Background:  The effect of hepatitis B virus (HBV) genotype on drug resistance evolution is not known. Goal of this study is to investigate lamivudine (3TC) resistance profiles on different HBV genotypes in HBV-infected and HBV/HIV-co-infected patients

Methods:  Full-length sequences of HBV reverse transcriptase (RT) from 68 patients (48 HBV-infected patients and 20 HBV/HIV-co-infected patients) treated with 3TC with detectable serum HBV DNA were analyzed. Genotypes were determined by phylogenetic analysis. The association of mutations with HBV genotypes was assessed by multivariate logistic regression analysis (predictors variable considered: subject demographic, HBV genotype, HIV co-infection, HBeAg status, adefovir (ADF) co-administration, therapy length). Co-variation analysis was based on hierarchical clustering

Results:  Patients are failing 3TC treatment after a median time of 41months (IQR 27 to 60) with a median viremia of 4.3 log UI/mL (IQR 3.9 to 5.4). D and A genotypes are the predominant genotypes in HBV-infected patients (42, 87.5%) and in HBV/HIV-co-infected patients (13, 65.0%), respectively. HBV genotype strongly influences the selection of 3TC-resistance mutations. In particular, we found that A genotype is more prone to develop M204V than M204I (83.3% vs 21.1%, p = 0.001). In addition, under 3TC pressure the selection of L229V is significantly greater in A than D genotype (p = 0.001), while the selection of L80IV and S135Y is significantly lower in A than D genotype (p = 0.02 to 0.03, respectively) (S135Y absent in A genotype). Multivariate analysis confirms that M204V and L80IV are A and D genotype dependent, respectively (OR 6.5; 95%CI 1.1 to 36.6; p = 0.03; OR 5.2; 95%CI 0.9 to 29.8; p = 0.02). HBV A and D-genotypes also differ in the patterns of compensatory mutations (p <0.05). Indeed, in A genotype M204I clusters with L80V (bootstrap = 0.85), while M204V with L180M and L229V (bootstrap = 1). In contrast, in D genotype, M204I clusters with L80I/V+S135Y (bootstrap = 0.85), while M204V with L180M and T184A (bootstrap = 0.7). The cluster M204V+L180M+T184A (in 11.9% in D genotype patients), known to confer also entecavir resistance, is never observed in A genotype, and correlates with higher HBV DNA and higher alanine aminotransferase (ALT) at therapeutic failure (5.3 log vs 3.3 log, and 93 UI/L vs 30 UI/L, p <0.05), compared to M204V+L180M.

Conclusions:  Our study shows that HBV genotype plays a key role in driving RT evolution under 3TC treatment. This effect upon either cross-resistance to other HBV drugs or viro-hepatological parameters can be relevant for therapeutic sequencing or for disease progression