We analysed TCRb clonotypes within the Vb8.3 as (i) it is still a preferred region (29.8%620.2) of NPN3A + CD8 + T cell response) and (ii) clonotypes within this region could be highly relevant for cross-reactive CD8 + T cell responses between NP 366 and NPN3A as they are prominent in both populations. Overall, the mutant and the wt immune Vb8.3 repertoires appear different. Single-cell RT-PCR and sequencing of the CDR3b region of tetramer + Vb8.3 + CD8 + T cells following either HK or HK-NPN3A infections showed that (Table S1) 2), and showed evidence of more variable CDR3b loop lengths (8-9 aa). The reduction (relative to the wt D b NP 366 ) in Vb8.3 usage by the D b NPN3A + CD8 + T cells reproduces the relative loss of ''public'' wt TCRs found for the naïve repertoire ( Fig 4B) . This likely reflects that the N3A mutation has disrupted an ''optimal'' TCR/ pMHC fit that maximizes antigen-driven clonal expansion. Indeed, the public TCRs were not a prominent feature of the D b NPN3A + CD8 + set, being found in only 4 of the 7 NPN3Ainfected mice at a very low frequency, namely 0% in the 1 0 response and 22.9% in the 2 0 response ( Table 2 ). This is in contrast to the D b NP 366 + CD8 + Vb8.3 + TCR repertoire [34] that is largely (90%) comprised of high-frequency, public clonotypes found in all infected B6 mice [34] .