Taken together, these data suggest that CD28 costimulation is required for HSK but that while initial infection of TG is greater in CD28<sup>-/-</sup> mice, this begins to normalize with time and this normalization is concurrent with the delayed development of antigen-specific CD8<sup>+</sup> T cells.<b>IMPORTANCE</b> We study the pathogenesis of herpes simplex virus-mediated corneal disease.