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Thymic regulatory T cells (tTreg) are critical in the maintenance of normal T cell immunity and tolerance. The role of TCR in tTreg selection remains incompletely understood. In this study, we assessed TCRα and TCRβ sequences of mouse tTreg and thymic conventional CD4+ T cells (Tconv) by high-throughput sequencing. We identified αβ TCR sequences that were unique to either tTreg or Tconv and found that these were distinct as recognized by machine learning algorithm and by preferentially used amino acid trimers in αβ CDR3 of tTreg. In addition, a proportion of αβ TCR sequences expressed by tTreg were also found in Tconv, and machine learning classified the great majority of these shared αβ TCR sequences as characteristic of Tconv and not tTreg. These findings identify two populations of tTreg, one in which the regulatory T cell fate is associated with unique properties of the TCR and another with TCR properties characteristic of Tconv for which tTreg fate is determined by factors beyond TCR sequence.

A competent T-cell receptor (TCR) repertoire contains TCRs recognizing both novel and experienced antigens. It is widely believed that the human TCR repertoire declines with age, but its precise change in size and clonal distribution with age has not been fully determined. Here, we investigated how the size and content of TCR repertoire changes with age by analyzing the TCR repertoire of human CD4+ and CD8+ T cells and their naïve and memory subsets from 30 healthy adults aged from 25 to 85 at first visit and an average of 9-year follow-up as second visit by RNAseq. First, we calculated abTCR repertoire changes with age and found a profound reduction of the TCRa and TCRb richness in naïve CD8+ T cells and an increase of clonal expansion especially in memory CD8 T cells compared to CD4+ T cells. We also study the degree of overlap of TCRa/b repertoire between naïve and memory T cells in each subject at the same visit and found little overlap of TCRa/b unique sequences between naïve and memory CD4 T cells and ~40% of the total TCRs in CD8 T cells. Moreover, we showed elevated overlap of TCR sequences between two visits in both CD4 and CD8 T cells with memory CD8 T cells as the highest. Finally, we determined the degree of TCR clonotypes shares among different subjects via the analysis of the sharing of TCR sequences in the 30 healthy adults. As results, we observed increased sharing of identical TCR between CD4 and CD8 T cells suggesting that the public clonotypes may share with the common pathogens shared in the population, particularly in the old population. Our findings showed more profound reduction in the CD8+TCR repertoire with age compared to CD4+ TCR repertoire. All together provide evidence of ab TCR sequence-based age-associated changes of T cells and their subsets.

Aging of immune system is characterized by progressive decline of physiological and cellular function of T cells, leading to a reduced immune function in the old. Recent studies of naïve T cells from young and old mice have identified age-related altered gene expressions, but the mechanisms underlying age associated changes of naïve T cells remain poorly understood. Here, we compared chromatin accessibility and the transcriptome in mature thymocytes and in naïve T cells of spleen between young (6–8 weeks) and old (95–114 weeks) C57BL/6 mice, using Assay for Transposase Accessible Chromatin with high-throughput sequencing (ATAC-seq) and Agilent microarray methods, respectively. We identified age-related changes of chromatin accessibility that are correlated with the gene expression changes, providing a chromatin basis of age-related changes in gene expression. Interestingly, some age-related changes of CD4 and CD8 T cells in thymus did not retain in the spleen, and others appeared later only in the spleen, suggesting different tissue environment may contribute to the age-related changes of T cells. To directly address environmental effects, we currently examine changes of naïve T cells from old mouse before and after hosted in young mouse for 21 days in chromatin accessibility, transcriptomes, and protein expression. Collectively, these approaches will allow us to dissect the time and environmental influences in naïve T cell function in old mice. Our findings will have important implications both for better understanding the mechanisms underlying these age-related changes as well as opening potential new targets to mitigate the age-related reduced T cell functions.

