Epitopes of CMVpp65 Co-Presented by Multiple Allelic Variants of HLA Class-I Antigens: Implications for Adoptive Immunotherapy for CMV Using Third Party Donor –Derived CMV Specific CTLs

CMV infections cause significant morbidity & mortality, particularly among HLA mismatched HSCT recipients.  Adoptive immunotherapy using donor derived CMV-Specific cytotoxic T-cells (D-CMV-CTLs) can treat CMV infection in such patients.  However, D-CMV- CTLs cannot be generated for HSCT recipients from CMV seronegative donors, and generation of such T-cells (TC) from cord blood has been difficult.  Furthermore, D-CMV-CTLs in recipients of HLA disparate HSCT maybe ineffective if the HLA allele restricting their cytotoxic activity is not shared between the donor and host.  In these conditions, persistent CMV reactivation can be treated using pre-generated CMV-CTLs of defined epitope specificity and HLA restriction from third party donors.

Many HLA antigens (ags) have multiple allelic variants.  We asked if TC specific for epitopes of CMVpp65 presented by one allelic variant might also recognize the same epitope presented by other variants of the same HLA ag.  We characterized the epitope specificities and HLA restrictions of 105 CMV-CTLs generated and banked for a phase I clinical trial, plus 41 additional donors.  CMV-CTLs in 37 HLA A0201⁺ donors were consistently responsive to the A0201 presented NLV epitope.  These NLV responsive TC from HLA A0201⁺donors were also cytotoxic against NLV loaded targets expressing HLA A0201, 0205 and 0206, but not HLA 0202, 0211 and 0220.  In 13 donors expressing HLA B40, B44 and B42 ag, CMV-CTLs were responsive to the HERNGFTVL epitope when presented by APCs expressing any one of the following alleles: HLA B 4001, 4002, 4006, 4401, 4403 or 4202.  Importantly, CTLs from any one of these donors were also cytotoxic against HERNGFTVL loaded targets bearing one each of these alleles.  TC from 9 donors inheriting HLA B35, all elicited responses to the epitope EVQAIRETVE  which could be presented by either HLA B3501, 3502, 3503, 3508 or 3511; each CTL line was also cytotoxic against EVQAIRETVE loaded targets bearing one of these HLA B35 alleles. Similar cross reactivity was demonstrated for the QYDPVAALF epitope which can be recognized when presented by HLA A2402, 2404 and A2407.  In contrast, allelic variants for a given HLA class-II allele do not share epitope specific responses in all donors; e.g. T-cells responding to the FTSQYRIQGKL are cytotoxic against peptide loaded DRB1 1101 targets, but do not lyse FTSQYRIQGKL loaded DRB1 1104 targets; DRB1 1104 presents a different epitope VAALFFFDIDL.

Our findings indicate that certain immunodominant viral epitopes may be presented by multiple allelic variants of class-I HLA ags.  These data suggest that HLA class-I restricted epitope specific CMV-CTLs from HLA disparate donors can be effective in recipients sharing certain allelic variants within the same class-I family.  Thus, generation of a bank of CTLs responding to common immunodominant epitopes could also potentially be used for treatment of a broader patient population at risk for CMV.