Establishing a local bank and comparing efficacies of third party viral-specific cytotoxic T cells (VST) and cytokine induced killer cells (VSCIK)

Abstract

Background & Aim Reactivation of dormant viruses is not uncommon after allogeneic haematopoietic stem cell transplants (allo-HSCT), which invariably carry risk of opportunistic infections. Although antiviral drugs are effective against a few viruses, drug therapy is limited by refractory strains and toxicities, while matched donor-derived VSTs have been successfully used to treat allo-HSCT patients with viral reactivation and there is promising data that minimally matched 3rd party banked VSTs are also effective and safe. Hence, we seek to establish a compact but effective bank of multi virus-specific cytotoxic cells for antiviral therapy not only for allo-HSCT patients but other immune compromised patients and patients with virus-associated malignancies more common in Asia. Methods, Results & Conclusion Previous studies have identified the common HLA types in Singaporeans: 96% of Singaporeans carry one or more of the common 6 HLA*A, 6 HLA*B and 5 HLA*C alleles. We are recruiting donors with these HLA types and screening their cells for reactivity against CMV, HHV6, AdV, EBV and BKV. Donor cells that express CD137 upon stimulation with commercially available virus-specific peptides will be further cultured with viral peptides, antibodies and cytokines to produce vsCIKs (with anti-CD137, IFNγ, OKT3 and IL2) or VSTs (with IL4 and IL7). Both cell types have, in clinical studies, been shown to be effective in modulating viral infections and elicit minimal or no graft-vs-host disease (GvHD). VsCIKs also have the advantage of retaining non-HLA restricted anti-tumour effects. As expected, both protocols produce a very small subset of naive T cells, which predicts low GvHD potential. Interestingly, vsCIKs consistently kill more target cells than VSTs, although a larger fraction of cells in VST cultures degranulate upon peptide stimulation. This incongruity warrants a more detailed study of the cytokines/enzymes released by the vsCIKs and VSTs, and the mechanisms involved. So far, no donor cells have shown reactivity against EBV or BKV peptides. This is despite a high percentage of EBV carriers among Singaporeans and the successful use of the same peptides in published reports. We are unsure if this is due to the unique repertoire of HLA types or the prevalent EBV strains in the local population. We have successfully generated CMV, HHV6 and AdV-specific vsCIKs and VSTs. However, further screening of viral peptides and mechanistic studies will be required to determine a suitable cell type for the proposed bank.