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Abstract

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

A randomized, double-blind, dose-escalation study evaluated the safety and efficacy of hepatitis C virus (HCV)-AbXTL68, a neutralizing, high-affinity, fully human, anti-E2 monoclonal antibody, in 24 HCV-positive patients undergoing liver transplantation. HCV-AbXTL68 or placebo was administered at doses from 20-240 mg as 2-4 infusions during the first 24 hours after transplantation, followed by daily infusions for 6 days, weekly infusions for 3 weeks, and either 2 or 4 weekly infusions for 8 weeks. Serum concentrations of total anti-E2 obtained during daily infusions of 120-240 mg HCV-AbXTL68 were 50-200 μg/mL above concentrations in the placebo group. Median serum concentration of HCV RNA dropped below baseline in all groups immediately after transplantation. On day 2, median change from baseline in HCV RNA was −1.8 and −2.4 log in the 120-mg and 240-mg groups, respectively, compared with −1.5 log with placebo. The difference was lost after day 7 when the dosing frequency was reduced. The coincidence of increases in anti-E2 with decreases in HCV RNA concentration indicate that the dose-related changes in HCV RNA concentration were a result of HCV-AbXTL68 administration in the 120- and 240-mg groups. The overall incidence of nonfatal serious adverse events was higher with placebo (60%) vs. all active treatments combined (42%). In conclusion, HCV-AbXTL68 may decrease serum concentrations of HCV RNA in patients after liver transplantation. Studies evaluating more frequent daily dosing at doses >120 mg are necessary to investigate sustained viral suppression in this population. Liver Transpl 12:1381–1389. 2006. © 2006 AASLD.

Almost all patients with hepatitis C virus (HCV) are reinfected immediately after liver transplantation (LT). In many cases, the recurrent infection leads to chronic hepatitis and ultimately to graft failure, with 20% of patients dying or requiring a second transplant within 5 years of LT.1 For these patients, a therapeutic agent is needed to prevent reinfection of the transplanted liver. The use of interferon-based therapies in this population has proven problematic, accompanied by a high risk of treatment-limiting toxicity and poor response rates.2–7 Although passive immunotherapy has shown some promising results,8–11 there is no satisfactory therapy for treatment or prevention of recurrent HCV in LT recipients.

HCV-AbXTL68 is a fully human monoclonal antibody that binds to the E2 envelope protein of HCV, generated by immortalizing peripheral blood mononuclear cells that were obtained from donors who tested positive for HCV. HCV-AbXTL68 is of the IgG1 isotype with V/H subgroups VH3/Vκ and VH1/Vκ, respectively.12 Four amino acids at the C-terminal end of hypervariable region (HVR) 1 and a further unknown number of E2 amino acids specify the epitope recognized by HCV-AbXTL68. The epitope is conformational and is relatively well conserved across HCV genotypes. The affinity constant (Kd) for binding to various E2 constructs ranges from 1.2 × 10−10 to 1.2 × 10−11. HCV-AbXTL68 immunoprecipitates HCV RNA in sera from HCV-infected patients with virus of genotype 1a/1b, 2a/2c, and 3a. Furthermore, immunohistochemical staining with HCV-AbXTL68 specifically stains the cytoplasm of hepatocytes from HCV-infected liver fragments, thus verifying that the antibody recognizes viral antigen in infected cells. The neutralizing activity of HCV-AbXTL68 can also be demonstrated in vitro with HCV pseudoparticles and Huh-7 cells. Further characterization of HCV-AbXTL68 in the HCV-Trimera mouse model13, 14 demonstrates that HCV-AbXTL68 inhibits ex vivo infection of liver fragments, reducing the percentage of infected animals, and reduces the mean virus load in animals treated with antibody after infection.

