Pathophysiologic implications of elevated prevalence of hereditary alpha-tryptasemia in all mastocytosis subtypes.

BACKGROUND: Mastocytosis and monoclonal mast cell (MC) activation syndrome (MMAS) are heterogeneous conditions characterized by the accumulation of atypical MCs. Despite the recurrent involvement of KIT mutations, the pathophysiologic origin of mastocytosis and MMAS is unclear. Although hereditary α-tryptasemia (HαT, related to TPSAB1 gene duplication) is abnormally frequent in these diseases, it is not known whether the association is coincidental or causal. OBJECTIVE: We evaluated the prevalence of HαT in all mastocytosis subtypes and MMAS and assessed the pathophysiologic association with HαT. METHODS: Clinical data, laboratory data, KIT mutations, TPSAB1 duplication (assessed by droplet digital PCR), and HαT prevalence were retrospectively recorded for all patients with mastocytosis and MMAS registered in the French national referral center database and compared to a control cohort. To increase the power of our analysis for advanced systemic mastocytosis (advSM), we pooled our cohort with literature cases. RESULTS: We included 583 patients (27 with MMAS and 556 with mastocytosis). The prevalence of HαT in mastocytosis was 12.6%, significantly higher than in the general population (5.7%, P = .002) and lower than in MMAS (33.3%, P = .02). HαT+ patients were more likely to have anaphylactic reactions and less likely to have cutaneous lesions than HαT- patients (43.0% vs 24.4%, P = .006; 57.7% vs 75.6%, respectively, P = .006). In the pooled analysis, the prevalence of HαT was higher in advSM (11.5%) than in control cohorts (5.2%, P = .01). CONCLUSION: Here we confirm the increase incidence of anaphylaxis in HαT+ mastocytosis patients. The increased prevalence of HαT in all subtypes of systemic mastocytosis (including advSM) is suggestive of pathophysiologic involvement.

Efficacy and safety of daratumumab in multiresistant immune-mediated thrombotic thrombocytopenic purpura.

The immunosuppressive treatment of immune-mediated thrombotic thrombocytopenic purpura (iTTP) in patients with intolerance or refractoriness to the B-cell depleting monoclonal antibody rituximab remains debated. Daratumumab, a plasma cell-directed monoclonal antibody targeting CD38, represents a therapeutic option, but data are scarce. The French Thrombotic Microangiopathies Reference Center conducted a nationwide survey on iTTP patients treated with daratumumab. Nine episodes from seven patients were identified. Treatment was administered for A Disintegrin And Metalloproteinase with ThromboSpondin-1 motifs, 13th member (ADAMTS13) relapses while patients were otherwise in clinical response (N = 8), or during the acute phase of the disease following rituximab intolerance (N = 1). Patients have received a median of three previous therapeutic lines. ADAMTS13 activity improved in eight cases following daratumumab administration, including three cases where ADAMTS13 normalized. ADAMTS13 relapses occurred in three patients; in two cases, retreatment with daratumumab was successful. Median ADAMTS13 relapse-free survival was not reached; 12-month ADAMTS13 relapse-free survival was 56%. Daratumumab-related adverse events occurred in five cases and were non-severe infusion-related reactions in all cases. These results suggest that daratumumab may be an effective treatment option for iTTP patients with intolerance or refractoriness to rituximab.

CXCR4 WHIM syndrome is a cancer predisposition condition for virus-induced malignancies.

Warts, hypogammaglobulinaemia, infections and myelokathexis syndrome (WHIMS) is a rare combined primary immunodeficiency caused by the gain of function of the CXCR4 chemokine receptor. We present the prevalence of cancer in WHIMS patients based on data from the French Severe Chronic Neutropenia Registry and an exhaustive literature review. The median follow-up of the 14 WHIMS 'patients was 28.5 years. A central review and viral evaluation of pathological samples were organized, and we conducted a thorough literature review to identify all reports of WHIMS cases. Six French patients were diagnosed with cancer at a median age of 37.6 years. The 40-year risk of malignancy was 39% (95% confidence interval [CI]: 6%-74%). We observed two human papillomavirus (HPV)-induced vulvar carcinomas, three lymphomas (two Epstein-Barr virus [EBV]-related) and one basal cell carcinoma. Among the 155 WHIMS cases from the literature, 22 cancers were reported in 16 patients, with an overall cancer 40-year risk of 23% (95% CI: 13%-39%). Malignancies included EBV-associated lymphoproliferative disorders and HPV-positive genital and anal cancers as in the French cohort. Worldwide, nine cases of malignancy were associated with HPV and four with EBV. Immunocompromised WHIMS patients appear to be particularly susceptible to developing early malignancy, mainly HPV-induced carcinomas, followed by EBV-related lymphomas.

