The effects of female sex, viral genotype, and IL28B genotype on spontaneous clearance of acute hepatitis C virus infection
The Kirby Institute, University of New South Wales, Sydney, New South Wales, Australia
Address reprint requests to: Jason Grebely, Ph.D., Viral Hepatitis Clinical Research Program, The Kirby Institute, The University of New South Wales, 2052, Sydney, New South Wales, Australia. E-mail: firstname.lastname@example.org; fax: +61-2-9385 0876.
Potential conflict of interest: Dr. Bruneau received grants from Merck. Dr. Dore consults, advises, is on the speakers' bureau, and received grants from Merck and Janssen. He advises, is on the speakers' bureau, and received grants from Roche. Dr. Grebely advises and received grants from Merck. He owns stock in Gilead.
The InC3 Study is supported by the National Institute on Drug Abuse (NIDA; award no.: R01DA031056). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIDA or the National Institutes of Health (NIH). The Kirby Institute is funded by the Australian Government Department of Health and Ageing. The views expressed in this article do not necessarily represent the position of the Australian Government. J.Gr. is supported by a National Health and Medical Research Council (NHMRC) Career Development Fellowship. J.B. and N.H.S. are supported by Fonds de la Recherche du Québec-Santé Research Career Awards. B.H. is supported by an Australian Postgraduate Ph.D. Award. G.D. and A.L. are supported by NHMRC Practitioner Research Fellowships. M.H. and L.M. were supported by NHMRC Senior Research Fellowships and M.H. additionally by a VicHealth Senior Research Fellowship. R.S.D. was supported by an NHMRC postgraduate scholarship and a Centre for Research Excellence into Injecting Drug Use postgraduate top-up scholarship. Other research support includes NIH U19 AI088791 (to A.C.), NIH U19 AI066345 (to A.Y.K., G.M.L., and B.H.M.), U19 AI082630 (the National Institute of Allergy and Infectious Diseases; to G.M.L.), R01 DA033541 (NIDA; to A.Y.K.), MOP-103138 and MOP-210232 (the Canadian Institutes of Health Research; to J.B. and N.H.S.), and the Netherlands National Institute for Public Health and the Environment (to M.Svd.L. and M.P.). J.Ge. is supported by the Sydney Medical Foundation and grants from the NHMRC.
Although 20%-40% of persons with acute hepatitis C virus (HCV) infection demonstrate spontaneous clearance, the time course and factors associated with clearance remain poorly understood. We investigated the time to spontaneous clearance and predictors among participants with acute HCV using Cox proportional hazards analyses. Data for this analysis were drawn from an international collaboration of nine prospective cohorts evaluating outcomes after acute HCV infection. Among 632 participants with acute HCV, 35% were female, 82% were Caucasian, 49% had interleukin-28 (IL28)B CC genotype (rs12979860), 96% had injected drugs ever, 47% were infected with HCV genotype 1, and 7% had human immunodeficiency virus (HIV) coinfection. Twenty-eight percent were HCV antibody negative/RNA positive at the time of acute HCV detection (early acute HCV). During follow-up, spontaneous clearance occurred in 173 of 632, and at 1 year after infection, 25% (95% confidence interval [CI]: 21, 29) had cleared virus. Among those with clearance, the median time to clearance was 16.5 weeks (IQR: 10.5, 33.4), with 34%, 67%, and 83% demonstrating clearance at 3, 6, and 12 months. Adjusting for age, factors independently associated with time to spontaneous clearance included female sex (adjusted hazards ratio [AHR]: 2.16; 95% CI: 1.48, 3.18), IL28B CC genotype (versus CT/TT; AHR, 2.26; 95% CI: 1.52, 3.34), and HCV genotype 1 (versus non-genotype 1; AHR: 1.56; 95% CI: 1.06, 2.30). The effect of IL28B genotype and HCV genotype on spontaneous clearance was greater among females, compared to males. Conclusions: Female sex, favorable IL28B genotype, and HCV genotype 1 are independent predictors of spontaneous clearance. Further research is required to elucidate the observed sex-based differences in HCV control. (Hepatology 2014;58:109–120)
Hepatitis C Incidence and Transmission Study-Community
human immunodeficiency virus
The International Collaboration of Incident HIV and Hepatitis C in Injecting Cohorts
people who inject drugs
Although 20%-40% of persons with acute hepatitis C virus (HCV) infection demonstrate spontaneous clearance, the time course and predictors of clearance remain poorly understood. Knowledge of clearance after acute HCV infection is limited because of the generally asymptomatic nature of initial infection and the highly marginalized nature of at-risk populations, such as people who inject drugs (PWID). Understanding the time course and predictors of clearance provides insight into HCV pathogenesis and improves clinical decision making regarding the need for early therapeutic intervention.
