A pharmacokinetic-pharmacodynamic model for the mobilization of CD34+ hematopoietic progenitor cells by AMD3100.

BACKGROUND: AMD3100 is a small-molecule CXCR4 antagonist that has been shown to induce the mobilization of CD34 + hematopoietic progenitor cells from bone marrow to peripheral blood. AMD3100 has also been shown to augment the mobilization of CD34 + cells in cancer patients when administered in combination with granulocyte colony-stimulating factor (G-CSF) (filgrastim). The purpose of this study was to characterize the exposure-response relationship of AMD3100 in mobilizing CD34 + cells when administered as a single agent in healthy volunteers. METHODS: AMD3100 concentrations and CD34 + cell counts obtained from 29 healthy subjects in a single-dose, intensively sampled pharmacokinetic/pharmacodynamic (PK-PD) study were analyzed by use of nonlinear mixed effects regression with the software NONMEM. FOCE (first order conditional estimation) with interaction was the estimation method, and simultaneous PK-PD fitting was adopted. RESULTS: The pharmacokinetics of AMD3100 was described by a 2-compartment model with first-order absorption. The population estimates (+/-SE) for clearance and central volume of distribution were 5.17 +/- 0.49 L/h and 16.9 +/- 3.79 L, respectively. CD34 + cell mobilization was best described by an indirect effect model that stimulates the entry process of CD34 + from bone marrow to peripheral blood in the form of a sigmoid maximum effect model. The population estimates (+/-SE) of maximum effect, concentration causing 50% of maximum response, and equilibration time were 12.6 +/- 4.89, 53.6 +/- 11.9 mug/L, and 5.37 +/- 1.31 hours, respectively. CONCLUSIONS: This study characterizes the exposure-response relationship of AMD3100 in mobilizing CD34 + cells after subcutaneous administration. This PK-PD model will be useful in assessing relevant covariates and for optimizing the use of AMD3100 in various patient populations.

Vaccine induced immunologic memory for hepatitis B surface antigen: implications for policy on booster vaccination.

This paper reviews published literature on the long-term persistence of immunologic memory for HBsAg after a course of hepatitis B vaccine and the functional significance this has for policy on booster vaccination. Several studies have shown that vaccine induced antibody (anti-HBs) specific for the surface antigen (HBsAg) of hepatitis B virus (HBV) is protective at a serum concentration of 10 milli-International Units per milliliter (mIU ml-1). When acquired passively (e.g. from hepatitis B immune globulin), susceptibility to infection returns as antibody declines. However, vaccine induces active synthesis of anti-HBs accompanied by immunologic memory for HBsAg that affords ongoing protection independent of antibody. Persistent memory over periods of 5 years or more is evident from large, rapid increases in antibody following booster vaccination, even in subjects who have lost antibody. Complementary studies, using an in vitro enzyme linked immunosorbent assay (spot-ELISA), show that the number of memory B lymphocytes able to produce anti-HBs does not diminish as the level of antibody declines. That immunologic memory provides effective immunity is suggested by serologic studies over periods of 5 years or more of vaccinees frequently exposed to HBV. Although many failed to maintain at least 10 mIU ml-1 of antibody, there have been very few clinically significant breakthrough infections. Thus, it appears unnecessary to give healthy vaccinees a booster vaccination when the level of anti-HBs falls below 10 mIU ml-1. Current studies suggest good retention of immunologic memory in healthy vaccinees over periods of 5-12 years. While additional studies will better define the limits of this phenomenon, routine booster vaccination should not be needed to sustain immunologic memory and protection within 5 years and perhaps longer after the primary vaccination series.

Antibody responses of healthy infants to a recombinant hepatitis B vaccine administered at two, four, and twelve or fifteen months of age.

Hepatitis B vaccine was administered to healthy infants on two investigational schedules that fall within ranges recommended by the U.S. Public Health Service Advisory Committee on Immunization Practices and by the American Academy of Pediatrics Committee on Infectious Diseases. A month after receiving vaccine at 2, 4, and 12 or 15 months of age, 98% and 100% of the children had > 10 mIU antibodies to hepatitis B surface antigen per milliliter, with gemometric mean titers of 1358 mIU/ml and 3424 mIU/mL, respectively.

