Citations

Abstract Introduction: It has become increasingly apparent that chimeric antigen receptor T (CART) cell activation and differentiation level is an important determinant of CART cell fate and response to therapy. In this study, we aimed to 1) measure levels of activation-induced surface death receptors and ligands on CART cells; 2) investigate how CART cell activation could impact their fitness and clinical responses, and 3) identify cell-based targets to modulate CART cell activation, apoptosis, and cytotoxicity to improve anti-tumor activity. Methods: We performed flow cytometric studies on ex-vivo stimulated, clinically annotated CART products of patients with large B cell lymphoma from the pivotal ZUMA-1 clinical trial that led to FDA-approved Axicabtagene ciloleucel (Axi-Cel). We investigated possible correlations of a number of surface death receptors and ligands with T cell differentiation status and post-infusion CART cell expansion, utilizing samples from ZUMA-1 patients who achieved a complete response as a best outcome ('responders') vs patients who achieved stable or progressive disease('non-responders'). CART cell effector functions in vitro were measured, and CART apoptosis was assessed using Annexin V. For in vitro and in vivo functional studies, we used CART19 generated from healthy donors (HD CART19) as indicated in the specific experiment. CRISPR/Cas9 was employed during CART cell production to disrupt specific genes. A xenograft model of lymphoma was used to investigate the in vivo antitumor activity of CART19. Results: Following an ex vivo stimulation of Axi-Cel products with CD19 + target cells, we observed upregulation of death receptors and ligands in CART19 from non-responders, compared to responders. We also observed a possible association between such upregulated surface markers with CART cell differentiation as measured by CCR7 expression. In an extended in vitro co-culture assay, where HD CART19 cells were repeatedly stimulated through the CAR, we found that tumor necrosis factor α receptor 2 (TNFR2), unlike other death receptors and ligands, was persistently elevated, suggesting a possible role for TNFR2 in long-term antigen-dependent CART19 dysfunction (Figure 1A). We further found that HD CART19 upregulate TNFR2, but not TNFR1, upon CAR stimulation (Figure 1B). While non-specific TCR activation (CD3 stimulation) of HD CART19 cells protected them from activation-induced apoptosis, antigen-specific activation through the CAR resulted in significant initiation of apoptosis within 2 hours of stimulation (Figure 1C). Having identified a possible association between TNFR2 and CART19 dysfunction, we aimed to study the impact of TNFR2 knockout on HD CART19 functions. Using CRISPR/Cas9 during CART cell manufacturing, we generated TNFR2 k/o HD CART19 cells with a knockout efficiency of around 50%, where the expression levels of TNFR2 in activated CART19 cells were reduced, compared to control CART19 cells (with non-targeting gRNA CRISPR/Cas9, Figure 1D). TNFR2 k/o CART19 cells demonstrated reduced early activation surface markers compared to control CART19, as measured by CD25 and CD69 surface expression (Figure 1E), reduced apoptosis initiation as measured by the Annexin V assay (Figure 1F), and enhanced antigen-specific proliferation and cytotoxicity (Figure 1G). Finally, in an in vivo xenograft model of CD19 + lymphoma, TNFR2 k/o CART19 resulted in enhanced CART cell expansion and anti-tumor activity (Figure 1H). Conclusions: Our results indicate that TNFR2 plays a role in early activation and apoptosis initiation of CART19 following CAR stimulation with CD19 + target cells and present TNFR2 knockout as a strategy to enhance CART19 anti-tumor activity. Figure 1 Figure 1. Disclosures Cox: Humanigen: Patents & Royalties. Sakemura: Humanigen: Patents & Royalties. Ding: Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; DTRM: Research Funding; Octapharma: Membership on an entity's Board of Directors or advisory committees. Parikh: Pharmacyclics, MorphoSys, Janssen, AstraZeneca, TG Therapeutics, Bristol Myers Squibb, Merck, AbbVie, and Ascentage Pharma: Research Funding; Pharmacyclics, AstraZeneca, Genentech, Gilead, GlaxoSmithKline, Verastem Oncology, and AbbVie: Membership on an entity's Board of Directors or advisory committees. Kay: Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; MEI Pharma: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees; Targeted Oncology: Membership on an entity's Board of Directors or advisory committees; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Acerta Pharma: Research Funding; Genentech: Research Funding; Behring: Membership on an entity's Board of Directors or advisory committees; CytomX Therapeutics: Membership on an entity's Board of Directors or advisory committees; Sunesis: Research Funding; TG Therapeutics: Research Funding; Tolero Pharmaceuticals: Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees. Scholler: Kite: Current Employment. Bot: Kite, a Gilead Company: Current Employment; Gilead Sciences: Consultancy, Current equity holder in publicly-traded company, Other: Travel support. Mattie: Kite: Current Employment. Kim: Gilead Sciences: Current equity holder in publicly-traded company; Kite, a Gilead Company: Current Employment. Filosto: Kite, a Gilead Company: Current Employment; Tusk Therapeutics: Patents & Royalties: or other intellecular property; Gilead Sciences: Other: stock or other ownership . Kenderian: Humanigen, Inc.: Consultancy, Honoraria, Research Funding.