Mechanims of peripheral tolerance include molecular controls and the presence of regulatory lymphocytes. Regulatory T lymphocytes (Tregs) correspond to different sub-populations of T cells that control immune responses due to the production of cytokines, such as IL-10 and with direct cell-to-cell contacts. Tregs targets are antigen presenting cells, such as dendritic cells, effector CD4(+) and CD8(+) lymphocytes but also effector antibody-producing B lymphocytes. Regulatory B lymphocytes (Bregs) have been more recently described and likely represent different sub-populations of B cells that control the development of autoimmune and inflammatory diseases due to the production of IL-10 and using intercellular contacts. Bregs targets encompass all the cells involved in the immune responses which are thus under a dual control by regulatory lymphocytes. Development and efficient activity of Tregs appear dependent of Bregs for a better regulation of autoimmune reactions, of anti-infectious reactions, but also of anti-tumor reactions.

Background Follicular helper T (T FH ) cells support terminal B-cell differentiation. Human regulatory B (Breg) cells modulate cellular responses, but their control of T FH cell–dependent humoral immune responses is unknown. Objective We sought to assess the role of Breg cells on T FH cell development and function. Methods Human T cells were polyclonally stimulated in the presence of IL-12 and IL-21 to generate T FH cells. They were cocultured with B cells to induce their terminal differentiation. Breg cells were included in these cultures, and their effects were evaluated by using flow cytometry and ELISA. Results B-cell lymphoma 6, IL-21, inducible costimulator, CXCR5, and programmed cell death protein 1 (PD-1) expressions increased on stimulated human T cells, characterizing T FH cell maturation. In cocultures they differentiated B cells into CD138 + plasma and IgD − CD27 + memory cells and triggered immunoglobulin secretions. Breg cells obtained by Toll-like receptor 9 and CD40 activation of B cells prevented T FH cell development. Added to T FH cell and B-cell cocultures, they inhibited B-cell differentiation, impeded immunoglobulin secretions, and expanded Foxp3 + CXCR5 + PD-1 + follicular regulatory T cells. Breg cells modulated IL-21 receptor expressions on T FH cells and B cells, and their suppressive activities involved CD40, CD80, CD86, and intercellular adhesion molecule interactions and required production of IL-10 and TGF-β. Conclusion Human Breg cells control T FH cell maturation, expand follicular regulatory T cells, and inhibit the T FH cell–mediated antibody secretion. These novel observations demonstrate a role for the Breg cell in germinal center reactions and suggest that deficient activities might impair the T FH cell–dependent control of humoral immunity and might lead to the development of aberrant autoimmune responses.

Anti-Saccharomyces cerevisiae antibodies (ASCA) had been known to be specific for Crohn's disease, but they had also been found in many other autoimmune diseases.The aim of this study was to evaluate the prevalence of ASCA in patients with autoimmune thyroid disease (AITD).One hundred and ninety-seven patients with AITD and 160 healthy controls were included in the study. One hundred and nineteen patients had Graves' disease (GD) and 78 patients had Hashimoto's thyroiditis (HT). ASCA IgG and IgA were determined by ELISA.ASCA IgG were significantly more frequent in patients with GD than in control group (11.8% vs. 3.1%, p = 0.002). In HT, the frequency of ASCA IgG was similar to that of the control group (3.8% and 3.1% respectively). The frequency of ASCA IgA was similar in GD (0.8%), HT (2.6%), and the control group (3.1%). In all GD patients, the frequency of ASCA IgG was significantly higher than that of ASCA IgA (11.8% vs. 0.8%, p = 0.001). These results were also true even in male and female groups (10.4% vs. 1.3%, p = 0.01 and 14.3% vs. 0%, p = 0.01, respectively). ASCA IgG levels were significantly higher in GD patients (6.7 ± 11.1 vs. 2.2 ± 2.8, p = 3 × 10(-6)) and in HT patients (4.2 ± 4.7 vs. 2.2 ± 2.8, p = 0.0002) than those in the control group. ASCA IgA levels were comparable among patients with GD, HT, and the control group. In GD patients, the mean titer of ASCA IgG was significantly higher than that of ASCA IgA (6.7 ± 11.1 vs. 3.6 ± 4.2, p = 0.005).Patients with GD had a higher frequency of ASCA IgG than controls.

