T-cell therapy in the treatment of post-transplant lymphoproliferative disease

Abstract

Post-transplant lymphoproliferative diseases (PTLD) associated with Epstein-Barr virus (EBV) infection often develop after organ and haematopoietic stem-cell transplantation. These lymphoproliferative diseases are tumours that usually express all latent EBV viral proteins, and are therefore amenable to T-cell-based immune therapies, such as donor lymphocyte infusions and the adoptive transfer of EBV-specific cytotoxic T lymphocytes. In this Review, we describe current approaches of T-cell-based therapies to treat PTLD, and describe strategies that improve the feasibility of such treatment.

Figure 1. Epstein-Barr virus life cycle, latency states and lymphoma

The Epstein-Barr virus (EBV) life cycle involves at least five distinct stages and four are associated with disease. During primary infection, EBV infects naïve B-cells and expresses its entire latency gene complex, including 10 proteins and 2 small RNAs (type III latency). Type III latency drives B-cell transformation and proliferation, but because the cells are highly immunogenic, they are rapidly eliminated by EBV-specific T-cells. The virus survives in B-cells by downregulating its immunogenic proteins in two phases. Initially B-cells enter lymphoid follicles where they proliferate and express only three viral proteins (type III latency). Finally they exit the lymph node and downregulate viral proteins altogether (type 0 latency), and thus are invisible to the immune response. If circulating infected B-cells divide homeostatically they express a single viral protein (EBNA1, type I latency) that ensures that the virus genome divides with the cell genome. When infected B-cells circulate through the oropharynx they transfer the virus to epithelial cells, where it is replicated to infect new hosts by salivary transfer and where it infects new B cells to maintain the infected B-cell pool. With the exception of type I latency, each latency state is observed in specific types of lymphoma. Abbreviations: EBNA, Epstein-Barr nuclear antigen; EBV, Epstein-Barr virus

Figure 2. EBV-specific CTL production

EBV-transformed B-cell LCLs are prepared from the CTL donor by infection of PBMCs with a clinical grade laboratory strain of EBV (B95-8) in the presence of cyclosporin A. Once the LCL is established (about 6 weeks), it is irradiated and used to stimulate PBMCs from the same donor and a 40:1 ratio of PBMC to LCL. From 9 to 12 days later and weekly thereafter, the T-cells are re-stimulated with the LCL at a 4:1 ratio. IL-2 is added 3 days after the second stimulation and twice weekly thereafter. The CTLs should kill autologous LCLs but not autologous PHA blasts. Their specificity is donor dependent and they may have specificity for any of the 10 latency associated antigens and or for early lytic cycle proteins that are express by a small fraction of the LCLs, which are grown in acyclovir to prevent the production of infectious virus by blocking the viral thymidine kinase. Abbreviations: CTL, cytotoxic T-lymphocyte; EBNA, Epstein-Barr nuclear antigen; EBV, Epstein-Barr virus; IL-2, Interleukin-2; LCL, lymphoblastoid cell lines; PHA, phytohaemagglutinin, PBMCs, peripheral blood mononuclear cell.