CD4 and congenital T-cell immunodeficiency: Insofar as the extreme CD4 T cell deficiency characteristic of cit homozygotes was not observed in chimeras with WT thymic epithelium while the tumor resistance was still observed, we conclude that CD4 T cell deficiency (including Treg deficiency) is not a prerequisite for restriction of tumor growth in H2-Aacit/cit mice.