Florian Babor

The role of KIR genes and ligands in leukemia surveillance

The antileukemic potential of natural killer (NK) cells has been of rising interest in recent years. Interactions between inhibitory killer cell immunoglobulin-like receptors (KIR) and HLA class I ligands seem to be critically involved in the immunosurveillance process. It is also well established that mismatching of HLA class I-encoded KIR ligands in the setting of hematopoietic stem cell transplantation leads to allorecognition of leukemic cells by NK cells, which is in line with the concept of missing-self recognition. Recent data now suggest that KIR gene polymorphism constitutes another important parameter that needs to be taken into account for selection of suitable stem cell donors. Moreover, the role of KIR gene polymorphism for predisposition to leukemia is a current matter of debate. Here, we would like to review the role of KIR function and genetic polymorphism for recognition of leukemia and discuss the impact of these findings for developing novel concepts for NK cell-based immunotherapy strategies.

KIR ligand C2 is associated with increased susceptibility to childhood ALL and confers an elevated risk for late relapse.

A role for HLA class I polymorphism in childhood acute lymphoblastic leukemia (ALL) has been suggested for many years, but unambiguous associations have not been found. Here, we show that the HLA-C-encoded supertypic epitope C2, which constitutes a high-affinity ligand for the inhibitory natural killer (NK) cell receptor KIR2DL1, is significantly increased in ALL patients (n = 320; P = .005). Stratification for ethnicity and disease subtype revealed a strong association of C2 with B-ALL in German cases (P = .0004). The effect was independent of KIR2DS1 and KIR2DL1 allelic polymorphism and copy number. Analysis of clinical outcome revealed a higher incidence of late relapse (> 2.5 years) with increasing number of C2 alleles (P = .014). Our data establish C2 as novel risk factor and homozygosity for C1 as protective for childhood B-ALL supporting a model in which NK cells are involved in immunosurveillance of pediatric B-ALL via interaction of KIR with HLA-C ligands.

Hematopoietic stem cell transplantation rescues the hematological, immunological and vascular phenotype in DADA2

Deficiency of adenosine deaminase 2 (DADA2) is caused by biallelic deleterious mutations in CECR1 DADA2 results in variable autoinflammation and vasculopathy (recurrent fevers, livedo reticularis, polyarteritis nodosa, lacunar ischemic strokes, and intracranial hemorrhages), immunodeficiency and bone marrow failure. Tumor necrosis factor-α blockade is the treatment of choice for the autoinflammation and vascular manifestations. Hematopoietic stem cell transplantation (HSCT) represents a potential definitive treatment. We present a cohort of 14 patients from 6 countries who received HSCT for DADA2. Indication for HSCT was bone marrow dysfunction or immunodeficiency. Six of 14 patients had vasculitis pre-HSCT. The median age at HSCT was 7.5 years. Conditioning regimens were myeloablative (9) and reduced intensity (5). Donors were HLA-matched sibling (n = 1), HLA-matched unrelated (n = 9), HLA-mismatched unrelated (n = 3), and HLA haploidentical sibling (n = 1). All patients are alive and well with no new vascular events and resolution of hematological and immunological phenotype at a median follow-up of 18 months (range, 5 months to 13 years). Plasma ADA2 enzyme activity normalized in those tested post-HSCT (7/7), as early as day +14 (myeloid engraftment). Post-HSCT hematological autoimmunity (cytopenias) was reported in 4 patients, acute graft-versus-host disease grade 1 in 2, grade 2 in 3, and grade 3-4 in 1, and moderate chronic graft-versus-host disease in 1 patient. In conclusion, in 14 patients, HSCT was an effective and definitive treatment of DADA2.

Epidemiology and clinical characteristics of pandemic (H1N1) 2009 influenza infection in pediatric hemato‐oncology and hematopoietic stem cell transplantation patients

For children with hemato‐oncologic diseases, especially after hematopoietic stem cell transplantation (HSCT), the risk for developing complications related to pandemic influenza A (H1N1) 2009 (pH1N1) infection is largely unknown.

Invasive aspergillosis in pediatric oncology patients: a rare event with poor prognosis--case analysis to plan better targeted prophylactic or therapeutic measurement.

Despite the implementation of new antifungal drugs, invasive aspergillosis (IA) still remains a considerable challenge in pediatric oncology with a severe mortality. Prophylactic and therapeutic measurement have to be evaluated in these rare but poor prognostic patients. Therefore the entire group of patients at risk of developing IA has to be defined before cooperative prospective trials. In a retrospective analysis including all our patients with malignancies we looked for patients with proven/probable IA. Cases of the period from 2003 to 2008 were analyzed in detail.In the period between 2003 to 2008 24 of 755 patients were affected by proven/ probable IA. Compared to former studies incidence increased from 1.3%in 1980 to 3.4% in 2008. AML patients with or without allogeneic/haploidentical stem cell transplantation were at highest risk (24% and 25% respectively, in comparison to 1% in ALL-patients). Survival after 2 years was 50% for patients with AML and IA. In patients with high risk to develop IA the effect of intensified, intravenous antimycotic prophylaxis has to be proven prospectively in a cooperative and randomized setting.

