Evidence for antibody as a protective correlate for COVID-19 vaccines

A correlate of protection (CoP) is urgently needed to expedite development of additional COVID-19 vaccines to meet unprecedented global demand. To assess whether antibody titers may reasonably predict efficacy and serve as the basis of a CoP, we evaluated the relationship between efficacy and in vitro neutralizing and binding antibodies of 7 vaccines for which sufficient data have been generated. Once calibrated to titers of human convalescent sera reported in each study, a robust correlation was seen between neutralizing titer and efficacy (ρ = 0.79) and binding antibody titer and efficacy (ρ = 0.93), despite geographically diverse study populations subject to different forces of infection and circulating variants, and use of different endpoints, assays, convalescent sera panels and manufacturing platforms. Together with evidence from natural history studies and animal models, these results support the use of post-immunization antibody titers as the basis for establishing a correlate of protection for COVID-19 vaccines.

Consensus summary report for CEPI/BC March 12-13, 2020 meeting: Assessment of risk of disease enhancement with COVID-19 vaccines

A novel coronavirus (CoV), Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in late 2019 in Wuhan, China and has since spread as a global pandemic. Safe and effective vaccines are thus urgently needed to reduce the significant morbidity and mortality of Coronavirus Disease 2019 (COVID-19) disease and ease the major economic impact. There has been an unprecedented rapid response by vaccine developers with now over one hundred vaccine candidates in development and at least six having reached clinical trials. However, a major challenge during rapid development is to avoid safety issues both by thoughtful vaccine design and by thorough evaluation in a timely manner. A syndrome of “disease enhancement” has been reported in the past for a few viral vaccines where those immunized suffered increased severity or death when they later encountered the virus or were found to have an increased frequency of infection. Animal models allowed scientists to determine the underlying mechanism for the former in the case of Respiratory syncytial virus (RSV) vaccine and have been utilized to design and screen new RSV vaccine candidates. Because some Middle East respiratory syndrome (MERS) and SARS-CoV-1 vaccines have shown evidence of disease enhancement in some animal models, this is a particular concern for SARS-CoV-2 vaccines. To address this challenge, the Coalition for Epidemic Preparedness Innovations (CEPI) and the Brighton Collaboration (BC) Safety Platform for Emergency vACcines (SPEAC) convened a scientific working meeting on March 12 and 13, 2020 of experts in the field of vaccine immunology and coronaviruses to consider what vaccine designs could reduce safety concerns and how animal models and immunological assessments in early clinical trials can help to assess the risk. This report summarizes the evidence presented and provides considerations for safety assessment of COVID-19 vaccine candidates in accelerated vaccine development.

High-throughput sequencing analysis of post-liver transplantation HCV E2 glycoprotein evolution in the presence and absence of neutralizing monoclonal antibody

Chronic hepatitis C virus (HCV) infection is the most common cause of end-stage liver disease, often leading to liver transplantation, in which case circulating virions typically infect the transplanted liver within hours and viral concentrations can quickly exceed pre-transplant levels. MBL-HCV1 is a fully human monoclonal antibody recognizing a linear epitope of the HCV E2 envelope glycoprotein (amino acids 412–423). The ability of MBL-HCV1 to prevent HCV recurrence after liver transplantation was investigated in a phase 2 randomized clinical trial evaluating six MBL-HCV1-treated subjects and five placebo-treated subjects. MBL-HCV1 treatment significantly delayed time to viral rebound compared with placebo treatment. Here we report results from high-throughput sequencing on the serum of each of the eleven enrolled subjects prior to liver transplantation and after viral rebound. We further sequenced the sera of the MBL-HCV1-treated subjects at various interim time points to study the evolution of antibody-resistant viral variants. We detected mutations at one of two positions within the antibody epitope—mutations of N at position 415 to D, K or S, or mutation of N at position 417 to S. It has been previously reported that N415 is not glycosylated in the wild-type E2 protein, but N417S can lead to glycosylation at position 415. Thus N415 is a key position for antibody recognition and the only routes we identified for viral escape, within the constraints of HCV fitness in vivo, involve mutating or glycosylating this position. Evaluation of mutations along the entire E1 and E2 proteins revealed additional positions that changed moderately before and after MBL-HCV1 treatment for subsets of the six subjects, yet underscored the relative importance of position 415 in MBL-HCV1 resistance.

Identification of human monoclonal antibodies specific for human SOD1 recognizing distinct epitopes and forms of SOD1

Mutations in the gene encoding human SOD1 (hSOD1) can cause amyotrophic lateral sclerosis (ALS) yet the mechanism by which mutant SOD1 can induce ALS is not fully understood. There is currently no cure for ALS or treatment that significantly reduces symptoms or progression. To develop tools to understand the protein conformations present in mutant SOD1-induced ALS and as possible immunotherapy, we isolated and characterized eleven unique human monoclonal antibodies specific for hSOD1. Among these, five recognized distinct linear epitopes on hSOD1 that were not available in the properly-folded protein but were available on forms of protein with some degree of misfolding. The other six antibodies recognized conformation-dependent epitopes that were present in the properly-folded protein with two different recognition profiles: three could bind hSOD1 dimer or monomer and the other three were specific for hSOD1 dimer only. Antibodies with the capacity to bind hSOD1 monomer were able to prevent increased hydrophobicity when mutant hSOD1 was exposed to increased temperature and EDTA, suggesting that the antibodies stabilized the native structure of hSOD1. Two antibodies were tested in a G93A mutant hSOD1 transgenic mouse model of ALS but did not yield a statistically significant increase in overall survival. It may be that the two antibodies selected for testing in the mouse model were not effective for therapy or that the model and/or route of administration were not optimal to produce a therapeutic effect. Therefore, additional testing will be required to determine therapeutic potential for SOD1 mutant ALS and potentially some subset of sporadic ALS.

Human monoclonal antibody HCV1 effectively prevents and treats HCV infection in chimpanzees

Hepatitis C virus (HCV) infection is a leading cause of liver transplantation and there is an urgent need to develop therapies to reduce rates of HCV infection of transplanted livers. Approved therapeutics for HCV are poorly tolerated and are of limited efficacy in this patient population. Human monoclonal antibody HCV1 recognizes a highly-conserved linear epitope of the HCV E2 envelope glycoprotein (amino acids 412–423) and neutralizes a broad range of HCV genotypes. In a chimpanzee model, a single dose of 250 mg/kg HCV1 delivered 30 minutes prior to infusion with genotype 1a H77 HCV provided complete protection from HCV infection, whereas a dose of 50 mg/kg HCV1 did not protect. In addition, an acutely-infected chimpanzee given 250 mg/kg HCV1 42 days following exposure to virus had a rapid reduction in viral load to below the limit of detection before rebounding 14 days later. The emergent virus displayed an E2 mutation (N415K/D) conferring resistance to HCV1 neutralization. Finally, three chronically HCV-infected chimpanzees were treated with a single dose of 40 mg/kg HCV1 and viral load was reduced to below the limit of detection for 21 days in one chimpanzee with rebounding virus displaying a resistance mutation (N417S). The other two chimpanzees had 0.5–1.0 log₁₀ reductions in viral load without evidence of viral resistance to HCV1. In vitro testing using HCV pseudovirus (HCVpp) demonstrated that the sera from the poorly-responding chimpanzees inhibited the ability of HCV1 to neutralize HCVpp. Measurement of antibody responses in the chronically-infected chimpanzees implicated endogenous antibody to E2 and interference with HCV1 neutralization although other factors may also be responsible. These data suggest that human monoclonal antibody HCV1 may be an effective therapeutic for the prevention of graft infection in HCV-infected patients undergoing liver transplantation.

The majority of individuals infected with hepatitis C virus (HCV) become chronically infected and many go on to develop liver failure requiring liver transplantation. Unfortunately, the transplanted liver becomes infected with HCV in nearly 100% of transplant patients. Current treatments for HCV are poorly tolerated after liver transplantation and graft health is compromised by infection. We have developed a monoclonal antibody called HCV1 that blocks HCV from infecting liver cells in culture. Using chimpanzees as a model for HCV infection, we demonstrate that HCV1 has the ability to prevent HCV infection. We also show that HCV1 can treat chimpanzees chronically infected with HCV and reduce plasma viral load to below the level of detection for a period of 7 to 21 days. The virus that reemerges in the treated chimpanzees was resistant to HCV1 neutralization demonstrating target engagement. Given the ability of HCV1 to protect chimpanzees from HCV infection, we speculate that HCV1 may be beneficial in HCV- infected patients undergoing liver transplant.