Maternal HEL immunization has no lasting effects on the immune response of offspring to immunization with hen egg-white lysozyme.

The effect of prior maternal immunization on the murine offspring response to subsequent immunization with hen egg-white lysozyme was examined. Adult female A/J mice were immunized with 100 micrograms HEL-CFA intraperitoneally 10-27 weeks before conception. The offspring of these experimental female mice were then immunized with HEL-CFA at differing ages. Suppression of the anti-HEL IgG B cell response was observed when the offspring were immunized prior to 3 weeks of age when high levels of maternal antibody were still present. Older offspring, more than 8 weeks of age, were immunized with HEL-CFA to determine if exposure to maternal immunoglobulin early in ontogeny had primed or altered the offspring response to HEL. At this age, suppressive effects of transferred maternal antibody were no longer evident. Priming was not detected in the offspring as judged by the total magnitude of the anti-HEL antibody response or the kinetics of the response when experimental and age-matched control offspring were examined. Furthermore, qualitative differences in the response as evidenced by IgG vs IgM content and fine specificity of the response (primary vs secondary antibody) were not observed. No evidence was found to suggest that exposure to polyclonal maternal anti-HEL antibody had primed the offspring for a more efficient or qualitatively different response to immunization with the protein antigen HEL. After maternal antibody levels decreased, the offspring response was similar to that of controls, suggesting that the response had not been permanently altered by the prior exposure early in ontogeny to polyclonal maternal antibody.

Control of hepatitis B through routine immunization of infants: the need for flexible schedules and new combination vaccine formulations.

Universal immunization of infants is essential to the control of hepatitis B in areas of high endemicity where infection commonly occurs in infants and children. It is also an attractive strategy for ultimately reducing hepatitis-B-associated acute and chronic liver disease in areas of lower endemicity where infections occur primarily in adolescents and adults. Integration of hepatitis B vaccine with other routine paediatric immunizations, using flexible scheduling, will enhance compliance while minimizing the need for additional resources. Clinical studies demonstrate that a very high proportion of healthy infants and adults develop a protective level of antibody when given hepatitis B vaccine using a wide range of schedules. Compliance with universal vaccination of infants against hepatitis B may be enhanced by the development of new combination vaccines (e.g. diphtheria-tetanus-pertussis-Haemophilus influenzae b-hepatitis B) that allow complete immunization against several antigens with a minimal number of injections.

Anti-PRP antibody levels after a primary series of PRP-OMPC and persistence of antibody titres following primary and booster doses.

The Haemophilus influenzae capsular polysaccharide-outer membrane protein conjugate, PRP-OMPC (PedvaxHIB) elicits very good antibody responses in infants > or = 2 months of age after the first dose. Increasing age at time of first vaccination correlates with higher antibody responses. Anti-PRP responses are consistently high with the first injection among all population groups studied. Booster doses stimulate anamnestic antibody responses after one year of age. Among US children (excluding Navajo and Apache children) given a primary injection at 14-18 months of age, the geometric mean titre (GMT) after 2 to 3 years was > 1 micrograms/ml. US children (excluding Navajo and Apache children) given a primary series at 2 and 4 months of age and a booster at 18 months of age also had an anti-PRP GMT > 1 micrograms/ml 2.5 years later. Navajo and Apache children given a primary series at 2 and 4 months of age and a booster at 12-15 months had antibody levels of 1.50 micrograms/ml one year later. Antibody persistence data suggest there will be long-term protection against Haemophilus influenzae b disease following immunization with PRP-OMPC.

Worldwide experience with the CR326F-derived inactivated hepatitis A virus vaccine in pediatric and adult populations: an overview.

The worldwide experience to date with VAQTA, a highly purified formalin-inactivated hepatitis A vaccine containing alum-adjuvant, is reviewed. No serious adverse experience related to vaccination has been reported. The vaccine has proven highly immunogenic, with seroconversion detectable after a single dose in 90-99% of children 2-16 years old, and of adults under 77 kg (170 lb) body weight. There is a trend toward lower one-dose seroconversion rates with increasing age and with weight > 77 kg. Early seroconversion in the latter groups may require two 25-unit doses given 2, 4 or 8 weeks apart, or a higher priming dose. Seroconversion induced by this vaccine has been shown to signify protection from clinical hepatitis A disease. The few vaccines whose titers have waned to borderline levels responded anamnestically to a booster, suggesting that the vaccine induces an immune memory response and should provide long-term protection.