Phase 1 studies of HCV-AbXTL68 in patients with chronic HCV infection indicate the product can be administered safely at doses up to at least 120 mg. Transient decreases in HCV RNA have been observed in some patients who had detectable increases in anti-E2 antibody concentration.15 This report describes the results of a pilot, phase 2, placebo-controlled trial that examined the safety and efficacy of HCV-AbXTL68 for prevention of HCV disease recurrence in patients undergoing LT.

Ethical Considerations

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

This study followed principles set forth in Declaration of Helsinki, the United States 21 Code of Federal Regulations, and International Conference on Harmonization. Approval was obtained from respective institutional review boards or ethics committees before study initiation.

Study Design

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

This was a multicenter, randomized, double-blind, placebo-controlled, dose-escalation trial. The study was conducted in 2 parts. Dose escalation was achieved in part 1 by administration of increasing doses of HCV-AbXTL68 and in part 2 by administration of increasing doses of HCV-AbXTL68 and increasing frequency of infusion.

In part 1, patients were enrolled onto 1 of 3 dose levels (20, 40, or 80 mg; N = 4 per dose level). In part 2, additional patients were to be enrolled onto 1 of 3 higher dose levels (120, 240, or 480 mg; N = 4 per dose level). For each dose, patients were randomized to treatment with HCV-AbXTL68 or placebo in a 3:1 ratio. In part 1, study drug was intravenously infused once during the anhepatic phase, once postoperatively, after admission to the intensive care unit, daily for 6 days, weekly for 3 weeks, and then every 4 weeks for 8 weeks. In part 2, 4 loading doses of HCV-AbXTL68 or placebo were intravenously infused as follows: the first dose was infused over 2 hours at the start of the anhepatic phase; and the second, third, and fourth doses were infused consecutively over approximately 8 hours per dose beginning at the time of liver reperfusion. Patients in this part of the study then received doses of placebo or HCV-AbXTL68 daily for 6 more days, weekly for 3 weeks, and then every 2 weeks for 8 weeks. For each part of the study, dose escalation occurred after the explicit approval of the sponsor.

Study Population

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

Patients were eligible for the study participation if aged 18-65 years, were undergoing primary LT for HCV infection, and were HCV RNA positive before LT as determined by HCV RNA concentration above the local limit of detection within 1 year. Acceptable methods of contraception were required. Only deceased donor livers that were negative for HBV, HCV, and HIV were used; donor livers could be used if they were HBV surface antibody positive.

Patients were excluded from participation if they were previous LT recipients, pregnant or breast-feeding, had evidence of HIV infection or chronic HBV infection within 1 year, or were undergoing concurrent transplantation in addition to LT.

Study Outcomes

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

Virologic and pharmacokinetic activities were based on measurements of serum HCV RNA and anti-E2 concentrations, respectively. Serum samples were obtained before and at the end of each infusion, and at weekly intervals after the first week of daily study drug administration. Serum concentrations of HCV RNA (determined by real-time polymerase chain reaction [Taqman] in 23 patients or Roche Amplicor in 1 patient with HCV genotype 2 infection) and anti-E2 antibody were determined by XTL Biopharmaceuticals Ltd. from batched frozen serum samples by enzyme-linked immunosorbent assay methods.12

Statistical Methods

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

HCV RNA and anti-E2 serum concentrations were summarized by descriptive statistics. Adverse event (AE) incidence was tabulated by treatment. For all analyses, patients assigned to placebo were combined into a single group. Efficacy and safety analyses were performed on an intent-to-treat basis by using all data available at each time point. Sample size selection was based on clinical judgment. Efficacy analyses were conducted by nonparametric 1-way analysis to test the difference at day 5 in the area under the curve (AUC) of serum HCV RNA concentration over time.16 Descriptive statistics were calculated describing the HCV RNA serum concentration-over-time curve through day 5 by using the log HCV RNA concentrations for each patient. Because of the small number of patients per dose cohort, the median was chosen as the parameter of analysis. We used the median AUC for each dose cohort to perform a nonparametric 1-way analysis to test the difference at day 5 between the AUC for placebo vs. the AUC for the high-dose cohort.

