Individuals with HCV and HIV coinfection are especially hard to treat, and as a result, account for a high rate of deaths each year. Because HCV and HIV share transmission routes, HCV/HIV coinfection is common. Liver disease has emerged as a significant cause of death in individuals coinfected with HCV and HIV. Currently, the mechanisms by which HCV and HIV interact in HCV/HIV-coinfected individuals, including how these infections affect immune responses, are poorly understood. Research suggests that vaccination may prevent other comorbidities associated with HCV/HIV coinfection; however, responses to new vaccine antigens have been shown to be impaired in HCV or HIV-infected individuals. The purpose of this study is to identify the innate and adaptive immune defects present in HCV-infected, HIV-infected, and HCV/HIV-coinfected individuals. This study will evaluate whether these innate and adaptive immune defects predict responses to HBV neoantigen in the form of both a diphtheria/tetanus toxoid immunization (Decavac)and a hepatitis A-hepatitis B immunization (Twinrix).