Cytotoxic T Cells to Prevent Virus Infections

Umbilical cord blood (UCB) is a readily available alternative source of Hemotopoietic Stem Cells (HSCs) that is capable of reconstituting hematopoiesis after myeloablative therapy. More than 280,000 UCB units have been banked world-wide and more than 13,000 unrelated donor UCB transplantations have been performed. UCB transplants offer several advantages over adult bone marrow or peripheral blood stem cell transplants, including: 1) rapid availability, 2) absence of donor risk, 3) low risk of transmissible infectious diseases, 4) low risk of acute Graft versus Host Disease (GvHD) in the setting of Human Leukocye Antigen (HLA) mismatch (as compared to recipients of unrelated donor marrow and peripheral blood). UCB is particularly beneficial for patients of ethnic and racial minority descent for whom adult marrow and blood donors often cannot be identified. In a larger series the neutrophil engraftment has been reported as high as 92%. The incidence of acute GvHD reported in larger series ranges from 33-44% to 11-22% for grades II-IV and III-IV acute GvHD, respectively. The incidence of chronic GvHD ranges from 0-25%. These results are particularly notable since most UCB donor-recipient pairs are 1-2 HLA antigen mismatched. However, infection related TRMs are still of concern after UCBT. The rate of hemopoietic recovery is slower after UCBT; therefore infectious complications including viral infections occur frequently. Multi virus Specific T cells from Cord Blood could be applied with comparable success to recipients of CB transplants; however, certain obstacles to the extension of this approach must be circumvented. These include: (i) the limited numbers of CB T-cells available for manipulation and (ii) the naivety of CB T-cells. Hence, the development of virus-protective T-cell therapy for patients undergoing CBT requires the priming and extensive expansion of naïve T-cells rather than the more limited and simple direct expansion of pre-existing virus-specific memory T-cell populations from virus-experienced donors. Further, CB T-cells have lower cytotoxic activity and higher activation-induced cell death than peripheral blood T-cells. These limitations have prevented the production of virus-specific cord blood-derived CTL in sufficient numbers for clinical use. Because of these challenges, only a few reports document the generation of antigen-specific T cells from CB. Sun et al first reported the ability to generate EBV-specific CD4+ T cells using EBV-transformed B-cells, or lymphoblastoid cell lines (LCL). Park et al then reported the ability to generate CMV-pp65-specific T cells from cord blood by using CMV-immune complex-loaded DCs, CMV lysate, and IL-12 and IL-7. The study at Baylor College of Medicine (BCM)showed that Ad5f35pp65-transduced CB-derived APC could be used to generate large numbers of autologous T-cells specific for both CMV and Ad, even from the phenotypically naive T-cell subpopulation. Addition of EBV-transformed B-lymphoblastoid cell lines (LCL) to the APCs allowed the Ad/CMV specificity of the CB T-cells to be extended to EBV. In addition, the multivirus-specific T-cells recognized an array of epitopes after only 2 weeks expansion in vivo. We therefore suggest that our ability to generate virus-specific CTL from CB against a plethora of epitopes recognized by both CD4+ and CD8+ T-cells should minimize the risk of viral escape and maximize therapeutic benefit on administration of these cells to cord blood recipients at risk of severe viral disease. A clinical trial using CB-derived multi-virus specific T cells for the prevention and treatment of viral infection after CBT was started at BCM. (Clinical Trial #: NCT01017705).