Abstract Anti-CD19 chimeric antigen receptor T (CART19) cell therapy has resulted in unprecedented outcomes in patients with relapsed/refractory B-cell malignancies, which led to the FDA approval for several indications. However, CART19 cell therapy is limited by the development of severe life-threatening toxicities, as well as by the limited rates of durable response. It has become apparent that myeloid cells contribute to the development of both CART cell toxicity and also to the inhibitory tumor microenvironment. We and others have identified that granulocyte-monocyte-colony-stimulating factor (GM-CSF) depletion results in decreased myeloid activation, reduced toxicities, and enhancement of CART19 cell therapy efficacy in pre-clinical models. Furthermore, we observed that GM-CSF knockout (GM-CSF k/o) in CART19 cells resulted in the improvement of their functions (in vitro and in vivo). These findings suggest that there is also a direct effect of GM-CSF on CART19 cells, which is independent of the GM-CSF impact on myeloid cell activation. To further evaluate this, we first examined GM-CSF receptor alpha (GM-CSFRα) expression by flow cytometry on resting and activated CART19 cells (using FMC63-41BBζ). When CART19 cells were stimulated with either anti-CD3/CD28 beads or lethally irradiated (120 Gy) CD19 + Nalm6 cells (B cell acute lymphoblastic leukemia cancer cell line), GM-CSFRα expression was upregulated upon both T cell receptor (TCR) (data not shown) and CAR stimulation (Figure 1A). Having demonstrated that GM-CSFRα is significantly upregulated on stimulated CART19 cells, we aimed to determine the impact of GM-CSF neutralization (clinical-grade anti-GM-CSF antibody, lenzilumab, 10 µg/mL) versus GM-CSFRα blockade (research-grade antibody, 10 µg/mL) on CART19 cell function and CART cell-monocyte interactions. An IgG isotype antibody was used as a control antibody. Neither the GM-CSF neutralizing antibody, nor GM-CSFRα blocking antibody, had any impact on CART19 cell antigen-specific killing against the CD19 + JeKo-1 cells (mantle cell lymphoma cancer cell line), in the presence or absence of CD14 + monocytes (ratio 1:1:1) isolated by magnetic beads from healthy donors (Figures 1B-C). Next, we compared the effects of GM-CSF neutralization versus GM-CSFRα blockade on CART19 cell antigen-specific proliferation. Here, CART19 cells were co-cultured with lethally irradiated CD19 + cell line JeKo-1 at 1:1 ratio in the presence of 10 µg/mL of the GM-CSF neutralizing antibody, increasing doses of the GM-CSFRα blocking antibody (10-100 µg/mL), or an IgG control. The absolute number of CART cells was measured by flow cytometry on day 5. GM-CSF neutralization did not affect CART19 cell proliferation, but GM-CSFRα blocking antibody significantly inhibited CART19 cell proliferation in a dose-dependent manner. Then, we assessed the effects of GM-CSF neutralizing antibody (20 µg/mL) versus GM-CSFRα blocking antibody (20 µg/mL) on CART19 cell antigen-specific proliferation in the presence of healthy donor monocytes (ratio 1:1:0.5) on day 3. Flow cytometric analysis revealed that GM-CSF neutralization, but not GM-CSFRα blockade, mitigated monocyte-suppression of CART19 antigen-specific proliferation (Figure 1E). In summary, our findings indicate significant differences on CART cell functions and CART cell-monocyte interactions when a specific cytokine, GM-CSF, is neutralized compared to blocking its receptor. Further mechanistic studies are ongoing to assess the functions of GM-CSFRα k/o and GM-CSF k/o CART cells. Figure 1 Figure 1. Disclosures Sakemura: Humanigen: Patents & Royalties. Parikh: Pharmacyclics, MorphoSys, Janssen, AstraZeneca, TG Therapeutics, Bristol Myers Squibb, Merck, AbbVie, and Ascentage Pharma: Research Funding; Pharmacyclics, AstraZeneca, Genentech, Gilead, GlaxoSmithKline, Verastem Oncology, and AbbVie: Membership on an entity's Board of Directors or advisory committees. Kay: Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AstraZeneca: Membership on an entity's Board of Directors or advisory committees; Tolero Pharmaceuticals: Research Funding; CytomX Therapeutics: Membership on an entity's Board of Directors or advisory committees; MEI Pharma: Research Funding; Dava Oncology: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Morpho-sys: Membership on an entity's Board of Directors or advisory committees; TG Therapeutics: Research Funding; Acerta Pharma: Research Funding; Genentech: Research