Fusion to the lysosome targeting signal of the invariant chain alters the processing and enhances the immunogenicity of HIV-1 reverse transcriptase

Intracellular processing of the antigen encoded by a DNA vaccine is one of the key steps in generating an immune response. Immunization with DNA constructs targeted to the endosomal-lysosomal compartments and to the MHC class II pathway can elicit a strong immune response. Herein, the weakly immunogenic reverse transcriptase of HIV-1 was fused to the minimal lysosomal targeting motif of the human MHC class II invariant chain. The motif fused to the N-terminus shifted the enzyme intracellular localization and accelerated its deg- radation. Degradation of the chimeric protein occurred predominantly in the lysosomal compartment. BALB/c mice immunized with the plasmid encoding the chimeric protein demonstrated an enhanced immune response, in the form of an increased antigen-specific production of Th1 cytokines, INF-γ and IL-2, by mouse splenocytes. Moreover, the majority of the splenocytes secreted both cytokines; i.e., were polyfunctional. These findings sug- gest that retargeting of the antigen to the lysosomes enhances the immune response to DNA vaccine candidates with low intrinsic immunogenicity. KeyWordS reverse transcriptase; invariant chain; antigen processing; DNA immunization; T-helper immune response. abbreViationS HIV - Human immunodeficiency virus; MHC - major histocompatibility complex; ER - endo- plasmic reticulum; Ii - MHC class II-associated invariant chain; IFN-γ - interferon-gamma; IL-2 - Interleukin 2; RT - reverse transcriptase.