Onset of the disease above the age of 65 years is unusual. This study was undertaken to determine retrospectively the clinical and laboratory features in SLE patients aged over 65 years. It is a retrospective study about 18 elderly patients with SLE out of 342 diagnosed between 1994 and 2009 in the center of Tunisia. All patients had at least 4 of 11 revised ACR criteria of SLE. The frequency of SLE in the elderly was 5.3%. The median age was 70 years (range 66 and 78 years). The sex ratio F/M was 5. The most frequent clinical signs were anemia (83.3%), arthralgia (55.5%), arthritis (38.9%), and malar rash (33.3%). The proteinuria and the neuropsychiatric troubles were present in 27.8% of cases. The pericarditis was present in 16.7% of cases. Antibodies to double stranded DNA (anti-dsDNA) were detected in 66.7%, anti-nucleosome in 50%, anti-SSA and anti-RNP in 27.8%, anti-Sm in 22%, and anti-SSB in 11%. Elderly patients with SLE exhibit distinct clinical and biological manifestations from the classic form. Thus, greater attention should be given for this particular subgroup of SLE patients to avoid delays in diagnosis or misdiagnosis.

Aging of immune system is characterized by progressive decline of physiological and cellular function of T cells. Recent studies of naïve T cells from young and old mice have identified age-related altered gene expressions but the mechanisms underlying age associated changes of naïve T cells remain poorly understood. Here we compared the transcriptome and chromatin accessibility in mature CD4 and CD8 thymocytes and in naïve CD4 and CD8 T cells of spleen between young (6–8 weeks) and old (95–110 weeks) C57Bl/6 mice. We used Agilent microarray method and identified the age-related altering gene expressions 1) only in mature CD4 and CD8 T cell from thymus, 2) shared by both thymus and spleen naïve T cells, and 3) only in naïve T cells from spleen. The shared changes include increased chemokine and chemokine receptor expressions and decreased cell cycle regulator expression. We further analyzed the chromatin basis of altered gene expression using ATAC seq between young and old mice. We have identified age-related changes of chromatin accessibility in T cells from thymus and spleen, and some correlated changes between gene expression and chromatin accessibility. Overall, we observed more age-related alterations of gene expression and chromatin accessibility in thymus than in spleen, suggesting some age-related changes of T cells in thymus did not retain in periphery. Together, our findings have identified tissue specific altered gene expressions and chromatin status in T cells during aging and further study of these altered genes will shed new insights into the mechanisms underlying these age-related changes. This research was supported in part by the Intramural Research Program of the NIH, National Institute on Aging.

Follicular helper T (TWe sought to assess the role of Breg cells on THuman T cells were polyclonally stimulated in the presence of IL-12 and IL-21 to generate TB-cell lymphoma 6, IL-21, inducible costimulator, CXCR5, and programmed cell death protein 1 (PD-1) expressions increased on stimulated human T cells, characterizing THuman Breg cells control T

International audience; BACKGROUND AND OBJECTIVES: Follicular helper T (Tfh) cells are instrumental in the development of humoral responses. They support the terminal differentiation of B cells into memory and antibody-producing cells within germinal centers. Regulatory B (Breg) cells can modulate inflammatory reactions through the control of dendritic cell maturation and function, and through the control of T cell proliferation and Th1 polarization. Our aimed was to evaluate the control of humoral responses by Breg cells. MATERIALS AND METHODS: We developed in vitro models of human Tfh cell polarisation and function. They were obtained by stimulation of purified T cells with anti-CD3 and anti-CD28 Abs in the presence of IL-12 and IL-21. Expression of Bcl-6, IL-21, ICOS, CXCR5 and PD-1, all characteristics of Tfh cells were determined by flow cytometry. Tfh functions were studied by co-cultures with non-stimulated purified B cells. Their differentiation into memory and plasma cells was appraised by flow cytometry and by ELISA to measure the production of immunolgobulins. Breg cells were obtained by stimulation of purified B cells with CpG-ODN on CD40L-transfected fibroblasts. Their effect on Tfh cell maturation and function were studied in co-culture experiments. RESULTS: in vitro Tfh cells were obtained. Thus, Bcl-6 was up-regulated, IL-21 induced and ICOS, CXCR5 and PD-1 expression increased after stimulation. Furthermore, differentiated Tfh cells fostered the maturation of IgD-CD27 + memory B cells and CD138 + plasma cells, and triggered the secretion of IgM, IgG and IgA. Added to the T cells, Breg cells restrained the expression of Tfh markers. In the co-cultures of Tfh with B cells, Breg cells inhibited the induction of IgD-CD27 + and CD138 + B cells. They also impeded the secretion of immunoglobulins. Using blocking antibodies, suppressive activities of Bregs were found to be dependent on IL-10 and TGFbeta and based on direct contact with Tfh cells involving CD40, CD80, CD86 and CD54 molecules. CONCLUSIONS: Human Breg cells can modulate the development of humoral responses through the control of Tfh cell polarization and of Tfh-dependent terminal differentiation of B cells. Whether these properties are impaired and responsible for abnormal humoral responses in autoimmune diseases needs now to be established.

