Memory T cells need CD28 costimulation to remember.

Area of Science:

• Immunology
• T cell biology
• Adaptive immunity

Background:

• Naïve T cell activation requires costimulatory signals like CD28.
• Previously, memory T cells were thought to be independent of CD28 costimulation for secondary responses.
• In vitro studies suggested memory T cell re-activation is costimulation-independent.

Purpose of the Study:

• To investigate the role of CD28 costimulation in memory T cell expansion during secondary immune responses.
• To challenge the long-held belief regarding memory T cell costimulation independence.
• To clarify the necessity of CD28 for effective host defense and vaccine development.

Main Methods:

• In vivo studies were conducted to assess memory T cell responses.
• Both CD4+ and CD8+ memory T cell populations were analyzed.
• The impact of CD28 costimulation on T cell expansion and pathogen clearance was evaluated.

Main Results:

• Recent in vivo evidence demonstrates that both CD4+ and CD8+ memory T cells require CD28 costimulation.
• Maximal expansion of memory T cells is dependent on CD28 signals.
• CD28 costimulation is essential for efficient pathogen clearance by memory T cells.

Conclusions:

• CD28 costimulation is critical for the expansion and function of memory T cells in vivo.
• These findings necessitate a re-evaluation of T cell activation requirements.
• The results have significant implications for understanding host immunity, designing vaccines, and developing immunotherapeutics.