Disposition and Baseline Characteristics

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

The study was conducted between January 2003 and July 2004. Twenty-four patients were enrolled and received at least 1 dose of study drug (5 placebo, 19 HCV-AbXTL68) (Table 1). A single patient was enrolled at the highest (480 mg) dose level. This patient died during the LT procedure, and the death was initially considered to be possibly related to study drug; the sponsor elected to terminate the study.

Table 1. Disposition of Study Population and Patient Evaluability
CategoryPlaceboLow-dose cohortHigh-dose cohortTotal
20 mg40 mg80 mg120 mg240 mg480 mg
Randomized (N)553334124
Completed study, n (%)5 (100%)2 (40%)3 (100%)3 (100%)2 (67%)3 (75%)018 (75%)
Discontinued, n (%)03 (60%)001 (33%)1 (25%)1 (100%)6 (25%)
 Death01 (20%)001 (33%)01 (100%)3 (13%)
 Adverse event01 (20%)0001 (25%)02 (8%)
 Withdrew consent01 (20%)000001 (4%)
Safety population (N)553334124
Efficacy population (N)553334023

Of the 24 treated patients, 18 completed the study through day 85 as planned (Table 1). Three patients, one each in the HCV-AbXTL68 20-mg, 120-mg, and 480-mg groups, died before study completion. Other reasons for discontinuation were AE (one each in the 20-mg and 240-mg groups) and withdrawal of consent (one in the 20-mg group). Twenty-three patients had postbaseline efficacy data that could be evaluated for the efficacy analyses.

Demographic and baseline characteristics were comparable among the placebo and HCV-AbXTL68 groups (Table 2). The majority (14/24, 58%) of patients were white, and all but one were male. Mean age of the study population was 50.8 years (range 35-69 years). Of the 24 study participants, 20 had HCV genotype 1. Mean baseline log HCV RNA concentration ranged from 4.5 log IU/mL (80-mg group) to 5.3 log IU/mL (placebo, 120-mg group); the overall mean log HCV RNA concentration was 5.0 log IU/mL. Likewise, mean anti-E2 concentrations at baseline ranged from 89.9 μg/mL in the 40-mg dose group to 137.2 μg/mL in the 80-mg dose group. These differences are not substantial given the wide variation that is often detected from patient to patient. Furthermore, it is not clear that these differences affected outcome in any way.

Table 2. Demographics and Baseline Characteristics of the Study Participants
ParameterPlacebo (N = 5)Low-dose cohortHigh-dose cohortTotal
20 mg (N = 5)40 mg (N = 3)80 mg (N = 3)120 mg (N = 3)240 mg (N = 4)480 mg (N = 1)(N = 24)
  • *

    Patients received a course of tacrolimus as well as a course of cyclosporine.

  • A total of 22 of 24 patients received a course of tacrolimus for immunosuppression.

  • One patient died during transplant surgery, and one patient received corticosteroids for immunosuppression.