Twice-weekly induction with ixazomib-lenalidomide-dexamethasone (IRd) combination followed by extended IRd consolidation and lenalidomide maintenance in transplant-eligible patients with newly diagnosed multiple myeloma: Results of the phase 2 study IFM2014-03.

Therapeutic strategies for patients with newly diagnosed multiple myeloma (NDMM) have considerably improved during the last 10 years. The IFM2014-03 trial proposed an all-oral triplet induction/consolidation regimen in transplant-eligible NDMM patients, followed by lenalidomide maintenance. Induction consisted of three 21-day cycles of ixazomib, lenalidomide and dexamethasone (IRd), before high-dose Melphalan with transplant followed by eight 28-day cycles of IRd consolidation before 13 cycles of lenalidomide maintenance. Forty-six patients were enrolled and received at least one dose of therapy, and 39 entered the maintenance phase. The primary end-point was stringent complete response after consolidation, and was achieved in nine patients (20.9%, 90% CI 11.4-33.7; p = 0.998). Ten patients (24.4%) had an undetectable minimal residual disease. The overall response rate was 95.7%. The 3-year progression-free survival was 66.3%. No unexpected toxicities were recorded, and only eight patients suspended from any study drug. Of note, 21 (45.7%) patients reported peripheral neuropathy (PN) (grades 1-2 with no serious adverse events). IRd induction and consolidation with transplant before lenalidomide maintenance shows lower response rates compared to other triplet therapies. It could be an alternative for patients who require an all-oral regimen and/or with pre-existent PN, especially if quadruplet regimens including anti-CD38 antibody are not available.

Characteristics and outcomes associated with CD2 and CD25 expression on bone marrow mast cells in patients with systemic mastocytosis.

Not available.

Histological characterization of liver involvement in systemic mastocytosis.

BACKGROUND AND AIMS: Systemic mastocytosis (SM) is characterized by the accumulation of atypical mast cells (MCs) in organs. Liver histology of SM has been marginally described and accurate histological classification is critical, given the consequences of aggressive SM diagnosis. We aimed to describe the histological features associated with liver SM using updated tools. METHODS: Using the database of the French Reference Centre for Mastocytosis, we retrospectively identified patients with a liver biopsy (LB) and a diagnosis of SM. All LB procedures were performed according to the local physician in charge and centrally reviewed by an expert pathologist. RESULTS: A total of 28 patients were included: 6 had indolent SM, 9 had aggressive SM, and 13 had SM with an associated hematologic neoplasm. Twenty-five (89%) patients presented hepatomegaly, and 19 (68%) had portal hypertension. The LB frequently showed slight sinusoid dilatation (82%). Fibrosis was observed in 3/6 indolent SM and in almost all advanced SM cases (21/22), but none of them showed cirrhosis. A high MC burden (>50 MCs/high-power field) was correlated with elevated blood alkaline phosphatase levels (p = .030). The presence of portal hypertension was associated with a higher mean fibrosis grade (1.6 vs. 0.8 in its absence; p = .026). In advanced SM, the presence of nodular regenerative hyperplasia (NRH) was associated with decreased overall survival (9.5 vs. 46.3 months, p = .002). CONCLUSIONS: MC infiltration induced polymorphic hepatic lesions and the degree of fibrosis is associated with portal hypertension. NRH identifies a poor prognosis subgroup of patients with advanced SM. Assessing liver histology can aid in SM prognostic evaluation.

CALR-mutated patients with low allele burden represent a specific subtype of essential thrombocythemia: A study on behalf of FIM and GBMHM.

A low allele burden (i.e., <20%) of the CALR driver mutation is found in 10.8% of CALR-mutated MPNs, mostly in essential thrombocythemia, and correlates with a milder phenotype and a more indolent evolution compared to patients with an allele burden ≥20%.

Efficacy and safety of mammalian target of rapamycin inhibitors in systemic mastocytosis: A nationwide French pilot study.