Host factors such as female sex,[1-4] immune responses,[5, 6] virus-specific neutralizing antibodies (Abs), and host genetics[8, 9] have been associated with clearance in prospective studies of acute HCV infection. The strongest host factor associated with clearance is polymorphisms in the interleukin-28(IL28B) gene region, which encodes the interferon (IFN)-λ3 protein (IFN-λ3, IFNL3)[8-10] and is involved in viral control. Individuals with nonfavorable IL28B genotypes (rs12979860 CT/TT alleles) are less likely to clear HCV infection, compared to those with favorable genotypes (CC alleles).[4, 8, 9] Pathogen factors, such as diversity of the HCV viral quasispecies and HCV genotype, might also be linked with clearance. The majority of studies of people with acute HCV and clearance are limited by the small number of cases, which restricts statistical power, inference, and generalizability.
The International Collaboration of Incident HIV and Hepatitis C in Injecting Cohorts (InC3) Study, a collaborative of pooled data from nine prospective international cohorts mainly following PWID, provides a unique opportunity to assess clearance in a large number of well-characterized HCV-infected participants with prospective follow-up. The aim of this study was to investigate time to, and predictors of, clearance subsequent to acute HCV infection.
Patients and Methods
Study Population and Design
The InC3 Study, a collaboration of nine prospective cohorts evaluating human immunodeficiency virus (HIV) and HCV infection outcomes from Australia, Canada, the Netherlands, and the United States has been previously described. All cohorts follow participants at regular intervals using standardized methods. Participants were recruited and followed between 1985 and 2010. The InC3 Study includes both (1) participants without HCV infection (≥2 HCV-negative Ab tests) and (2) participants with documented acute HCV infection (≥2 HCV Ab or RNA tests).
For the current study, only individuals with documented acute HCV were included. Documented acute HCV is defined as either (1) HCV seroconversion with an HCV Ab-negative test followed by either an HCV Ab- or RNA-positive test within 2 years of the HCV Ab-negative test or (2) evidence of symptomatic HCV infection (defined by a positive HCV Ab/RNA test, jaundice or alanine aminotransferase (ALT) elevation >400 U/L, and detection of HCV RNA or history of high-risk exposure within 3 months of clinical manifestation of acute HCV). Individuals who were HCV Ab negative/HCV RNA positive at the time of acute HCV detection (early acute HCV infection) were identified for subanalyses, given the well-defined estimated time of infection in this subgroup. Individuals treated for HCV with an estimated duration of infection <26 weeks were excluded to reduce misclassification bias resulting from uncertainty around subsequent spontaneous clearance in the absence of treatment (n = 37). All participants provided written informed consent and cohort protocols approved by local ethics committees.
