CD8A and neuroblastoma: BM-infiltrating NB cells, freshly isolated from BM, express co-stimulatory molecules, such as CD80, CD86, OX40L and 4-1BBL43 [27], but the absence of HLA class I molecules on the surface of NB cells, due to multifactorial mechanisms [28,29,30], does not allow their functional engagement by cytotoxic CD8+ T cells.