Treatment with monoclonal antibodies against Clostridium difficile toxins

BACKGROUND

New therapies are needed to manage the increasing incidence, severity, and high rate of recurrence of Clostridium difficile infection.

METHODS

We performed a randomized, double-blind, placebo-controlled study of two neutralizing, fully human monoclonal antibodies against C. difficile toxins A (CDA1) and B (CDB1). The antibodies were administered together as a single infusion, each at a dose of 10 mg per kilogram of body weight, in patients with symptomatic C. difficile infection who were receiving either metronidazole or vancomycin. The primary outcome was laboratory-documented recurrence of infection during the 84 days after the administration of monoclonal antibodies or placebo.

RESULTS

Among the 200 patients who were enrolled (101 in the antibody group and 99 in the placebo group), the rate of recurrence of C. difficile infection was lower among patients treated with monoclonal antibodies (7% vs. 25%; 95% confidence interval, 7 to 29; P<0.001). The recurrence rates among patients with the epidemic BI/NAP1/027 strain were 8% for the antibody group and 32% for the placebo group (P=0.06); among patients with more than one previous episode of C. difficile infection, recurrence rates were 7% and 38%, respectively (P=0.006). The mean duration of the initial hospitalization for inpatients did not differ significantly between the antibody and placebo groups (9.5 and 9.4 days, respectively). At least one serious adverse event was reported by 18 patients in the antibody group and by 28 patients in the placebo group (P=0.09).

CONCLUSIONS

The addition of monoclonal antibodies against C. difficile toxins to antibiotic agents significantly reduced the recurrence of C. difficile infection. (ClinicalTrials.gov number, NCT00350298.)

Recombinant protein-based assays for detection of antibodies to severe acute respiratory syndrome coronavirus spike and nucleocapsid proteins

Recombinant severe acute respiratory syndrome (SARS) nucleocapsid and spike protein-based immunoglobulin G immunoassays were developed and evaluated. Our assays demonstrated high sensitivity and specificity to the SARS coronavirus in sera collected from patients as late as 2 years postonset of symptoms. These assays will be useful not only for routine SARS coronavirus diagnostics but also for epidemiological and antibody kinetic studies.

Identification and characterization of a human monoclonal antibody that potently neutralizes a broad panel of rabies virus isolates

Rabies is a zoonosis that results in millions of human exposures worldwide each year. Human monoclonal antibodies (HuMAbs) that neutralize rabies virus may represent one viable strategy for post-exposure prophylaxis in humans, and have many advantages over current human or equine rabies immune globulin. Transgenic mice carrying human immunoglobulin genes were used to isolate human monoclonal antibodies that neutralized rabies virus. Several HuMAbs were identified that neutralized rabies virus variants from a broad panel of isolates of public health significance. HuMAb 17C7 was the most promising antibody identified because it neutralized all rabies virus isolates tested. HuMAb 17C7 recognizes a conformational epitope on the rabies virus glycoprotein which includes antigenic site III. HuMAb 17C7 protected hamsters from a lethal dose of rabies virus in a well-established in vivo model of post-exposure prophylaxis.

Human monoclonal antibodies directed against toxins A and B prevent Clostridium difficile-induced mortality in hamsters

Clostridium difficile is the leading cause of nosocomial antibiotic-associated diarrhea, and recent outbreaks of strains with increased virulence underscore the importance of identifying novel approaches to treat and prevent relapse of Clostridium difficile-associated diarrhea (CDAD). CDAD pathology is induced by two exotoxins, toxin A and toxin B, which have been shown to be cytotoxic and, in the case of toxin A, enterotoxic. In this report we describe fully human monoclonal antibodies (HuMAbs) that neutralize these toxins and prevent disease in hamsters. Transgenic mice carrying human immunoglobulin genes were used to isolate HuMAbs that neutralize the cytotoxic effects of either toxin A or toxin B in cell-based in vitro neutralization assays. Three anti-toxin A HuMAbs (3H2, CDA1, and 1B11) could all inhibit the enterotoxicity of toxin A in mouse intestinal loops and the in vivo toxicity in a systemic mouse model. Four anti-toxin B HuMAbs (MDX-1388, 103-174, 1G10, and 2A11) could neutralize cytotoxicity in vitro, although systemic toxicity in the mouse could not be neutralized. Anti-toxin A HuMAb CDA1 and anti-toxin B HuMAb MDX-1388 were tested in the well-established hamster model of C. difficile disease. CDA1 alone resulted in a statistically significant reduction of mortality in hamsters; however, the combination treatment offered enhanced protection. Compared to controls, combination therapy reduced mortality from 100% to 45% (P<0.0001) in the primary disease hamster model and from 78% to 32% (P<0.0001) in the less stringent relapse model.

Therapy with a severe acute respiratory syndrome-associated coronavirus-neutralizing human monoclonal antibody reduces disease severity and viral burden in golden Syrian hamsters

BackgroundImmunotherapy with monoclonal antibodies (MAbs) offers safe interventions for the prevention of infection in patients after organ transplantation and for the treatment of cancers and autoimmune diseases. MAb 201 is a severe acute respiratory syndrome–associated coronavirus (SARS-CoV)–specific MAb that prevents establishment of viral replication in vitro and prevents viral replication in vivo when administered prophylactically. The efficacy of MAb 201 in the treatment of SARS was evaluated in golden Syrian hamsters, an animal model that supports SARS-CoV replication to high levels and displays severe pathological changes associated with infection, including pneumonitis and pulmonary consolidation

MethodsGolden Syrian hamsters that were intranasally inoculated with SARS-CoV were treated with various doses of MAb 201 or an irrelevant MAb 24 h after inoculation. Two to 7 days after infection, the hamsters were killed, and their lungs were collected for evaluation of viral titers and pathological findings

ResultsPostexposure treatment with MAb 201 can alleviate the viral burden and associated pathological findings in a golden Syrian hamster model of SARS-CoV infection. After a hamster is treated with MAb 201, its viral burden is reduced by 10^2.4–10^3.9 50% tissue-culture infectious doses per gram of tissue, and the severity of associated pathological findings, including interstitial pneumonitis and consolidation, is also remarkably reduced

ConclusionsThe demonstration of successful postexposure MAb 201 therapy in an animal model that demonstrates viral replication and associated pulmonary pathological findings suggests that MAb 201 may be useful in the arsenal of tools to combat SARS

Monoclonal antibodies to SARS-associated coronavirus (SARS-CoV): identification of neutralizing and antibodies reactive to S, N, M and E viral proteins

Monoclonal antibodies (Mabs) against the Urbani strain of the SARS-associated coronavirus (SARS-CoV) were developed and characterized for reactivity to SARS-CoV and SARS-CoV S, N, M, and E proteins using enzyme-linked immunoabsorbent (ELISA), radioimmunoprecipitation, immunofluorescence, Western Blot and microneutralization assays. Twenty-six mAbs were reactive to SARS-CoV by ELISA, and nine were chosen for detailed characterization. Five mAbs reacted against the S protein, two against the M protein, and one each against the N and E proteins. Two of five S protein mAbs neutralized SARS-CoV infection of Vero E6 cells and reacted to an epitope within amino acids 490–510 in the S protein. While two of the three non-neutralizing antibodies recognized at second epitope within amino acids 270–350. The mAbs characterized should prove useful for developing SARS-CoV diagnostic assays and for studying the biology of infection and pathogenesis of disease.

Development and characterization of a severe acute respiratory syndrome-associated coronavirus-neutralizing human monoclonal antibody that provides effective immunoprophylaxis in mice

Background. Severe acute respiratory syndrome (SARS) remains a significant public health concern after the epidemic in 2003. Human monoclonal antibodies (MAbs) that neutralize SARS-associated coronavirus (SARSCoV) could provide protection for exposed individuals.

Methods. Transgenic mice with human immunoglobulin genes were immunized with the recombinant major surface (S) glycoprotein ectodomain of SARS-CoV. Epitopes of 2 neutralizing MAbs derived from these mice were mapped and evaluated in a murine model of SARS-CoV infection.

Results. Both MAbs bound to S glycoprotein expressed on transfected cells but differed in their ability to block binding of S glycoprotein to Vero E6 cells. Immunoprecipitation analysis revealed 2 antibody-binding epitopes: one MAb (201) bound within the receptor-binding domain at aa 490–510, and the other MAb (68) bound externally to the domain at aa 130–150. Mice that received 40 mg/kg of either MAb prior to challenge with SARS-CoV were completely protected from virus replication in the lungs, and doses as low as 1.6 mg/kg offered significant protection.