International audience; Mechanims of peripheral tolerance include molecular controls and the presence of regulatory lymphocytes. Regulatory T lymphocytes (Tregs) correspond to different sub-populations of T cells that control immune responses due to the production of cytokines, such as IL-10 and with direct cell-to-cell contacts. Tregs targets are antigen presenting cells, such as dendritic cells, effector CD4(+) and CD8(+) lymphocytes but also effector antibody-producing B lymphocytes. Regulatory B lymphocytes (Bregs) have been more recently described and likely represent different sub-populations of B cells that control the development of autoimmune and inflammatory diseases due to the production of IL-10 and using intercellular contacts. Bregs targets encompass all the cells involved in the immune responses which are thus under a dual control by regulatory lymphocytes. Development and efficient activity of Tregs appear dependent of Bregs for a better regulation of autoimmune reactions, of anti-infectious reactions, but also of anti-tumor reactions.

Backgroundand objectives Mature dendritic cells (DCs) are stimulators of T cell immune response, whereas immature DCs support T cell tolerance. Murine B cells can inhibit the production of interleukin 12 (IL-12) by DCs, and thereby, hinder the inflammatory response. Notwithstanding the importance of this modulation, only a few studies are available in humans. The current study was aimed at determining the regulatory capacity of human B cells on DC maturation and function, and at evaluating their efficiency in autoimmune disorder. Materials and methods Peripheral blood B cells from six healthy donors (HDs) and six systemic lupus erythematosus (SLE) patients were stimulated by CD40 and TLR9. Peripheral blood monocytes were differentiated into immature DCs and then into mature DCs. Activated B cells were co-cultured with DCs and HLA-DR, CD80, CD86 expressions and IL-12 production by the DCs evaluated by flow cytometry. Variations of expressions were used to determine the B cell regulatory effects on maturation. CFSE-labelled T cells were cultured with mature DCs and the DC-dependent proliferative response evaluated in the presence of activated B cells to determine their influence on the function of DCs. Results Activated B cells restrained the development of monocytes into immature DCs and their differentiation into mature DCs. They decreased the density of HLA-DR from mature DCs, the expression of CD80 and CD86 co-activation molecules, the production of IL-12p70 required for antigen presentation and Th1 differentiation. They also inhibited the DC-induced T cell proliferation. These modulations were mediated by CD19+IgDlowCD38+CD24lowCD27- B cells and needed CD62L interaction for the control of CD80 and CD86 expression, and a soluble factor for the control of IL-12 production. Finally, mature DCs from SLE patients displayed insensitivity to the regulation of IL-12 by both normal and SLE B cells. Conclusions Human B cells can regulate DC maturation and function. However, they are inefficient in SLE due to refractory DCs. This may influence an improper balance between an effector inflammatory response triggered by mature DCs, and tolerance induction favoured by immature DCs, and thereby, may contribute to the pathogenesis of SLE.

