Abstract: The immune defects occurring in chronic lymphocytic leukemia are responsible for the frequent occurrence of infections and autoimmune phenomena, and may be involved in the initiation and maintenance of the malignant clone. Here, we evaluated the quantitative defects of newly produced B and T lymphocytes. Methods The output of B and T lymphocytes from the production and maturation sites was analyzed in chronic lymphocytic leukemia patients and healthy controls by quantifying kappa-deleting recombination excision circles (KRECs) and T-cell receptor excision circles (TRECs) by a Real-Time PCR assay that simultaneously detects both targets. T-lymphocyte subsets were analyzed by six-color flow cytometric analysis. Data comparison was performed by two-sided Mann-Whitney test. Results KRECs level was reduced in untreated chronic lymphocytic leukemia patients studied at the very early stage of the disease, whereas the release of TRECs + cells was preserved. Furthermore, the observed increase of CD4 + lymphocytes could be ascribed to the accumulation of CD4 + cells with effector memory phenotype. Conclusions The decreased number of newly produced B lymphocytes in these patients is likely related to a homeostatic mechanism by which the immune system balances the abnormal B-cell expansion. This feature may precede the profound defect of humoral immunity characterizing the later stages of the disease.

Abstract: LAPTM5 c403t and HCLS1g496a are potentially novel contributors for the genetic predisposition to familial WM. LAPTM5 c403t and HCLS1g496a represent possible candidates for screening in familial WM.

Abstract: It has been proposed that patients with hematologic malignancy and autoimmune diseases receiving anti-CD20 monoclonal antibody (mAb) therapy are particularly at risk of severe Coronavirus disease (COVID-19) because the profound and long-lasting B-cell depletion induced by anti-CD20 mAb may impair virus clearance and may also contribute to reactivation of latent viruses, especially hepatitis B and JC viruses. As of July 20, 2020, the total number of COVID-19 cases reported by the Italian authorities reached 245,000. The north of the country was mostly hit, and Milan and Brescia were among the Italian provinces that registered the highest number of COVID-19 cases. Consistent with this, a high number of COVID-19 patients affected with multiple types of hematological disorders (n. 137) and with multiple sclerosis (MS, n. 114) were referred to ASST Spedali Civili di Brescia. Antibodies to SARS-CoV-2 were analyzed in 70 patients with hematological disease, and in few patients with MS. Among these, 10 patients (7 with hematologic disease and 3 with MS) had received treatment with rituximab or ocrelizumab, two anti-CD20 mAbs, within 3 months prior to COVID-19 onset. Clinical indication to CD20-depleting treatment for patients with hematological disorders included Diffuse Large B Cell Lymphoma (DLBCL) or Follicular Non Hodgkin Lymphoma (NHL). Anti-spike protein (anti-S) and anti-nucleocapsid (anti-N) antibodies to SARS-CoV-2 were analyzed during the acute phase of infection and up to 3 months since the onset of symptoms by quantitative measurements of plasma or serum antibodies with luciferase immune precipitation assay systems (LIPS). With this technique, production of anti-S and anti-N antibodies has been demonstrated between day 8 and day 14 after onset of symptoms in immunocompetent individuals, whereas specific antibody production was delayed by few days in immunocompromised patients (Burbelo PD et al, medRxiv. 