The V-region repertoire of Haemophilus influenzae type b polysaccharide antibodies induced by immunization of infants

λ Light Chain Bias Associated With Enhanced Binding and Function of Anti-HIV Env Glycoprotein Antibodies

The humoral response to human immunodeficiency virus (HIV) remains incompletely understood. In this report, we describe biased λ light chain use during the HIV Env glycoprotein (Env) response in HIV infection and vaccination. We examined HIV Env binding (and neutralization) in the context of light chain use in subjects with acute HIV infection, chronic HIV infection, and among HIV vaccinees. In all populations tested, there was a λ chain bias for HIV Env binding antibodies, compared with other HIV antigens (such as p24) or tetanus toxoid. In subjects with chronic HIV infection, a λ bias was noted for neutralization, with λ antibodies accounting for up to 90% of all neutralization activity observed. This is the first report of antibody function in a human infection being tied to light chain use. In HIV infection, antibodies expressing λ light chains tended to have longer CDRL3s, increased light chain contact with HIV Env, and less hypermutation in the heavy chain, compared with antibodies using the κ light chain. These data also support an evolutionary model for the understanding the various κ to λ light chain ratios observed across species and suggest that the λ light chain bias against HIV provides the host an advantage in developing a more efficient humoral response.

Sensitization with Xenogeneic Tissues Alters the Heavy Chain Repertoire of Human Anti-Galα1–3Gal Antibodies

BACKGROUND

Antigen sensitization alters the use of genes encoding the variable and constant regions of immunoglobulin, changing avidity, and function. Alterations in variable region genes induced by carbohydrate antigens have been studied extensively in animals but are incompletely characterized in humans. We asked how sensitization with the carbohydrate Galalpha1-3Gal modifies antibody heavy chain use.

METHODS

To overcome limited access to B cells, we analyzed anti-Galalpha1-3Gal antibodies from the serum of naïve and sensitized human subjects with anti-sera specific for VH families.

RESULTS

We find that in preimmune subjects, heavy chains of IgM anti-Galalpha1-3Gal derived primarily from VH3 family members, whereas the heavy chains of IgG are from diverse VH families. After sensitization, heavy chains of IgM and IgG antibodies both derived from diverse VH families.

CONCLUSIONS

The preimmune repertoire of IgM antibodies to Galalpha1-3Gal is thus more restricted than the antibody repertoire after sensitization, suggesting an antigen-induced shift in the repertoire.

Multi-valent human monoclonal antibody preparation against Pseudomonas aeruginosa derived from transgenic mice containing human immunoglobulin loci is protective against fatal pseudomonas sepsis caused by multiple serotypes

Pseudomonas aeruginosa is a serious human pathogen in a variety of patient groups including those with burns, hospitalized in intensive care, cystic fibrosis and neutropenia. Since there is no vaccine available, passive antibody prophylaxis against protective epitopes is an alternative strategy to prevent P. aeruginosa infection. However, immunoglobulin derived from multiple donors has variable anti-pseudomonas antibody titers, and human Mab are difficult to make from patient samples. We previously reported the use of XenoMouse mice, Ig-inactivated transgenic mice reconstituted with human immunoglobulin loci, to generate human Mab against a single serotype of P. aeruginosa lipopolysaccharide O-specific side chain (PS). We now report the creation of a panel of anti-PS human IgG2 Mab against nine additional O-specific side chain P. aeruginosa serotypes. The majority of the Mab were highly opsonic for uptake and killing of homologous P. aeruginosa by human PMN in the presence of human complement, and all the Mab protected cyclophosphamide-induced neutropenic mice from fatal P. aeruginosa sepsis with homologous serotypes. DNA sequence analysis showed that the Mab used V(H)3, V(H)4, V(H)5 and V(H)6 and Vkappa2, 3 and 4 variable region genes consistent with the heterogeneity of P. aeruginosa LPS O-side chain structure. We conclude that human Mab made in these transgenic mice against common pathogenic serotypes of P. aeruginosa are opsonic and highly protective, and that a high titer, multi-valent human Mab preparation against the majority of circulating O-side chain serotypes of P. aeruginosa could be used as prophylaxis against invasive infections in selected patient groups.

