alloreactivity, number of CD34+ cells infused) could predict the risk of disease recurrence. The critical parameter in the immune reconstitution was the iNKT/T cell ratio, which was on average 20 iNKT cells/106T cells in relapsed patients and 100 iNKT cells/106T cells in patients maintaining remission, during the same observation time. Although we do not yet have clear mechanistic insight, these findings suggested that, in the critical equilibrium conditions represented by References 1. Bendelac A, Savage PB, Teyton L. The biology of NKT cells. Annu Rev Immunol 2007; 25:297-336; PMID: 17150027; http://dx.doi.org/10.1146/annurev.immunol. 25.022106.141711 2. Aversa F, Tabilio A, Velardi A, Cunningham I, Terenzi A, Falzetti F, et al. Treatment of high-risk acute leukemia with T-cell-depleted stem cells from related donors with one fully mismatched HLA haplotype. N Engl J Med 1998; 339:1186-93; PMID:9780338; http://dx.doi.org/ 10.1056/NEJM199810223391702 3. Fry TJ, Mackall CL. Immune reconstitution following hematopoietic progenitor cell transplantation: chal- lenges for the future. Bone Marrow Transplant 2005; 35(Suppl 1):S53-7; PMID:15812532; http://dx.doi. org/10.1038/sj.bmt.1704848 4. de Lalla C, Festuccia N, Albrecht I, Chang HD, Andolfi G, Benninghoff U, et al. Innate-like effector differentiation of human invariant NKT cells driven by IL-7. J Immunol 2008; 180:4415-24; PMID: 18354162 the early post-transplantation period, iNKT cells are an essential part of the effector mosaic that maintains the control on the minimal residual leukemia cells that might have escaped the preparative regimen. This is consistent with other human critical cancer contexts, such as head and neck squamous cell carcinoma, where the disease progression following radiotherapy was found to correlate with a very low iNKT/T cell ratio (, 47 iNKT cells/106 T cells) present in the patients.10 5. Gumperz JE, Miyake S, Yamamura T, Brenner MB. Functionally distinct subsets of CD1d-restricted natural killer T cells revealed by CD1d tetramer staining. J Exp Med 2002; 195:625-36; PMID:11877485; http://dx. doi.org/10.1084/jem.20011786 6. Lee PT, Benlagha K, Teyton L, Bendelac A. Distinct functional lineages of human V(alpha)24 natural killer T cells. J Exp Med 2002; 195:637-41; PMID: 11877486; http://dx.doi.org/10.1084/jem.20011908 7. Vesely MD, Kershaw MH, Schreiber RD, Smyth MJ. Natural innate and adaptive immunity to cancer. Annu Rev Immunol 2011; 29:235-71; PMID:21219185; http:// dx.doi.org/10.1146/annurev-immunol-031210-101324 8. Kohrt HE, Pillai AB, Lowsky R, Strober S. NKT cells, Treg, and their interactions in bone marrow trans- plantation. Eur J Immunol 2010; 40:1862-9; PMID: 20583031; http://dx.doi.org/10.1002/eji.201040394 Our findings have also potential clinical implications. The molecular determina- tion of the iNKT cell reconstitution trend following hHSCT could become a predictive therapeutic marker. Further- more, children who do not properly reconstitute the iNKT cell compartment within the first 2–6 mo after hHSCT could receive infusions of donor-derived iNKT cells to prevent possible leukemia recurrence, with minimal risk of inducing GVHD. 9. de Lalla C, Rinaldi A, Montagna D, Azzimonti L, Bernardo ME, Sangalli LM, et al. Invariant NKT cell reconstitution in pediatric leukemia patients given HLA-haploidentical stem cell transplantation defines distinct CD4+ and CD4- subset dynamics and correlates with remission state. J Immunol 2011; 186:4490-9; PMID:21357532; http://dx.doi.org/10. 4049/jimmunol.1003748 10. Molling JW, Langius JA, Langendijk JA, Leemans CR, Bontkes HJ, van der Vliet HJ, et al. Low levels of circulating invariant natural killer T cells predict poor clinical outcome in patients with head and neck squamous cell carcinoma. J Clin Oncol 2007; 25: 862-8; PMID:17327607; http://dx.doi.org/10.1200/ JCO.2006.08.5787 www.landesbioscience.com OncoImmunology 357