Table 1

Sequence Requirements for Cross-reactive T Cells

Secondary vaccinationMutation(s)No. of CD8+ T cells (×1,000)/spleen
Cross-reactiveVariant-specific
Primary infection A/NT/60/68 (ASNENMDAM)
ASNENMDTMA→T1,60022
ASNENMDTMA→T650≤2
ASNENMDNMA→N260≤5
ASNENMDNMA→N110≤2
ASNENMEAMD→E160≤2
ASNENMEAMD→E12≤5
ASNENMETMDA→ET22012
ASNENMETMDA→ET417
ASNENVEAMMD→VE20≤1
ASNENVEAMMD→VE≤3≤2
ASNENVETMMDA→VET≤3≤1
ASNENVETMMDA→VET≤2≤5
Primary infection A/HKx31 (ASNENMETM)
ASNENMEAMT→A100≤4
ASNENMDTME→D200≤3
ASNENVETMM→V73≤4
ASNENMDAMET→DA106
ASNENMDNMET→DN≤3≤2
ASNENVEAMM.T→V.A8≤1
  • Mice were infected with influenza A/NT/60/68 (10 HAU) (top) or A/HKx31 (200 HAU) (bottom). 4–6 wk after the primary infection, mice were challenged with synthetic peptides corresponding to the various naturally occurring influenza A NP366–374 variants, in combination with anti-CD40 mAb, FGK.45. At day 10 after challenge, spleen CD8+ T cells were analyzed by flow cytometry. Data represent the number of CD8+ T cells per spleen that stain with MHC tetramers of both the primary and secondary NP366–374 epitope or that are specific for the variant antigen. Each data point represents a single mouse; two mice per peptide challenge with A/NT/60/68, one mouse per peptide challenge with A/HKx31. Variants are depicted in order of descending homology with the primary antigen, based on the contribution of the mutated residue to the TCR-exposed surface (reference 22) and the nature of the amino acid substitution. Background values are ≤0.5 × 104 MHC tetramer–positive CD8+ T cells/spleen. For the NP366–374 epitope, no detectable antigen-specific T cell population can be induced in naive mice by this vaccination strategy, suggesting that this type of vaccination may not be as effective as a viral infection in inducing a CD8+ T cell response (not shown).