Systemic mastocytosis (SM) corresponds to a rare and heterogeneous spectrum of diseases characterized by the accumulation of atypical mast cells (MCs). Advanced mastocytosis (Adv-SM) is associated with poor survival; in contrast, patients with non-advanced SM (non-Adv-SM) usually have a normal life expectancy but may experience poor quality of life. Despite recent therapeutic progress including tyrosine kinase inhibitors, new treatment options are needed for refractory and/or intolerant patients with both severely symptomatic and Adv-SM. In vitro, the mTOR pathway is activated in MCs from patients bearing the KIT D816V mutation. Furthermore, rapamycin induces the apoptosis of KIT D816V MCs selectively. In this nationwide study, we report the outcomes of patients diagnosed with SM and treated with a mammalian target of rapamycin inhibitor (imTOR) within the French National Reference Center for mastocytosis (CEREMAST). All patients registered were relapsing, treatment-refractory, or ineligible for other cytoreductive therapy. Non-Adv-SM patients received imTOR as a monotherapy (rapamycin/everolimus), and Adv-SM patients received imTOR as a monotherapy or in combination with cytarabine. The objective response rate (ORR) in non-Adv-SM was 60% (partial response in 40% and major response in 20%), including reductions in skin involvement, mediator release symptoms, and serum tryptase. In the Adv-SM group, the ORR was 20% (including one major response and one partial response, both in patients with a KIT D816V mutation), which enabled a successful bridge to allogeneic stem cell transplantation in one patient. Our results suggest that imTOR treatment has potential benefits in patients with SM harboring a KIT D816V mutation.

Comparison of prognostic scores according to WHO classification in 170 patients with advanced mastocytosis and C-finding treated with midostaurin.

Advanced systemic mastocytosis (AdvSM) encompasses heterogeneous mastocytosis subtypes and is associated with poor outcomes. Although midostaurin was the first tyrosine kinase inhibitor to be approved for AdvSM patients, long-lasting responses are limited. The mutation-Adjusted Risk Score (MARS), the International Prognostic Scoring System for mastocytosis (IPSM) and the Global Prognostic Score for Systemic Mastocytosis (GPSM) have been established to characterize the outcomes of patients with overall AdvSM. However, given the outcome's dependency on the AdvSM subtype, prognostic characterization within each subtype is critical. We aimed to study the predictive ability using Harrell's concordance index of prognostic scores according to the AdvSM subtype. We conducted a nationwide retrospective study using the French mastocytosis reference center's registry and included all midostaurin-treated patients with C finding. Overall, 170 patients were identified: 46 aggressive SM (ASM), 11 mast cell leukemia (MCL), and 113 SM with associated hematological neoplasm (SM-AHN). All risk scores improved their discriminative value for overall survival (OS) when combined with the AdvSM subtype. The best predictive value was for adjusted MARS (C-index = 0.689), followed by GPSM (C-index = 0.677) and IPSM (C-index = 0.618). In a multivariable analysis, MARS stratification and the AdvSM subtype were both prognostic for OS. Accordingly, five subgroups of patients with AdvSM and a different median OS were identified: 9.9 months for MCL, 24 months for intermediate/high-risk SM-AHN, 33 months for intermediate/high-risk ASM, 58 months for low-risk SM-AHN and was not reached for low-risk ASM (p < 0.001). The AdvSM subtype and the MARS are the most predictive of OS and should prompt specific management.

EFL1 mutations impair eIF6 release to cause Shwachman-Diamond syndrome.

Shwachman-Diamond syndrome (SDS) is a recessive disorder typified by bone marrow failure and predisposition to hematological malignancies. SDS is predominantly caused by deficiency of the allosteric regulator Shwachman-Bodian-Diamond syndrome that cooperates with elongation factor-like GTPase 1 (EFL1) to catalyze release of the ribosome antiassociation factor eIF6 and activate translation. Here, we report biallelic mutations in EFL1 in 3 unrelated individuals with clinical features of SDS. Cellular defects in these individuals include impaired ribosomal subunit joining and attenuated global protein translation as a consequence of defective eIF6 eviction. In mice, Efl1 deficiency recapitulates key aspects of the SDS phenotype. By identifying biallelic EFL1 mutations in SDS, we define this leukemia predisposition disorder as a ribosomopathy that is caused by corruption of a fundamental, conserved mechanism, which licenses entry of the large ribosomal subunit into translation.