Choice of qualitative and quantitative HCV RNA testing varied by cohort but were consistent at each site. Qualitative HCV RNA testing was performed using the following assays: Versant TMA (<10 IU/mL; Bayer, Pymble, New South Wales, Australia); COBAS AmpliPrep/COBAS TaqMan (<15 IU/mL; Roche, Branchburg, NJ); COBAS Amplicor HCV Test (v2.0; <50 IU/mL; Roche Diagnostics, Mannheim, Germany); or discriminatory HCV transcription-mediated amplification component of the Procleix HIV-1/HCV (<12 copies/mL; Gen-Probe, San Diego, CA). Quantitative HCV RNA testing was performed using the Versant HCV RNA 3.0 (<615 IU/mL; Bayer), COBAS Amplicor HCV Monitor (version 2.0; <600 IU/mL; Roche Diagnostics), COBAS AmpliPrep/COBAS TaqMan (<15 IU/mL; Roche), or an in-house polymerase chain reaction (<1,000 IU/mL).[15, 16] HCV genotype was determined by line-probe assay (Versant LiPa1/LiPa2; Bayer) or HCV sequencing at acute HCV detection. Among those with undetectable HCV RNA (no genotype) and available samples, Murex HCV serotyping was performed to determine HCV genotype (Murex Biotech Limited, Dartford, UK). IL28B genotype was determined by sequencing of the rs12979860 single-nucleotide polymorphism, as previously described.[4, 9, 10] For the UFO Study, IL28B genotype was obtained from stored frozen plasma samples. Genomic DNA was extracted from 200µL of plasma sample using the QIAamp DNA Blood Mini kit (Qiagen Sciences, Maryland USA), and amplified with the primers specific to the sequence of IL28B using a real-time PCR.
Estimating the Date of Acute HCV Infection
The estimated date of acute HCV infection was calculated based on a hierarchy using the most precise information indicating the time of infection. Among individuals who were HCV Ab negative/HCV RNA positive at the time of acute HCV detection (early acute HCV infection undergoing HCV seroconversion), the estimated date of HCV infection was calculated as 4 weeks preceding the date of acute HCV detection (mid-point between HCV infection and detection of HCV Abs [8 weeks]).[17, 18] Among individuals with symptomatic acute HCV, the estimated date of infection was calculated as 6 weeks before its onset (jaundice or ALT >400 IU/mL). Among individuals with HCV seroconversion, the estimated date of infection was calculated as the mid-point between the last negative HCV Ab and first positive HCV Ab or RNA test.
Spontaneous clearance was defined by two consecutive undetectable HCV RNA test results ≥4 weeks apart after infection. Estimated date of clearance was defined as the mid-point between the first of two consecutive undetectable qualitative HCV RNA tests and either the last sample with detectable HCV RNA or the estimated date of infection, in the event that the sample collected at the time of acute detection was HCV RNA undetectable.
Time to clearance was calculated as the time from the estimated date of infection to the estimated date of clearance. For those without clearance, follow-up time was calculated from the estimated date of infection until the date of the last therapy-naïve detectable HCV RNA test. For participants with only one undetectable HCV RNA as their last measurement, follow-up time was calculated from the estimated date of infection until the date of the last positive HCV RNA test. Participants treated for HCV were censored at the date of treatment.
Time to, and predictors of, clearance were assessed. Hypothesized predictors were determined a priori and included age (categorized as <30, 30-39, and ≥40 years), sex,[1-4] symptomatic HCV infection,[3, 8] ethnicity, IL28B genotype (SNP rs12979860; CC versus CT/TT),[8-10] HIV infection, HCV genotype (genotype 1 versus genotype non-1 [those with unknown genotypes were not included])[13, 22] and cohort site (given that site may introduce unmeasured confounders). The effects of these variables on time to clearance were assessed by Kaplan-Meier analyses (significance assessed by log-rank test). Median (interquartile range; IQR) time to clearance among those with clearance was also estimated.
Cox proportional hazards analyses were used to identify predictors of clearance. In multivariate analyses, all variables with P < 0.20 in unadjusted analysis were considered as potential independent predictors. Initial models were adjusted for age and built using a backward stepwise approach with factors sequentially eliminated according to result of the likelihood ratio test. Additional models were also considered using a shared “frailty” random-effect term to provide improved variance estimates and control for potential confounding by site.