Evaluation of new anti-infective drugs for the treatment of selected infections of the skin and skin structure. Infectious Diseases Society of America and the Food and Drug Administration.

No method for classifying infections of the skin and skin structure is uniformly accepted. Therefore, each protocol for the evaluation of new anti-infective drugs must include definitions of the skin and skin-structure infections to be treated. Clinical findings may suggest the etiology. Cultures should be performed by the best available technique. Because the yield of pathogens from sites of skin and skin-structure infection is often low, monitoring of the clinical response to therapy is paramount. Randomized, double-blind, active-control comparative studies are needed, and maintenance of blinding is recommended, even with a change in the route of administration of the study and/or control drugs. The period of follow-up should be defined for each type of infection.

Evaluation of new anti-infective drugs for the treatment of osteomyelitis in adults. Infectious Diseases Society of America and the Food and Drug Administration.

Cases of osteomyelitis can be divided into four categories: acute hematogenous, vertebral, secondary to a contiguous focus of infection without vascular disease, and secondary to a contiguous focus of infection with vascular disease. Each category may be further divided into acute and chronic forms. Clinical symptoms persisting for > or = 10 days correlate roughly with the development of necrotic bone and chronic osteomyelitis. Patients enrolled in clinical trials should generally be > or = 12 years of age. Prior antimicrobial treatment does not exclude patients if the culture of a bone sample obtained at the time of enrollment yields pathogenic bacteria. Randomized, double-blind, active-control comparative studies are encouraged. Clinical outcome should be assessed during therapy and within 5-9 days, 4-6 weeks, and 11-13 months after completion of therapy. In the final assessment, clinical appraisal is paramount.

Evaluation of new anti-infective drugs for the treatment of acute hematogenous osteomyelitis in children. Infectious Diseases Society of America and the Food and Drug Administration.

Most children with acute hematogenous osteomyelitis have no preceding illness. Their early symptoms are pain and fever. A bacterial etiology is established in approximately 75% of cases by needle aspiration of the affected site or blood culture. Clinical trials should be limited to cases of bacterial origin. The antimicrobial agents studied should be active against Staphylococcus aureus and streptococci. If children < 5 years of age are included, the drug should also be active against beta-lactamase-negative and -positive strains of Haemophilus influenzae. Randomized, prospective, double-blind comparative studies are preferable to open, evaluator-blinded trials. Clinical outcome is appraised by physical signs and symptoms. A successful microbiological outcome consists of presumptive eradication. The final assessment should be made 1 year after completion of therapy.

Evaluation of new anti-infective drugs for the treatment of infectious arthritis in adults. Infectious Diseases Society of America and the Food and Drug Administration.

This guideline describes clinical trials of new anti-infective drugs for the treatment of septic arthritis due to bacteria other than Neisseria gonorrhoeae in adults. Septic arthritis is associated with fever and with physical findings at the affected joint. Diagnosis is established by culture of synovial fluid. Treatment includes the administration of antimicrobial drugs and drainage of the joint by needle aspiration or surgery. Multicenter, randomized comparative clinical trials that are single-, double-, or evaluator-blinded should be performed. However, an open trial of a new antimicrobial agent with historical controls is acceptable. Patients should receive treatment for at least 2-3 weeks. After 5 days of antimicrobial therapy, synovial fluid should be sterile and clinical signs and symptoms should have diminished. Patients should be followed for 2-4 weeks after completion of therapy.

Evaluation of new anti-infective drugs for the treatment of acute suppurative arthritis in children. Infectious Diseases Society of America and the Food and Drug Administration.