Age (yr), mean ± SD50.8 ± 5.856.4 ± 12.851.3 ± 6.044.3 ± 8.651.0 ± 2.648.8 ± 5.24850.8 ± 7.8
Weight (kg)        
 Mean ± SD85.0 ± 12.076.7 ± 5.775.1 ± 15.587.3 ± 14.288.2 ± 6.586.1 ± 6.977.182.6 ± 10.3
 Range70.7–99.870.3–84.059.0–89.871.0–96.682.0–94.977.1–93.0 59.0–99.8
Height (cm), mean ± SD179.5 ± 8.6168.2 ± 7.4176.2 ± 8.3177.1 ± 1.0178.4 ± 5.7170.7 ± 10.4 174.5 ± 8.1
Gender, n (%)        
 Male5 (100%)5 (100%)3 (100%)3 (100%)3 (100%)3 (75%)1 (100%)23 (96%)
 Female000001 (25%)01 (4%)
Genotype, n (%)        
 14 (80%)3 (60%)3 (100%)3 (100%)2 (67%)4 (100%)1 (100%)20 (83%)
 201 (20%)001 (33%)002 (8%)
 301 (20%)000001 (4%)
 Missing1 (20%)0000001 (4%)
Ethnic origin, n (%):        
 White2 (40%)4 (80%)1 (33%)3 (100%)2 (67%)2 (50%)014 (58%)
 Black1 (20%)0001 (33%)01 (100%)3 (13%)
 Other2 (40%)1 (20%)2 (67%)002 (50%)07 (29%)
HCV RNA (log IU/mL)        
 Mean ± SD5.3 ± 0.54.6 ± 1.04.6 ± 0.54.5 ± 0.55.3 ± 0.55.2 ± 0.2 5.0 ± 0.6
 Range4.6–5.93.9–5.84.3–4.93.9–4.94.8–5.75.0–5.4 3.9–5.9
Anti-E2 (μg/mL), mean ± SD132.9 ± 234.7105.9 ± 62.289.9 ± 62.2137.2 ± 104.8129.4 ± 202.699.0 ± 58.9 118.9 ± 139.1
ALT (U/L), mean ± SD195.8 ± 240.9371.6 ± 647.7107.3 ± 45.073.0 ± 72.1109.0 ± 117.849.5 ± 40.3 186.6 ± 341.9
Immunosuppression medication        
 Cyclosporine-based therapy*01 (20%)01 (33%)1 (33%)003 (13%)
 Tacrolimus-based therapy5 (100%)5 (100%)3 (100%)2 (67%)3 (100%)4 (100%)022 (92%)
 Other0001 (33%)001 (100%)2 (8%)

One of the patients died before immunosuppression was begun. Of the other 23 patients, 22 received a tacrolimus-based regimen (Table 2). Of these 22 patients, 3 subsequently received cyclosporine. Prednisone was the only immunosuppressive agent recorded for one patient.

Change in Log HCV RNA Concentration

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

HCV RNA concentrations declined rapidly during the first 24 hours after LT in all dose groups (Fig. 1). The greatest median decrease in HCV RNA was observed in all groups at day 1 (2.5 log, 1.8 log, and 1.4 log in the 240-mg, 120-mg, and placebo groups, respectively) but was not sustained. Median 1.4 log and 2.2 log decreases were observed on day 2 in the 120-mg and 240-mg groups, respectively, vs. a median 1.3 log decrease in the placebo group. Median HCV RNA concentrations returned to baseline by day 14 in all groups except the 20-mg and 120-mg groups.

thumbnail image

Figure 1. Log change from baseline in HCV RNA concentration (IU/mL) over time (days). The change in serum concentrations of HCV RNA in individual patients after liver transplantation is illustrated in (A-G). (A) All placebo recipients. (B-F) All participants in the 20-, 40-, 80-, 120-, and 240-mg treatment groups, respectively. (G) Median change from baseline HCV RNA concentration for all treatment groups. Serum concentrations decrease rapidly immediately after LT in all patients. However, the change from median change from baseline in HCV RNA is greater in the 120- and 240-mg dose groups than in the placebo group or any of the low dose groups. This difference is established within 24 hours of the anhepatic phase (during which the antibody was administered 5 times at the indicated dose to patients in the 120- and 240-mg dose groups) and persists through the first 7 days after LT, when the antibody was administered on a daily basis. This apparent treatment effect diminishes after the first 7 days, after which time HCV RNA concentrations have returned to and exceeded baseline. The only patient with genotype 2 infection enrolled onto the 2 highest-dose groups is represented by the black line in (E) (120-mg dose group). The virologic response in this patient persisted longer than that apparent in any of the other patients.