Given previous data demonstrating an interaction between sex and IL28B genotype in HCV clearance, it was hypothesized that sex would modify the effect of IL28B genotype and HCV genotype on clearance. Analyses were performed by investigating the separate effects of these factors and their joint effect. Differences in the susceptibility of the effect of sex and dichotomous exposures of interest (IL28B and HCV genotype) on clearance were explored by testing for interaction: A new composite variable with four categories (a−b−, a−b+, a+b−, and a+b+) was redefined for sex and the dichotomous exposure of interest (a− and b− denote absence of exposure). Adjusted hazard ratios (AHRs) were calculated for each category after adjustment for age and other variables significant in the final multivariate model. Furthermore, given data suggesting different distributions of HCV genotypes according to IL28B genotype, similar analyses were performed to assess whether the effect of IL28B genotype on clearance would vary by HCV genotype. Analyses stratified by sex and IL28B genotype were also performed.
Sensitivity analyses were performed to assess time to, and predictors of, HCV clearance among individuals with early acute HCV infection. All analyses were repeated using the mid-point estimation method for calculating the estimated date of HCV infection for those with symptomatic acute symptomatic infection and excluding participants receiving HCV treatment. Statistically significant differences were assessed at P < 0.05; P values are two-sided. All analyses were performed using Stata statistical software (v12.0; StatCorp LP, College Station, TX).
Among the 632 participants with acute HCV infection included, the median age was 26 years, 36% were female, 96% had a history of injecting drug use, and 16% received HCV treatment during follow-up (all treated participants that were included started treatment at an estimated duration of infection >6 months; Table 1 and Supporting Table 1). Among those with data on infecting HCV genotype (n = 537), 55% had genotype 1. Among all genotypes, 42% were determined by INNO-LiPA, 48% by sequencing, and 9% by serotyping. Forty-nine percent (266 of 542 with test results) were IL28B CC genotype favorable, with no differences among females and males (48% versus 50%; P = 0.606) or those with HCV genotype 1 and non-1 infection (48% versus 50%; P = 0.592). Untreated individuals had similar proportions with IL28B CC and HCV genotype 1 infection, but a greater proportion of females (38% versus 26%; P = 0.017; Supporting Table 2).
Table 1. Characteristics of Participants With Acute HCV Infection in the InC3 Studya
Abbreviations: UFO, UFO STUDY; ATAHC, Australian Trial in Acute Hepatitis C; BAHSTION, Boston Acute HCV Study: Transmission, Immunity and Outcomes Network; BBAASH, Baltimore Before and After Acute Study of Hepatitis; HEPCO, St. Luc Cohort, HEPCO; HITS-c, Hepatitis C Incidence and Transmission Study-Community; HITS-p, Hepatitis C Incidence and Transmission Study-Prison; N2, Networks 2; ACS, Amsterdam Cohort Studies.
Acute HCV infection was documented by HCV seroconversion in 98% (n = 621) of participants, with 2% (n = 11) identified by acute symptomatic infection and a recent history of high-risk exposure. Among those with available data on symptomatic infection (n = 249; 383 missing), 54% (n = 138) had symptomatic HCV infection. Twenty-nine percent (n = 183) were HCV Ab negative/HCV RNA positive at acute HCV detection and were defined as having early acute HCV infection.
Subsequent to the estimated date of HCV infection, participants had a median of five HCV RNA tests (IQR, 2, 9; range, 1-55), with a median of 60 days (IQR, 28, 120) between tests. The overall median follow-up time from the estimated date of infection to the last HCV RNA measurement was 1.51 years (IQR, 0.72, 2.99). Across cohorts, the median follow-up ranged from 0.63 (Hepatitis C Incidence and Transmission Study-Community; HITS-c) to 9.42 years (Amsterdam Cohort Studies; ACS). The median interval from the estimated date of infection to the first positive HCV Ab or RNA test at the time of acute HCV detection was 9.0 weeks (IQR, 4.0, 20.4).
