A Phase I Dose Escalation Trial of Donor T Cells Sensitized with Pentadecapeptides of the CMV-pp65 Protein for the Treatment of CMV Infections Following Allogeneic Hematopoietic Stem Cell Transplants.

Abstract Abstract 2262 Poster Board II-239 We have developed a novel alternative method of generating donor-derived T-cell lines specific for CMV-pp65 peptides for use in adoptive immunotherapy. In this approach, 138 pentadecapeptides (15-mers), with 11 amino acid overlaps spanning the entire 561 amino acid sequence of the CMV protein pp65 were synthesized and manufactured under conditions ensuring their purity and sterility for application in clinical trials. A pool of the 138 pentadecapeptides is loaded onto monocyte-derived dendritic cells derived from seropositive donors and the same donor's T cells are sensitized under GMP conditions. In our preclinical studies, we have been able to generate CMV-pp65 specific T-cell lines from each seropositive donor tested, irrespective of HLA genotype. During the culture period of 21-28 days, populations of T cells specific for CMV-pp65 selectively expanded 200-300 fold while T cells reactive against major or minor alloantigens were depleted. Currently, 9 patients (pts) with persistent/refractory CMV antigenemia, one pt with CMV pneumonia diagnosed four weeks after treatment, have been treated using cells manufactured by this method on a clinical trial approved by the FDA. One pt was treated on a single patient IND prior to final FDA approval; 8 pts were enrolled onto the clinical trial - 3 pts at a T cell dose of 5×105/kg; 3 pts at dose level II of 1×106/kg and 2 pts at dose level III of 2×106/kg. We report here the results of the first 7 pts, (the 2 latter pts are too early in treatment to be included at time of abstract admission). CMV specific CTLs were generated from HLA-identical unrelated donors (3 pts) or from HLA-identical siblings (6 pts) for 2 pts who underwent non-myeloablative conventional and 7 pts who received myeloablative T-cell depleted allogeneic transplants. Pts were eligible if they had persistent CMV antigenemia despite treatment with antiviral drugs or had toxicities precluding further treatment with antiviral agents. Prior to infusion, the T cells were tested to be CMV specific by cytotoxicity, intracellular Interferon gamma (IFN-g) production and MHC-tetramer staining (if available). Cells were also assayed to establish lack of alloreactivity, microbiological sterility and low endotoxin levels. The cytotoxic T cells demonstrated cytolytic activity against peptide-loaded autologous PHA blasts, but exhibited no cytotoxicity against non-pulsed HLA-matched or pulsed HLA-mismatched target cells. The HLA-restriction and the specific pp65-derived epitopes of the CMV-specific T-cells were characterized prior to the infusion. CMV-specific frequencies of the CD8+ cells measured by intracellular IFN-g or MHC tetramers ranged from 2 -70%. Post infusion, an increase in the absolute lymphocyte count correlated with an increase in CMV-specific T-cell frequencies to levels as high as 12% of CD8+ cells. These persisted for at least 7 months (10% of CD8+ cells) following the infusion. Notably, the same pp65-derived epitopes and their HLA-restrictions, which characterized the pre-infusion CTLs were detected in the pt specimens post infusion. Freshly isolated T cells from the blood of HLA-A*0201 positive pts obtained 3 months post infusion showed significant lysis of CMV infected and peptide-pulsed MRC-5 fibroblasts, while non infected/pulsed fibroblasts and pulsed HLA-mismatched targets were not lysed. Three of the treated pts exhibited an HLA-A*0201 as well as HLA-B*0701 allele. In all three pts, epitope-specific T cells for the HLA-A*0201 restricted NLVPMVATV peptide and the B*0701 restricted RPHERNGFTV peptide were detected and monitored in pre and post infusion T-cell populations. All 7 pts who were treated for persistent CMV antigenemia tolerated treatment well. None developed early signs or symptoms of GvHD at the dose levels tested. Six of the 7 pts cleared CMV viremia by 2-4 weeks following the T-cell infusions. One of the pts died six weeks after the CTL infusion of respiratory failure despite clearing CMV from blood and bronchial aspirates. The one pt who remained viremic following the CTL infusion continued on oral Valgancyclovir and subsequently became CMV antigen negative. The clearance of CMV antigenemia was preceded by an initial spike of CMV antigenemia and/or CMV PCR in all pts. These results from the first 7 pts on this trial indicate that donor T cells sensitized with this pool of synthetic overlapping CMV pp65 15-mers are safe and clear CMV viremia resistant to standard therapy. Disclosures: No relevant conflicts of interest to declare.