Allogeneic Multivirus - Directed Cytotoxic T Lymphocytes (CTL) Targeting CMV (IE1 and pp65), EBV (LMP2, EBNA1), and Adv (Hexon and Penton)

Viral infections are normally controlled by T-cell immunity and so are an important cause of morbidity and mortality during the period of immune recovery after hematopoietic stem cell transplantation (HSCT).1 Risk for infection is impacted by the degree of tissue mismatch between donor and recipient and the immune status of the donor, including the degree and length of immunosuppression following transplantation. Reactivation of latent viruses such as cytomegalovirus (CMV) and Epstein-Barr virus (EBV) are common and often cause symptomatic disease. Respiratory viruses such as adenovirus also frequently cause infection. Antiviral pharmacologic agents are only effective against some of these viruses; their use is costly, and associated with significant toxicities and the outgrowth of drug-resistant mutants. As delay in recovery of virus-specific cellular immune response is clearly associated with viral reactivation and disease in these patients, cellular immunotherapy to restore viral-specific immunity is an attractive option that has already been successfully used to target some of these viruses. Multivirus-Specific T Cells To broaden the specificity of single CTL lines to include the three most common viral pathogens of stem cell recipients, investigators reactivated CMV and adenovirus-specific T cells by using mononuclear cells transduced with a recombinant adenoviral vector encoding the CMV antigen pp65 (Ad5f35CMVpp65). Subsequent stimulations with EBV-LCL transduced with the same vector both reactivated EBV-specific T cells and maintained the expansion of the activated adenovirus and CMV-specific T cells. This method reliably produced CTLs with cytotoxic function specific for all three viruses, which investigators infused into 14 stem cell recipients in a Phase I prophylaxis study. They observed recovery of immunity to CMV and EBV in all patients but an increase in adenovirus-specific T cells was only seen in patients who had evidence of adenovirus infection pre-infusion. A follow-up study in which the frequency of adenovirus-specific T cells was increased in the infused CTLs produced similar results, thus highlighting the importance of endogenous antigen to promote the expansion of infused T cells in vivo. Nevertheless, all patients in both clinical trials with pre-infusion CMV, adenovirus or EBV infection or reactivation were able to clear the infection, including one patient with severe adenoviral pneumonia requiring ventilatory support. CTLs recognizing multiple antigens can therefore produce clinically relevant effects against all three viruses. CTLs for HSCT patients with virus naïve donors All the donor specific T cell strategies discussed so far have utilized products derived from donors who are seropositive for the virus of interest. With the increasing use of cord blood (CB) grafts there are appreciable numbers of patients who are recipients of virus naïve donor grafts. CMV reactivation usually occurs from endogenous virus and seropositive recipients with seronegative donors remain the highest risk group for developing CMV. The development of multivirus specific T cells from recipients of cord blood grafts requires the priming of naïve T-cells rather than the simple expansion of pre-existing memory T-cells from seropositive donors. Using a protocol stimulating CB-derived T-cells with autologous CB-derived dendritic cells and EBV-LCL transduced with the Ad5f35CMVpp65 vector in the presence of IL-7, 12 and 15, multivirus specific T cells can be primed in vitro from the 20% fraction of a cord blood unit. So far, eight patients have received CTL as prophylaxis or treatment after CBT without toxicity. No infusion-related toxicities/GvHD have been observed and despite receiving only 80% of the CB unit, all patients engrafted neutrophils within 30 days. Early evidence of efficacy has also been demonstrated with clearance of EBV, CMV and adenovirus in two patients and decreasing EBV viral load in a third with the other 5 patients remaining virus free. Therefore, these results suggest that transfer of naïve T cell (CB)-derived virus specific T cells to patients after CBT may be safe and facilitate long term reconstitution of virus-specific T-cells in vivo.