2020 Apr 24:2020.04.20.20071423). All 10 patients remained seronegative to SARS-CoV-2 for the first 20 days since onset of symptoms. One patient with DLBCL secondary to Follicular NHL had detectable anti-S and anti-N antibodies at day +25, and one patient with MS developed anti-N antibodies by day +23. Two patients, one with DLBCL secondary to Follicular NHL and one with Follicular NHL were still seronegative for both anti-S and anti-N antibodies at 133 and 74 days since onset of symptoms. Two MS patients were seronegative at the last examination, and one other MS patient was anti-S seronegative at day +74. Three of the 10 patients have died; all three were SARS-CoV-2 RT-qPCR+ and seronegative at the time of death. While it has been reported that SARS-CoV-2 is cleared without significant problems by the majority of people with MS or other autoimmune diseases on immunotherapy, these data indicate that treatment with anti-CD20 mAb may significantly alter humoral responses to the virus. Until a vaccine to SARS-CoV-2 is available, the risk-benefit ratio of anti-CD20 mAb therapy in areas with high rates of SARS-CoV-2 infection should be carefully weighed. Moreover, for patients with B-cell malignancies or autoimmune diseases, transient discontinuation of this therapy, or use of alternative therapeutic approaches, should be considered once an efficacious vaccine becomes available. This study was performed according to protocol NP-4000 (Comitato Etico Provinciale), and supported by Regione Lombardia and by the Division of Intramural Research, NIAID. Figure 1 Disclosures Imberti: Biogen: Honoraria; Genzyme-Sanofi: Honoraria; Meck-Serono: Honoraria; Novartis: Honoraria; Biogen: Other: Advisory board; FISM (Fondazione Italiana Sclerosi Multipla): Research Funding; Regione Lombardia: Research Funding. Capra:Biogen: Other: travel grants, Speakers Bureau; Roche: Other: travel grants, Speakers Bureau; Celgene: Other: travel grants, Speakers Bureau; Merck: Other: travel grants, Speakers Bureau; Novartis: Other: travel grants, Speakers Bureau. Rossi:Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Pfizer: Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; Abbvie: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Advisory board; Daiichi Sankyo: Consultancy, Honoraria; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. Notarangelo:NIAID, NIH: Research Funding. Cohen:NIAID, NIH: Research Funding.

Abstract: Introduction. Covid-19 patients (pts) with hematologic malignancies have a severe prognosis with mortality rates around 40%, particularly when on active treatment (Cattaneo et al, Cancer, in press). However, the long-term prognosis and persistence of specific immune responses among those who survive acute infection are unclear. Aim: Pts with hematological diseases were followed longitudinally after the acute phase of COVID-19 according to protocol NP4156 approved by the local EC. Clinical outcome and specific antibody responses to SARS-CoV-2 were monitored during convalescence, and correlated to the diagnosis and treatment of the underlying hematological disease. Pts and Methods. Pts affected by multiple myeloma (MM), follicular (FL) and diffuse large B-cell (DLC) lymphoma (NHL), chronic lymphoproliferative disorders (CLD), myelodysplastic/chronic myeloproliferative syndromes (MDS/MPN) and surviving the acute phase of virologic-proven COVID-19 were eligible. Immune response parameters were evaluated at +1, +3, +6, +9 and +12 months after nasal swab negativization. Antibodies (Ab) to different conformations of COVID-19 virus proteins, nucleocapsid (N) and spike (S), were measured using a highly sensitive luciferase-immunoprecipitation system (LIPS) assay. Results. Of 51 eligible pts, 41 were tested for SARS-CoV-2 Ab at first timepoint (+1m) (6 pts too early, 2 refusal, 2 lost to follow-up). For 9 of them, Ab levels at +3m were also available. Ab levels of 14 controls without hematologic disorders (Ctrls) also surviving COVID-19 were evaluable at +1m and in 9 of them at +3 months as well. Diagnoses included FL (9) and DLC (6) NHL, CLD (7), MM (10), MDS/MPS (9). The status of hematological disease at the time of COVID-19 diagnosis was as