To evaluate, retrospectively, the frequency of antithyroid antibodies (ATA) in patients with type 1 diabetes (T1D).Antithyroperoxidase antibodies (TPO-Ab), antithyroglobulin antibodies (TG-Ab), and antithyroid-stimulating hormone receptor antibodies (TSHR-Ab) were determined by enzyme-linked immunosorbent assay. Sera of 312 patients (166 children and 146 adults) with T1D were analyzed. Sera of 276 healthy subjects (87 children and 189 blood donors) served as controls.Out of 312 patients with T1D, 44 (14%) had ATA (TPO-Ab or TG-Ab or TSHR-Ab). The frequency of ATA in patients with T1D was significantly higher than in the control group (14% vs. 2.8%; p10(-5)). ATA were significantly more frequent in adult patients with T1D than in the blood donor group (20% vs. 1.6%; p10(-8)). The frequency of ATA in adult patients was significantly higher than in pediatric patients (20% vs. 9%; p=0.006). The frequency of TPO-Ab and TG-Ab was significantly higher in patients with T1D than in the control group (13.5% vs. 2%; p10(-8) and 7% vs. 2.2%, p=0.008), respectively. Out of 312 patients with T1D, only one had TSHR-Ab. The simultaneous presence of three autoantibodies was found in one patient with T1D.ATA were frequent in patients with T1D. Serological screening of autoimmune thyroid disease is suggested in patients with T1D.

Anti-Saccharomyces cerevisiae antibodies (ASCA) had been known to be specific for Crohn's disease but it has been found in many other autoimmune diseases like systemic lupus erythematosus (SLE). Furthermore, cross-reactive epitopes on β2-glycoprotein I (β2GPI) and Saccharomyces cerevisiae were found in SLE patients. The aims of this study were to evaluate the frequency of ASCA in patients with SLE and to compare it with that of anti-β2GPI antibodies (aβ2GPI). Sera of 116 patients with SLE were analyzed in this retrospective study. All patients fulfilled at least 4 criteria of the 1997 American College of Rheumatology updated criteria for the classification of SLE. Sera of 160 blood donors were included as normal controls. ASCA IgA and IgG and aβ2GPI antibodies were determined by enzyme-linked immunosorbent assays. The frequency of ASCA (IgG and/or IgA) was significantly higher in SLE patients than in control group (31.9 vs. 3.7 %, p10(-6)). ASCA IgG and ASCA IgA were more frequent in SLE patients than in control group (29.3 vs. 3.1 %, p10(-6) and 12.1 vs. 0.6 %, p = 10(-4), respectively). The mean level of ASCA IgG was higher than that of ASCA IgA (9.5 vs. 6.4 U/ml) but the difference was not statistically significant. The frequencies of aβ2GPI (IgG and/or IgA) and aβ2GPI IgA were significantly higher than those of ASCA (IgG and/or IgA) and ASCA IgA (54.3 vs. 31.9 %, p = 5 × 10(-4) and 50.9 vs. 12.1 %, p10(-6), respectively). Increased ASCA IgG was observed in patients with SLE, suggesting a role of environmental stimuli in its pathogenesis.

Mature dendritic cells (DCs) are stimulators of T-cell immune response, whereas immature DCs support T-cell tolerance. Murine B cells can inhibit the production of IL-12 by DCs and thereby hinder the inflammatory response. Notwithstanding the importance of this modulation, only a few studies are available in humans. Here, we have developed an in vitro model of cocultures to assess its significance. We establish that human activated B cells restrained the development of monocytes into immature DCs and their differentiation into mature DCs. In addition, they decreased the density of HLA-DR from mature DCs, the expression of CD80 and CD86 coactivation molecules, the production of IL-12p70 required for antigen presentation and Th1 differentiation, and inhibited the DC-induced T-cell proliferation. These modulations were mediated by CD19+IgDlowCD38+CD24lowCD27− B cells and needed direct cell-to-cell contacts that involved CD62L for the control of CD80 and CD86 expression and a soluble factor for the control of IL-12 production. Moreover, mature DCs from patients with systemic lupus erythematosus displayed insensitivity to the regulation of IL-12. Overall, it appears that human B cells can regulate DC maturation and function and that inefficient B-cell regulation may influence an improper balance between an effector inflammatory response and tolerance induction.