Benefits and pitfalls of pegylated interferon-α2a therapy in patients with myeloproliferative neoplasm-associated myelofibrosis: a French Intergroup of Myeloproliferative neoplasms (FIM) study.

We have previously described the safety and efficacy of pegylated interferon-α2a therapy in a cohort of 62 patients with myeloproliferative neoplasm-associated myelofibrosis followed in centers affiliated to the French Intergroup of Myeloproliferative neoplasms. In this study, we report their long-term outcomes and correlations with mutational patterns of driver and non-driver mutations analyzed by targeted next generation sequencing. The median age at diagnosis was 66 years old, the median follow-up since starting pegylated interferon was 58 months. At the time of analysis, 30 (48.4%) patients were alive including 16 still being treated with pegylated interferon. The median survival of patients with intermediate and high-risk prognostic Lille and dynamic International Prognostic Scoring System scores treated with pegylated interferon was increased in comparison to that of historical cohorts. In addition, overall survival was significantly correlated with the duration of pegylated interferon therapy (70 versus 30 months after 2 years of treatment, P<10-12). JAK2V617F allele burden was decreased by more than 50% in 58.8% of patients and two patients even achieved complete molecular response. Next-generation sequencing analyses performed in 49 patients showed that 28 (57.1%) of them carried non-driver mutations. The presence of at least one additional mutation was associated with a reduction of both overall and leukemia-free survival. These findings in a large series of patients with myelofibrosis suggest that pegylated interferon therapy may provide a survival benefit for patients with intermediate- or high-risk Lille and dynamic International Prognostic Scoring System scores. It also reduced the JAK2V617F allele burden in most patients. These results further support the use of pegylated interferon in selected patients with myelofibrosis.

Natural history of GATA2 deficiency in a survey of 79 French and Belgian patients.

Heterozygous germline GATA2 mutations strongly predispose to leukemia, immunodeficiency, and/or lymphoedema. We describe a series of 79 patients (53 families) diagnosed since 2011, made up of all patients in France and Belgium, with a follow up of 2249 patients/years. Median age at first clinical symptoms was 18.6 years (range, 0-61 years). Severe infectious diseases (mycobacteria, fungus, and human papilloma virus) and hematologic malignancies were the most common first manifestations. The probability of remaining symptom-free was 8% at 40 years old. Among the 53 probands, 24 had missense mutations including 4 recurrent alleles, 21 had nonsense or frameshift mutations, 4 had a whole-gene deletion, 2 had splice defects, and 2 patients had complex mutations. There were significantly more cases of leukemia in patients with missense mutations (n=14 of 34) than in patients with nonsense or frameshift mutations (n=2 of 28). We also identify new features of the disease: acute lymphoblastic leukemia, juvenile myelomonocytic leukemia, fatal progressive multifocal leukoencephalopathy related to the JC virus, and immune/inflammatory diseases. A revised International Prognostic Scoring System (IPSS) score allowed a distinction to be made between a stable disease and hematologic transformation. Chemotherapy is of limited efficacy, and has a high toxicity with severe infectious complications. As the mortality rate is high in our cohort (up to 35% at the age of 40), hematopoietic stem cell transplantation (HSCT) remains the best choice of treatment to avoid severe infectious and/or hematologic complications. The timing of HSCT remains difficult to determine, but the earlier it is performed, the better the outcome.

Associations between gender, disease features and symptom burden in patients with myeloproliferative neoplasms: an analysis by the MPN QOL International Working Group.

