CD8 is needed for development of cytotoxic T cells but not helper T cells.

Fung-Leung WP, Schilham MW, Rahemtulla A, Kundig TM, Vollenweider M, Potter J, van Ewijk W, Mak TW:
CD8 is needed for development of cytotoxic T cells but not helper T cells.
Cell 1991 May 3; 65(3):443-9

ABSTRACT
A mutant mouse strain without CD8 (Lyt-2 and Lyt-3) expression on the cell surface has been gernerated by disrupting the Lyt-2 gene using embryonic stem cell technology. In these mice, CD8+ T lymphocytes are not present in peripheral lymphoid organs, but the CD4+ T lymphocyte population seems to be unaltered. Cytotoxic response of T lymphocytes from these mice against alloantigens and viral antigens is dramatically decreased. Proliferative response against alloantigens and in vivo help to B lymphocytes, however, are not affected. These data suggest that CD8 is necessary for the maturation and positive selection of class I MHC restricted cytotoxic T lymphocytes but is not required on any of the intermediate thymocyte populations (CD8+CD4-TcR- or CD4+CD8+TcRlow) during the development of functional class II MCH restricted helper T cells.