The early expansion of a defective NKG2Apos/CD56dim/CD16neg NK cell subset represents a therapeutic target in haploidentical HSCT

Natural Killer (NK) cells are the first lymphocyte population to reconstitute early after non myelo-ablative and T cell-replete haploidentical hematopoietic stem cell transplantations (h-HSCTs) with post-transplant infusion of cyclophosphamide. The present study characterizes the transient and predominant expansion starting from the 2nd week after h-HSCT of a donor-derived unconventional subset of CD56dim/CD16neg (uCD56dim) NK cells expressing remarkable high levels of NKG2A and low levels of NKp46. Both transcription and phenotypic profiles indicated that uCD56dim NK cells are a distinct NK cell subpopulation with features of late differentiation, yet retaining proliferative capability and functional plasticity to generate conventional CD56bright/CD16pos NK cells in response to IL-15 plus IL-18. uCD56dim NK cells represent by far the largest NK cell subset detectable in the following 7 weeks after h-HSCT and they also express high levels of the activating receptors NKGD and NKp30 as well as of the lytic granules Granzyme-B and Perforin. Nonetheless, uCD56dim NK cells displayed a defective cytotoxicity that could be reversed by blocking the inhibitory receptor CD94/NKG2A. These data open new important perspectives to better understand the ontogenesis/homeostasis of human NK cells and to develop a novel immune-therapeutic approach by targeting the inhibitory NKG2A check point, thus enhancing NK cell alloreactivity early after h-HSCT.

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Roberto A, Di Vito C, Zaghi E, Mazza EMC, Capucetti A, Calvi M, Tentorio P, Zanon V, Sarina B, Mariotti J, Bramanti S, Tenedini E, Tagliafico E, Bicciato S, Santoro A, Roederer M, Marcenaro E, Castagna L, Lugli E, Mavilio D