Selective downregulation of HLA‐C and HLA‐E in childhood acute lymphoblastic leukaemia

We have recently shown that susceptibility to childhood B-cell acute lymphoblastic leukaemia (B-ALL) is influenced by the presence of HLA-C encoded ligands C1 and C2 for killer cell immunoglobulin-like receptors (KIR), (Babor et al, 2014). B-ALL patients exhibited an increased frequency of the C2 ligand and, moreover, C2 was associated with increased risk of late relapse. The study suggested that the expression of HLA class I-encoded KIR ligands on tumour

Hematopoietic Stem Cell Transplantation in an Infant with Immunodeficiency, Centromeric Instability, and Facial Anomaly Syndrome

Immunodeficiency, centromeric instability, and facial anomaly (ICF) syndrome is a rare autosomal recessive genetic condition with severe immunodeficiency, which leads to lethal infections if not recognized and treated in early childhood. Up-to-date treatment regimens consist of prophylactic and supportive treatment of the recurrent infections. Here, we report the case of a 1-year-old boy of Moroccan consanguineous parents, who was diagnosed at 4 months of age with ICF syndrome with a homozygous missense mutation in the DNMT3B gene. He was initially admitted to the hospital with recurrent pulmonary infections from the opportunistic pathogen Pneumocystis jirovecii (PJ). Further immunological workup revealed agammaglobulinemia in the presence of B cells. After successful recovery from the PJ pneumonia, he underwent hematopoietic stem cell transplantation (HSCT) from the HLA-matched healthy sister using a chemotherapeutic conditioning regimen consisting of treosulfan, fludarabine, and thiotepa. Other than acute chemotherapy-associated side effects, no serious adverse events occurred. Six months after HSCT immune-reconstitution, he had a stable chimerism with 2.9% autologous portion in the peripheral blood and a normal differential blood cell count, including all immunoglobulin subtypes. This is one of the first cases of successful HSCT in ICF syndrome. Early diagnosis and subsequent HSCT can prevent severe opportunistic infections and cure the immunodeficiency. Centromeric instability and facial anomaly remain unaffected. Although the long-term patient outcome and the neurological development remain to be seen, this curative therapy for immunodeficiency improves life expectancy and quality of life. This case is meant to raise physicians awareness for ICF syndrome and highlight the consideration for HSCT in ICF syndrome early on.

Clearance of treatment-refractory adenoviremia via adenovirus-specific donor T-cell transfer during aplasia after αβTCR-CD19-depleted stem cell transplantation

Here, we report the case of severe adenoviremia in a 7-year-old boy with highly-resistant, acute leukemia. A combined approach of αβTCR-CD19-depleted stem cell transplantation, enabling immunosuppression-free post-transplant care, and early transfer of adenovirus-specific donor T cells during aplasia resulted in rapid and complete clearance of the treatment-refractory adenoviremia.

Targeting HSP90 dimerization via the C-terminus is effective in imatinib resistant CML and lacks heat shock response.

Heat shock protein 90 (HSP90) stabilizes many client proteins, including the BCR-ABL1 oncoprotein. BCR-ABL1 is the hallmark of chronic myeloid leukemia (CML) in which treatment-free remission (TFR) is limited, with clinical and economic consequences. Thus, there is an urgent need for novel therapeutics that synergize with current treatment approaches. Several inhibitors targeting the N-terminal domain of HSP90 are under investigation, but side effects such as induction of the heat shock response (HSR) and toxicity have so far precluded their US Food and Drug Administration approval. We have developed a novel inhibitor (aminoxyrone [AX]) of HSP90 function by targeting HSP90 dimerization via the C-terminal domain. This was achieved by structure-based molecular design, chemical synthesis, and functional preclinical in vitro and in vivo validation using CML cell lines and patient-derived CML cells. AX is a promising potential candidate that induces apoptosis in the leukemic stem cell fraction (CD34+CD38-) as well as the leukemic bulk (CD34+CD38+) of primary CML and in tyrosine kinase inhibitor (TKI)-resistant cells. Furthermore, BCR-ABL1 oncoprotein and related pro-oncogenic cellular responses are downregulated, and targeting the HSP90 C terminus by AX does not induce the HSR in vitro and in vivo. We also probed the potential of AX in other therapy-refractory leukemias. Therefore, AX is the first peptidomimetic C-terminal HSP90 inhibitor with the potential to increase TFR in TKI-sensitive and refractory CML patients and also offers a novel therapeutic option for patients with other types of therapy-refractory leukemia because of its low toxicity profile and lack of HSR.

Characterization of leukemia-specific NK cell subsets against acute lymphoblastic leukemia in children

Human natural killer (NK) cells and their antileukemic potential have been of rising interest over the last years. However, it is controversially discussed how NK cells can be best exploited for anti-leukemic therapy in the clinic. Accordingly, we performed a first detailed analysis of the NK cell repertoire specific for childhood ALL in order to investigate the participation of NK cell subsets in the killing of pediatric leukemic blasts. PBMCs from 4 healthy volunteer samples were incubated with ALL blasts of two pediatric patients. We observed a variable frequency of NK cells (0.5%-15.6%) that showed degranulation of CD107 in the presence of ALL blasts and this frequency was strongly dependent on the donor. In a next step NK cells were characterized by means of KIR2DL1, KIR2DL3 and NKG2A by 6-color flow cytometry. Analysis of CD107 mobilization revealed that especially single-KIR+ NK cells showed the highest killing ability: in single-KIR2DL1+ NK cells the frequency of CD107+ cells was 7.6% and in single-KIR2DL3+ cells 6.7%. In contrast, NK cells not expressing any of these three receptors had a reduced anti-leukemic activity, which is compatible with previous studies showing that KIR-NKG2A- NK cells are hyporesponsive. In general, KIR+NKG2A- NK cells appeared to have the highest frequency of anti-leukemic NK cells in our experiments, whereas KIR-NKG2A- consistently showed the lowest reactivity. In summary, our results showed that participation of NK cell subsets in ALL killing is dependent on respective expression levels and expression clusters of KIR and other receptors. Single KIR+ NK cell subsets appeared to be most effective against childhood ALL blasts. With further advancements in isolation and expansion techniques, development of novel characterized ALL-specific NK cells appears feasible for future donor-derived NK cell transfer as supportive treatment in childhood ALL.