follows: diagnosis (n=4; 10%), complete or partial remission (n=16; 39%), relapse/refractory (n=6; 15%; stable (n=15; 36%). Twenty-one pts (51%) were on active treatment, including 6 on chemoimmunotherapy; 7 pts had received chemoimmunotherapy previously. Median time from SARS-CoV-2 detection to swab negativity was 30d (range 8-63), and was not influenced by sex, age, hematologic diagnosis, disease status, nor treatment received. Two pts, both affected by DLC secondary to FL, remained swab-positive at day 119+ and 123+. At +1m, both N- and S- seropositivity rate was slightly lower in pts [N+ in 30/41 (73%); S+ in 27/41 (66%)] vs 13/14 for both N+ and S+ in Ctrls (93%) (P=0.16 and 0.08, respectively). Discrepancies between N and S seropositivity were observed in 7 (17%) pts, all with lymphoid disorders. Ab levels were similar in hematologic pts and in Ctrls (N+ 894,707 vs 870,541 LU and S+ 907,591 LU vs 724,120 LU, respectively, P=NS) (Fig.1a). Both seroconversion rates and Ab levels were not influenced by age, sex, status of hematologic disease, ongoing treatment, time to swab negativity, severity of pneumonia and steroid treatment during acute COVID-19. However, a diagnosis of NHL negatively impacted on seroconversion for both N and S. In 15 pts with NHL compared to 26 pts with other hematologic cancers, the N-seropositivity rate was 47% vs 92%, and the S-seropositivity rate was 40% vs 85%y (P=0.002 and 0.0053, respectively). N and S Ab levels were also lower than in other hematologic diseases (515,281 LU vs 1105409 LU, P=.002 and 474,309 LU vs 1,148,303 LU, P=.005 respectively) (Fig.1b). Rituximab (RTX) had been used in 13 of 15 NHL (87%), and treatment was ongoing in 6/13. While N-seroconversion and Ab levels were not influenced, no pts on ongoing RTX had S-seroconversion vs 5/7 pts with past RTX use (P=0.021) and mean antibody levels were 17622 LU vs 668548 LU, respectively (P=0.008). At +3m, no significant variations of both anti-N and anti-S antibody levels had occurred compared to timepoint +1m. Seroconversion status was maintained by 9/9 Ctrls and by 8/8 pts; the only pt with Ab levels below the cut-off at +1m did not show seroconversion at+3m. Conclusions: Overall, hematologic pts surviving COVID-19 have N- and S- antibodies levels and seroconversion rates similar to controls without hematologic disorders, although time to swab negativity seems more similar to critically ill pts than in the general population. A diagnosis of NHL negatively impacts on seroconversion and Ab levels, and ongoing RTX seems to have a negative role specifically on anti-S Ab production. Ab response persists at 3 months; the study is ongoing and further data will be available at time of meeting. Disclosures Tucci: Amgen: Consultancy. Rossi:Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; Amgen: Honoraria; Novartis: Other: Advisory board; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria. Imberti:Biogen: Honoraria; Genzyme-Sanofi: Honoraria; Meck-Serono: Honoraria; Novartis: Honoraria; Biogen: Other: Advisory board; FISM (Fondazione Italiana Sclerosi Multipla): Research Funding; Regione Lombardia: Research Funding. Notarangelo:NIAID, NIH: Research Funding. Cohen:NIAID, NIH: Research Funding.

Abstract: Background. p53 is a well defined tumor suppressor involved in the modulation of cell proliferation, cell cycle progression and programmed cell death. BLIMP-1 plays a crucial role in modulating B-cell differentiation towards Ig-secreting plasma cells, and it acts as a tumor suppressor, as documented in both diffuse large B-cell lymphoma and Burkitt lymphoma. Whether B-cell specific loss of both p53 and BLIMP-1 may favor a B-cell lymphoma phenotype remains unanswered. We therefore aimed to generate in vivo dual p53/BLIMP-1-floxed conditional inactivation in B-cells, and to define the functional relevance of both p53 and BLIMP-1 n B-cell