The density of two types of these cells forms the basis of a classification scheme proposed by Jérôme Galon, which ranges from I0 to I4 and may outperform traditional TNM staging. A type of these cells requires B7 proteins to provide costimulatory signals that prevent incomplete activation, which can lead to anergy. A type of these cells begins to express FOXP3 (-5[2])after receiving intermediate strength signals during negative selection. These cells, (-5[1])which include a “regulatory” subtype, have receptors that bind to MHCs found on (10[1])antigen-presenting cells. CD4-positive and CD8-positive (10[1])types of these cells, which mature in the thymus, (10[1])are respectively (10[1])known as these cells’ helper and killer varieties. For 10 points, the adaptive immune system primarily consists of B cells and what other white blood cells? ■END■ (10[2])