Spontaneous Clearance of Acute HCV Infection
During follow-up, clearance was observed in 173 of 632 overall and 43 of 183 in those with early acute HCV infection. At 1 year after infection, 25% (95% confidence interval [CI]: 21, 29) had cleared virus overall and 22% (95% CI: 17, 30; 43 of 183) had cleared virus among those with early acute HCV. Figure 1 shows the proportion with viral persistence as a function of number of years after HCV infection among the overall population (Fig. 1A) and those with early acute HCV infection (Fig. 1B). Among those who cleared HCV, the median time to clearance was 16.5 weeks (IQR, 10.5, 33.4) overall and 18.9 (IQR, 13.3, 33.4) among those with early acute HCV.
Among those with clearance, 34% (95% CI: 27, 42; n = 59) and 67% (95% CI: 60, 74; n = 116) had cleared infection by 3 and 6 months after infection, respectively. At 12, 18, and 24 months after infection, 83% (95% CI: 77, 88; n = 144), 92% (95% CI: 87, 96; n = 160), and 97% (95% CI: 93, 99; n = 167) of those who did clear had cleared infection. Among those with early acute HCV infection and clearance (n = 43), the proportion of participants with clearance by 3, 6, 12, 18, and 24 months were 23% (95% CI: 12, 39; n = 10), 63% (95% CI: 47, 77; n = 27), 84% (95% CI: 69, 93; n = 36), 88% (95% CI: 75, 96; n = 38), and 93% (95% CI: 81, 99; n = 40). The rate of spontaneous clearance was 42 per 100 person-years (95% CI: 35, 51) within the first 6 months of infection and 10 per 100 person-years (95% CI: 8, 13) 6 months after infection.
Factors Predicting Spontaneous Clearance of Acute HCV Infection
In Kaplan-Meier and unadjusted Cox proportional hazards analyses, clearance was associated with female sex, symptomatic HCV infection, IL28B CC genotype, and HCV genotype 1 (Fig. 2; Table 2). Given that, for 61% (n = 383) of participants, data were missing on symptomatic infection, this variable was not explored in multivariate analyses. Because of the a priori hypothesis that HCV genotype 1 would have higher clearance,[13, 22] the small numbers within some genotype categories (2/4/6/mixed) and the observation that all genotypes other than genotype 1 demonstrated lower clearance in unadjusted analysis (Table 2), all HCV genotype non-1 infections were grouped together. There was no difference in clearance by HCV genotyping assay. Neither ethnicity nor HIV status was associated with clearance.
Table 2. Cox Proportional Hazards Analysis of Predictors of Time to Spontaneous HCV Clearance Among Participants With Acute HCV Infectiona
Abbreviations: pyo, person-years observation; HR, hazard ratio; UFO, UFO STUDY; ATAHC, Australian Trial in Acute Hepatitis C; BAHSTION, Boston Acute HCV Study: Transmission, Immunity and Outcomes Network; BBAASH, Baltimore Before and After Acute Study of Hepatitis; HEPCO, St. Luc Cohort, HEPCO; HITS-c, Hepatitis C Incidence and Transmission Study-Community, HITS-p, Hepatitis C Incidence and Transmission Study-Prison; N2, Networks 2.
Factors independently predicting clearance included female sex (versus male; AHR, 2.16; 95% CI: 1.48, 3.18; P < 0.001), IL28B CC genotype (versus CT/TT; AHR, 2.26; 95% CI: 1.52, 3.34; P < 0.001), and HCV genotype 1 (versus non-genotype 1; AHR, 1.56; 95% CI: 1.06, 2.30; P = 0.025; Table 2; Fig. 3). In sensitivity analyses, results did not substantially change when analyses were restricted to individuals with early acute HCV infection, when the mid-point method was used to estimate the date of HCV infection or when participants treated for HCV infection were excluded (Supporting Table 2). Adjustment for site also did not change the results (Table 2).