Conclusions. Two neutralizing epitopes were defined for MAbs to SARS-CoV S glycoprotein. Antibodies to both epitopes protected mice against SARS-CoV challenge. Clinical trials are planned to test MAb 201, a fully human MAb specific for the epitope within the receptor-binding region.

CD209L (L-SIGN) is a receptor for severe acute respiratory syndrome coronavirus

Angiotensin-converting enzyme 2 (ACE2) is a receptor for SARS-CoV, the novel coronavirus that causes severe acute respiratory syndrome [Li, W. Moore, M. J., Vasilieva, N., Sui, J., Wong, S. K., Berne, M. A., Somasundaran, M., Sullivan, J. L., Luzuriaga, K., Greenough, T. C., et al. (2003) Nature 426, 450-454]. We have identified a different human cellular glycoprotein that can serve as an alternative receptor for SARS-CoV. A human lung cDNA library in vesicular stomatitis virus G pseudotyped retrovirus was transduced into Chinese hamster ovary cells, and the cells were sorted for binding of soluble SARS-CoV spike (S) glycoproteins, S(590) and S(1180). Clones of transduced cells that bound SARS-CoV S glycoprotein were inoculated with SARS-CoV, and increases in subgenomic viral RNA from 1-16 h or more were detected by multiplex RT-PCR in four cloned cell lines. Sequencing of the human lung cDNA inserts showed that each of the cloned cell lines contained cDNA that encoded human CD209L, a C-type lectin (also called L-SIGN). When the cDNA encoding CD209L from clone 2.27 was cloned and transfected into Chinese hamster ovary cells, the cells expressed human CD209L glycoprotein and became susceptible to infection with SARS-CoV. Immunohistochemistry showed that CD209L is expressed in human lung in type II alveolar cells and endothelial cells, both potential targets for SARS-CoV. Several other enveloped viruses including Ebola and Sindbis also use CD209L as a portal of entry, and HIV and hepatitis C virus can bind to CD209L on cell membranes but do not use it to mediate virus entry. Our data suggest that the large S glycoprotein of SARS-CoV may use both ACE2 and CD209L in virus infection and pathogenesis.

Amino acids 270 to 510 of the severe acute respiratory syndrome coronavirus spike protein are required for interaction with receptor

A novel coronavirus, severe acute respiratory syndrome coronavirus (SARS-CoV), has recently been identified as the causative agent of severe acute respiratory syndrome (SARS). SARS-CoV appears similar to other coronaviruses in both virion structure and genome organization. It is known for other coronaviruses that the spike (S) glycoprotein is required for both viral attachment to permissive cells and for fusion of the viral envelope with the host cell membrane. Here we describe the construction and expression of a soluble codon-optimized SARS-CoV S glycoprotein comprising the first 1,190 amino acids of the native S glycoprotein (S(1190)). The codon-optimized and native S glycoproteins exhibit similar molecular weight as determined by Western blot analysis, indicating that synthetic S glycoprotein is modified correctly in a mammalian expression system. S(1190) binds to the surface of Vero E6 cells, a cell permissive to infection, as demonstrated by fluorescence-activated cell sorter analysis, suggesting that S(1190) maintains the biologic activity present in native S glycoprotein. This interaction is blocked with serum obtained from recovering SARS patients, indicating that the binding is specific. In an effort to map the ligand-binding domain of the SARS-CoV S glycoprotein, carboxy- and amino-terminal truncations of the S(1190) glycoprotein were constructed. Amino acids 270 to 510 were the minimal receptor-binding region of the SARS-CoV S glycoprotein as determined by flow cytometry. We speculate that amino acids 1 to 510 of the SARS-CoV S glycoprotein represent a unique domain containing the receptor-binding site (amino acids 270 to 510), analogous to the S1 subunit of other coronavirus S glycoproteins.

Donor immunization with pneumococcal conjugate vaccine and early protective antibody responses following allogeneic hematopoietic cell transplantation

Patients undergoing hematopoietic cell transplantation (HCT) are at increased risk for infections with Streptococcus pneumoniae and have long-lasting, impaired antibody responses to pneumococcal polysaccharide vaccines. We examined whether donor immunization with a heptavalent pneumococcal conjugate vaccine (PCV7) would elicit protective antibody responses to additional doses of vaccine administered early after transplantation. Ninety-six patients scheduled to receive an allogeneic hematopoietic cell transplant were randomized with their donors to receive either a dose of PCV7 vaccine or no vaccine before transplantation. All patients received PCV7 at 3 months, 6 months, and 12 months following transplantation, and serotype-specific antibody concentrations were determined after each dose. Following HCT, geometric mean antibody concentrations of patients in the immunized donor group were significantly higher for 5 of the 7 vaccine serotypes after one dose (P <.05) and for 4 of the 7 serotypes after 2 doses of vaccine (P <.03). Sixty-seven percent of patients in the immunized donor group had presumed protective IgG concentrations more than or equal to 0.50 microg/mL to all 7 serotypes following the first dose of vaccine compared to 36% in the unimmunized donor group (P =.05). After the third dose of vaccine, both groups had more than 60% of patients with concentrations at least 0.50 microg/mL to all vaccine serotypes. Donor immunization enhances early antibody responses of patients undergoing HCT to pneumococcal conjugate vaccine. A 3-dose schedule of PCV7 vaccine at 3, 6, and 12 months is immunogenic in these patients regardless of donor immunization.

Effect of monophosphoryl lipid A (MPL) on T-helper cells when administered as an adjuvant with pneumocococcal-CRM197 conjugate vaccine in healthy toddlers

As new vaccines are developed, novel adjuvants may play an important role in eliciting an effective immune response. We evaluated the safety and adjuvant properties of monophosphoryl lipid A (MPL in 129 healthy toddlers immunized with two doses of nine-valent pneumococcal-CRM(197) protein conjugate vaccine (PCV9) combined with 10, 25, or 50 micro g of MPL with or without alum (AlPO(4)). Vaccine-specific humoral and cell-mediated responses were examined following the second dose of study vaccine. All doses of MPL were well-tolerated and a dose-dependent effect of MPL on specific cellular responses was observed. The 10 micro g MPL dose significantly enhanced CRM(197)-specific T-cell proliferation (P=0.02) and interferon-gamma (INF-gamma) production (P=0.009) compared to responses of controls who received PCV9 with AlPO(4). In contrast, CRM(197)-specific T-cell proliferation and interferon-gamma production of the 50 micro g MPL/AlPO(4) group were decreased when compared to controls although these differences did not reach statistical significance. IL-5 and IL-13 responses after immunization showed a similar pattern with increased production in the 10 micro g MPL group and decreased production in the 50 micro g MPL/AlPO(4) group compared to controls. There were no differences in serum IgG antibody concentrations to the nine vaccine pneumococcal capsular polysaccharides and carrier protein between the MPL-containing and control vaccine groups. These findings demonstrate a dose-dependent effect of MPL on T-helper cell type 1 (TH-1) responses to the carrier protein and also suggest an effect on T-helper cell type 2 (TH-2) responses.

Comparison of an opsonophagocytic assay and IgG ELISA to assess responses to pneumococcal polysaccharide and pneumococcal conjugate vaccines in children and young adults with sickle cell disease

Children with sickle cell disease were immunized with either 2 doses of 7-valent pneumococcal conjugate vaccine followed by 1 dose of 23-valent pneumococcal polysaccharide vaccine or a single dose of 23-valent vaccine. Functional antibodies to 7 vaccine serotypes were measured by a flow cytometric opsonophagocytic assay (OPA) and compared with IgG anticapsular polysaccharide antibody concentrations measured by ELISA. Moderate correlations were found between OPA and ELISA antibody titers for all 7 serotypes (r values, 0.41-0.70; P<.001 for all serotypes). After immunization with 23-valent vaccine, geometric mean antibody titers by OPA were significantly higher in the combined schedule group for 5 of 7 vaccine serotypes but were significantly higher for only 2 of 7 serotypes as measured by ELISA. The ability of OPA to show a greater differential response to the 2 immunization schedules used in this study suggests that it may be useful in the evaluation of immunization regimens involving pneumococcal conjugate vaccines.

Enzyme-linked immunosorbent assay to assess respiratory syncytial virus concentration and correlate results with inflammatory mediators in tracheal secretions

OBJECTIVE

We developed an enzyme-linked immunosorbent assay (ELISA) for the quantitation of respiratory syncytial virus (RSV) in respiratory secretions in intubated patients infected with RSV.

