Short Vi-polysaccharide abrogates T-independent immune response and hyporesponsiveness elicited by long Vi-CRM₁₉₇conjugate vaccine

Abstract

Polysaccharide-protein conjugates have been developed to overcome the T-independent response, hyporesponsiveness to repeated vaccination, and poor immunogenicity in infants of polysaccharides. To address the impact of polysaccharide length, typhoid conjugates made with short- and long-chain fractions of Vi polysaccharide with average sizes of 9.5, 22.8, 42.7, 82.0, and 165 kDa were compared. Long-chain-conjugated Vi (165 kDa) induced a response in both wild-type and T cell-deficient mice, suggesting that it maintains a T-independent response. In marked contrast, short-chain Vi (9.5 to 42.7 kDa) conjugates induced a response in wild-type mice but not in T cell-deficient mice, suggesting that the response is dependent on T cell help. Mechanistically, this was explained in neonatal mice, in which long-chain, but not short-chain, Vi conjugate induced late apoptosis of Vi-specific B cells in spleen and early depletion of Vi-specific B cells in bone marrow, resulting in hyporesponsiveness and lack of long-term persistence of Vi-specific IgG in serum and IgG+ antibody-secreting cells in bone marrow. We conclude that while conjugation of long-chain Vi generates T-dependent antigens, the conjugates also retain T-independent properties, leading to detrimental effects on immune responses. The data reported here may explain some inconsistencies observed in clinical trials and help guide the design of effective conjugate vaccines.

Effect of O-Antigen Chain Length Regulation on the Immunogenicity of Shigella and Salmonella Generalized Modules for Membrane Antigens (GMMA)

“…Moreover, we have recently verified the ability of S. sonnei GMMA to boost the immune response in healthy European adults primed 2–3 years earlier [ 29 ]. Therefore, while polysaccharide length can dramatically impact the ability of glycoconjugate vaccines to induce T-independent responses [ 18 ], it might have a more limited role in the complex immunological response to GMMA [ 29 ].…”

“…Importantly, when comparing typhoid conjugates made with short- or long-chain Vi polysaccharide, long–chain-conjugated Vi (165 kDa) induced a response in both wild-type and T-cell-deficient mice, while short-chain Vi (9.5 to 42.7 kDa) conjugates induced a response in wild-type mice but not in T-cell-deficient mice. This suggested that the response elicited by longer Vi chains was partially T-independent, consequently resulting in hyporesponsiveness [ 18 ]. Selection of optimal length in glycoconjugates can avoid detrimental effects on memory and subsequent boosting.…”

Glycoconjugate vaccines against Salmonella enterica serovars and Shigella species: existing and emerging methods for their analysis

“…For a full-sized antigen, the response was similar irrespective of protein conjugate, but in formulation with fragmented Vi, after second immunisation a booster response was only observed with TT but not with CRM 197 and DT that may be linked to the larger size of TT as well as its T-cell epitopes (Arcuri et al 2017 ; Wessels et al 1998 ; Lockyer et al 2020 ). With a CRM 197 conjugate, Vi PS of less than 50 kDa gave a booster dose, while full-length Vi PS led to hypo-responsiveness (Micoli et al 2020a , b ). Although Vi-CRM 197 and Vi- r EPA behaved differently when tested in infants, the source and size of Vi PS were different, and these factors should also be considered (Thiem et al 2011 ; Bhutta et al 2014 ; Micoli et al 2020a , b ).…”

“…With a CRM 197 conjugate, Vi PS of less than 50 kDa gave a booster dose, while full-length Vi PS led to hypo-responsiveness (Micoli et al 2020a , b ). Although Vi-CRM 197 and Vi- r EPA behaved differently when tested in infants, the source and size of Vi PS were different, and these factors should also be considered (Thiem et al 2011 ; Bhutta et al 2014 ; Micoli et al 2020a , b ). Another study has also confirmed that immune response to Vi-DT in mice was stronger with an increasing amount of cross-linking and the subsequent size of the conjugate (An et al 2011 ).…”

“…Moreover, for Vi-CRM 197 , studies in mice indicated that shorter polysaccharide have less risk of inducing unfavourable T-independent immune response and hypo-responsiveness compared to long-chain Vi conjugates. Therefore, the elimination of T-independent responses elucidated by potential glycan candidates may be the next important control used for rational vaccine design and testing (Micoli et al 2020a , b ). For Shigella , use of a succinylated carrier protein was found to produce more immunogenic glycoconjugates compared to the unaltered version so chemical modifications of carrier proteins are also important to consider and need to be analysed (Barel and Mulard 2019 ).…”