T cells but not NK cells are associated with a favourable outcome for resected colorectal liver metastases.

BACKGROUND: The adaptive immune response to colorectal cancer is important for survival. Less is understood about the role of innate lymphocytes, such as Natural Killer (NK) cells, which are abundant in human liver. METHODS: Samples of fresh liver (n = 21) and tumour (n = 11) tissue were obtained from patients undergoing surgical resection of colorectal liver metastases. Flow cytometry was used to analyse the presence and phenotype of NK cells, as compared to T cells, in the tumour and liver tissue. Results were correlated with survival. RESULTS: NK cells were poorly recruited to the tumours (distant liver tissue 38.3%, peritumoural liver 34.2%, tumour 12.9%, p = 0.0068). Intrahepatic and intratumoural NK cells were KIR (killer immunoglobulin-like receptor)loNKG2Ahi whereas circulating NK cells were KIRhiNKG2Alo. By contrast T cells represented 65.7% of the tumour infiltrating lymphocytes. Overall survival was 43% at 5 years, with the 5-year survival for individuals with a T cell rich infiltrate being 60% (95% CI 17-93%) and for those with a low T cell infiltrate being 0% (95% CI 0-48%). Conversely individuals with higher levels of NK cells in the tumour had an inferior outcome, although there were insufficient numbers to reach significance (median survivals: NKHi 1.63 years vs NKLo 3.92 years). CONCLUSIONS: T cells, but not NK cells, are preferentially recruited to colorectal liver metastases. NK cells within colorectal metastases have an intrahepatic and potentially tolerogenic, rather than a peripheral, phenotype. Similar to primary tumours, the magnitude of the T cell infiltrate in colorectal metastases is positively associated with survival.

Key features determining the specificity of aspartic proteinase inhibition by the helix-forming IA3 polypeptide.

The 68-residue IA(3) polypeptide from Saccharomyces cerevisiae is essentially unstructured. It inhibits its target aspartic proteinase through an unprecedented mechanism whereby residues 2-32 of the polypeptide adopt an amphipathic alpha-helical conformation upon contact with the active site of the enzyme. This potent inhibitor (K(i) < 0.1 nm) appears to be specific for a single target proteinase, saccharopepsin. Mutagenesis of IA(3) from S. cerevisiae and its ortholog from Saccharomyces castellii was coupled with quantitation of the interaction for each mutant polypeptide with saccharopepsin and closely related aspartic proteinases from Pichia pastoris and Aspergillus fumigatus. This identified the charged K18/D22 residues on the otherwise hydrophobic face of the amphipathic helix as key selectivity-determining residues within the inhibitor and implicated certain residues within saccharopepsin as being potentially crucial. Mutation of these amino acids established Ala-213 as the dominant specificity-governing feature in the proteinase. The side chain of Ala-213 in conjunction with valine 26 of the inhibitor marshals Tyr-189 of the enzyme precisely into a position in which its side-chain hydroxyl is interconnected via a series of water-mediated contacts to the key K18/D22 residues of the inhibitor. This extensive hydrogen bond network also connects K18/D22 directly to the catalytic Asp-32 and Tyr-75 residues of the enzyme, thus deadlocking the inhibitor in position. In most other aspartic proteinases, the amino acid at position 213 is a larger hydrophobic residue that prohibits this precise juxtaposition of residues and eliminates these enzymes as targets of IA(3). The exquisite specificity exhibited by this inhibitor in its interaction with its cognate folding partner proteinase can thus be readily explained.