Increase in IFNγ−IL-2+ Cells in Recent Human CD4 T Cell Responses to 2009 Pandemic H1N1 Influenza

Abstract

Human CD4 T cell recall responses to influenza virus are strongly biased towards Type 1 cytokines, producing IFNγ, IL-2 and TNFα. We have now examined the effector phenotypes of CD4 T cells in more detail, particularly focusing on differences between recent versus long-term, multiply-boosted responses. Peptides spanning the proteome of temporally distinct influenza viruses were distributed into pools enriched for cross-reactivity to different influenza strains, and used to stimulate antigen-specific CD4 T cells representing recent or long-term memory. In the general population, peptides unique to the long-circulating influenza A/New Caledonia/20/99 (H1N1) induced Th1-like responses biased toward the expression of IFNγ+TNFα+ CD4 T cells. In contrast, peptide pools enriched for non-cross-reactive peptides of the pandemic influenza A/California/04/09 (H1N1) induced more IFNγ−IL-2+TNFα+ T cells, similar to the IFNγ−IL-2+ non-polarized, primed precursor T cells (Thpp) that are a predominant response to protein vaccination. These results were confirmed in a second study that compared samples taken before the 2009 pandemic to samples taken one month after PCR-confirmed A/California/04/09 infection. There were striking increases in influenza-specific TNFα+, IFNγ+, and IL-2+ cells in the post-infection samples. Importantly, peptides enriched for non-cross-reactive A/California/04/09 specificities induced a higher proportion of Thpp-like IFNγ−IL-2+TNFα+ CD4 T cells than peptide pools cross-reactive with previous influenza strains, which induced more Th1 (IFNγ+TNFα+) responses. These IFNγ−IL-2+TNFα+ CD4 T cells may be an important target population for vaccination regimens, as these cells are induced upon infection, may have high proliferative potential, and may play a role in providing future effector cells during subsequent infections.

Vaccine-Induced Boosting of Influenza Virus-Specific CD4 T Cells in Younger and Aged Humans

“…However, it is unclear in such a model why the magnitude of these responses is not larger suggesting that an upper limit to the size of these responses may exist. It should be noted that the magnitude of the vaccine induced CD4 T cell responses observed here (0-0.227% of CD4 T cells) are in good agreement with previous studies using ELISPOT or ICS following peptide pool or whole virus stimulation [7,8,24], suggesting that TIV induced CD4 T cell responses are typically in the 0.005-0.1% range, at least for Th1-like responses. An alternative possibility is that boosted CD4 T cells in aged subjects may undergo more rapid contraction.…”

“…The no stimulation control gate was set at or below 0.005% of CD4+ T cells with a mean of 0.0037% and median of 0.0022% (minimum 0.0 and maximum 0.0585% for all subjects and responses). Positive responses ranged from ~0.01-0.25% of CD4 T cells, similar what other groups have shown [7,8,24]. Positive responses were defined as a two-fold increase over background (no stimulation control) and greater than 0.005% of CD4 T cells.…”

“…Recent data have demonstrated that cytokine production by influenza virus-specific CD4 T cells may be altered based on how many times these cells have been stimulated. CD4 T cells responding to novel epitopes of more recently circulating virus strains retained a Th0 phenotype and produced more IL-2 and less IFNγ while cells responding to conserved epitopes and presumably stimulated repeatedly due to a history of vaccination and/or infection, produced less IL-2 and more IFNγ [24]. In agreement with these recent studies, we observed an increase in H1 and NP+M responding CD4 T cells producing IL-2 in young TIV responders compared to the aged group (Figure 2E ).…”

“…A third possibility is a decrease in repertoire diversity in the aged leading to fewer new (i.e. 1°) T cell responses upon vaccination [24]. Although, we observed no negative correlation between the size of the naïve CD4 T cell pool and the magnitude of the CD4 T cell response (data not shown), this study was not powered to detect small changes and there is previous evidence of constriction of the naïve T cell repertoire with age [33,34].…”

Competitive SWIFT cluster templates enhance detection of aging changes

“…Cells were centrifuged and re‐suspended in RPMI 1640, supplemented with 8% FBS. PBMC were labeled with a 15‐color T cell phenotyping panel of antibodies (Supporting Information Table 2) using a micromethod 12, 13. Cell data were acquired using an LSR II cytometer (BD Immunocytometry Systems).…”