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The AUC for HCV RNA over time is a sensitive statistic to compare differences in HCV RNA concentrations between treatment groups and placebo. In order to increase the number of patients contributing to the calculation of the AUC, data from the 120- and 240-mg groups between days 1 and 5 were combined in the high-dose cohort (n = 6) (data not shown). The median AUC exhibited a dose relationship. The median AUC for the placebo group at day 5 was 21.2 log IU/mL, compared with the median AUC for the high-dose group, which was 19.8 log IU/mL (data not shown). This difference was statistically significant (P = 0.045).

One of the 6 patients in the 2 high-dose groups (120 and 240 mg) was infected with genotype 2 virus. The change in HCV RNA observed in this patient was similar to that observed in all other patients in the 120-mg and 240-mg groups (Fig. 1). This result is consistent with in vitro neutralization experiments indicating that HCV-AbXTL68 neutralizes HCV from serum of infected patients regardless of genotype.12

Serum Concentrations of Anti-E2 Antibody

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

No consistent accumulation of anti-E2 antibody above endogenous background levels was detected during part 1 (20, 40, or 80 mg) (Fig. 2), although one patient who received 80-mg doses of HCV-AbXTL68 appeared to have accumulated antibody levels approximately 25 μg/mL above baseline during the first 7 days of daily dosing. Baseline data for one patient in the 40-mg treatment group was not available, and hence data for this patient is not included in analyses of change from baseline. In contrast, an accumulation of HCV-AbXTL68 above endogenous background concentrations is evident from the median change from baseline in anti-E2 concentration detected during the first week of the study in the 2 highest groups, when antibody was administered daily at doses of 120 or 240 mg (Fig. 2). Substantial variability in change from baseline in anti-E2 concentration was apparent from patient to patient.

thumbnail image

Figure 2. Change from baseline in anti-E2 antibody concentration (μg/mL) over time (days). The change in serum concentration of total anti-E2 antibody in individual patients after LT is illustrated in (A-G). (A) All placebo recipients. (B-F) All participants in the 20-, 40-, 80-, 120-, and 240-mg groups, respectively. (G) Median change from baseline in anti-E2 antibody concentration for all treatment groups. A baseline value for one patient in the 40-mg treatment group was not available, and hence data for this patient are not included in analyses of change from baseline in anti-E2 antibody concentration. No consistent accumulation of anti-E2 antibody above the endogenous background levels was detected during part 1 of the study (20, 40, or 80 mg), although 1 patient who received 80-mg doses of HCV-AbXTL68 appeared to have accumulated antibody levels approximately 25 μg/mL above baseline during the first 7 days of daily dosing (D). In contrast, an accumulation of HCV-AbXTL68 is evident during the first week of the study in the 2 highest groups, when antibody was administered daily. Anti-E2 concentration decreased rapidly after 7 days, when the infusion frequency was decreased to weekly.

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Median anti-E2 concentrations accumulated to a maximum of 100 μg/mL above baseline on day 2 and were sustained above baseline levels during the first 7 days of treatment in the 240-mg group, reaching an absolute concentration of 200 μg/mL after 5 days of daily antibody administration. Anti-E2 concentration decreased rapidly after 7 days (Fig. 2), when the infusion frequency was decreased to weekly. Anti-E2 concentrations in the 120-mg group declined to below baseline levels by day 8. Levels remained around baseline in the 240-mg group until day 22 but declined to below baseline by day 30.

