Characterization of the MN gp120 HIV-1 Vaccine: Antigen Binding to Alum

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Abstract
Purpose. The characterization of recombinant MN gp120/alum vaccine requires the study of the gp120-alum interaction for the successful formulation of an alum-based HIV-1 vaccine. Methods. Several observations suggest that the gpl20-alum interaction is weak, wherein buffer counterions such as phosphate, sulfate, bicarbonate may cause the desorption of gp120 from alum. Comparison of gp120 with other proteins using particle mobility measurements shows that the weak binding of gp120 to alum is not an anomaly. Serum and plasma also cause desorption of gp120 from alum with a half-life of only a few minutes, wherein this half-life may be faster than the in-vivo recruitment of antigen presenting cells to the site of immunization. Results. Immunization of guinea pigs, rabbits and baboons with gp120 formulated in alum or saline demonstrated that alum provides adjuvant activity for gp120, particularly after early immunizations, but the adjuvant effect is attenuated after several boosts. Conclusions. These observations indicate that both the antigen and the adjuvant require optimization together.