Detection and ex vivo expansion of dormant anti-viral CTL precursors isolated from recipients of unrelated umbilical cord blood transplant (UCBT). (145.31)

Abstract

Abstract Two potentially fatal viruses ,CMV and adenovirus can be detected 2-4 weeks after UCBT. Infection may trigger in vivo priming of the infused na ve T cells despite immunosuppressive (IS)medications. We hypothesized that 1) threshold numbers of CTL precursors can be identified that may influence outcome 2) CTL precursors may reside below the level of detection during IS. Methods: Monocytes infected with an adenovirus vector encoding CMV pp65 (Ad5f35pp65) were used as APC in the presence of IL7. Antiviral CTLp was quantitated by IFNg ELISPOT among 1x10e5 responders after overlapping peptide pool stimulation. Results: 8 infected patients at a median age of 9.9 years have been studied before day 100 . Only 1/3 patients with adenovirus exhibited viremia while all 5 patients with CMV had viremia. In freshly drawn blood, 1/8 patients had any detectable reactivity. However, after 9-12 days of stimulation we could enumerate CTLp in 7/8 patients. For adenovirus, the median hexon-specific response was 52 SFC, and the penton-specific CTLp frequency was 13 SFC. CMV pp65-specific response was 6.7 SFC. No responses were found against CMV EI-1 demonstrating critical role for antigenic restimulation. All patients survive beyond 6 months. Conclusion: To our knowledge these are the first data demonstrating that dormant virus-specific CTLp are present already in the first 3 months in infected UCBT recipients. Although these rare events are below detection ex vivo expansion permits quantitation.