Biological process

down regulation of T-helper 1 cell differentiation, down-regulation of T-helper 1 cell differentiation, downregulation of T-helper 1 cell differentiation

Any process that stops, prevents, or reduces the frequency, rate or extent of T-helper 1 cell differentiation.

negative regulation of T-helper 1 cell development

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'.