lymphomagenesis in vivo Methods.Cre recombinase under the control of CD19 promoter (C57BL/6 CD19Cre/Cre) mice were crossed with either C57BL/6 BLIMPflox/flox or C57BL/6 p53flox/flox mice to achieve deletion of BLIMP or p53, respectively, in B cells. Secondly, CD19Cre/Cre BLIMPflox/flox mice were crossed with CD19Cre/Cre p53flox/flox to achieve concomitant deletion of both BLIMP and p53 in B cells (CD19Cre/Cre BLIMPflox/flox p53flox/flox), referred as CD19/Bl-/p53- mice. Transgenic experimental mice (CD19/Bl-/p53-) where characterized for B cell infiltration using immunohistochemistry, flow cytometry; clonotypic immunoglobulin heavy-chain rearrangement was assessed by Southern Blotting. Whole exome sequencing was performed using DNA isolated from B220+ selected cells obtained from pathological lymph nodes of CD19/Bl-/p53- mice and from matched tail-derived tissues, used as germline (Illumina HiSeq 2500 platform; Agilent SureSelectXT). MTT assay was used to BTK-inhibitor-dependent cytotoxicity using CD19/Bl-/p53-derived B220 cells. Results.We generated dual p53/BLIMP-1-floxed conditional inactivation in B-cells, using mice expressing Cre recombinase under the control of CD19 promoter. 100% of the CD19/Bl-/p53- mice presented with diffuse lymphadenomegalies, and splenomegaly, hepatomegaly (90.3% and 77.4%, respectively). Other clinical manifestations included presence of ascites and hind lymb paralysis (12.9% and 19.3%, respectively). The CD19/Bl-/p53- showed worse survival compared to Bl-/p53- mice non-expressing the CD19/Cre recombinase, CD19/p53-, or CD19/Bl- (363, 469.5, 460.5, and 770 days, respectively). H.E. staining of CD19/Bl-/p53--derived lymph nodes, defined a nodal architecture with a monomorphic population of large sized atypical lymphoid cells with finely clumped and dispersed chromatin, and multiple basophilic medium sized, paracentrally situated nucleoli. A "starry sky" pattern was also observed. Overall, these features are compatible with a high-grade lymphomas. IHC analysis confirmed a marked positivity for B220 staining (TdT, Bcl6, CD138 and CD4, CD8 negative). Tumors were confirmed to be B220+/IgM+, with either Igk- or Ig-lambda-restriction as demonstrated by flow cytometry; and either mono- or bi-clonal, as demonstrated by Southern blotting, thus further confirming the clonal transformation induced by dual BLIMP/p53 deletion in B cells. Whole exome sequencing was performed from B220+ selected cells obtained from pathological lymph nodes of CD19/Bl-/p53- mice and identified 143 SNVs. Among them, non-synonymous somatic mutations were mapped on genes involved in the regulation of focal adhesion, PDGF signaling, p53-downstream pathway, and lipoprotein metabolism. B220+ cells selected from CD19/Bl-/p53--derived lymph nodes were implanted subcutaneously into recipient SCID/Bg mice (n: 10), and presented with 100% engraftment, with a monomorphic lymphoid infiltration of B220+ and IgM+ cells. B220 positive cells were selected from the s.q. tumor and intravenous injected into recipient SCID/Bg (n: 10) and BL/6 mice (n: 10). Engraftment was demonstrated in all the mice, where hepatomegaly, splenomegaly and hind lymb paralysis were observed. Infiltration of B220+ cells was documented within bone marrow, liver and spleen. We next investigated the anti-tumor activity of BTK-inhibitor, and found that B220+ cells selected from lymph nodes harvested from CD19/Bl-/p53-mice were sensitive to ibrutinib treatment. Conclusion. These studies demonstrate that the specific dual inactivation of p53 and BLIMP in B-cells promotes oncogenic transformation, resulting in aggressive B-cell lymphoma development. Disclosures Ghobrial: Celgene: Other: Advisory Board; BMS: Other: Advisory Board; Amgen: Other: Advisory Board; Takeda: Other: Advisory Board; Janssen: Other: Advisory Board. Roccaro:Takeda Pharmaceutical Company Limited: Honoraria.

