CTL was characterized as to eps specificity and restricting HLA allele. The pool of CTL donors inherited HLA alleles in frequencies similar to those in caucasian and black populations, with certain alleles overrepresented. In 55% of the CTL lines, the ID T-cell response (TCr) was restricted (restr.) by 3 HLA alleles: A0201(25%), B0702(21%) and B 3501-11(9%); 45% of CTL lines were restr. by other class-I alleles, and 17/123(14%) were restr. by class-II alleles. Certain CMVpp65 15 mers contained overlapping eps presented by both class-I and class-II, which elicited more robust TCr. CTLs from all B0702 + donors (26/26) were restr. by B0702. In comparison, CTLs from 30/39(77%) A0201 + donors and 9/19 (47%) HLA B3501-11 + donors were restr. by A0201 and B3501-11 respectively. Donors coinheriting A0201 and B 0702 (9/9) universally demonstrated B0702 restr. ID TCr. In comparison, 11/12 (91.6%) donors coinheriting A0201 and B 4401-04 demonstrated HLA A0201 restr. CTLs. Strikingly, only 1/123 and 0/123 A1101 + and A0301 + donors respectively demonstrated CTLs restr. by these commonly inherited class eI alleles. This analysis thus indicates an immunodominance hierarchy for CMVpp65 eps and their presenting HLA alleles. In a series of 239 MUD, 137 MMUD, and 100 DUCB consecutive HSCT at MSKCC, we could identify an immediately available CMVpp65 specific CTL line matched with the patient at 2-3 alleles and restr. by a shared HLA allele in this GMP-CTL bank in 86%, 89% and 80% cases respectively. This CTL bank thus provides a clinical reagent for the treatment of CMV infections in HSCT recipients. The delineated immunodominance hierarchy for CMVpp65 may also facilitate selection of an appropriately restr. CTL line for treatment with predicted activity in the recipient. We can also successfully generate CMV-CTLs against subdominant CMVpp65 eps presented prevalent HLA alleles using a panel of artificial antigen presenting cells (AAPCs). Expansion of this bank with CTLs generated with AAPCs can broaden its applicability to almost all HSCT recipients.

BackgroundThe costimulatory receptor CD137 (also known as 4-1BB and TNFRSF9) plays an important role in sustaining effective cytotoxic T cell immune responses and its agonism has been investigated as a cancer immunotherapy. In clinical trials, the systemic administration of the 1st generation CD137 agonist monotherapies, utomilumab and urelumab, were suspended due to either low anti-tumor efficacy or hepatotoxicity mediated by recognized epitope on CD137 and FcγR ligand-dependent clustering.MethodsM9657, a bispecific antibody was engineered a tetravalent bispecific antibody (mAb2) format with the Fab portion binding to the tumor antigen Mesothelin (MSLN) and a modified CH2-CH3 domain as Fc antigen binding (Fcab) portion binding to CD137. M9657 has a human IgG1 backbone with LALA mutations to abrogate the binding to Fcγ receptor. The biological characteristics and activities of M9657 were investigated in a series of in vitro assays and the in vivo efficacy was investigated in syngeneic tumor models with FS122m, a murine-reactive surrogate with the same protein structure of M9657.ResultsM9657 binds efficiently to both human and Cynomolgus CD137 as well as MSLN. In the cellular functional assay, M9657 displayed MSLN- and TCR/CD3 interaction (signal 1)-dependent cytokine release and tumor cell cytotoxicity associated with Bcl-XL activation and immune memory formation. FS122m demonstrated potent MSLN- and dose- dependent in vivo anti-tumor efficacy (figure 1). Comparing with 3H3, a Urelumab surrogate Ab, FS122m displayed an improved therapeutic window with significantly lower for on-target /off-tumor toxicity.ConclusionsTaken together, M9657 exhibits a promising developability profile as a tumor-targeted immune agonist with potent anti-cancer activity, but without systemic immune activation.Ethics ApprovalAll animal experiments were performed in accordance with EMD Serono Research & Development Institute (protocol 17-008, 20-005) and Wuxi AppTec Animal Care and Use Committee (IACUC) guidelines.Abstract 757 Figure 1FS122m displayed dose-dependent anti-tumor efficacy

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