Case presentationsCase 1. Robert Davies, a 50-year-old man, presents with tiredness and lethargy. Examination demonstrates pallor and jaundice. Investigations reveal anemia that is consistent with warm autoimmune hemolytic anemia (AIHA; Figure 1). He has no evidence of any other autoimmune disease or chronic lymphocytic leukemia (CLL) and is not taking any medications; these factors suggest idiopathic AIHA. How should he be treated?* AIHA is an uncommon but potentially fatal condition. It results from autoantibodies with specificity against RBC Ags leading to the premature removal of red cells from the circulation. Anemia may occur if the rate of red cell removal exceeds the ability of the BM to produce new red cells. AIHA may be secondary to drugs or underlying conditions such as CLL, infections, or autoimmune disorders. This guideline will deal specifically with idiopathic AIHA, and will not discuss secondary AIHA.Several of the treatments in this article are not licensed for the treatment of AIHA and come with little evidence, so clinicians and patients should be informed of known risks.A decision was made a priori to limit this review to published data only. Where there is no published evidence, or only expert opinion, we suggest referring to the recent Blood "How I treat" article on AIHA. 1 Medline, Embase, and the Cochrane Library were searched for relevant articles, along with reference lists of identified articles. Search strategies are found in supplemental Data (available on the Blood Web site; see the Supplemental Materials link at the top of the online article). Identified articles were then screened for inclusion. English-language articles were included only if they provided useful extractable data on adult (Ͼ 18 years) patients with idiopathic AIHA. Secondary AIHA, cold hemagglutinin disease, and patients with concomitant thrombocytopenia (Evans syndrome) were excluded.Secondary AIHA was defined as AIHA in the presence of other autoimmune conditions, hematologic malignancies, or drugs known to cause AIHA, or where the authors of the article described the anemia as secondary. Conference abstracts were not searched. To reduce the number of articles, it was decided a priori that if a randomized controlled trial (RCT) was found, then nonrandomized controlled studies and case series would be excluded. If no RCT was found, only nonrandomized controlled studies would be included. If there were no nonrandomized controlled studies then case series with Ͼ 10 participants would be included; if there were no case series with Ͼ 10 participants then any case series would be included. Case reports were excluded. This is similar to the method used in the recent American Society of Hematology (ASH) Immune Thrombocytopenia Guidelines. 2 Articles meeting the inclusion criteria underwent data extraction and quality assessment using pre-prepared forms (example found in supplemental data). Searching, data extraction, and quality assessment were all done in duplicate. The guidelines were given a Grading of Recommendation...

Background: Natural killer (NK) cells are cytotoxic lymphocytes that lack CD3 and express variable levels of CD16, CD56 and CD57. In recent years NK cells have been categorised into two major groups based on the level of CD56 expression. This phenotypic classification correlates with functional activity as CD56 bright NK cells are the major cytokine producing subset whereas CD56 dim NK cells exhibit greater cytotoxic activity. Previous studies have revealed a reduction in total NK cell numbers in association with ageing and this study sought to determine the potential influence of ageing on the number of NK cell subsets within peripheral blood.

Natural killer (NK) cells rapidly reconstitute following allogeneic stem cell transplantation (allo‐SCT), at the time when alloreactive T cell immunity is being established. We investigated very early NK cell reconstitution in 82 patients following T cell‐depleted allo‐SCT. NK cell number rapidly increased, exceeding T cell reconstitution such that the NK:T cell ratio was over 40 by day 14. NK cells at day 14 (NK‐14) were donor‐derived, intensely proliferating and expressed chemokine receptors targeted to lymphoid and peripheral tissue. Spontaneous production of the immunoregulatory cytokine IL‐10 was observed in over 70% of cells and transcription of cytokines and growth factors was augmented. NK‐14 cell number was inversely correlated with the incidence of grade II‐IV acute graft versus host disease (GVHD). These findings reveal that robust reconstitution of immunoregulatory NK cells by day 14 after allo‐SCT is an important determinant of the clinical outcome, suggesting that NK cells may suppress the development of the T cell‐mediated alloreactive immune response through production of IL‐10.

Transplantation is an effective treatment of many clinical disorders, but the mechanisms that regulate immunological tolerance are uncertain and remain central to improving patient outcome. Hemopoietic stem cell transplantation (SCT) often establishes “mixed chimerism” in which immune cells from both the donor and patient coexist in vivo in a setting of immunological tolerance. We studied immune function in 69 patients within 2 months following SCT; 37 were fully donor and 32 displayed mixed chimerism. The proportion of T regulatory (Treg) cells was increased during mixed chimerism and comprised equal numbers of donor and host-derived regulatory cells. This was associated with a tolerogenic PD-L1+ profile on dendritic cells. Importantly, effector T cells from patients with mixed chimerism exhibited reduced cytotoxicity against host target cells in vitro, but this was restored following depletion of CD4+ Treg cells. These data show that Treg cells play a major role in sustaining immunological tolerance during mixed chimerism. These insights should help to guide novel interventions to improve clinical transplantation.

Key Points• A stem cell graft NK cell dose below 6.3 3 10 6 cells per kg associates with risk of disease relapse following T-cell-depleted allo-HSCT.• Clinical outcomes of patients undergoing allo-HSCT may be improved by setting an NK cell threshold within donor stem cell grafts.The graft-versus-leukemia (GVL) effect of allogeneic hemopoietic stem cell transplantation (allo-HSCT) is mediated by the donor immune system and acts to decrease the rate of disease relapse. Although studies of posttransplant immune reconstitution have identified correlates of clinical outcome, the number and profile of mature immune cells infused with the stem cell graft is also likely to be an important determinant and has been relatively poorly studied.We characterized immune cells within the stem cell graft of 107 patients who underwent T-cell-depleted allo-HSCT and related this to clinical outcome. The number of natural killer (NK) cells and T cells that were infused varied markedly between patients, but T-cell dosewas not an important factor in subsequent outcome. In contrast, the number of NK cells was a powerful determinant of the risk of disease relapse. Patients who received an NK cell dose below the median level of 6.3 3 10 6 cells per kg had a relapse rate of 40% at 2 years posttransplant compared with only 6% for those whose stem cell graft contained a dose above this value. Analysis of NK subsets showed that this effect was mediated primarily by the CD56 dim population of mature effector cells and that high-level expression of the activatory protein DNAM on donor NK cells was also strongly protective. These observations offer important insights into the mechanism of GVL and suggest that optimization studies of the number of NK cells within the stem cell graft should be considered as a means to reduce disease relapse.