CD28 and neoplasm: Thereby, antigen presentation is augmented via mechanisms such as antigen cross-presentation, HLA up-regulation of tumor or stromal cells leading to enhanced donor TCR-mediated T cell recognition and further activation of the transplanted adaptive immune system via cytokines (e.g., IL-2, TNF, and IFNg) and higher expression of co-stimulatory molecules (e.g., CD40/CD40L or B7/CD28) [2, 11].