Anti-Saccharomyces cerevisiae antibodies (ASCA) have been described in many autoimmune diseases in which there is an increased intestinal permeability. Also in type 1 diabetes (T1D), there is an increased intestinal permeability. Since no data are available about ASCA in T1D, we evaluated, retrospectively, the frequency of ASCA in this disease. ASCA, IgG, and IgA, were determined by ELISA in sera of 224 T1D patients in which coeliac disease has been excluded and 157 healthy control group. The frequency of ASCA (IgG or IgA) was significantly higher in T1D patients than in the control group (24.5% vs. 2.5%, p < 10−7). The same observation was found in children and in adult patients when we compare them to healthy children and blood donors group respectively. Compared to children, adult patients with T1D showed significantly higher frequencies of ASCA of any isotype (38% vs. 13.7%, p < 10−4), both ASCA IgG and IgA (12% vs. 1.6%, p = 0.002), ASCA IgG (35% vs. 9.8%, p < 10−5) and ASCA IgA (15% vs. 5.6%, p = 0.001). The frequency of ASCA was statistically higher in females of all T1D than in males (30.8% vs.17.7%, p = 0.03), in girls than in boys (22% vs.6.2%, p = 0.017), and significantly higher in men than in boys (35.7% vs. 6.2%, p < 10−4). The frequency of ASCA IgG was significantly higher than that of ASCA IgA in all T1D patients (21% vs. 9.8%, p < 0.002), in all females (26.5% vs. 10.2%, p < 0.002), in women (37.9% vs. 12%, p < 0.001). The frequency of ASCA was significantly higher in all long-term T1D than in an inaugural T1D (29% vs. 14.5%, p = 0.019). The same observation was found in adults (45.8% vs. 17.8%, p = 0.01). In long-term T1D patients, ASCA were significantly more frequent in adults than children (45.8% vs. 14.5%, p < 10−4). The frequency of ASCA IgG was significantly higher in long-term T1D than in an inaugural T1D (25.2% vs. 11.6%, p = 0.03). Patients with T1D had a high frequency of ASCA.

4879 Background: In Waldenstrom9s Macroglobulinemia (WM), response rates to rituximab (RTX) range from 30% to 75%. RTX is also known to generate a transient IgM flare in some patients. Our study aimed to characterize this phenomenon using the newly Hevylite® assay developed by The Binding Site that specifically quantifies IgM-kappa(K) and IgM-lambda(L). Methods: Between 2007 and 2009, 33 WM patients received a 6-course fludarabine-based regimen, 32 as first and 1 as second line. Partial response (PR), defined as a reduction ≥50% but Results: Of the 33 tested, at a variation threshold ≥20% relative to baseline IgM levels, 3 subgroups were defined: 15 or 45.5%, the no-flare patients, showed an increase or a decrease vs 1 L ( p p p =0.22). We also analyzed the data without defining a critical threshold in monoclonal IgM level variations. Patients were, then, separated in 2 subgroups: 17 flare patients and 16 anti-flare patients. Monoclonal K light chain was overrepresented in the 2 subgroups, with 13 K vs 4 L in flare patients and 13 K vs 3 L in anti-flare patients; no statistically significant difference was found between them regarding monoclonal K and L light chains ( p =0.32). No association was seen with demographic and hematologic characteristics and RTX pharmacokinetics. Regarding FcgR IIIa-158 polymorphism, there was a statistically significant difference ( p =0.03) as 12 patients were of the FF subtype and 5 of the VF one in the flare subgroup while 4 were of the FF subtype, 11 of the VF one and 1 of the VV one in the anti-flare subgroup. At response evaluation 3 months after the fourth injection of RTX, all patients were screened for SPE and 22 for IF. When we compared the 17 patients of the flare subgroup to the 16 ones of the anti-flare subgroup, no patient vs 1 reached complete remission defined as disappearance of BMP on SPE and negativity of IF, 1 vs 6 advanced to very good partial response defined as a decrease ≥90% in BMP on SPE and positivity of IF and the remaining 16 vs 9 improved their partial response by a mean additional reduction of 20% (range: 0–30%) vs 18.75% (range: 0–50%) in BMP, but there was no statistically significant difference in this regard ( p =0.79). Conclusions: Using Hevylite® assay, monoclonal IgM up and down variations of at least 20% following RTX occurred in up to 54.5% of our patients and this raised to 100% when no threshold value was considered. Such assay provides a reliable and highly sensitive quantitative assessment, especially in patients whose monoclonal IgM was at low concentration. Patients of the flare subgroup were predominantly of the FF subtype of FcgR IIIa-158 polymorphism while patients of the anti-flare subgroup were predominantly of VF subtype, which was statistically significant. It is tempting to hypothesize a difference in RTX mechanism of action, with ADCC predominating in the anti-flare subgroup and CDC in the flare subgroup. It would be of interest to assess such an hypothesis on a larger cohort and to analyze its impact on response profile. Disclosures: Pietrantuono: The Binding Site: Employment.

