Biological process

Any process that stops, prevents, or reduces the frequency, rate or extent of natural killer cell differentiation as part of an immune response.

down regulation of natural killer cell differentiation during immune response, down-regulation of natural killer cell differentiation during immune response, downregulation of natural killer cell differentiation during immune response, negative regulation of NK cell differentiation during immune response, negative regulation of natural killer cell development involved in immune response, negative regulation of natural killer cell differentiation during immune response

Note that immunologists typically use the word 'development' to refer to cells of B or T cell lineages undergoing the process that GO describes as 'cell differentiation'.