Correlation Between Anti-E2 and HCV RNA

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

Log of the serum HCV RNA and anti-E2 concentrations were examined over the first 30 days of the study to assess the coincidence of lower HCV RNA and higher anti-E2 concentrations. The serum anti-E2 concentrations in the 240-mg dose group were increased above baseline during the first 7 days of the study when HCV-AbXTL68 was administered daily (Fig. 3). Likewise, HCV RNA serum concentrations were below baseline during this same period. The coincidence of decreased HCV RNA and increased anti-E2 suggest that the transient decreases in HCV RNA were due to elevations in circulating anti-E2. Sufficient circulating concentrations of anti-E2 to affect serum concentrations of HCV RNA could only be established and maintained when HCV-AbXTL68 was administered at doses of 120 mg or greater and with a frequency of once daily. Decreases in the regimen (dose or frequency of administration) appeared to result in a loss of antibody excess and a rebound in serum HCV RNA concentrations.

thumbnail image

Figure 3. Log change from baseline in HCV RNA and change from baseline in anti-E2 concentration over time. The serum anti-E2 antibody concentration in the 240-mg dose group was increased above baseline during the first 7 days of the study when HCV-AbXTL68 was administered daily. Likewise, serum HCV RNA was below baseline during this same period. The coincidence of decreased HCV RNA and increased anti-E2 suggest that sufficient circulating concentrations of anti-E2 to affect serum concentrations of HCV RNA could only be established and maintained when HCV-AbXTL68 was administered at doses of 120 mg or greater and with a frequency of once daily.

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Safety

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

Nearly all study patients experienced at least one AE, consistent with the severity of the underlying disease and the complications typically associated with LT. The overall incidence of serious AEs (SAEs) was higher with placebo (60%) vs. all active treatments combined (42%). The most common SAEs were elevated aspartate aminotransferase and alanine aminotransferase, complications of surgery, and abdominal pain (2 patients each). Of the AEs reported, only 6 events (including the one SAE) were attributed to the use of the study drug (Table 3). One of the SAEs was attributed to use of study drug (pulmonary embolism) and was fatal.

Table 3. Drug-Related Adverse Events
Adverse eventPlaceboLow doseHigh doseTotal
20 mg40 mg80 mg120 mg240 mg480 mg
  • *

    Infusion-related adverse events occurred during or immediately after the infusion procedure.

  • Pulmonary embolism resulting in the intraoperative death of the patient was the only drug-related serious adverse event reported during the study.

Postinfusion adverse events        
 Hypertension00001 (33%)001 (4%)
 Influenzalike illness000001 (25%)01 (4%)
 Infusion-related reaction00001 (33%)001 (4%)
 Pyrexia1 (20%)0000001 (4%)
Infusion-related adverse events*        
 Pulmonary embolism0000001 (100%)1 (4%)
 Rigors1 (20%)0000001 (4%)

Five patients (21%) discontinued infusion as a result of an AE. Nonfatal events leading to discontinuation were anuria with renal failure (20-mg group) and hepatopulmonary syndrome (240-mg group). Three other patients died during the study; each patient received HCV-AbXTL68 (20, 120, or 480 mg). Two deaths (one attributed to intra-abdominal sepsis and one to herpes simplex hepatitis) were not drug related. One death (postmortem diagnosis of multiple pulmonary emboli) in the 480-mg group was initially attributed to use of study drug.

DISCUSSION

  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES

The goal of immunoprophylaxis after LT for viral hepatitis is protection of the liver graft from reinfection, as has been successful with hepatitis B hyperimmune globulin in the setting of HBV.17–19 In this context, we must regard the outcome of the current study as less than satisfactory. A significant decrease in HCV RNA was observed in all study participants immediately after LT, as is consistent with the previously reported early post-LT kinetics of HCV replication,20–24 but no patient had serum concentrations of HCV RNA measured below lower limits of detection at any time during the study. Nonetheless, an effect of HCV-AbXTL68 on serum concentrations of HCV RNA was indeed apparent in patients enrolled onto the 120-mg and the 240-mg groups. Patients in these treatment groups had a transient median change from baseline in HCV RNA of 1.8 log and 2.5 log, respectively, compared with a maximum median change from baseline of 1.4 log in the placebo group. Furthermore, HCV RNA concentrations in these 2 dose groups remained lower than that observed in the placebo group through day 7, when infusion frequency was reduced to weekly. Although the magnitude of the response is minimal and not likely to be of clinical significance, the relationship of changes in HCV RNA to changes in anti-E2 antibody concentration indicates an apparent treatment effect. The doses of HCV-AbXTL68 administered did produce serum concentrations of anti-E2 that were above baseline only during the first 7 days, when dosing was most frequent. Even with these dose regimens, serum concentrations of anti-E2 were achieved that were expected to have only minimal effect on changes in HCV RNA on the basis of preclinical data from the Trimera mouse model of HCV infection used to characterize the antibody.13, 14