METHODS

We compared the quantitative ELISA and a standardized plaque assay in intubated children <2 years of age who were mechanically ventilated for severe RSV disease and enrolled in a randomized double blind placebo-controlled treatment trial of a monoclonal antibody to the F protein of RSV (palivizumab; Synagis). We also examined the relationship between the concentrations of virus as measured by ELISA and of three inflammatory indices in respiratory secretions (white blood cell count, myeloperoxidase and eosinophilic cationic protein).

RESULTS

Quantitative ELISA and plaque assay were highly correlated for both tracheal aspirates (r = 0.67, P = 0.001) and nasal wash specimens (r = 0.75, P = 0.001). Treatment with palivizumab significantly neutralized RSV in tracheal aspirates as measured by plaque assay. In contrast quantitation of RSV by ELISA was not affected by palivizumab treatment. This finding is consistent with results that were obtained in preliminary studies of RSV-containing media treated with monoclonal antibody, where we found that the ELISA measured virus whether antibody-bound or not. The inflammatory indices were not correlated with RSV concentration measured by ELISA or plaque assay.

CONCLUSIONS

We conclude that this quantitative ELISA is a potentially useful tool for measurement of RSV concentration in respiratory secretions that may help elucidate the pathophysiology of acute RSV infection. Specific antiviral strategies for the treatment of RSV disease could be evaluated by this method.

Normal IgG and impaired IgM responses to polysaccharide vaccines in asplenic patients

Asplenic patients are at increased risk for life-threatening infections with polysaccharide-encapsulated organisms, and reports of responses to polysaccharide vaccines have been conflicting. Thirty-six asplenic patients and 15 healthy controls were immunized with pneumococcal, Haemophilus influenzae type b (Hib), and meningococcal vaccines. Antibody concentrations to Hib and pneumococcal serotypes 14 and 18C were measured by ELISA. IgG antibody responses to all three antigens were similar in asplenic patients and controls at 28 days following immunization. In contrast, asplenic patients had significantly lower IgM concentrations in response to Hib (P<.05) and to both pneumococcal serotypes 14 (P<. 005) and 18C (P<.001). IgA anti-Hib antibody was also lower in the asplenic group, as was total anti-Hib antibody measured by RIA. These results document that IgG responses to polysaccharide vaccines are normal in asplenic patients. The impaired IgM responses of these patients may explain conflicting reports from studies that measured only total antibody-binding concentrations.

Reduction of respiratory syncytial virus (RSV) in tracheal aspirates in intubated infants by use of humanized monoclonal antibody to RSV F protein

Thirty-five children <2 years of age mechanically ventilated for respiratory syncytial virus (RSV) infection were randomized to receive an intravenous infusion of 15 mg/kg MEDI-493 or placebo. RSV concentration was measured in tracheal secretions by plaque assay before and at 24-h intervals after treatment. The reduction in tracheal RSV concentration from day 0 to day 1 (-1.7+/-0.28 vs. -0. 6+/-0.21 log10 pfu/mL; P=.004) and from day 0 to day 2 (-2.5+/-0.26 vs. -1.0+/-0.41 log10 pfu/mL; P=.012) was significantly greater in the MEDI-493 group than in the placebo group. RSV concentration in nasal aspirates did not differ significantly between the groups. No significant differences were observed in the tracheal aspirate white blood cell count, or myeloperoxidase or eosinophilic cationic protein concentration, or in measures of disease severity between the groups. Thus, treatment with 15 mg/kg MEDI-493 intravenously was well-tolerated and significantly reduced RSV concentration in tracheal aspirates of children with respiratory failure due to RSV.

Comparison of multiple immunization schedules for Haemophilus influenzae type b-conjugate and tetanus toxoid vaccines following bone marrow transplantation

Antibody concentrations to vaccine-preventable diseases decline following BMT and an optimal schedule for vaccination after transplant has not been established. We examined antibody responses to tetanus toxoid (TT) and Haemophilus influenzae type b-conjugate (HIB) vaccines of BMT patients immunized at 6, 12 and 24 months (6 month group, n = 21) and compared them to those previously reported for patients immunized at 3, 6, 12 and 24 months (3 month group, n = 74) or at 12 and 24 months (12 month group, n = 17) following transplantation. Geometric mean total anti-HIB and IgG anti-TT concentrations were significantly higher after the 12 month dose in the 3 and 6 month immunization groups compared to the group who received their first dose at 12 months. Although HIB antibody concentrations were higher in the 3 month and 6 month groups 12 to 24 months after BMT, the proportion of patients with protective levels was not significantly different from the proportion protected in the 12 month group. Following the 24 month immunizations, geometric mean antibody concentrations to HIB and TT were similar for all three immunization groups. The proportion of patients in each group with protective levels of HIB antibody after the 24 month dose was > or = 80%. A two dose schedule of HIB and TT vaccines at 12 and 24 months after BMT should afford protection.

Antibody responses to tetanus toxoid and Haemophilus influenzae type b conjugate vaccines following autologous peripheral blood stem cell transplantation (PBSCT)

Accelerated granulocyte and platelet recovery following peripheral blood stem cell transplantation (PBSCT) are well documented. We hypothesize that functional immunity may also be enhanced in PBSCT and performed a phase II trial of immunizations in patients with lymphoma undergoing autologous transplantation with peripheral blood stem cells or bone marrow. Seventeen BMT and 10 PBSCT recipients were immunized at 3, 6, 12, and 24-months post-transplantation with Haemophilus influenzae type b (HIB)-conjugate and tetanus toxoid (TT) vaccines. IgG anti-HIB and anti-TT antibody concentrations were measured and compared between the two groups. Geometric mean IgG anti-HIB antibody concentrations were significantly higher for PBSCT recipients compared to BMT recipients at 24 months post-transplantation (11.3 micrograms/ml vs 0.93 microgram/ml, P = 0.051) and following the 24 month immunization (66.2 micrograms/ml vs 1.30 micrograms/ml, P = 0.006). Similar results were noted for IgG anti-TT antibody with significantly higher geometric mean antibody concentrations in the PBSCT group at 24 months post-transplantation (182 micrograms/ml vs 21.6 micrograms/ml, P = 0.039). Protective levels of total anti-HIB antibody were achieved earlier in PBSCT recipients compared with those of BMT recipients. PBSCT recipients had higher antigen-specific antibody concentrations following HIB and TT immunizations. These results suggest enhanced recovery of humoral immunity in PBSCT recipients and earlier protection against HIB with immunization.

Haemophilus influenzae type b (HIB)-conjugate immunization before bone marrow harvest in autologous bone marrow transplantation

Immune reconstitution following autologous bone marrow transplantation (ABMT) is characterized by defects in B cell and T cell function and loss of specific antibody. In the late post-transplant period, patients are at risk for infections with polysaccharide encapsulated organisms and respond poorly to polysaccharide vaccines. We examined whether immunizing ABMT patients before bone marrow (BM) harvest enhanced the early recovery of specific antibody. Twelve patients were immunized before BM harvest with Haemophilus influenzae type b (HIB)-conjugate, tetanus toxoid and polysaccharide pneumococcal vaccines. Forty-one comparable ABMT patients not immunized prior to BM harvest were also studied. Following ABMT, both groups of patients were immunized with HIB-conjugate and tetanus toxoid vaccines at 3, 6, 12 and 24 months and with pneumococcal vaccine at 12 and 24 months. Patients immunized before BM harvest had higher HIB antibody concentrations during the first 2 years post-transplant, the differences reaching significance at 3 months (P = 0.0001) and following the 24-month dose (P = 0.048). Tetanus toxoid antibody concentrations were also significantly higher at 3 months (P = 0.001) and 6 months (P = 0.032) in patients immunized before BM harvest. There were no differences in pneumococcal antibody concentrations between the two groups. Immunization of patients before bone marrow harvest resulted in higher anti-HIB antibody concentrations following ABMT and may be an effective strategy to prevent infectious complications.

