Refocusing neutralizing antibody response by targeted dampening of an immunodominant epitope.

Abstract

Immunodominant epitopes are known to suppress a primary immune response to other antigenic determinants by a number of mechanisms. Many pathogens have used this strategy to subvert the immune response and may be a mechanism responsible for limited vaccine efficacies. HIV-1 vaccine efficacy appears to be complicated similarly by a limited, immunodominant, isolate-restricted immune response generally directed toward determinants in the third variable domain (V3) of the major envelope glycoprotein, gp120. To overcome this problem, we have investigated an approach based on masking the V3 domain through addition of N-linked carbohydrate and reduction in net positive charge. N-linked modified gp120s were expressed by recombinant vaccinia virus and used to immunize guinea pigs by infection and protein boosting. This modification resulted in variable site-specific glycosylation and antigenic dampening, without loss of gp120/CD4 binding or virus neutralization. Most importantly, V3 epitope dampening shifted the dominant type-specific neutralizing Ab response away from V3 to an epitope in the first variable domain (V1) of gp120. Interestingly, in the presence of V3 dampening V1 changes from an immunodominant non-neutralizing epitope to a primary neutralizing epitope with broader neutralizing properties. In addition, Ab responses were also observed to conserved domains in C1 and C5. These results suggest that selective epitope dampening can lead to qualitative shifts in the immune response resulting in second order neutralizing responses that may prove useful in the fine manipulation of the immune response and in the development of more broadly protective vaccines and therapeutic strategies.

Glycan masking in vaccine design: Targets, immunogens and applications

“…Immunogens created against HIV presents the trimeric env protein in its native conformation, using the full gp160 gene ( 16 ), or gp140 (referred also as sEnv), a soluble version of gp160 lacking the intracellular and transmembrane domains ( 21 , 27 ). Immunogens against influenza virus present the full trimeric HA antigen, including the intracellular C-terminal region and the transmembrane domain ( 22 ), or the soluble ectodomain version sHA ( 33 , 38 ), or both ( 23 – 25 , 28 ).…”

“…To overcome this limitation, Garrity et al. used recombinant vaccinia virus, an enveloped virus widely used in human vaccination ( 95 ), to expose the full glycosylated Env protein and immunize animal models ( 16 ).…”

“…Most commonly the goal of glycan masking is to shift away from immuno-dominant epitopes, which elicit high antibody titers but low neutralization activity and thus low protection. Such epitopes are also called “immune decoy epitopes” or “decotopes” by ( 16 ).…”

“…For the env protein of HIV, immuno-dominant and highly variable epitopes are the V1, V2 and V3 loops. V3 only can be mutated to insert additional glycosylations ( 16 , 27 ), or all three loops can be glycosylated ( 21 ). For influenza virus, the head domain of HA is the immuno-dominant domain and glycosylation was used to shift immune-response to the more conserved stalk ( 28 , 33 ).…”

“…From a biomedical point of view, the ability to target multiple viral strains with a single vaccine is of high interest, and in nine out of the 19 references the goal of glycan masking is to broaden the immune response. In five cases immuno-broadening is reached by immuno-shifting: shifting away from the hyper-variable regions of HIV-1 ( 16 , 21 ) and influenza virus ( 23 – 25 ), or by shifting away from the immuno-dominant epitopes in the HA protein of influenza ( 28 ). In three cases immuno-broadening is reached by immuno-focusing: for HIV-1 by focusing on the conserved receptor binding site, CD4bs ( 17 – 20 , 29 ), and for influenza virus by focusing on the conserved stalk domain ( 37 ).…”