The myeloproliferative neoplasms, including polycythemia vera, essential thrombocythemia and myelofibrosis, are distinguished by their debilitating symptom profiles, life-threatening complications and profound impact on quality of life. The role gender plays in the symptomatology of myeloproliferative neoplasms remains under-investigated. In this study we evaluated how gender relates to patients' characteristics, disease complications and overall symptom expression. A total of 2,006 patients (polycythemia vera=711, essential thrombocythemia=830, myelofibrosis=460, unknown=5) were prospectively evaluated, with patients completing the Myeloproliferative Neoplasm-Symptom Assessment Form and Brief Fatigue Inventory Patient Reported Outcome tools. Information on the individual patients' characteristics, disease complications and laboratory data was collected. Consistent with known literature, most female patients were more likely to have essential thrombocythemia (48.6% versus 33.0%; P<0.001) and most male patients were more likely to have polycythemia vera (41.8% versus 30.3%; P<0.001). The rate of thrombocytopenia was higher among males than females (13.9% versus 8.2%; P<0.001) and males also had greater red-blood cell transfusion requirements (7.3% versus 4.9%; P=0.02) with shorter mean disease duration (6.4 versus 7.2 years, P=0.03). Despite there being no statistical differences in risk scores, receipt of most therapies or prior complications (hemorrhage, thrombosis), females had more severe and more frequent symptoms for most individual symptoms, along with overall total symptom score (22.8 versus 20.3; P<0.001). Females had particularly high scores for abdominal-related symptoms (abdominal pain/discomfort) and microvascular symptoms (headache, fatigue, insomnia, concentration difficulties, dizziness; all P<0.01). Despite complaining of more severe symptom burden, females had similar quality of life scores to those of males. The results of this study suggest that gender contributes to the heterogeneity of myeloproliferative neoplasms by influencing phenotypic profiles and symptom expression.

Efficacy and safety of pegylated-interferon α-2a in myelofibrosis: a study by the FIM and GEM French cooperative groups.

Myeloproliferative neoplasm-related myelofibrosis is associated with cytopenic or proliferative phases, splenomegaly and constitutional symptoms. Few effective treatments are available and small series suggested that interferon could be an option for myelofibrosis therapy. We performed a retrospective study of pegylated-interferon α-2a (Peg-IFNα-2a) therapy in myelofibrosis. Sixty-two patients treated with Peg-IFNα-2a at 17 French and Belgian centres were included. Responses were determined based on the criteria established by the International Working Group for Myelofibrosis Research and Treatment. Mean follow-up was 26 months. Sixteen of 25 anaemic patients (64%) (eight concomitantly receiving recombinant erythropoietin) achieved a complete response and transfusion-independence was obtained in 5/13 patients (38·5%). Constitutional symptoms resolved in 82% of patients. All five leucopenic patients normalized their leucocyte counts, whereas a normal platelet count was obtained in 5/8 thrombocytopenic patients. Splenomegaly was reduced in 46·5% of patients, and complete resolution of thrombocytosis and leucocytosis were observed in 82·8% and 68·8% of patients, respectively. Side effects (mostly haematological) were mainly of grade 1-2. The only factor independently associated with treatment failure was a spleen enlargement of more than 6 cm below the costal margin. In conclusion, Peg-IFNα-2a induced high response rates with acceptable toxicity in a large proportion of patients with primary and secondary myelofibrosis, especially in early phases.

Effective Anti-SARS-CoV-2 Immune Response in Patients With Clonal Mast Cell Disorders.

BACKGROUND: Mast cells are key players in innate immunity and the TH2 adaptive immune response. The latter counterbalances the TH1 response, which is critical for antiviral immunity. Clonal mast cell activation disorders (cMCADs, such as mastocytosis and clonal mast cell activation syndrome) are characterized by abnormal mast cell accumulation and/or activation. No data on the antiviral immune response in patients with MCADs have been published. OBJECTIVE: To study a comprehensive range of outcomes in patients with cMCAD with PCR- or serologically confirmed coronavirus disease 2019 and to characterize the specific anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immune response in this setting. METHODS: Clinical follow-up and outcome data were collected prospectively over a 12-month period by members of the French Centre de Référence des Mastocytoses rare disease network. Anti-SARS-CoV-2-specific T-cell activity was measured with an ELISA, and humoral responses were evaluated by assaying circulating levels of specific IgG, IgA, and neutralizing antibodies. RESULTS: Overall, 32 patients with cMCAD were evaluated. None required noninvasive or mechanical ventilation. Two patients were admitted to hospital for oxygen and steroid therapy. The SARS-CoV-2-specific immune response was characterized in 21 of the 32 patients. Most had high counts of circulating SARS-CoV-2-specific, IFN-γ-producing T cells and high titers of neutralizing antispike IgGs. The patients frequently showed spontaneous T-cell IFN-γ production in the absence of stimulation; this production was correlated with basal circulating tryptase levels (a marker of the mast cell burden). CONCLUSIONS: Patients with cMCADs might not be at risk of severe coronavirus disease 2019, perhaps due to their spontaneous production of IFN-γ.

