High-affinity T helper epitope induces complementary helper and APC polarization, increased CTL, and protection against viral infection
Jeffrey D. Ahlers, Igor M. Belyakov, Elaine K. Thomas, Jay A. Berzofsky
Jeffrey D. Ahlers, Igor M. Belyakov, Elaine K. Thomas, Jay A. Berzofsky
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High-affinity T helper epitope induces complementary helper and APC polarization, increased CTL, and protection against viral infection

Abstract

Natural viral proteins do not always make optimal vaccines. We have found that sequence modification to increase epitope affinity for class II MHC molecules (epitope enhancement) can improve immunogenicity. Here we show first that a higher-affinity helper epitope-enhanced HIV vaccine not only induces more cytotoxic T lymphocytes (CTLs), but also skews helper cells toward Th1 cytokine production and protects against HIV-1 recombinant vaccinia viral challenge. Furthermore, we elucidate a novel mechanism in which the higher-affinity vaccine induces dramatically more effective helper cells with a higher level of CD40L per helper cell and more positive cells, which in turn more effectively conditions dendritic cells (DCs) for CTL activation in a second culture. The improved helper cells also induce much greater IL-12 production by DCs, accounting for the reciprocal T helper polarization to Th1, and increase costimulatory molecule expression. Thus, increasing affinity for class II MHC results in a complementary interaction in which T helper and antigen-presenting cells polarize each other, as well as increase CTL, and provide greater vaccine efficacy against viral infection.

Authors

Jeffrey D. Ahlers, Igor M. Belyakov, Elaine K. Thomas, Jay A. Berzofsky

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Qualitative and quantitative upregulation of CD40L on CD4+ T cells stimu...
Qualitative and quantitative upregulation of CD40L on CD4+ T cells stimulated with T1(A) and concordant increased activation of DCs to stimulate CTL. (a) CD40L expression on T1-specific CD4+ T cells incubated overnight with different concentrations of T1 (dashed line) or T1(A) (solid line) and DCs, or without peptide (shaded area). (b) CD40L expression on gated CD4+ T1-specific T cells stimulated 36 hours with indicated concentrations of T1 or T1(A) peptide and naïve A.AL splenic B cells (B220+ selected). The bar in the left panel indicates background CD40L without peptide. (c) Percentage CD4+/ CD40L+ cells plotted versus peptide concentration for Th1 (5 × 104 CD4+) cells incubated 24 hours with 5 × 105 BALB.A10 DCs and T1 or T1(A) peptide, or no peptide (open diamond). (d) 5 × 106 DCs of the same preparation as in c were incubated with different concentrations of peptide and 5 × 105 of the same CD4+ cells, but in 12 well plates. CD4+ cells were depleted by magnetic beads 24 hours later. Remaining DCs were pulsed with 0.5 μM CTL epitope P18IIIB, irradiated, and 5 × 106 added to 5 × 106 purified CD8+ cells from spleens of 3 mice immunized 8 weeks earlier with PCLUS3-18IIIB, and rmIL-2 (10 U/ml) was added on day 0. Specific lysis 7 days later on P18IIIB-pulsed P815 targets at a 50:1 E:T ratio is plotted versus Th peptide concentration used in conditioning cultures, or without Th peptide (open diamonds). Similar results were obtained in 2 other experiments. (e) Level of CD40L expression on the Th cells as a function of peptide concentration, using less rested Th cells which were 93% CD40L+ even without stimulation. (f) P18-I10/H-2Dd tetramer staining of CD8+ cells stimulated with 1 μM P18-pulsed DC conditioned with Th cells from the same experiment as in (e) (less control 3.3% with unconditioned DCs).