An alternate pathway for CD4 T cell development: thymocyte-expressed MHC class II selects a distinct T cell population

Immunity. 2005 Oct;23(4):375-86. doi: 10.1016/j.immuni.2005.09.002.


Conventional understanding of CD4 T cell development is that the MHC class II molecules on cortical thymic epithelial cell are necessary for positive selection, as demonstrated in mouse models. Clinical data, however, show that hematopoietic stem cells reconstitute CD4 T cells in patients devoid of MHC class II. Additionally, CD4 T cells generated from human stem cells in immunocompromised mice were restricted to human, but not mouse, MHC class II. These studies suggest an alternative pathway for CD4 T cell development that does not normally exist in mice. MHC class II is expressed on developing human thymocytes, indicating a possible role of MHC II on thymocytes for CD4 T cell generation. Therefore, we created mice in which MHC class II is expressed only on T lineage cells. Remarkably, the CD4 compartment in such mice is efficiently reconstituted with unique specificity, demonstrating a novel thymocyte-driven pathway of CD4 T cell selection.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antigens, Differentiation, T-Lymphocyte / immunology
  • CD4-Positive T-Lymphocytes / immunology*
  • CD4-Positive T-Lymphocytes / metabolism
  • Cell Proliferation
  • Epithelial Cells / immunology
  • Genes, MHC Class II / immunology*
  • Humans
  • Mice
  • Mice, Transgenic
  • Receptors, Antigen, T-Cell / immunology
  • Signal Transduction / immunology*
  • T-Lymphocyte Subsets / immunology*
  • Thymus Gland / cytology
  • Thymus Gland / immunology*


  • Antigens, Differentiation, T-Lymphocyte
  • Receptors, Antigen, T-Cell