Kinetics and avidity of antibodies evoked by heptavalent pneumococcal conjugate vaccines PncCRM and PncOMPC in the Finnish Otitis Media Vaccine Trial

The licensure of new pneumococcal conjugate vaccines (PCVs) relies on immunogenicity data. When defining correlates of protection, vaccine efficacy data must be included. In the FinOM Vaccine Efficacy Trial, the PncOMPC vaccine showed an efficacy profile similar to that of the licensed PncCRM vaccine despite different antibody responses after primary and booster vaccinations. We determined antibody kinetics and avidities in a subgroup of infants participating in the FinOM trial. A total of 166 infants in three vaccine groups were immunized at 2, 4, 6, and 12 months of age with 7-valent PCV, PncCRM or PncOMPC, or hepatitis B vaccine. Concentrations of serum immunoglobulin G (IgG) against pneumococcal capsular polysaccharides were determined at 2, 4, 6, 7, 12, 13, and 24 months of age, and the avidity index (AI) to serotypes 6B, 19F, and 23F were determined at 7, 12, 13, and 24 months of age by enzyme immunoassay. Both PCVs were highly immunogenic, but they demonstrated different kinetics of antibody response; the concentration of IgG against serotypes 6B, 19F, and 23F declined faster after the third and fourth doses of vaccine in the PncCRM group than in the PncOMPC group. For both PCVs, the mean AI of anti-6B and -23F, but not of anti-19F, increased during the follow-up, which is in line with serotype-specific protection in the FinOM trial. Our data suggest that the kinetics and avidities of antibodies should be considered, in addition to antibody responses, when defining correlates of protection.

Status and opportunities for genomics research with rainbow trout

The rainbow trout (Oncorhynchus mykiss) is one of the most widely studied of model fish species. Extensive basic biological information has been collected for this species, which because of their large size relative to other model fish species are particularly suitable for studies requiring ample quantities of specific cells and tissue types. Rainbow trout have been widely utilized for research in carcinogenesis, toxicology, comparative immunology, disease ecology, physiology and nutrition. They are distinctive in having evolved from a relatively recent tetraploid event, resulting in a high incidence of duplicated genes. Natural populations are available and have been well characterized for chromosomal, protein, molecular and quantitative genetic variation. Their ease of culture, and experimental and aquacultural significance has led to the development of clonal lines and the widespread application of transgenic technology to this species. Numerous microsatellites have been isolated and two relatively detailed genetic maps have been developed. Extensive sequencing of expressed sequence tags has begun and four BAC libraries have been developed. The development and analysis of additional genomic sequence data will provide distinctive opportunities to address problems in areas such as evolution of the immune system and duplicate genes.

Human monoclonal antibodies against Pseudomonas aeruginosa lipopolysaccharide derived from transgenic mice containing megabase human immunoglobulin loci are opsonic and protective against fatal pseudomonas sepsis

Pseudomonas aeruginosa is a significant human pathogen, and no vaccine is commercially available. Passive antibody prophylaxis using monoclonal antibodies (MAb) against protective P. aeruginosa epitopes is an alternative strategy for preventing P. aeruginosa infection, but mouse MAb are not suitable for use in humans. Polyclonal human antibodies from multiple donors have variable antibody titers, and human MAb are difficult to make. We used immunoglobulin-inactivated transgenic mice reconstituted with megabase-size human immunoglobulin loci to generate a human MAb against the polysaccharide (PS) portion of the lipopolysaccharide O side chain of a common pathogenic serogroup of P. aeruginosa, 06ad. The anti-PS human immunoglobulin G2 MAb made from mice immunized with heat-killed P. aeruginosa was specific for serogroup 06ad pseudomonas. The MAb was highly opsonic for the uptake and killing of P. aeruginosa by human polymorphonuclear leukocytes in the presence of human complement. In addition, 25 microg of the MAb protected 100% of neutropenic mice from fatal P. aeruginosa sepsis. DNA sequence analysis of the genes encoding the MAb revealed V(H)3 and Vkappa2/A2 variable-region genes, similar to variable-region genes in humans immunized with bacterial PS and associated with high-avidity anti-PS antibodies. We conclude that human MAb to P. aeruginosa made in these transgenic mice are highly protective and that these mice mimic the antibody response seen in humans immunized with T-cell-independent antigens such as bacterial PS.

Somatic hypermutation in T-independent and T-dependent immune responses to Haemophilus influenzae type b polysaccharide

Secondary immune responses to T-independent antigens are characterized by little or no affinity maturation, a phenomenon attributed to limited somatic hypermutation. In the human immune response to Haemophilus influenzae type b capsular polysaccharide, however, there are numerous differences between rearranged heavy chain variable region gene segments and candidate germline genes, irrespective of antigen presentation in a T-independent or T-dependent form. To determine the characteristics of somatic hypermutation in this response, we analyzed rearranged heavy chain variable region segments and associated 3' untranslated JH4-JH5 introns from monoclonal anti-Hib PS antibodies. Mutation of untranslated introns and heavy chain variable segments in both T-independent and T-dependent responses resembles that described in murine and unselected human immune responses. Although mutation is frequent in both T-independent and T-dependent anti-Hib PS responses, there is little evidence of antigen-driven selection, suggesting that ongoing pressure to conserve the variable segment germline configuration limits affinity maturation in this immune response.

