The anti-T cell monoclonal antibody 9.3 (anti-CD28) provides a helper signal and bypasses the need for accessory cells in T cell activation with immobilized anti-CD3 and mitogens

Cell Immunol. 1989 Apr 15;120(1):205-17. doi: 10.1016/0008-8749(89)90188-3.


CD28 is an antigen of 44 kDa which is expressed on the membrane of the majority of human T cells. The present study examines the functional effects of an anti-CD28 monoclonal antibody (mAb 9.3) on T cell activation induced with immobilized anti-CD3 mAb OKT3 or with mitogens, in the absence of accessory cells. To this end, we used blood resting T cells that were completely depleted of accessory cells (monocytes, B cells, and natural killer cells), and consequently did not respond to recombinant interleukin-2 (rIL-2), to immobilized OKT3, to PHA, or to Con A. Addition of mAb 9.3 to the cultures enhanced IL-2 receptor expression (Tac antigen) on PHA- or immobilized OKT3-stimulated T cells and induced IL-2 receptors on Con A-stimulated T cells. Moreover, addition of mAb 9.3 to cultures of T cells stimulated with PHA, Con A, or immobilized OKT3 resulted in IL-2 production. Soluble mAb 9.3 was a sufficient helper signal for T cell proliferation in response to PHA or immobilized OKT3. Crosslinking of mAb 9.3 by culture on anti-mouse IgG-coated plates enhanced the helper effect and was an essential requirement for the induction of T cell proliferation in response to Con A. No other anti-T cell mAb (anti-CD2, -CD4, -CD5, -CD7, -CD8) was found to provide a complete accessory signal for PHA or Con A stimulation of purified T cells. T cell proliferation induced by the combination of PHA and mAb 9.3 was strongly inhibited by the anti-IL-2 receptor mAb anti-Tac. In conclusion, mAb 9.3 can provide a signal bypassing monocyte requirement in T cell activation with immobilized OKT3, PHA, and Con A, resulting in an autocrine IL-2-dependent pathway of proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal / immunology
  • Antigen-Antibody Reactions
  • Antigens, Differentiation, T-Lymphocyte / immunology*
  • CD28 Antigens
  • CD3 Complex
  • Concanavalin A / pharmacology
  • Humans
  • In Vitro Techniques
  • Interleukin-2 / biosynthesis
  • Lymphocyte Activation*
  • Phytohemagglutinins / pharmacology
  • Receptors, Antigen, T-Cell / immunology
  • Receptors, Interleukin-2 / physiology
  • T-Lymphocytes / immunology*


  • Antibodies, Monoclonal
  • Antigens, Differentiation, T-Lymphocyte
  • CD28 Antigens
  • CD3 Complex
  • Interleukin-2
  • Phytohemagglutinins
  • Receptors, Antigen, T-Cell
  • Receptors, Interleukin-2
  • Concanavalin A