We stimulate purified CD4+ T cells in vitro with agonistic anti-CD3 and anti-CD28 monoclonal antibodies bound to microspheres. I am wondering if the usage of an anti-CD4 antibody during cell purification, which would remain bound to cells, might hinder their subsequent binding to anti-CD3. I am thinking of a possible steric hindrance of the anti-CD4 upon the TCR-CD3-CD4 complex on the cell surface.