CD28 and glioblastoma: Additionally, CTLA4 a member of the CD28 family of receptors, a strong inhibitor of T lymphocyte co-stimulation was although elevated in some individual patient samples, generally its expression was not significantly increased making it questionable whether therapeutic monoclonal antibodies would successfully affect tumor cell growth in GBM or MNG if sufficient level of cytotoxic T cells were present in the tumor tissues [18,19,40,41,42].