region genes being utilised. These studies have relied on
 traditional vector cloning and Sanger sequencing of rearranged heavy chain loci of single
 cells, and are limited in the scope of their analysis of potential repertoire.

 Massive parallel sequencing and emulsion PCR are powerful new tools enabling large scale DNA
 sequencing with the potential to simultaneously sequence up to one million reads per run.
 These techniques have been applied to look at the potential antibody repertoire in zebrafish,
 the human antibody repertoire in specific B cell subsets[20] and to assess clonality of
 leukaemoid cells. This study aims to compare the VDJ repertoire in memory B cell populations
 before and after polysaccharide and conjugate ACWY vaccination.

 ANALYSIS OF GENETIC INFLUENCES ON THE IMMUNE RESPONSE

 A further aspect to be assessed in this study is the impact of genetic factors on the
 response to immunisation. Twin studies on several vaccines including measles, mumps and
 rubella, have shown high heritability of vaccine antibody responses. Some genetic
 associations have already been identified between genes of the adaptive and innate immune
 response and some vaccines, for example human leukocyte antigen (HLA) alleles and measles
 antibody responses and IL-1β polymorphisms and hepatitis B vaccine responses. These studies
 have been small scale and based on single candidate genes and the extent to which genetic
 variation contributes to vaccine responses remains poorly understood. Insight into which
 genetic variants affect responses to specific vaccines will help identify the critical immune
 pathways leading to protection after vaccination and lead to the production of more effective
 vaccines. In addition, the identification of genes that may play important roles in wild-type
 infection will allow a better understanding of disease pathogenesis, which in turn may lead
 to the development of novel therapies

 The blood samples obtained in this study provide a source of DNA can then contribute to a DNA
 bank pooling samples from multiple different Oxford Vaccine Group studies. These DNA samples
 can then be used for genome wide analysis of the genetic factors influencing the host
 response to the vaccines received in the relevant studies. This DNA extraction and storage
 will only occur with the specific consent of participants, and DNA will not be analysed for
 any other purpose than to assess factors influencing the immune response to vaccines. Serum
 left over from separation of the cellular plug for DNA extraction will also be stored and
 further immunological assays such as the quantification of functional antibody by serum
 bactericidal activity may also be performed on them.

 SUMMARY

 This study aims to investigate in detail aspects of the B cell response to conjugate and
 polysaccharide quadrivalent meningococcal vaccines in healthy adults using a variety of novel
 laboratory methods.
Inclusion Criteria:

 Participants must meet the following conditions in order to be enrolled:

 -  Between 30 and 70 years of age inclusive;

 -  Willing and able to give informed consent for participation after the nature of the
 study has been explained;

 -  In good health as determined by:

 medical history history-directed physical examination clinical judgment of the investigator

 -  Able (in the Investigators opinion) and willing to comply with all study requirements
 including be available for all the visits scheduled in the study;

 -  Willing to allow his or her General Practitioner and consultant, if appropriate, to be
 notified of participation in the study.

 Exclusion Criteria:

 Participants with any of the following conditions or characteristics will be excluded from
 study enrolment:

 -  Prior receipt of a meningococcal vaccine;

 -  Prior laboratory confirmed disease caused by N meningitides;

 -  Prior history of any anaphylactic shock, asthma, urticarial or other allergic reaction
 after previous vaccinations or known hypersensitivity to any vaccine component;

 -  Known or suspected autoimmune disease or impairment /alteration of immune function
 resulting from (for example):

 -  Receipt of immunostimulants

 -  Congenital or acquired immunodeficiency, or receipt of immunosuppressive therapy
 such as anti-cancer chemotherapy or radiation therapy within the preceding year
 or long-term systemic corticosteroid therapy (prednisolone or equivalent for more
 than two consecutive weeks within the past 3 months).

 -  Suspected or known HIV infection or HIV related disease;

 -  Receipt of blood, blood products and/or plasma derivatives or any parenteral
 immunoglobulin preparation in the past 3 months

 -  Known bleeding diathesis, or any condition that may be associated with a prolonged
 bleeding time;

 -  Any condition, which, in the opinion of the investigator, might interfere with the
 evaluation of the study objectives;

 -  Participation in another clinical trial investigating a vaccine, a drug, a medical
 device, or a medical procedure;

 -  Pregnancy as confirmed by a positive pregnancy test ;

 -  Concurrent breast-feeding.