Diagnostic criteria for bacterial suppurative arthritis include the demonstration of an inflammatory exudate by aspiration of synovial fluid and the isolation of bacteria from cultures of synovial fluid and/or blood. Clinical manifestations include joint effusion, swelling, tenderness, and pain, with or without redness of the overlying skin. Management consists of antimicrobial therapy, measures designed to relieve symptoms, surgical drainage of infected fluid, and physical therapy. Studies of new anti-infective therapy should be limited to cases of bacterial origin. Prospective, randomized, double-blind, or evaluator-blinded, active-control comparative clinical trials should be performed. Clinical response is characterized as success (cure), failure, or indeterminate outcome. The most common successful microbiological outcome is presumptive eradication. Follow-up should continue for 1 year before the final assessment.

Evaluation of new anti-infective drugs for the treatment of infections of prosthetic hip joints. Infectious Diseases Society of America and the Food and Drug Administration.

Infections of a prosthetic hip are of three types: acute contiguous, chronic contiguous, and hematogenous. Acute contiguous infections result from contamination of the operative field at the time of surgery; clinical manifestations of infection become apparent within 6 months. Chronic contiguous infections are diagnosed 6-24 months postoperatively and are believed to be caused by intraoperative contamination. Hematogenous seeding of prosthetic joints accounts for infections that develop > or = 2 years after surgery. Fever and pain or dysfunction of the joint may be the only signs or symptoms of prosthetic hip joint infection. Definitive diagnosis is established by culture of a needle aspirate from the joint space or by intraoperative culture. Prospective, randomized, double-blind or evaluator-blinded, active-control comparative studies are preferable to open trials. Success rates 10-14 weeks after completion of a 4- to 6-week course of antimicrobial therapy should be > or = 90%.

Evidence for idiotypic sharing between conventional and naturally activated B cells.

In the primary immune response to hen egg-white lysozyme (HEL), approximately 50% of the primary anti-HEL antibody-forming cells (AFC) express IdXE, an idiotype absent from the secondary response. Spontaneous IgM enzyme-linked immunosorbent assay (ELISA)-AFC in spleen cells from naive A/J mice were analyzed for the occurrence of IdXE by use of two affinity-purified rabbit antisera, R213 and R8, each raised against a different primary IdXE+, anti-HEL mAb. Two ELISA-AFC assay methods were used: direct coating of immunoplates with R213 or development of IgM-producing ELISA-AFC with biotinylated R8. From ages 7 days until 6 months, 10-20% of spontaneous IgM AFC were found to be IdXE+. IdXE+ anti-HEL IgG1 monoclonal antibodies, 2F4 or 3C11 (100 micrograms/ml), completely inhibited binding of biotinylated R8 (0.5 micrograms/ml) to spontaneous IgM-AFC while IdXE-, anti-HEL IgG1, 5E11 and 2C7, showed no significant inhibition. Greater than 90% of IdXE+ spontaneous IgM-AFC were not HEL specific. We conclude that a dominant set of idiotopes found in a conventional antigen-driven immune response can also play a major role in the spontaneously activated B cell repertoire. Our data argue against a bifurcation of the immune system into a compartment of idiotypic network-related cells and an independent set of non-network cells subject to antigenic stimulation.

Clinical experience with PedvaxHIB, a conjugate vaccine of Haemophilus influenzae type b polysaccharide--Neisseria meningitidis outer membrane protein.

PedvaxHIB, a Haemophilus influenzae type b (Hib) conjugate vaccine composed of Hib capsular polysaccharide covalently bound to an outer membrane protein complex of Neisseria meningitidis serogroup B, was evaluated for immunogenicity and safety in infants and children 2 months of age and older. A significant and consistent antibody response was seen after a single dose of the vaccine in all age groups, including infants as young as 2 months of age. In addition, the vaccine elicited a good booster response when given at 12 to 17 months of age. Subjects from diverse subpopulations, including those with impaired antibody response to Hib polysaccharide vaccines, showed a significant response to vaccination. The vaccine was well tolerated when administered alone or concurrently with other paediatric vaccines. A protective efficacy study, recently completed, has shown the vaccine to be highly effective in 2-month-old infants.

Varicella vaccine (VARIVAX) in healthy children and adolescents: results from clinical trials, 1987 to 1989.