The Effect of Sex and IL28B Genotype on Spontaneous Clearance
Clearance rates were highest among females with the IL28B CC genotype (Fig. 4A). After adjusting for age and HCV genotype (Table 3), females with the IL28B CC genotype had the greatest probability of clearance, as compared to males with the CT/TT genotype (AHR, 4.65; 95% CI: 2.71, 7.96; P < 0.001). The AHR for males with the CC genotype was close to the AHR for females with the CT/TT genotype (Table 3). The interaction between sex and IL28B was not significant on the multiplicative scale (P = 0.265).
Table 3. Cox Proportional Hazards Models of Predictors of Time to Spontaneous HCV Clearance Among Participants With Acute HCV Infection
The Effect of Sex and HCV Genotype on Spontaneous Clearance
Clearance rates were highest among females with HCV genotype 1 (Fig. 4B). After adjusting for age and IL28B genotype (Table 3), females with HCV genotype 1 had the greatest probability of clearance, as compared to males with HCV genotype non-1 (AHR, 3.30; 95% CI: 1.94, 5.62; P < 0.001). The AHR for males with the HCV genotype 1 was close to the AHR for female with HCV genotype non-1 (Table 3). The interaction between sex and HCV genotype was not statistically significant on the multiplicative scale (P = 0.560).
The Effect of HCV Genotype and IL28B Genotype on Spontaneous Clearance
Clearance rates were lowest among individuals with HCV genotype non-1 and CT/TT IL28B genotype (Fig. 4C). After adjusting for age and sex (Table 3), compared to those with HCV genotype non-1 and CT/TT IL28B genotype, individuals with HCV genotype non-1 and IL28B CC genotype (AHR, 3.82; 95% CI: 1.86, 7.84; P < 0.001), HCV genotype 1 and CT/TT IL28B genotype (AHR, 2.66; 95% CI: 1.30, 5.47; P = 0.008), and HCV genotype 1 and IL28B CC genotype (AHR, 4.56; 95% CI: 2.28, 9.12; P < 0.001) all had an increased probability of clearance. The interaction between HCV genotype and IL28B genotype did not reach statistical significance on the multiplicative scale (P = 0.068).
Spontaneous Clearance in Females and Males
Given the differential effect of IL28B genotype and HCV genotype on time to clearance by sex, the effect of IL28B genotype and HCV genotype was also explored separately for females and males. Among females, after adjusting for age (Table 3), IL28B CC genotype (versus CT/TT; AHR, 2.89; 95% CI: 1.60, 5.22; P < 0.001) and HCV genotype 1 (versus non-genotype 1; AHR, 1.78; 95% CI: 1.00, 3.17; P = 0.052) independently predicted clearance. Among males, after adjusting for age, only IL28B CC genotype (versus CT/TT; AHR, 1.79; 95% CI: 1.05, 3.06; P = 0.033) independently predicted clearance, but genotype did not (genotype 1 versus non-1; AHR, 1.40; 95% CI: 0.82, 2.38; P = 0.220).
Spontaneous Clearance Stratified by IL28B Genotypes
Given the differential effect of HCV genotype on clearance by IL28B genotype, the effect of HCV genotype on clearance was examined separately for those with CT/TT and CC IL28B genotypes after adjusting for age and female sex. Among those with CT/TT IL28B genotype, HCV genotype 1 (versus non-genotype 1; AHR, 2.65; 95% CI: 1.29, 5.46; P = 0.008) independently predicted clearance. Among those with CC IL28B genotype, after adjusting for age and sex, there was no statistically significant effect of HCV genotype 1 on clearance (versus non-genotype 1; AHR, 1.18; 95% CI: 0.74, 1.90; P = 0.488).
This study describes the time course and independent predictors of spontaneous clearance in a large sample of participants with well-defined acute HCV infection, the majority of whom were PWID. The proportion with clearance at 1 year was 25%. Among those with clearance, the median time to clearance was 16.5 weeks, with two thirds clearing within the first 6 months of infection. Independent predictors of clearance included female sex, favorable IL28B genotype, and HCV genotype 1 infection. The effect of both IL28B genotype and HCV genotype on clearance tended to be greater in females, compared to males. This study provides important insights into factors affecting HCV viral control and offers guidance in clinical decision making for treatment of acute HCV infection.