Donor immunization with Haemophilus influenzae type b (HIB)-conjugate vaccine in allogeneic bone marrow transplantation

Bone marrow transplant patients are at increased risk for infections with polysaccharide encapsulated organisms and respond poorly to polysaccharide vaccines. We evaluated the effect of donor immunization with Haemophilus influenzae type b (HIB) polysaccharide-conjugate vaccine on recipient antibody responses following allogeneic bone marrow transplantation. Thirty-two allogeneic transplant patients and their donors were immunized before transplantation with HIB-conjugate, tetanus toxoid and 23-valent pneumococcal vaccines. Following transplantation, patients received HIB-conjugate and tetanus toxoid vaccines at 3, 6, 12, and 24 months and 23-valent pneumococcal vaccine at 12 and 24 months. Thirty-three patients with unimmunized donors were immunized following transplantation in an identical manner. Patients whose donors were immunized had significantly higher total anti-HIB antibody concentrations at 3 months (P = .0001), 6 months (P = .0001), 12 months (P = .0001), and 24 months (P = .002) after transplant compared with patients whose donors were unimmunized. Higher antitetanus toxoid antibody concentrations were also noted in patients with immunized donors, whereas donor immunization with pneumococcal vaccine had no effect on antibody concentrations following transplantation. Donor immunization with HIB-conjugate vaccine resulted in higher antibody concentrations in patients as early as 3 months after allogeneic transplantation and may be an effective strategy to prevent HIB infections.

Pneumococcal conjugate vaccine primes for antibody responses to polysaccharide pneumococcal vaccine after treatment of Hodgkin's disease

Thirty-nine previously treated Hodgkin's disease (HD) patients were immunized with 7-valent pneumococcal conjugate vaccine (7-OMPC) followed by one dose of 23-valent polysaccharide pneumococcal vaccine (23-PS). To determine the priming effect of 7-OMPC vaccine, their antibody responses to six serotypes contained in both vaccines were compared to those of 57 HD patients who received 23-PS vaccine only. The geometric mean antibody concentrations after immunization with 23-PS vaccine were significantly higher for five of the six measured serotypes in HD patients primed with 7-OMPC vaccine compared with responses in HD patients who received 23-PS vaccine only. The mean of the six antibody concentrations was significantly higher for the primed group at 12.5 micrograms/mL and 7.76 micrograms/mL, respectively (P = .015). Priming with a conjugate vaccine should be considered as a strategy to protect high-risk adults.

Antibody responses to polysaccharide and polysaccharide-conjugate vaccines after treatment of Hodgkin disease

OBJECTIVE

To compare the immunogenicity of polysaccharide-conjugate vaccines with that of polysaccharide vaccines in patients previously treated for Hodgkin disease.

DESIGN

All patients were immunized with Haemophilus influenzae type b (HIB)-conjugate and 4-valent meningococcal polysaccharide vaccines. Subgroups of patients were randomly assigned to receive either 23-valent pneumococcal polysaccharide vaccine or a 7-valent pneumococcal-conjugate vaccine that links seven pneumococcal serotypes to the outer membrane protein complex of Neisseria meningitidis.

PATIENTS

144 patients who had completed treatment for Hodgkin disease, which had been diagnosed at least 2 years before the study.

MEASUREMENTS

Antigen-specific antibody concentrations before and 3 to 6 weeks after immunization; number of persons who achieved anti-HIB antibody concentrations considered to be in the protective range.

RESULTS

The geometric mean anti-HIB antibody concentration increased from 1.79 micrograms/mL before immunization to 54.1 micrograms/mL after; the percentage of persons with antibody concentrations in the protective range increased from 62% before immunization to 99% after. Patients immunized with 23-valent pneumococcal vaccine had a geometric mean pneumococcal antibody concentration after immunization (9.15 micrograms/mL) that was similar to that of healthy controls (10.0 micrograms/mL) for the seven serotypes measured. In contrast, patients who received 7-valent pneumococcal-conjugate vaccine had a significantly lower mean response compared with patients who received 23-valent; their geometric mean antibody concentration after immunization was 4.95 micrograms/mL (P = 0.005).

CONCLUSION

A single dose of HIB-conjugate vaccine was immunogenic in patients who had completed treatment for Hodgkin disease diagnosed at least 2 years before immunization. In addition, responses to the 23-valent pneumococcal and 4-valent meningococcal vaccines were equivalent to those seen in healthy controls. Finally, patients had a significantly lower response to a single dose of 7-valent pneumococcal-conjugate vaccine than to 23-valent vaccine.

Impaired human responses to tetanus toxoid in vitamin A-deficient SCID mice reconstituted with human peripheral blood lymphocytes

Vitamin A deficiency is associated with increased childhood morbidity and mortality from respiratory and diarrheal diseases. In order to evaluate the effect of vitamin A on human antibody responses, we developed a vitamin A-deficient severe combined immunodeficient (SCID) mouse model. Vitamin A-deficient mice were produced by depriving them of vitamin A at day 7 of gestation. Mice were reconstituted with human peripheral blood lymphocytes (huPBL) from tetanus toxoid immune donors at 6 weeks of age and immunized with tetanus toxoid at 6 and 8 weeks of age. Secondary human antibody responses were determined 10 days later. The geometric mean human anti-tetanus toxoid immunoglobulin G concentrations were 3.75 micrograms/ml for the deficient mice and 148 micrograms/ml for controls (P = 0.0005). Vitamin A-deficient mice had only a 2.9-fold increase in human anti-tetanus toxoid antibody compared with a 74-fold increase in controls (P < 0.01). Supplementation with vitamin A prior to reconstitution restored human antibody responses to normal. These data suggest that vitamin A deficiency impairs human antibody responses. We speculate that impaired responses could increase susceptibility to certain infections. Furthermore, we propose that effects of other nutritional deficiencies on the human immune system could be evaluated in the SCID-huPBL model.

Recombinant interleukin-2 infusions and decreased IgG2 subclass concentrations

The administration of low doses of recombinant interleukin-2 (rIL-2) in vivo to patients with malignant neoplasms has been demonstrated to selectively increase the number of circulating natural killer (NK) cells in these patients. Recent evidence from SCID mouse models suggests that IgG subclass levels can be influenced by the presence and activity of NK cells. Therefore, we sought to examine the effect of rIL-2 infusions on human serum IgG subclass concentrations. We determined serum IgG subclass concentrations in 27 cancer patients receiving low-dose rIL-2 by daily continuous intravenous infusion. Eleven of these patients had active, metastatic, nonhematologic tumors; 16 patients had received IL-2 when they were in a minimal residual disease state after autologous or allogeneic bone marrow transplantation. Samples obtained before beginning IL-2 therapy and 8 to 10 weeks into therapy were tested. Treatment with IL-2 resulted in an increase in the percentage of CD56+ NK cells from 18% to 54% (P = .0001). A significant decrease in geometric mean IgG2 concentration from 2,017 micrograms/mL to 1,655 micrograms/mL was noted over this time interval (P = .03). Furthermore, the geometric mean IgG2 concentration after treatment was significantly lower than that of healthy controls (P = .026). In contrast, no significant changes in serum IgG1, IgG3, or IgG4 were noted during r-IL2 infusions. Our data suggest that rIL-2 treatment selectively decreases serum IgG2 concentrations. We speculate that increased NK cells mediate downregulation of human serum IgG2.

T cells and natural killer cells regulate human IgG subclass concentrations in SCID mice

Cytokine regulation of human IgG subclass production is not well understood. Since T cells and natural killer (NK) cells produce IL-4 and/or IFN-gamma, we examined the effect of these cells on human IgG subclass concentration in reconstituted severe combined immunodeficient (SCID) mice. SCID mice receiving only B-cell-enriched splenocyte preparations had significantly decreased IgG concentrations and significantly decreased IgG1/IgG2 ratios compared to mice receiving B cells plus T cells (P = 0.02). IgG2 represented 58% of the total IgG at 28 days in mice receiving B-cell-enriched preparations compared to 19% of the total for the group receiving both B cells and T cells (P = 0.013). The effect of natural killer cells (CD16+) on IgG subclass was also studied in this model. IgG2 concentrations were twofold higher in mice receiving CD16-depleted cells compared to controls (P = 0.004). No significant differences were noted for IgG1, IgG3, or IgG4 subclass concentrations. In conclusion, T cells and natural killer cells influence human IgG subclass regulation in the SCID mouse model. We propose that the regulation of human IgG subclass production can be further examined in the SCID model.