The virologic effect observed in the 120-mg and 240-mg groups was established during the first 24 hours after removal of the infected liver, when the frequency of dosing was high and in the 240-mg dose group, over 1000 mg of HCV-AbXTL68 were administered within the 24 hours beginning with the anhepatic phase. During the first week after LT, a correlation between decreases in HCV RNA and periods of high concentrations of circulating anti-E2 was apparent, suggesting that there was sufficient excess in circulating antibody at this time to clear some portion of circulating virus. When the frequency of antibody administration was decreased to weekly, the median change from baseline in anti-E2 antibody returned to 0 or less and concentrations of HCV RNA increased. This finding is consistent with a previous study in which HCV-AbXTL68 was administered to patients with chronic HCV infection.15

The degree of decrease in HCV RNA concentration observed in participants of this study after reperfusion of the hepatic allograft is consistent with that reported by other investigators as part of the typical kinetics after LT.20–24 The presence of a nonhepatic compartment22, 23 suggested by the detailed analysis of HCV RNA kinetics after transplantation validates the importance of immunoprophylaxis after LT to protect the liver from reinfection with virus from extrahepatic origins. Antiviral therapy alone is not likely to be adequate to prevent hepatic reinfection even in patients with a sustained virologic response.25 However, as with HBV,17 combination of specific antivirals and immunoglobulin therapy may provide and sustain adequate prophylaxis.

Preclinical characterization of HCV-AbXTL68 indicates that it recognizes virus from a variety of patients regardless of genotype.12 All but one patient in the current study in the 2 high-dose groups were genotype 1. The one genotype 2 patient responded similarly to the genotype 1 patients, verifying the genotype independence of the antibody determined in preclinical experiments. Furthermore, HCV-AbXTL68 recognizes a conformational epitope that is relatively well conserved across HV isolates, suggesting that escape from neutralization may be less likely than that observed with hyperimmune sera, which may depend largely on linear epitopes highly sensitive to changes in HVR1. A new product, XTL 6865, a combination of HCV-AbXTL68 and a second fully human monoclonal antibody (AbXTL65), which recognize a different epitope on the E2 protein, is currently under development by XTL Biopharmaceuticals Inc. and may further diminish the risk of the emergence of escape mutants.12

A clinical trial with one hyperimmune globulin preparation (Civacir) administered to patients undergoing LT has recently been completed.26 Although Civacir was relatively safe and well tolerated at doses of 75 or 200 mg/kg, no effect of the immunoglobulin on HCV RNA concentrations could be detected. Decreases from baseline in median HCV RNA concentration were observed with all treatments, and no effect of Civacir on the rate of decline, the duration of time before viral rebound, or the rate of rebound were reported. Total anti-HCV antibodies levels decreased over time, and most notably, anti-E2 antibodies were above baseline by less than 20% only when measured on day 4. At all other times measured, anti-E2 antibody levels were below baseline values, despite continued infusions.

The results obtained with HCV-AbXTL68 and reported here differ from the results with HCIG reported by Davis et al.26 in 2 significant ways. Levels of anti-E2 antibody ranged 20-100% above baseline for the 7 days when antibody was infused on a daily basis. After that, when the dosing frequency was reduced, anti-E2 antibody levels declined to below baseline levels as reported with Civacir. Furthermore, in the current study, during the period when anti-E2 antibody could be detected above baseline levels, even though a decrease in HCV RNA was observed across treatment groups, the decrease observed in the 120-mg and 240-mg treatment groups exceed that observed in the placebo group and in any of the other low-dose treatment groups. When compared with the safety profile reported by Davis et al. for Civacir in a similar population, HCV-AbXTL68 appears to have been better tolerated, with fewer AEs or SAEs attributed to antibody.