The overall proportion with spontaneous clearance of 25% at 1 year is consistent with a weighted mean clearance of 26% reported in a systematic review of prospective acute HCV studies. Confirmation of this estimate is important, given that the systematic review by Micallef et al. was limited by heterogeneity of studies in terms of sample size, inclusion criteria, and follow-up. The large sample size, well-defined population, and frequent follow-up within the InC3 study provide a more precise estimate of the rate of clearance among individuals with acute HCV infection.
The median time from the estimated date of infection to clearance was 16.5 weeks. This is longer than previously reported (8-11 weeks),[19, 24, 25] but these studies had larger proportions of cases with symptomatic infection.[19, 24, 25] Consistent with another study, symptomatic infection was associated with clearance in this study. Unfortunately, the majority of cohorts in the InC3 study did not systematically collect information on the presence of symptoms at the time of infection, precluding the ability to assess this factor in adjusted analyses. Previous studies are limited by short follow-up time (and thus less likely to include late clearance), small sample sizes, and heterogeneous definitions for infection and clearance, which may also affect estimates of time to clearance.
The finding that one third of participants who demonstrated clearance did so more than 6 months after infection must be interpreted with caution. This is greater than reported in previous studies.[19, 24, 25] Although one explanation for this difference might be longer follow-up in InC3,[19, 24, 25] it is more likely that there is imprecise characterization of time of clearance in InC3, particularly in cases with broader intervals of HCV RNA testing.
Female sex independently predicted spontaneous clearance, after adjusting for IL28B genotype and HCV genotype, consistent with previous reports.[1-4] The effect of IL28B genotype on clearance was greater among females than among males. Though this is consistent with previous data demonstrating an interaction between female sex and IL28B genotype on clearance, this interaction was not statistically significant in the current study. The effect of HCV genotype 1 on clearance was also greater among females. This is consistent with very high proportions of females with clearance (52%-54%) after HCV genotype 1 infection through contaminated anti-D immune globulin.[26, 27] Taken together, these results are striking and suggestive of the potential role of sex in modifying factors important in HCV clearance.
Mechanisms behind the association of female sex and clearance may be linked to sex-based differences in immunity. Females have a lower burden of infections, a higher prevalence of several autoimmune diseases, and an increased number and magnitude of immune and inflammatory responses, as compared to males. The prevailing hypothesis to explain immunological differences between males and females is that sex steroids bind to specific receptors expressed in lymphoid tissue cells, macrophages, dendritic cells, and lymphocytes, thereby influencing the function of immune cells. However, despite considerable research demonstrating differences in immune function between females and males, there are little data on sex-based differences in immune profiles in those with HCV. Further studies should focus on mechanisms explaining differences in clearance between males and females because this may contain important information for understanding HCV viral control.
Genetic variation in the IL28B gene independently predicted spontaneous clearance, consistent with previous reports.[4, 8-10] The large number of cases and detailed demographic and clinical information in InC3 provided sufficient power to adjust for multiple factors. The molecular mechanism linking IL28B genotype to clearance remains to be elucidated.
HCV genotype 1 was independently associated with spontaneous clearance. Few studies have investigated the effect of HCV genotype on clearance in acute HCV infection, partly because of the difficulties in identifying people early during infection to detect and genotype HCV RNA. Limitations of previous studies include small numbers, the potential misclassification of genotype by HCV serotyping assays,[13, 30] the large proportion with an unknown HCV genotype status among those with clearance who could not be genotyped or serotyped, and a lack of genotypic diversity in some groups. Among studies that have investigated the effect of HCV genotype on spontaneous clearance, results are conflicting,[13, 22, 30] with some studies demonstrating lower, higher,[13, 22] or comparable proportions with clearance among individuals with HCV genotype 1, when compared to other genotypes. The association between HCV genotype 1 and clearance observed in InC3 is convincing because of the well-defined nature of acute HCV infection and the fact that the large majority of HCV genotyping was performed by either line-probe assay or HCV sequencing at the time of acute HCV detection.
