Development of competitive inhibition ELISA as an effective potency test to analyze human rabies vaccines and assessment of the antigenic epitope of rabies glycoprotein.

The potency of all modern tissue culture human rabies vaccines is measured based on the National Institute of Health (NIH) potency test that is laborious, time-consuming, involves large test variations and requires sacrifice of large number of animals. To circumvent these limitations, several researchers and WHO expert working groups have discussed development of alternative in vitro methods to replace the NIH potency test. Although several immunochemical methods have been proposed to quantify rabies glycoprotein (G-protein) using multiple murine monoclonal antibodies, we report an In vitro competitive inhibition ELISA (CIA) method based on the use of a neutralizing rabies glycoprotein site III directed novel therapeutic human rabies monoclonal antibody (RAB1) that shows equivalence to the mice NIH potency test in recognition of neutralization site of the glycoprotein. In vitro potency testing of WHO 7th International Standard for rabies vaccine (IS) by CIA using RAB1 and In-house reference standard (IHRS) as a standard to assess its suitability for the assessment of validation parameters showed accurate and precise values with <15% coefficient variance. The method was validated using 5PL standard curve with linearity r > 0.98 and LLOQ of 0.125 IU/mL indicating sensitivity of the method. The method was found to be precise, robust and accurate to quantitate intact rabies glycoprotein in final vaccine and showed a strong correlation (Pearson's r = 0.81) with the NIH potency values of licensed Vero cell rabies vaccine. The CIA test using RAB1 was able to accurately quantitate degradation of rabies vaccine and assess loss in antigenicity of lyophilized and reconstituted liquid rabies vaccine under thermal stress conditions. The method was able to differentiate between potent and reduced potency vaccine samples. The new in vitro competitive inhibition ELISA method using RAB1 thus can be a valid alternative to the NIH test.