Bacterial polysaccharide immune globulin for prophylaxis of acute otitis media in high-risk children

We evaluated the prevention of recurrences of acute otitis media (AOM) by bacterial polysaccharide immune globulin (BPIG), a hyperimmune human immune globulin prepared by immunizing donors with bacterial polysaccharide vaccines. We used a randomized, stratified, double-blind, placebo-controlled design. Children < or = 24 months of age with 1 to 3 prior episodes of AOM received BPIG, 0.5 ml/kg, or saline placebo intramuscularly at entry and 30 days later. During the 120-day follow-up period, AOM was diagnosed by using clinical criteria and was confirmed with tympanocentesis and culture of the middle ear exudates. Eighty-eight episodes of AOM were observed in 76 patients who completed the study. The incidence of AOM during the entire 120-day study period was similar in BPIG and placebo recipients. Pneumococcal AOM was significantly less frequent in BPIG recipients (0.21 episode per patient) than in placebo recipients (0.45 episode per patient; p = 0.05). Time spent free of AOM was significantly prolonged in recipients of BPIG, in comparison with placebo recipients (51 vs 35 days; p = 0.034). This study demonstrated that circulating antibody, even without stimulation of specific local immunity, may prevent infection of the middle ear. The use of immune globulin preparations for longer periods or at a higher dosage might decrease the incidence of recurrent AOM in otitis-prone children, and deserves further evaluation.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. V. In vivo expression of individual antibody clones is dependent on Ig CH haplotypes and the categories of antigen

Antibodies (Ab) to the polysaccharide capsule of Haemophilus influenzae type b (Hib-PS) provide protection against Haemophilus influenzae type b disease in children, and Hib-PS vaccines with different immunologic properties are widely used clinically. The repertoire of human anti-Hib-PS Ab induced by these vaccines is relatively restricted and can be divided into two types by the structure of the light chain V region. Ab using A2-V kappa II gene product, which account for the majority of anti-Hib-PS Ab response in most patients, show little somatic mutations. In contrast, non-Ab using A2-V kappa II gene product use VL genes from the V kappa I, V kappa II, V kappa III, V kappa IV, and V lambda subgroups, are variably expressed among patients, and contain somatic mutations. To further study the expression of these two types of anti-Hib-PS Ab, we have produced KB13, a mAb specific for V kappa II subgroup, and used mAb specific for various other VL subgroups to develop immunoassays specific for anti-Hib-PS Ab of each VL subgroup. When Ig allotypes were studied for the effect on the Ab repertoire, A2-V kappa II (A2) Ab were found to be expressed less in patients expressing fb or zag CH haplotypes (p < 0.05). When the T cell-independent Hib-PS carbohydrate vaccine was compared to two T cell-dependent Hib-PS protein conjugate vaccines for their effect on Ab repertoire, Ab using V kappa III VL were found to be more often elicited with the conjugate vaccines than with the Hib-PS carbohydrate vaccine (p < 0.01). Thus, individual members of the anti-Hib-PS Ab repertoire differ not only in their V region structure but also in the control of their expression.

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. V. In vivo expression of individual antibody clones is dependent on Ig CH haplotypes and the categories of antigen

Antibodies (Ab) to the polysaccharide capsule of Haemophilus influenzae type b (Hib-PS) provide protection against Haemophilus influenzae type b disease in children, and Hib-PS vaccines with different immunologic properties are widely used clinically. The repertoire of human anti-Hib-PS Ab induced by these vaccines is relatively restricted and can be divided into two types by the structure of the light chain V region. Ab using A2-V kappa II gene product, which account for the majority of anti-Hib-PS Ab response in most patients, show little somatic mutations. In contrast, non-Ab using A2-V kappa II gene product use VL genes from the V kappa I, V kappa II, V kappa III, V kappa IV, and V lambda subgroups, are variably expressed among patients, and contain somatic mutations. To further study the expression of these two types of anti-Hib-PS Ab, we have produced KB13, a mAb specific for V kappa II subgroup, and used mAb specific for various other VL subgroups to develop immunoassays specific for anti-Hib-PS Ab of each VL subgroup. When Ig allotypes were studied for the effect on the Ab repertoire, A2-V kappa II (A2) Ab were found to be expressed less in patients expressing fb or zag CH haplotypes (p &lt; 0.05). When the T cell-independent Hib-PS carbohydrate vaccine was compared to two T cell-dependent Hib-PS protein conjugate vaccines for their effect on Ab repertoire, Ab using V kappa III VL were found to be more often elicited with the conjugate vaccines than with the Hib-PS carbohydrate vaccine (p &lt; 0.01). Thus, individual members of the anti-Hib-PS Ab repertoire differ not only in their V region structure but also in the control of their expression.

Critical appraisal of immunization strategies for prevention of infection in the compromised host

Chemotherapy and/or bone marrow transplantation clearly places individuals at increased risk for many vaccine-preventable diseases. Both active and passive immunization strategies have been considered for protecting immunocompromised patients. Many compromised hosts are capable of mounting protective responses to some protein toxoids, polysaccharide-conjugate, and viral vaccines. Effective, safe, and practical dosage schedules are evolving for individual vaccines and specific patient populations.

Effect of Haemophilus influenzae polysaccharide outer membrane protein complex conjugate vaccine on macrophages

Haemophilus influenzae type b polysaccharide-conjugate vaccines elicit protective antibody responses in young infants. One of these conjugates, polysaccharide linked to outer membrane protein complex (PRP-OMPC), is produced by linking the capsular polysaccharide to an outer membrane protein complex derived from group B Neisseria meningitidis. The outer membrane protein complex contains T cell carrier epitopes that elicit T cell-dependent antibody responses. OMPC also has been shown to increase the antibody response to other proteins administered concurrently that are not covalently linked (i.e., acts as an adjuvant). In this study PRP-OMPC immunized mice demonstrated significant increases in spleen size as well as in splenocyte number as compared to saline controls (p &lt; 0.01, p &lt; 0.001, respectively). No such increase was noted after immunization with another H. influenzae type b-conjugate vaccine, oligosaccharide linked to a variant of diphtheria toxin. By analytic flow cytometry, the mice immunized with PRP-OMPC demonstrated an increase in large splenocytes expressing the Ag Mac-1 (CD11b, CR3). Furthermore, the spleens on histologic examination were characterized by an increase in the red pulp area consisting predominantly of cells of macrophage morphology. By immunohistochemical staining, the cells were identified as macrophages due to expression of Mac-1 and p150,95 (CD11C) Ag. After PRP-OMPC immunization, severe combined immunodeficient mice also demonstrated significant splenomegaly with an increase in macrophages identified by expression of Mac-1 and MHC class II Ag. Thus PRP-OMPC vaccine resulted in T cell-independent splenomegaly with an increase number of macrophages. We propose that this unique property may confer increased immunogenicity to PRP-OMPC through macrophage activation and cytokine release. Furthermore, the effect on macrophages may explain the "adjuvant" capacity of OMPC.

Effect of Haemophilus influenzae polysaccharide outer membrane protein complex conjugate vaccine on macrophages

Haemophilus influenzae type b polysaccharide-conjugate vaccines elicit protective antibody responses in young infants. One of these conjugates, polysaccharide linked to outer membrane protein complex (PRP-OMPC), is produced by linking the capsular polysaccharide to an outer membrane protein complex derived from group B Neisseria meningitidis. The outer membrane protein complex contains T cell carrier epitopes that elicit T cell-dependent antibody responses. OMPC also has been shown to increase the antibody response to other proteins administered concurrently that are not covalently linked (i.e., acts as an adjuvant). In this study PRP-OMPC immunized mice demonstrated significant increases in spleen size as well as in splenocyte number as compared to saline controls (p < 0.01, p < 0.001, respectively). No such increase was noted after immunization with another H. influenzae type b-conjugate vaccine, oligosaccharide linked to a variant of diphtheria toxin. By analytic flow cytometry, the mice immunized with PRP-OMPC demonstrated an increase in large splenocytes expressing the Ag Mac-1 (CD11b, CR3). Furthermore, the spleens on histologic examination were characterized by an increase in the red pulp area consisting predominantly of cells of macrophage morphology. By immunohistochemical staining, the cells were identified as macrophages due to expression of Mac-1 and p150,95 (CD11C) Ag. After PRP-OMPC immunization, severe combined immunodeficient mice also demonstrated significant splenomegaly with an increase in macrophages identified by expression of Mac-1 and MHC class II Ag. Thus PRP-OMPC vaccine resulted in T cell-independent splenomegaly with an increase number of macrophages. We propose that this unique property may confer increased immunogenicity to PRP-OMPC through macrophage activation and cytokine release. Furthermore, the effect on macrophages may explain the "adjuvant" capacity of OMPC.