A total of 3303 healthy children and adolescents, aged 12 months to 17 years, were vaccinated with one of five production lots of a live attenuated varicella vaccine (VARIVAX) containing 1000 to 1625 plaque-forming units per dose. The vaccine was generally well tolerated. Ninety-six percent (2381/2475) of vaccinees responded to vaccination by producing antibody as measured by a glycoprotein-based enzyme-linked immunosorbent assay; 99% (569/576) of those tested maintained antibody at 1 year following vaccination. The incidence of varicella following household exposure in vaccinees was approximately 12%; household contact historically results in 87% infection. Nearly all of the vaccinees who had varicella after vaccination had a clinically modified disease.

Intramuscular imipenem/cilastatin in multiple-dose treatment regimens: review of the worldwide clinical experience.

Multicenter noncomparative trials of intramuscular administration of imipenem/cilastatin for the treatment of a variety of infections requiring multiple-dose therapy are reviewed. Fourteen centers in the United States and 18 centers elsewhere participated in these studies. A total of 686 patients (461 evaluable) were treated worldwide. The severity of the infection was rated as moderate in 58.9%, mild in 37.2% and severe in 0.6%. The most common sites of infection were the skin and soft tissue (36.2%) and intra-abdominal (17.6%). Polymicrobial infections were relatively common (27%). Dosing regimens in evaluable patients were 500 mg every 12 h (45.1%), 750 mg every 12 h (36.2%) and 500 mg every 8 h (18.6%). The overall clinical outcome was favorable (clinical cure or improvement) for 95% or more of the evaluable patients with the various body system infections, except in gynecologic infections where 89% of the evaluable patients had a favorable outcome and for sepsis where the favorable outcome was 76%. Where data were available for analysis (skin and soft tissue infections) there was no difference in favorable clinical outcome among patients with moderate infection treated with 1.0 g/day (95% favorable) compared with 1.5 g/day (94% favorable). The overall bacteriologic eradication rate was 91%. Clinical adverse effects were similar in type but less common in frequency than those noted in other studies with the intravenous formulation, with nausea, vomiting and diarrhea being most common; no instances of seizures or confusion were observed. The laboratory adverse effects were similar to those seen in other studies with the intravenous formulation, with increased liver enzyme values the most common. The intramuscular injection was well tolerated in 87% of the patients and moderately well tolerated in 6.6%. The efficacy and low incidence of side effects of the intramuscular formulation of imipenem/cilastatin are significant advantages in the cost-effective treatment of infections.

Inhibition of offspring response to HEL-CFA by administration of anti-HEL MAB to the mother is not related to the predominant idiotype, IdXE, or specificity of the MAB.

In the neonatal suckling mouse, the antibody response to HEL-CFA can be inhibited by administration of certain anti-HEL monoclonal antibodies to the mother. The murine primary response to hen egg-white lysozyme (HEL), which can be elicited in A/J mice as early as 7 days of age, is characterized by a predominant specificity that includes the 3 N-terminal amino acids of HEL (TIP-dependence) and by a predominant idiotype, IdXE. A panel of murine IgG1 anti-HEL mAbs was administered to the suckling offspring via the mother. These mAbs were not equivalent in their effects on the offspring. Only two of six IgG1 mAbs, 2F4/2E5 (IdXE-positive, TIP-dependent) and 2D1 (IdXE-negative, TIP-independent), consistently induced suppression of the response of A/J offspring when immunized at 16-20 days of age with HEL-CFA. Suppression averaged 71% for 2F4/2E5 and 74% for 2D1 and was always statistically significant (P less than .05) when 275 micrograms mAb was administered IP to the mother within 24 hr postpartum. Since 2D1 is IdXE-negative and TIP-independent, neither of these properties appears to be crucial for suppression. Differences in transfer of the mAbs from the mother to the offspring or differences in catabolism of the mAbs in the offspring were not detected. When various characteristics of the mAbs such as affinity, idiotypy, and fine specificity were considered, there was no single factor which determined suppression. One of the two mAbs that suppressed the offspring response, 2D1, is idiotypically highly connected in the anti-HEL mAb panel. This observation suggests that idiotypic interactions in the developing neonatal repertoire with subsequent perturbation of T and B cell repertoire development may be an area for future investigation.