Funding; Rigel: Membership on an entity's Board of Directors or advisory committees; Behring: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sunesis: Research Funding; Targeted Oncology: Membership on an entity's Board of Directors or advisory committees; Juno Therapeutics: Membership on an entity's Board of Directors or advisory committees; Bristol Meyer Squib: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Oncotracker: Membership on an entity's Board of Directors or advisory committees; Agios Pharm: Membership on an entity's Board of Directors or advisory committees. Durrant: Humanigen Inc.: Current Employment. Ahmed: Humanigen Inc.: Current Employment, Current equity holder in publicly-traded company. Chappell: Humanigen Inc.: Current Employment, Current equity holder in publicly-traded company, Divested equity in a private or publicly-traded company in the past 24 months. Cox: Humanigen: Patents & Royalties. Kenderian: Humanigen, Inc.: Consultancy, Honoraria, Research Funding.

AbstractMonoclonal B‐cell lymphocytosis (MBL) and chronic lymphocytic leukemia (CLL) are clonal B‐cell disorders associated with an increased risk of infections and impaired vaccination responses. We investigated the immunogenicity of recombinant zoster vaccine (RZV) in these patients. Individuals with MBL/untreated CLL and Bruton tyrosine kinase inhibitor (BTKi)‐treated CLL patients were given two doses of RZV separated by 2 months. Responses assessed at 3 and 12 months from the first dose of RZV by an anti‐glycoprotein E ELISA antibody assay and by dual‐color Interferon‐γ and Interleukin‐2FLUOROSPOT assays were compared to historic controls matched by age and sex. About 62 patients (37 MBL/untreated CLL and 25 BTKi‐treated CLL) were enrolled with a median age of 68 years at vaccination. An antibody response at 3 months was seen in 45% of participants, which was significantly lower compared to historic controls (63%, p = .03). The antibody response did not significantly differ between MBL/untreated CLL and BTKi‐treated CLL (51% vs. 36%, respectively, p = .23). The CD4+ T‐cell response to vaccination was significantly lower in study participants compared to controls (54% vs. 96%, p < .001), mainly due to lower responses among BTKi‐treated patients compared to untreated MBL/CLL (32% vs. 73%, p = .008). Overall, only 29% of participants achieved combined antibody and cellular responses to RZV. Among participants with response assessment at 12 months (n = 47), 24% had antibody titers below the response threshold. Hypogammaglobulinemia and BTKi therapy were associated with reduced T‐cell responses in a univariate analysis. Strategies to improve vaccine response to RZV among MBL/CLL patients are needed.

Abstract Although chimeric antigen receptor T (CART)–cell therapy has been successful in treating certain hematologic malignancies, wider adoption of CART-cell therapy is limited because of minimal activity in solid tumors and development of life-threatening toxicities, including cytokine release syndrome (CRS). There is a lack of a robust, clinically relevant imaging platform to monitor in vivo expansion and trafficking to tumor sites. To address this, we utilized the sodium iodide symporter (NIS) as a platform to image and track CART cells. We engineered CD19-directed and B-cell maturation antigen (BCMA)–directed CART cells to express NIS (NIS+CART19 and NIS+BCMA-CART, respectively) and tested the sensitivity of 18F-TFB-PET to detect trafficking and expansion in systemic and localized tumor models and in a CART-cell toxicity model. NIS+CART19 and NIS+BCMA-CART cells were generated through dual transduction with two vectors and demonstrated exclusive 125I uptake in vitro. 18F-TFB-PET detected NIS+CART cells in vivo to a sensitivity level of 40,000 cells. 18F-TFB-PET confirmed NIS+BCMA-CART-cell trafficking to the tumor sites in localized and systemic tumor models. In a xenograft model for CART-cell toxicity, 18F-TFB-PET revealed significant systemic uptake, correlating with CART-cell in vivo expansion, cytokine production, and development of CRS-associated clinical symptoms. NIS provides a sensitive, clinically applicable platform for CART-cell imaging with PET scan. 18F-TFB-PET detected CART-cell trafficking to tumor sites and in vivo expansion, correlating with the development of clinical and laboratory markers of CRS. These studies demonstrate a noninvasive, clinically relevant method to assess CART-cell functions in vivo.

