Lowest numbers of primary CD8(+) T cells can reconstitute protective immunity upon adoptive immunotherapy.

[severe combined immunodeficiency]

Patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT ) are threatened by potentially lethal viral manifestations like cytomegalovirus (CMV ) reactivation . Because the success of today 's virostatic treatment is limited by side effects and resistance development , adoptive transfer of virus-specific memory T cells derived from the stem cell donor has been proposed as an alternative therapeutic strategy . In this context , dose minimization of adoptively transferred T cells might be warranted for the avoidance of graft-versus-host disease (GVHD ), in particular in prophylactic settings after T -cell-depleting allo-HSCT protocols . To establish a lower limit for successful adoptive T -cell therapy , we conducted low -dose CD 8 (+) T -cell transfers in the well-established murine Listeria monocytogenes (L .m .) infection model . Major histocompatibility complex -Streptamer-enriched antigen-specific CD 6 2 L (hi ) but not CD 6 2 L (lo ) CD 8 (+) memory T cells proliferated , differentiated , and protected against L .m . infections after prophylactic application . Even progenies derived from a single CD 6 2 L (hi ) L .m .-specific CD 8 (+) T cell could be protective against bacterial challenge . In analogy , low -dose transfers of Streptamer-enriched human CMV-specific CD 8 (+) T cells into allo-HSCT recipients led to strong pathogen-specific T -cell expansion in a compassionate-use setting . In summary , low -dose adoptive T -cell transfer (ACT ) could be a promising strategy , particularly for prophylactic treatment of infectious complications after allo-HSCT .