In VivoAntigen Expression Regulates CD4 T Cell Differentiation and Vaccine Efficacy against Mycobacterium tuberculosis Infection

Abstract

New vaccines are urgently needed against Mycobacterium tuberculosis (Mtb), which kills more than 1.4 million people each year. CD4 T cell differentiation is a key determinant of protective immunity against Mtb, but it is not fully understood how host-pathogen interactions shape individual antigen-specific T cell populations and their protective capacity. Here, we investigated the immunodominant Mtb antigen, MPT70, which is upregulated in response to gamma interferon (IFN-γ) or nutrient/oxygen deprivation of in vitro-infected macrophages. Using a murine aerosol infection model, we compared the in vivo expression kinetics of MPT70 to a constitutively expressed antigen, ESAT-6, and analyzed their corresponding CD4 T cell phenotype and vaccine protection. For wild-type Mtb, we found that in vivo expression of MPT70 was delayed compared to ESAT-6. This delayed expression was associated with induction of less differentiated MPT70-specific CD4 T cells but, compared to ESAT-6, also reduced protection after vaccination. In contrast, infection with an MPT70-overexpressing Mtb strain promoted highly differentiated KLRG1+CX3CR1+ CD4 T cells with limited lung-homing capacity. Importantly, this differentiated phenotype could be prevented by vaccination, and against the overexpressing strain, vaccination with MPT70 conferred protection similar to vaccination with ESAT-6. Together, our data indicate that high in vivo antigen expression drives T cells toward terminal differentiation and that targeted vaccination with adjuvanted protein can counteract this phenomenon by maintaining T cells in a protective less differentiated state. These observations shed new light on host-pathogen interactions and provide guidance on how future Mtb vaccines can be designed to tip the immune balance in favor of the host. IMPORTANCE Tuberculosis, caused by Mtb, constitutes a global health crisis of massive proportions and the impact of the current coronavirus disease 2019 (COVID-19) pandemic is expected to cause a rise in tuberculosis-related deaths. Improved vaccines are therefore needed more than ever, but a lack of knowledge on protective immunity hampers their development. The present study shows that constitutively expressed antigens with high availability drive highly differentiated CD4 T cells with diminished protective capacity, which could be a survival strategy by Mtb to evade T cell immunity against key antigens. We demonstrate that immunization with such antigens can counteract this phenomenon by maintaining antigen-specific T cells in a state of low differentiation. Future vaccine strategies should therefore explore combinations of multiple highly expressed antigens and we suggest that T cell differentiation could be used as a readily measurable parameter to identify these in both preclinical and clinical studies.

A protective, single-visit TB vaccination regimen by co-administration of a subunit vaccine with BCG

“…Although all the antigens in H107e induce protection on their own 18 , we were intrigued to see responses against both ESAT-6 and MTP70 as immunization with truncated versions of H107 has revealed that both the ESAT-6 repeats and the ‘MPT tail’ of MPT64, MPT70, and MPT83 are necessary for intact long-term protection 18 . This is in agreement with previous long-term data for ESAT-6-containing fusions 27 and a recent study highlighting that MPT70 has a delayed in vivo expression profile and therefore might play a more prominent role during long-term infection 28 .…”

“…A pilot study, where the vaccines were administered on the same day, demonstrated that the vaccine material of the second vaccination was at risk of leaking out of the injection puncture site from the first vaccination. Spacing the two vaccinations by one day remedied this technical issue and is expected to have minimal effect on the resulting immune response given that the majority of antigen uptake after Ag/CAF01 immunization happens after day 1 28 , 29 and that BCG persists for several weeks-months 32 – 34 . For all three dose regimens animals were immunized at 2-week intervals.…”

M. orygis hypervirulence provides new insights into tuberculosis pathogenesis

“…Previously, we have shown that ESAT-6, but not MPT70, confers protection against M. tuberculosis challenge 24 . As an alternative means to test for a role of mpt70 on the outcome of M. orygis infection, we asked whether immunization with an MPT70 subunit vaccine could confer protection against disease.…”

Immunodominant influenza epitope GILGFVFTL engage common and divergent TCRs when presented as a 9-mer or a 15-mer peptide

“…Antigen dosage determines the quality of T-cells. Both preclinical models and human studies show that in TB and Leishmania major, for example, a higher antigen dose causes activation-induced cell death (AICD) of T-cells, selecting cells that may be functionally inferior in clearing infection and generating a robust protective immunity (17)(18)(19)(20)(21). By contrast, new-born and elderly population responded less well to low antigen dosage vaccination than individuals outside these age groups indicating lack of optimal T-cell repertoire diversity that may not have formed yet in the new-born and is lost in the aged population (9).…”