Treatment with Banked 3rd Party Donor Derived Virus Specific T Cells: The Advantages of Pre-Defined HLA restriction and Epitope Specificity

Abstract

Background & Aim For patients lacking a matched donor, transplant (HCT) from umbilical cord or T cell depleted (TCD) grafts, is potentially curative. However, these transplants are associated with high morbidity and mortality from reactivation of latent viruses. Adoptive therapy with CMV and EBV specific T cells expanded in vitro (CMV-CTLs and EBV-CTLs) is increasingly available to clear drug resistant CMV infections and induce durable remissions of refractory EBV+ lymphomas. Here we present studies that help elucidate mechanisms of T cell control of CMV and EBV in both the primary HCT and the adoptive T cell settings and provide rationale for pre-defined characterization of T cells generated for adoptive therapy. Methods, Results & Conclusion In a cohort (N=39) of CMV seropositive recipients of mismatched TCD-HCT, we established the HLA-restriction of the donor's endogenous CMV response. To evaluate instances where viral specific T cells failed to induce responses, we compared in vitro cytotoxicity of CMV-CTLs and EBV-CTLs against targets presenting CMVpp65 15-mers or lab strain EBV B95.8 to patient derived CMV or EBV targets. . Results In 15 of 39 recipients at risk for reactivation of CMV, the donor CMV response was restricted by an un-shared HLA allele.. Furthermore, 53% of these recipients developed persistent CMV viremia or invasive disease compared to none of those whosedonors CMV response was restricted by a shared HLA allele Our analyses show several mechanisms of immune escape leading to for the failure of CMV-CTLs or EBV-CTLs to recognize patient derived targets 1) deficient production of the viral protein (eg EBNA3B) 2) mutations of the viral epitopes (eg EBNA3B presented by HLA A1101) or 3) impaired processing or presentation of these epitopes (eg IPSI peptide of CMVpp65 presented by HLA B3501). In such cases, selection of 3rd party CTLs restricted by a different HLA allele (i.e. restriction switch) has induced remissions of EBV+ lymphomas in 60% of patients. Conclusions In HLA disparate HCT recipients, donor-derived virus-specific T-cells may be ineffective if the HLA restriction is not shared between the T-cells and the recipient. Even in the 3rd-party setting, where there is appropriate selection of shared HLA restrictions, clinical responses may be impacted by immune escape. Our banks of 3rd party virus-specific T-cells characterized by HLA restrictions permit accurate selection of T-cells. Importantly, restriction switch can overcome viral mechanisms of immune evasion.