Abstract: Abstract 2353 Poster Board II-330 Background Chronic lymphocytic leukemia (CLL) results in accumulation of mature, malignant, monoclonal B cells in blood, lymph nodes, spleen, liver, and bone marrow. Patients with CLL have fundamental defects in both humoral and cell-mediated immunity that significantly impact on its clinical course. It is still not known if these immune abnormalities include a decrease of new B- and T-cell mobilization from their production sites. During early lymphocyte development and differentiation, occurring in bone marrow and in thymus, B- and T-cells undergo rearrangements of B-cell and T-cell receptor genes whereby specific chromosomal sequences are excised to produce episomal DNA products identified respectively as T-cell receptor excisional circles (TRECs) and Kappa-deleting recombination excision circles (KRECs). Being stable circular fragments of DNA, TRECs and KRECs do not replicate during the mitotic process required for cell proliferation and, therefore, they are diluted out by cell divisions and are lost when the cells die. Since T-cells leaving the thymus are 70% TRECs+ and KRECs are present randomly in about 50% of neo-produced normal B-cells, the quantification of TRECs and KRECs allows a good estimation of the thymic and bone marrow output. Aim To investigate the extent of neo-synthesis of normal B and T cells in untreated patients with CLL. Patients and Methods Twelve previously untreated CLL patients were enrolled in this study. M:F ratio was 5:1; median age was 66; 7 patients had mutated IgVH genes, while 5 patients had unmutated IgVH genes; all patients were stage A Binet; FISH analysis including del(13q), del(11q), del(17p) and trisomy 12 detected 13q deletion in 6 patients while the other 6 patients presented no abnormalities. TRECs and KRECs were measured in mononuclear cells isolated from peripheral blood by duplex quantitative Real-Time PCR. This new assay, based on the use of a standard curve prepared with a plasmid containing fragments of TRECs, KRECs and of a reference gene, allows to quantify neo-produced B and T lymphocytes. T-cell subpopulations were determined by flow cytometry as follows: recent thymic emigrants (RTE) as cells with CD4+CD45RA+CCR7+CD31+ phenotype, regulatory T cells (Treg), as CD4+CD25int/highCD127low, RTE-Treg as Treg expressing CCR7+CD31+CD25int/high markers, effector memory (TEM) and central memory (TCM) T cells as lymphocytes displaying CD4+CD45RA-CCR7- and CD4+CD45RA-CCR7+ phenotype. Results The overall number of CD4+ lymphocytes was increased in chemotherapy-naïve patients with CLL (1585/μl vs 953/μl; p=0.02). TRECs were significantly higher in CLL patients compared to age-matched healthy controls (2.9/ml vs 1.4/ml; p=0.04), while the proportion of RTE was lower (24.9% vs 32.4%; p=0.02). No significant differences were observed in the percentage of Treg and RTE-Treg as well as of TCM. On the contrary, the percentage of TEM was higher (22.4% vs 10.4%; p=0.01) in CLL patients. The number of KRECs was lower in CLL patients than in controls (3.8/ml vs 7.4/ml; p=0.004). No correlation between IgVH gene mutational status, Ig levels and KRECs was found. Conclusions The neo-synthesis of normal T, with the exception of Treg, and B cells is reduced in patients with CLL compared to controls, even in a good prognosis, chemotherapy-naïve subset. The increased number of TRECs+ cells and TEM together with low RTE could be ascribed to the increased number of circulating CD4+ lymphocytes which do not appear to be recently mobilized from the thymus (CD31- cells) or to undergo peripheral expansion, but to accumulate in the peripheral blood. The low number of KRECs compared to normal controls could be interpreted as a consequence of the abnormal leukemic B-cell expansion which may impair normal B cell neo-synthesis. The level of KRECs did not seem to correlate to the mutational status of IgVH genes or the Ig level but a larger number of patients is needed to confirm these preliminary data and to establish whether the analysis of TRECs and KRECs may help clarify the complex immune abnormalities in CLL. Disclosures: No relevant conflicts of interest to declare.

Abstract: Combination of anti-retroviral therapy, high-dose chemotherapy (HCT) and autologous stem cell transplantation (ASCT) has led to an improved survival of HIV + non-Hodgkin lymphoma (NHL) patients. We compared T- and B-cell subset recovery and related capability to respond to in-vitro stimulation, as well as T-cell repertoire modifications of HIV + and HIV − NHL patients undergoing HCT and ASCT as first-line consolidation or salvage treatment, using sequential blood samples obtained before and at 3, 6, 12 and 24 months after ASCT. B lymphocyte recovery occurred earlier, reaching higher levels in HIV + patients as compared to HIV − patients and healthy controls; in particular, immature and naïve B cells were significantly higher in HIV + patients who had received rituximab in the pre-ASCT period. These lymphocytes equally responded to in-vitro stimulation. Newly produced T cells similarly increased in HIV + and HIV − NHL patients, but their levels remained constantly lower than in healthy controls. T lymphocytes showed a reduced proliferative capacity, but their repertoire was reassorted by the treatment. The functional and numeric B-cell recovery and the qualitative modifications of T-cell receptor repertoire may explain, at least in part, the success of this aggressive therapeutic approach in HIV + patients.