Hyperimmune globulins have been shown to change the course of acute viral infection in the chimpanzee model.8–10 However, the neutralizing antibodies generated in individual patients are isolate specific11 and are directed against epitopes encoded within the HVR of the envelope gene.27 Subsequent work that used refined neutralization assays has demonstrated that relatively high titers of broadly neutralizing anti-HCV antibodies are present in the serum from chronically infected patients, and these antibodies recognize regions within the HVR of the E2 protein as well as one or more epitopes elsewhere in the envelope.28, 29 However, current data suggest that the neutralizing activity in pooled polyvalent immunoglobulin reagents is either too low or is blocked by other competing nonneutralizing antibodies to provide a protective response. Data presented in this study indicate that the use of pure neutralizing monoclonal antibodies permits the serum concentration of neutralizing antibodies in the 500 μg/mL range or greater to be achieved without the introduction of similarly high concentrations of potentially competing nonneutralizing antibodies as might be present in preparations such as Civacir.26

HCV-AbXTL68 is a fully human antibody with associated low immunogenicity in humans. The intended use in the LT setting with associated immunosuppression should reduce the risk of the emergence of neutralizing antibodies. We have tested patients in previous studies of HCV-AbXTL68 who received up to 6 infusions of antibody and have not detected an anti-human antibody response.

The aim of immunoprophylaxis after LT in the HCV-infected recipient is to delay or decrease the aggressive reinfection of the allograft, with the ultimate goal of reducing the rapid progression of fibrosis and prolonging the function of the new liver. It is not clear what level of antiviral activity may be required to achieve these clinical results. However, a therapy that can be tolerated in this setting and that can substantially reduce viremia may have a significant clinical benefit over time. Although in the current study target HCV-AbXTL68 levels of 200-400 μg/mL (required for serum neutralization as predicted by preclinical models) were not sustained by any of the doses successfully administered during this study, reduction in virus load, though small, was detected at the highest doses administered. These results suggest that combinations with antiviral agents such as interferon will likely be required for successful posttransplantation treatment of the HCV-infected recipient.6, 7, 30, 31

Although the results from this study appear to indicate a virologic effect that is due to the experimental immunotherapy, HCV viremia was not reduced to below detectable limits, and the decrease in HCV RNA detected in individual patients was small and not durable. Nonetheless, a target therapeutic dosing regimen might be proposed on the basis of these results. Such a regimen would require more frequent administration of HCV-AbXTL68 at doses exceeding the 240-mg maximum dose and administered on a daily basis for inter vals exceeding 1 week. Furthermore, during the anhepatic phase, even higher doses (perhaps in the 500-2000-mg range) might be required to rapidly build antibody levels and maximize serum neutralization during this critical period. De novo infection of uninfected hepatocytes in the graft tissue with HCV from extrahepatic reservoirs must be prevented suggesting that establishment of a neutralizing environment during the anhepatic phase may be critical to preventing reinfection and subsequent increases in serum concentrations of HCV. This approach combined with effective and tolerated specific HCV antiviral chemotherapy may provide a strategy that improves long-term graft survival and function in the HCV-infected patient.

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  1. Top of page
  2. Abstract
  3. Ethical Considerations
  4. Study Design
  5. Study Population
  6. Study Outcomes
  7. Statistical Methods
  8. Disposition and Baseline Characteristics
  9. Change in Log HCV RNA Concentration
  10. Serum Concentrations of Anti-E2 Antibody
  11. Correlation Between Anti-E2 and HCV RNA
  12. Safety
  13. DISCUSSION
  14. REFERENCES