IgG1, IgG2 and IgM responses to two Haemophilus influenzae type b conjugate vaccines in young infants

PRP-meningococcal outer membrane protein complex (PRP-OMPC) and oligosaccharide linked to variant diphtheria toxin (HbOC) Haemophilus influenzae type b (HIB) conjugate vaccines have both been licensed for United States infants at 2 months of age. Differences in serologic responses for these vaccines have been noted with PRP-OMPC producing an early response at 2 months of age and HbOC producing a higher response after a third dose at 6 months of age. To further characterize the nature of these distinct responses, we measured the IgG1, IgG2 and IgM anti-HIB concentrations by enzyme-linked immunosorbent assay after administration of both vaccines. PRP-OMPC produced an IgM and IgG1 anti-HIB response following the initial dose at 2 months of age. After two doses of HbOC an increase in IgG1 and IgM were noted and after a third dose at 6 months of age an IgG2 anti-HIB response occurred. In addition 33 study subjects were boosted with PRP-OMPC at age 18 months and compared with 34 subjects who received only a primary dose. The anti-HIB IgG1 and IgG2 concentrations following the booster dose were both significantly higher for the primed group (P = 0.0001 and P = 0.001, respectively). Both HIB conjugate vaccines produce predominantly IgG1 anti-HIB antibody responses. The early response to PRP-OMPC vaccine at 2 months of age may result from adjuvant characteristics of the OMPC.

Response to Haemophilus influenzae type B conjugate vaccine in children undergoing splenectomy

Asplenic children are at increased risk for serious infection with polysaccharide encapsulated bacteria including Haemophilus influenzae type b (HIB), Streptococcus pneumoniae, and Neisseria meningitidis. Immunization with polysaccharide vaccines is recommended for children undergoing splenectomy. In 1987 a new more immunogenic HIB vaccine was licensed in the US to replace the pure HIB polysaccharide vaccine that was licensed in 1985. This polysaccharide-conjugate vaccine consists of the HIB polysaccharide linked to a protein carrier, diphtheria toxoid. Therefore, we evaluated the immune response of children undergoing splenectomy to HIB-conjugate vaccine. Thirteen children (7 with Hodgkin's disease, 4 with idiopathic thrombocytopenia, 2 with hereditary spherocytosis) aged 3 to 19 years were immunized with HIB-conjugate vaccine prior to splenectomy and serum was obtained following splenectomy. In addition, 15 healthy control children aged 2 to 14 years were immunized with the pure polysaccharide HIB vaccine for comparison. The patients undergoing splenectomy who received the HIB-conjugate vaccine had a geometric mean IgG anti-HIB antibody concentration of 48,106 ng/mL versus 10,786 ng/mL for the control patients who received the pure polysaccharide vaccine (P = .01). The presumed protective level of antibody is 1,000 ng/mL and all children were well above this concentration. Therefore, we propose that children undergoing splenectomy be immunized with an HIB-conjugate vaccine.

Immunoglobulin G subclass values in healthy black and white children

To determine whether IgG subclass concentrations differed between healthy black and white children, we measured IgG1, IgG2, IgG3, and IgG4 immunoglobulins by enzyme-linked immunosorbent assay in sera from 246 black children aged 6 to 42 months. We then compared these values with the normal values established for 664 white children aged 6 to 60 months. The IgG1, IgG2, and IgG4 subclass concentrations of the black children were lower than those for white children; many of the values were below the 95% confidence limits established for white children: 46 (19%) of 246 IgG2 values and 19 (8%) of 246 IgG4 values for black children were below the normal limits. We compared the geometric mean values for black and white children, as determined for each 6-month age grouping between 6 and 42 months of age; 367 of the 664 white children were less than 42 months of age and were included in this analysis. The geometric mean values for IgG1, IgG2, and IgG4 levels were consistently lower for black children than for white children. The differences were significant for IgG1 subclass values of those children older than 24 months and for IgG2 and IgG4 values of those children older than 18 months. No consistent differences were noted for IgG3 subclass values. We conclude that young black children have lower IgG1, IgG2, and IgG4 serum concentrations than are found in white children. If normal IgG values for white children are used, healthy black children may be erroneously classified as IgG subclass deficient. The mechanism and biologic relevance of these population differences need to be evaluated.

Human B cells secrete predominantly lambda L chains in the absence of H chain expression

Ig H and L chains are independently assembled in B cells and then secreted together as a functional protein. H chains cannot be secreted without assembly to L chains; however, L chains can be secreted in the absence of H chains by both mice and human cells. To examine the influence of H chain expression on human L chain isotype selection (kappa or lambda), we compared the kappa/lambda ratio of L chains unassociated with H chains (free L chains) to the kappa/lambda ratio of L chains associated with H chains. Culture supernatants of human splenocytes were assayed for kappa and lambda L chains. Free L chains were the predominant form of L chains detected in unstimulated cultures, accounting for 68 to 70% of the total. This was in contrast to the minor proportion that free L chains represented (less than 20%) in cultures stimulated with PWM or LPS (p less than 0.01). Furthermore, the kappa/lambda ratio of light chains detected in unstimulated cultures was 0.5 as compared to 1.3 for PWM stimulated cultures (p = 0.0001). To demonstrate that the decreased kappa/lambda ratio of L chains in the supernatants of cultures of unstimulated B cells was due to free L chains, we measured the kappa/lambda ratio of IgG and IgM-associated L chains. In both the stimulated and unstimulated cultures, the kappa/lambda ratio of L chains associated with H chains was greater than the ratio determined for free L chains. Free L chains were shown to be predominantly lambda as compared to the predominantly kappa phenotype of L chains associated with H chains. Thus absence of H chain expression affects selection of L chain isotypes secreted by human B cells.

Human B cells secrete predominantly lambda L chains in the absence of H chain expression

Ig H and L chains are independently assembled in B cells and then secreted together as a functional protein. H chains cannot be secreted without assembly to L chains; however, L chains can be secreted in the absence of H chains by both mice and human cells. To examine the influence of H chain expression on human L chain isotype selection (kappa or lambda), we compared the kappa/lambda ratio of L chains unassociated with H chains (free L chains) to the kappa/lambda ratio of L chains associated with H chains. Culture supernatants of human splenocytes were assayed for kappa and lambda L chains. Free L chains were the predominant form of L chains detected in unstimulated cultures, accounting for 68 to 70% of the total. This was in contrast to the minor proportion that free L chains represented (less than 20%) in cultures stimulated with PWM or LPS (p less than 0.01). Furthermore, the kappa/lambda ratio of light chains detected in unstimulated cultures was 0.5 as compared to 1.3 for PWM stimulated cultures (p = 0.0001). To demonstrate that the decreased kappa/lambda ratio of L chains in the supernatants of cultures of unstimulated B cells was due to free L chains, we measured the kappa/lambda ratio of IgG and IgM-associated L chains. In both the stimulated and unstimulated cultures, the kappa/lambda ratio of L chains associated with H chains was greater than the ratio determined for free L chains. Free L chains were shown to be predominantly lambda as compared to the predominantly kappa phenotype of L chains associated with H chains. Thus absence of H chain expression affects selection of L chain isotypes secreted by human B cells.

Interpretation of IgG subclass values: a comparison of two assays

Because we have noted discordant results in the measurement of IgG subclass concentrations by means of a widely available commercial radial immunodiffusion (RID) kit in comparison with an enzyme-linked immunosorbent assay (ELISA) developed at the Centers for Disease Control (CDC), we conducted in a blinded manner a comparison of the two assays, using sera from 48 healthy children. The correlation coefficients between the assays were 0.92, 0.82, 0.93, and 0.86 for the IgG1, IgG2, IgG3, and IgG4 assays, respectively. However, the RID assay assigned lower values for IgG1 and IgG4 determinations than the ELISA did. Furthermore, the "normal lower range values" provided by the RID assay were higher for each IgG subclass. When the sera from the healthy control subjects were analyzed with the RID assay, 12 (25%) of 48 subjects had values below the normal range for at least one subclass measurement. In contrast, with the CDC ELISA, all values were within the 95% confidence limits determined for the CDC ELISA. We suggest that age-specific normal limits be established with the use of sera from many healthy subjects for any assay measuring IgG subclass concentrations. As new groups of immunodeficiencies are defined and potential therapies are advocated, careful attention to assay standardization will result in a clearer delineation of these disease groups and of their response to treatment.