Polymorphonuclear neutrophils from JAK2(V617F) positive MPD patients do not support hypercoagulability: A study with calibrated automated thrombography (CAT).

Essential thrombocythemia and polycythemia vera are myeloproliferative disorders (MPD) with an elevated thrombotic risk. Leukocytosis has recently emerged as a new risk factor and there is increasing evidence that polymorphonuclear neutrophils (PMN) are involved. Procoagulant activity (PCA) of PMN in MPD has not yet been investigated. PCA of PMN from 22 patients with JAK2(V617F) positive MPD and 26 healthy subjects was studied using calibrated automated thrombography: in vitro thrombin generation induced with 1 pM tissue factor in the presence of added procoagulant phospholipids. There were no differences between patients and controls regarding the ability of PMN to increase thrombin generation. More surprisingly, basal thrombin generation in acellular MPD-plasma was found decreased for as yet unknown reasons. The presence of an active protein C pathway or platelets might provide a better insight into the coagulation phenotype in MPD.

Genomic analysis of primary and secondary myelofibrosis redefines the prognostic impact of ASXL1 mutations: a FIM study.

We aimed to study the prognostic impact of the mutational landscape in primary and secondary myelofibrosis. The study included 479 patients with myelofibrosis recruited from 24 French Intergroup of Myeloproliferative Neoplasms (FIM) centers. The molecular landscape was studied by high-throughput sequencing of 77 genes. A Bayesian network allowed the identification of genomic groups whose prognostic impact was studied in a multistate model considering transitions from the 3 conditions: myelofibrosis, acute leukemia, and death. Results were validated using an independent, previously published cohort (n = 276). Four genomic groups were identified: patients with TP53 mutation; patients with ≥1 mutation in EZH2, CBL, U2AF1, SRSF2, IDH1, IDH2, NRAS, or KRAS (high-risk group); patients with ASXL1-only mutation (ie, no associated mutation in TP53 or high-risk genes); and other patients. A multistate model found that both TP53 and high-risk groups were associated with leukemic transformation (hazard ratios [HRs] [95% confidence interval], 8.68 [3.32-22.73] and 3.24 [1.58-6.64], respectively) and death from myelofibrosis (HRs, 3.03 [1.66-5.56] and 1.77 [1.18-2.67], respectively). ASXL1-only mutations had no prognostic value that was confirmed in the validation cohort. However, ASXL1 mutations conferred a worse prognosis when associated with a mutation in TP53 or high-risk genes. This study provides a new definition of adverse mutations in myelofibrosis with the addition of TP53, CBL, NRAS, KRAS, and U2AF1 to previously described genes. Furthermore, our results argue that ASXL1 mutations alone cannot be considered detrimental.

Persistence of lymphocyte function perturbations after granulocyte-colony-stimulating factor mobilization and cytapheresis in normal peripheral blood stem cell donors.

BACKGROUND: The short-term effects of granulocyte-colony-stimulating factor (G-CSF) have been extensively studied, but recent reports of G-CSF-induced genetic perturbations raised concerns regarding its long-term safety. In this respect, duration of G-CSF-induced perturbations has been less studied than short-term effects and needs to be evaluated. STUDY DESIGN AND METHODS: G-CSF mobilization-induced immunologic alterations were prospectively analyzed in a cohort of 24 healthy donors. Blood samples were taken before G-CSF administration; at the time of administration; and at 1, 3, 6, and 12 months and analyzed for blood cell counts and in vitro cytokines (interleukin [IL]-2, -8, and -10) and immunoglobulin production, quantified in the culture supernatant of peripheral blood mononuclear cells (PBMNCs) after, respectively, phytohemagglutinin and pokeweed mitogen stimulation. RESULTS: Platelet, granulocyte, monocyte, B, and dendritic blood cell counts as well as the IL-2, -8, and -10 secretion by PBMNCs, perturbed at the time of G-CSF mobilization, returned to baseline values at 1 month, with T-cell and natural killer cell counts recovering at 3 months. In vitro immunoglobulin production was increased up to 6 months after mobilization. CONCLUSION: Although assessment of the potential long-term risk of G-CSF administration will require prolonged observation of larger cohorts, our data show that the duration of immunologic perturbations may be more persistent than previously anticipated, especially for B-cell functional alterations. Most perturbations remain, however, transient with a return to baseline values within 1 year.