Abstract Clinical practice guidelines recommend that individuals with HC MBL are evaluated annually for evidence of progression as it has been shown that they progress to develop CLL requiring therapy at a rate of 1-5%/year. Next-generation sequencing identified 59 genes recurrently mutated in CLL, and we previously showed that the tumor mutational load (TML), i.e., the total number of these genes mutated, is associated with a shorter time to first treatment (TTT) among 112 HC MBLs independent of the CLL international prognostic index (CLL-IPI), an established prognostic score. Herein, we continue to support our finding in additional HC MBLs and report the pooled results across the two cohorts. From the Mayo Clinic CLL Resource, we sequenced a total 167 HC MBL (112 from the initial round and 55 from additional sequencing). We extracted DNA from CD5+/CD19+ B-cells and sequenced the coding regions of 59 driver genes. Somatic mutations were called using MuTect2 in tumor-only mode. Germline variants were eliminated based on minor allele frequencies &gt;0.01% and by those identified in public databases, unless present in known CLL mutation hotspots. After filtering, we computed the TML based on the number of genes with high impact (nonsense, frameshift and splicing) and hotspot mutations. Cox regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI), adjusted for sex and CLL-IPI. Stratified analyses were conducted by low/intermediate risk and high/very high CLL-IPI. Of the 167 HC MBL, low risk CLL-IPI comprised 60%, intermediate risk 28%, high risk 12%; and none were very-high risk. The most commonly mutated genes were SF3B1 (11%), NOTCH1 (9%), TP53 (7%), BIRC3 (7%), and MYD88 (6%); and 52 (31%) individuals had mutations in at least one gene. The median follow-up was 4.4 years, and 26 of the 167 individuals progressed to CLL requiring therapy. HC MBL with ≥2 mutated genes had a 28% 5-year risk of needing therapy compared to 6% among those with no mutated genes. Similar to our initial finding (HR=1.53, CI:1.12-2.07; P=0.007), we found a shorter TTT in the additional HC MBLs (HR=4.63, CI:1.57-13.7, P=0.006), and in the pooled cohort (HR=1.72; CI:1.29-2.28, P=0.0002). When we stratified by CLL-IPI risk, TML remained associated with TTT among individuals with low/intermediate CLL-IPI risk in the additional HC MBLs (HR=3.52, CI:1.11-11.2, P=0.03) and in the pooled cohort (HR=2.25, CI:1.34-3.77, P=0.002). A non-significant 2.8 fold association was observed with high risk CLL-IPI in the pooled cohort. In conclusion, the TML along with the CLL-IPI provide clinicians with a more accurate prognostic information regarding disease progression requiring therapy, especially for those MBLs with low to intermediate risk based on CLL-IPI. If validated, these findings may modify current practice guidelines for individuals with HC MBL. Citation Format: Geffen Kleinstern, Cecilia Bonolo de Campos, Nicholas J. Boddicker, Daniel R. O'Brien, Shulan Tian, Chantel Barney, Kari G. Rabe, Cristine Allmer, Laura Bruins, Aaron D. Norman, Timothy G. Call, Sameer A. Parikh, Jose F. Leis, Wei Ding, Huihuang Yan, James R. Cerhan, Neil E. Kay, Celine Vachon, Esteban Braggio, Susan L. Slager. Tumor mutational load derived from recurrently mutated genes in chronic lymphocytic leukemia (CLL) predicts time-to-first treatment in high-count monoclonal B-cell lymphocytosis (HC MBL) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 884.