Kappa and lambda light chain composition of antibody to the capsular polysaccharide of Haemophilus influenzae type b

Concentrations of total immunoglobulins bearing kappa and lambda light chains were measured in the sera of 215 healthy white children aged 6 months to 10 years. Both kappa and lambda concentrations increased with age. However, the concentration of immunoglobulins bearing kappa light chains increased at a greater rate than those bearing lambda light chains (P = .01). Thus, the kappa:lambda ratio of the youngest children (6-24 months) was significantly lower than that of the oldest (25-130 months) (P = .0015). The relationship between the IgG antibody concentration and the light chain composition of the specific antibody directed to Haemophilus influenzae type b (Hib) polysaccharide was also assessed in 62 of 215 serum samples with detectable Hib antibody. The IgG Hib antibody concentration was strongly correlated with the kappa:lambda Hib antibody ratio (r = .60, P = .001), and this correlation was independent of age. Thus, light chain selection and response to polysaccharides may be regulated by common mechanisms that mature late in ontogeny.

Human polysaccharide-specific B cells are responsive to pokeweed mitogen and IL-6

The responsiveness of polysaccharide-specific B cells to PWM was examined in vitro. Spleen cells from six patients immunized with Haemophilus influenzae type b-diphtheria toxoid, pneumococcal and meningococcal vaccines were T cell-depleted and separated by Percoll density gradient centrifugation. In each B cell fraction, spontaneous antibody production was demonstrated to capsular polysaccharides as well as diphtheria toxoid. The peak of spontaneous antibody production was demonstrated to be five to seven days after immunization. When T cells and PWM were added, the total Ig secretion increased in all B cell fractions. PWM also enhanced IgG antibody directed to each of three polysaccharide Ag measured. This enhancement was most noticeable for nonresting B cells. The PWM effect was not confined to IgG, as IgM and IgA to Neisseria meningitidis type C were measured and also enhanced. The kinetics of the PWM response demonstrated the most IgG antibody to polysaccharide Ag from spleens immunized five to seven days before splenectomy. When the patients were immunized either 2 days or 4 mo before splenectomy, no spontaneous IgG antibody to polysaccharides was detected although PWM induced small amounts of antibody. Finally, anti-IL-6 antibody blocked PWM-induced total and polysaccharide-specific antibody production. We conclude that human polysaccharide-specific B cells are responsive to PWM and IL-6. We suggest that polysaccharide B cells are not truly "T cell-independent" and may respond to T cell lymphokines and thus are similar to protein-specific B cells.

Human polysaccharide-specific B cells are responsive to pokeweed mitogen and IL-6

The responsiveness of polysaccharide-specific B cells to PWM was examined in vitro. Spleen cells from six patients immunized with Haemophilus influenzae type b-diphtheria toxoid, pneumococcal and meningococcal vaccines were T cell-depleted and separated by Percoll density gradient centrifugation. In each B cell fraction, spontaneous antibody production was demonstrated to capsular polysaccharides as well as diphtheria toxoid. The peak of spontaneous antibody production was demonstrated to be five to seven days after immunization. When T cells and PWM were added, the total Ig secretion increased in all B cell fractions. PWM also enhanced IgG antibody directed to each of three polysaccharide Ag measured. This enhancement was most noticeable for nonresting B cells. The PWM effect was not confined to IgG, as IgM and IgA to Neisseria meningitidis type C were measured and also enhanced. The kinetics of the PWM response demonstrated the most IgG antibody to polysaccharide Ag from spleens immunized five to seven days before splenectomy. When the patients were immunized either 2 days or 4 mo before splenectomy, no spontaneous IgG antibody to polysaccharides was detected although PWM induced small amounts of antibody. Finally, anti-IL-6 antibody blocked PWM-induced total and polysaccharide-specific antibody production. We conclude that human polysaccharide-specific B cells are responsive to PWM and IL-6. We suggest that polysaccharide B cells are not truly "T cell-independent" and may respond to T cell lymphokines and thus are similar to protein-specific B cells.

Proliferation of resting B cells is modulated by CR2 and CR1

Absence of the third component of complement, C3, is associated with impaired ability to synthesize antibody, particularly in the presence of limiting antigen [1-9]. The mature B lymphocyte bearing the surface immunoglobulin receptor transduces signals for proliferation and differentiation upon binding of specific antigen. This mature B cell also bears two related membrane proteins, CR2 (the C3d/Epstein-Barr virus receptor) (CD35) [15], which can mediate the binding of ligands to which appropriate cleavage fragments of C3 have become attached [16]. It has been suggested that these receptors play a direct role(s) in B cell activation [17-25]. In light of previous in vivo observations we decided to assess the function of CR2 and CR1 in relation to B cell activation through the membrane IgM receptor. Highly purified splenic B cells were prepared. No contaminating T cells or macrophages were detected by flow cytometric analysis and no proliferative activity was present upon PHA or ConA stimulation of the purified cells. The B cells were separated into low (activated), medium (preactivated) and high density (resting) fractions by Percoll gradient density centrifugation [26]. The responses of the B cell subpopulations to various concentrations of anti mu (DA4.4 monoclonal antibody) [27] were examined for proliferation at 72 h and for IgM/IgG production at 7 days. Low density B cells were maximally stimulated and no concentration of anti-mu was effective in enhancing their responses. High density B cells proliferated to anti-mu in a concentration dependent manner. When substimulatory concentrations of anti-mu were employed, concomitant crosslinking of CR2 (with either of 2 distinct monoclonal antibodies HB-5 [28] or OKB7 [17]) resulted in a 45% enhancement of B cell proliferation above that observed by crosslinking of SIgM alone. In these studies, total IgM and IgG did not increase in the absence of T cells or T cell factors, indicating that terminal differentiation did not occur. In contrast, when a monoclonal antibody to CR1(44D) [29] was employed in an identical experiment, B cell proliferation was completely inhibited. Antibodies to CR2 or CR1 either alone or in crosslinked form did not enhance B cell proliferation. Immune complexes may crosslink the B cell surface in a manner analogous to our model when the immunoglobulin receptor and CR2 are simultaneously engaged. This activation signal may be particularly important in eliciting antibody responses when the quantity of specific antigen or the affinity for antigen is low. The marked inhibition of proliferation induced by CR1 suggests an alternate role for this receptor in modulation of B cell responses.

Ig allotype-linked regulation of class and subclass composition of natural antibodies to group A streptococcal carbohydrate

To determine the importance of genes located in or near the Ig constant regions in regulating the human antibody response, we correlated Ig allotypic markers with total Ig concentrations and natural antibody concentrations to the streptococcal group A carbohydrate (A-CHO) in 193 healthy adult blood donors. The major correlations between Ig allotypes and total Ig and specific antibody concentrations were observed with the Gm(f;n;b) haplotype. When compared with Gm(f;n;b) negative individuals, Gm(f;n;b) positives had significantly higher concentrations of total IgG2 (p less than 0.001) and IgG2 anti A-CHO (p less than 0.05), lower concentrations of total IgG1 (p less than 0.001) and IgG1 anti A-CHO (p less than 0.001), and lower concentrations of total IgM (p less than 0.001) and IgM anti A-CHO (p less than 0.05). We conclude that individuals with the Gm(f;n;b) haplotype respond preferentially with IgG2 rather than IgG1 subclass antibodies. This increased capacity to respond with IgG2 antibodies may be reflected in the magnitude of the total antibody response when the IgG2 subclass comprises a major proportion of the response, as occurs in the adult response to many polysaccharide Ag.

Ig allotype-linked regulation of class and subclass composition of natural antibodies to group A streptococcal carbohydrate

To determine the importance of genes located in or near the Ig constant regions in regulating the human antibody response, we correlated Ig allotypic markers with total Ig concentrations and natural antibody concentrations to the streptococcal group A carbohydrate (A-CHO) in 193 healthy adult blood donors. The major correlations between Ig allotypes and total Ig and specific antibody concentrations were observed with the Gm(f;n;b) haplotype. When compared with Gm(f;n;b) negative individuals, Gm(f;n;b) positives had significantly higher concentrations of total IgG2 (p less than 0.001) and IgG2 anti A-CHO (p less than 0.05), lower concentrations of total IgG1 (p less than 0.001) and IgG1 anti A-CHO (p less than 0.001), and lower concentrations of total IgM (p less than 0.001) and IgM anti A-CHO (p less than 0.05). We conclude that individuals with the Gm(f;n;b) haplotype respond preferentially with IgG2 rather than IgG1 subclass antibodies. This increased capacity to respond with IgG2 antibodies may be reflected in the magnitude of the total antibody response when the IgG2 subclass comprises a major proportion of the response, as occurs in the adult response to many polysaccharide Ag.