e170 with CD 34+ counts < 15/ml required a second day of leukapheresis. Median CD 34+ cells collected on Day 5 were 2.01 x 10/kg (0.67-8.04). Median total CD34+ cells collected were 3.55 x 10/kg (1.1811.75). Median days to neutrophil and platelet engraftment were 10 days (9-16 days) and 12 days (7-36 days) respectively. Conclusion: Day 4 stem cell collection is feasible and potentially cost effective in a majority of myeloma patients. A CD 34+ count of

Abstract 4879 Background: In Waldenström's Macroglobulinemia (WM), response rates to rituximab (RTX) range from 30% to 75%. RTX is also known to generate a transient IgM flare in some patients. Our study aimed to characterize this phenomenon using the newly Hevylite® assay developed by The Binding Site that specifically quantifies IgM-kappa(K) and IgM-lambda(L). Methods: Between 2007 and 2009, 33 WM patients received a 6-course fludarabine-based regimen, 32 as first and 1 as second line. Partial response (PR), defined as a reduction ≥50% but Results: Of the 33 tested, at a variation threshold ≥20% relative to baseline IgM levels, 3 subgroups were defined: 15 or 45.5%, the no-flare patients, showed an increase or a decrease We also analyzed the data without defining a critical threshold in monoclonal IgM level variations. Patients were, then, separated in 2 subgroups: 17 flare patients and 16 anti-flare patients. Monoclonal K light chain was overrepresented in the 2 subgroups, with 13 K vs 4 L in flare patients and 13 K vs 3 L in anti-flare patients; no statistically significant difference was found between them regarding monoclonal K and L light chains (p=0.32). No association was seen with demographic and hematologic characteristics and RTX pharmacokinetics. Regarding FcgR IIIa-158 polymorphism, there was a statistically significant difference (p=0.03) as 12 patients were of the FF subtype and 5 of the VF one in the flare subgroup while 4 were of the FF subtype, 11 of the VF one and 1 of the VV one in the anti-flare subgroup. At response evaluation 3 months after the fourth injection of RTX, all patients were screened for SPE and 22 for IF. When we compared the 17 patients of the flare subgroup to the 16 ones of the anti-flare subgroup, no patient vs 1 reached complete remission defined as disappearance of BMP on SPE and negativity of IF, 1 vs 6 advanced to very good partial response defined as a decrease ≥90% in BMP on SPE and positivity of IF and the remaining 16 vs 9 improved their partial response by a mean additional reduction of 20% (range: 0–30%) vs 18.75% (range: 0–50%) in BMP, but there was no statistically significant difference in this regard (p=0.79). Conclusions: Using Hevylite® assay, monoclonal IgM up and down variations of at least 20% following RTX occurred in up to 54.5% of our patients and this raised to 100% when no threshold value was considered. Such assay provides a reliable and highly sensitive quantitative assessment, especially in patients whose monoclonal IgM was at low concentration. Patients of the flare subgroup were predominantly of the FF subtype of FcgR IIIa-158 polymorphism while patients of the anti-flare subgroup were predominantly of VF subtype, which was statistically significant. It is tempting to hypothesize a difference in RTX mechanism of action, with ADCC predominating in the anti-flare subgroup and CDC in the flare subgroup. It would be of interest to assess such an hypothesis on a larger cohort and to analyze its impact on response profile. Disclosures: Pietrantuono: The Binding Site: Employment.