Haemophilus influenzae Type b Polysaccharides-Protein Conjugate Vaccine Elicits a More Diverse Antibody Repertoire in Infants Than in Adults

Conjugation of bacterial polysaccharides (PS) to protein carriers confers the ability to elicit protective serum Ab in infants, who respond poorly to plain PS. The serum Ab of young children immunized with Haemophilus influenzae type b (Hib) PS conjugate vaccine varies with age and Ag formulation. To understand these age-related changes in human anti-Hib PS immune responses we determined the variable region gene sequences encoding anti-Hib PS mAbs of infants immunized with Hib oligosaccharide-diphtheria toxin vaccine. The anti-Hib PS repertoire of children differs from that of adults. A smaller proportion of mAbs from children have high affinity for Hib PS, and the overall variable region gene repertoire of infants is more diverse than that in adults. Variable region genes encoding high affinity mAbs of infants are similar to the restricted repertoire described in adults. Low affinity anti-Hib PS mAbs of infants are encoded by a heterogeneous group of genes that are uncommonly observed in the adult repertoire. Abs with high affinity for Hib PS from infants, like most mAbs from adults, react only with Hib PS and the structurally similar PS of Escherichia coli K100, whereas low affinity mAbs of infants are polyreactive. The low affinity anti-Hib PS mAbs of infants immunized with Hib oligosaccharide-diphtheria toxin vaccine vaccine are not reflected in serum Ab. However, the differences between the variable region gene repertoires of adults and infants may account for the distinct immunologic characteristics of the anti-Hib PS responses in young children immunized with other vaccine formulations.

T cell receptor repertoire diversity and clonal expansion in human neonates

Newborn human infants, particularly those born prematurely, are susceptible to infection with a variety of microorganisms. We questioned whether limitations in the T cell repertoire contribute to the neonatal immunocompromised state. To describe developmental changes of the T cell repertoire, cDNA segments corresponding to third complementarity regions (CDR3) of human umbilical cord blood T cell receptors (TCR) from 24-41-wk gestational age were amplified with TCR family-specific probes. The resulting amplified CDRs were visualized by fingerprinting and single strand conformation polymorphism (SSCP) analysis. At 24-wk gestation there were no limitations in TCRBV family usage, and the degree of CDR3 size heterogeneity was not different from the adult. However, earlier in gestation, CDR3s were shorter for all families and gradually increased in size until term. The extent of oligoclonal expansion observed in cord blood was greater than in adult peripheral blood (p = 0.03). T cell oligoclonal expansion was greatest at 29-33-wk gestation and declined toward term. Expansions were detectable in both CD4+ and CD8+ subpopulations. Our findings indicate that the genetic mechanisms of repertoire diversification appear intact as early as 24 wk of gestation, but repertoire diversity is limited as a result of smaller CDR3 sizes. In addition, there was a developmentally regulated progression of oligoclonally expanded T cells. These differences in the TCRBV repertoire add to the body of evidence demonstrating immaturity of the neonatal immune system. However, the role that these subtle differences are likely to play in the relative immunodeficiency of the neonate remains to be determined.

Use of licensed vaccines for active immunization of the immunocompromised host

The latter part of the 20th century has witnessed an unprecedented rise in the number of individuals with impaired immunity. This is primarily attributable to the increased development and use of antineoplastic therapy for malignancies, organ and bone marrow transplantation, and the AIDS epidemic. Individuals with impaired immunity are often at increased risk for infections, and they can experience more severe and complicated courses of infection. The lack of therapy for a variety of viruses and the rise in antimicrobial resistance of many pathogens have focused attention on vaccination to prevent infectious diseases. The efficacy of most licensed vaccines has been established in immunocompetent hosts. However, there is also considerable experience with most vaccines in those with impaired immunity. We reviewed the use of licensed live, inactivated, and polysaccharide vaccines in this group, and several themes emerged: (i) most vaccines are less immunogenic in those with impaired immunity than in normal individuals; (ii) live vaccines are generally contraindicated in this group; and (iii) the efficacy of many commonly used vaccines has not been established in people with impaired immunity. This review suggests that for most vaccines there are little or no efficacy data in those with impaired immunity but their use in this patient group is generally safe.