A sensitive method to quantify HIV-1 antibody in mucosal samples

The AIDS epidemic is a global challenge with 38 million people living with HIV and 1.7 million new infections along with 690K deaths in 2019. To date, HIV-1 vaccine clinical trials have not been successful in eliciting robust broad neutralizing antibody responses that can prevent infections. Alternative approaches, such as passive immunization with broadly neutralizing monoclonal antibodies, are being considered to help prevent new HIV infections. VRC01, an HIV-gp120 CD4bs directed potent and broadly neutralizing antibody (bNAb), which neutralizes about 91% of HIV-1 strains of a panel consisting of 190 Env-pseudotyped viral strains with a half max inhibitory concentration (IC50) of <50 ug/mL, is being tested for safety and efficacy in preventing HIV infection. Since the majority of HIV-1 transmissions occur through mucosal routes, it is essential to quantify the levels of the passively administered bNAb in mucosal samples. This helps to determine the levels of the bNAbs that have localized to mucosal sites preventing infection by neutralizing the virus. Traditional ELISAs and other immunoassays with a lower limit of quantification (LLOQ) in the range of 1 ug/mL are not sensitive enough to accurately quantify the low levels of VRC01 in mucosal samples. Hence, we sought to develop a custom ultra-sensitive Single Molecule Counting (SMC™) magnetic microparticle-based immunoassay with a greater than 4-log linear dynamic range (LDR) and LLOQ less than 120 pg/mL. We successfully quantified VRC01 levels in rectal, cervical and oral mucosal samples in two passive immunization studies conducted with VRC01- VRC 601 and VRC 602. The assay was able to successfully quantify VRC01 levels in mucosal samples from all dosage groups from these trials. This accurate and sensitive immunoassay can be utilized in vaccine research for quantifying low antibody levels in mucosal and other sample types in the context of HIV-1 pre-clinical and clinical vaccine trials.