Those with CT/TT IL28B genotypes and HCV genotype non-1 infection demonstrated a lower likelihood of spontaneous clearance, suggesting a biological interaction between HCV genotype and IL28B genotype. Although it has been demonstrated that the expression of IFN-stimulated genes (ISG) is higher among individuals with HCV genotype 1 infection with chronic infection, there are no studies investigating ISG expression during acute infection stratified by IL28B and HCV genotype. The role of a potential interaction between the effect of HCV genotype and IL28B on clearance during acute HCV requires further investigation.
There are several limitations to this study. Nine cohorts of individuals with acute HCV (mainly PWID) were combined. Participating cohorts bring a range of data types and structures presenting issues surrounding both inconsistent measurement and biological data-testing protocols (e.g., HCV RNA assays differed across cohorts). As such, there was some heterogeneity across the cohorts with respect to the availability of data on certain variables known to be associated with clearance (e.g., symptomatic infection) and it was not possible to adjust our analyses for these factors. The availability of only one HCV RNA negative test at last follow-up limited the ability to assess late clearance outcome in a small minority (<5%). In contrast, some instances of late clearance may be the result of very early clearance and subsequent reinfection (with clearance of the second infection detected). Broad intervals of HCV RNA testing in some individuals reduced the precision of estimated time of clearance. There were also small numbers for some categorized variables in this study (HIV and ethnicity), and the absence of an observed effect does not imply the absence of an association. Furthermore, potential unmeasured confounding factors may have influenced the results.
In conclusion, female sex, favorable IL28B genotype, and HCV genotype 1 infection are independent predictors of spontaneous HCV clearance after acute infection. Further research is required to better understand the mechanism behind the potential effect of female sex on HCV viral control.
We wish to acknowledge the work and contribution of our collaborators at the Blood Systems Research Institute, and especially Dr. Tzong-Hae Lee, who developed and validated the methods to sequence IL28B from frozen plasma samples.
The InC3 study group steering committee includes: Kimberly Page (Chair, UFO STUDY); Julie Bruneau (HEPCO); Andrea L. Cox (BBAASH); Gregory J. Dore (ATAHC); Jason Grebely (ATAHC); Margaret Hellard (N2); Georg Lauer (BAHSTION); Arthur Y. Kim (BAHSTION); Andrew R. Lloyd (HITS-p); Lisa Maher (HITS-c); Barbara H. McGovern (BAHSTION); Maria Prins (ACS); and Naglaa H. Shoukry (HEPCO).
The coordinating center includes: Meghan Morris (study coordinator); Judy Hahn (coinvestigator); Thomas M. Rice (data manager); and Megan Rilla (administration).
The site data managers include: Maryam Alavi (ATAHC); Rachel Bouchard (HEPCO); Jennifer Evans (UFO Study); Bart Grady (ACS); Jasneet Aneja (BAHSTION); Rachel Sacks-Davis (Networks 2); Suzy Teutsch (HITS-p); Bethany White (HITS-c); Brittany Wells (BBAASH); and Geng Zang (HEPCO).
InC3 researcher acknowledgments include: ATAHC: Tanya Applegate, Gail Matthews, and Barbara Yeung; ACS: Bart Grady and Janke Schinkel; BAHSTION: Jasneet Aneja and Leslie Erin Prince; HEPCO: Elise Roy and Geng Zang; HITS-c: Anna Bates, Jarliene Enriquez, Sammy Chow, and Bethany White; HITS-p: Luke McCredie and Suzy Teutsch; N2: Campbell Aitken, Joseph Doyle, and Tim Spelman; and UFO: Jennifer Evans.