Abstract Chronic lymphocytic leukemia (CLL) is a neoplastic disease of mature B-cells with a highly heterogeneous clinical course. While European ancestry (EA) populations present an increased incidence of CLL, African ancestry (AA) populations have a younger median age of onset, higher frequency of adverse prognostic factors, and inferior clinical outcomes. Despite the considerable effort to characterize the genetic landscape of CLL, AA are overwhelmingly underrepresented. Our hypothesis is that the clinical differences observed between AA and EA populations are, in part, explained by underlying genetic features. To address this imbalance, we identified 90 AA patients diagnosed with CLL, 64% of which were untreated at sample collection. RNA and DNA were extracted from CD5+/CD19+ clonal B-cells. We performed mRNA-seq and targeted sequencing in 59 recurrently mutated somatic CLL driver genes. Differentially expressed genes were identified using edgeR. Data was compared to our previously analyzed EA CLL cohort (N=445). The median age at diagnosis was 59 years for AA and 66 for EA and 74% of AA and 50% of EA had unmutated IGHV (u-IGHV) status. When evaluating the entire AA and EA cohorts, there was a significant increased frequency of mutations in TP53, SF3B1, and NFKBIE, identified in 29%, 24%, and 20% of AA CLLs, compared to 5%, 9%, and 9%, respectively, in EA CLLs (p&lt;0.01). When exclusively evaluating the untreated and u-IGHV cases, AA CLLs showed greater proportion of TP53 (30% vs 12%; p=0.0145), NFKBIE (30% vs 15%; p=0.0492), BIRC3 (21% vs 10%; p=0.0697), and KRAS (15% vs 7%; p=0.1683). Furthermore, there was an increase in mutations targeting relevant molecular pathways, such as NF-κB (42% vs 15%) and MAPK (18% vs 8%). Upregulation MAPK pathway was also confirmed by mRNA-seq analysis in the AA u-IGHV CLLs. Because of the high prevalence of TP53 mutations in the AA cohort, we further evaluated differential gene expression in the DNA Damage/Telomere Stress-Induced Senescence pathway. AA CLLs presented a significant downregulation of multiple genes associated with genome stability and cellular DNA damage response - DDR (including TP53 and ATM), double strand break repair (H2AFX and RAD50), telomere maintenance (POT1 and ACD), and cell cycle regulation (RB1, CCNA1, and CCNE2) (FDR&lt;0.05). DDR is responsible for DNA repair or induction of apoptosis, with its deficiency resulting in the accumulation of chromosomal aberrations, negatively impacting clinical outcome in CLL. Disparities in cancer are influenced by numerous factors that affect disease risk, screening and diagnosis, access to treatment, and survival. We identified an increased number of genomic alterations in the AA CLL cohort, primarily inducing activation of NF-κB and MAPK pathways and DDR impairment, with the increased frequency of mutations, notably in TP53 and BIRC3, expected to negatively impact prognosis. Citation Format: Cecilia Bonolo de Campos, Daniel R. O'Brien, Chantal E. McCabe, Huihuang Yan, Geffen Kleinstern, Zhiquan Wang, Laura A. Bruins, Cristine Allmer, Nicholas J. Boddicker, Charla R. Secreto, Aaron D. Norman, Shulan Tian, Kari G. Rabe, Timothy G. Call, Sameer A. Parikh, Jose F. Leis, Wei Ding, Richard Furman, J Brice Weinberg, James R. Cerhan, Celine M. Vachon, Neil E. Kay, Susan L. Slager, Esteban Braggio. Characterization of underlying genomic features among African ancestry populations diagnosed with chronic lymphocytic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2209.

Abstract The utility of the chronic lymphocytic leukemia-international prognostic index (CLL-IPI) in predicting outcomes of individuals with Rai 0 stage CLL and monoclonal B-cell lymphocytosis (MBL) is unclear. We identified 969 individuals (415 MBL and 554 Rai 0 CLL; median age, 64 years; 65% men) seen at Mayo Clinic between 1 January 2001 and 1 October 2018, and ascertained time to first therapy (TTFT) and overall survival (OS). After a median follow up of 7 years, the risk of disease progression needing therapy was 2.9%/y for MBL (median, not reached) and 5%/y for Rai 0 CLL (median, 10.4 years). Among patients with low, intermediate, and high/very high-risk CLL-IPI risk groups, the estimated 5-year risk of TTFT was 13.5%, 30%, and 58%, respectively, P&lt; .0001 (c-statistic = 0.69); and the estimated 5-year OS was 96.3%, 91.5%, and 76%, respectively, P&lt; .0001 (c-statistic = 0.65). In a multivariable analysis of absolute B-cell count with individual factors of the CLL-IPI, the absolute B-cell count was associated with shorter TTFT (hazard ratio [HR] for each 10 × 109/L increase: 1.31; P&lt; .0001) and shorter OS (HR: 1.1; P = .02). The OS of the entire cohort was similar to that of the age- and sex-matched general population of Minnesota (P = .17), although Rai 0 CLL patients with high and very high-risk CLL-IPI score had significantly shorter OS (P= .01 and P= .0001, respectively). The results of this study demonstrate the ability of CLL-IPI to predict time from diagnosis to first treatment (an end point not affected by therapy) in a large cohort of patients whose only manifestation of disease is a circulating clonal lymphocyte population.

Abstract Background: There is little prospective, longitudinal data on the health outcomes of low count MBL in the U.S. adult population. We screened for MBL in asymptomatic adults with normal blood counts using highly sensitive flow-cytometry in a clinic-based cohort of participants from the Mayo Clinic Biobank and explored the relationship between MBL and risk of hospitalization with infection. Methods: The Mayo Clinic Biobank is a large scale biorepository of 50,000 adults (age&gt;18) seen in primary care-based clinics. All consented participants completed a health history questionnaire and provided blood samples. For the present study, we focused on the study participants from Olmsted County, Minnesota, 40 years of age or older who had stored PBMC. We used these PBMC to screen for MBL using an 8 color (CD38, CD45, Kappa, Lambda, CD19, CD23, CD5 and CD20) flow cytometry assay validated to consistently detect clonal B-cell events to the 0.005% level (1/20,000 events). The sensitivity of this approach of collecting 500,000 events from isolated PBMC is 2-3-fold higher than collecting 500,000 events from whole blood due to the increased concentration of lymphocytes in these samples. Infections associated with hospitalization were considered serious or life-threatening infections. Every hospitalization at both Mayo Clinic and Olmsted Medical Center hospitals in Olmsted County, MN following the sample collection was reviewed to document hospitalization with infection. Data on hospitalization with infection was abstracted from clinical records using our previously published approach (Moriera, Leukemia 27:136). This approach allows medical record validation and review of detailed clinical and treatment information related to infection. For this analysis, follow-up began at date of sample collection and ended at the earliest of death, migration from Olmsted County, or 12/31/2016. The individual abstracting information on hospitalization for infection was blinded to the results of MBL screening. Chi-square tests were used to assess associations between MBL status and demographic characteristics. Cox regression models were used to determine association with risk of hospitalization with infection accounting for the competing risk of death using Fine Gray models. Results : We screened for MBL in 1045 Olmsted County residents age 40 and older. Of these, 984 (94%) had interpretable results. 119 of these 984 (12%) had a clonal B-cell population detected including 106 (11%) with CLL phenotype (CD5, CD19, CD20 [dim], CD23, kappa or lambda light chain restriction [dim]).This analysis focused on the 106 individuals with CLL-like MBL clones (mean age 69 years, 55% male) and the 865 individuals with normal immunophenotype (mean age 61 years, 40% male). The presence of CLL phenotype MBL was strongly associated with age. MBL was detected in 3% of patients age 40-49 years, 7% of those 50-59, 10% of those 60-69, 20% of those 70-79, and 27% of those age 80+ (p&lt;0.001). MBL was also more common among men (women 8%; men 14%; p=0.003). After a median follow-up of 7 years from biobank enrollment, 76 of the 971 participants were hospitalized with infection in Olmsted County at least once. The estimated cumulative incidence of infections at 7 years was 19% for LC MBL and 9% for those without MBL (Figure). The most frequent site of infections for which these individuals were first hospitalized were pneumonia (14 individuals; 18%), cellulitis (20 individuals; 26%), urinary tract infection (21 individuals; 26%), and blood stream infection (6 individuals; 8%). An association between LC MBL and hospitalization with infection was observed with the unadjusted HR for hospitalization with infection among the 106 Olmsted County residents with LC MBL relative to the 865 Olmsted County residents with normal immunophenotype is 2.41 (95%CI: 1.39-4.19; p=0.002). After adjusting for age and sex, the HR is 1.65 (95% CI: 0.95-2.88; p=0.08). Conclusions: We report one of the first studies to systematically explore the relationship between LC MBL and the risk of serious infection. It appears that individuals with LC MBL may be at increased risk for serious infection. If this observation is confirmed, it would suggest that 5-10% of adults over age 40 (6-12 million U.S. adults) have a largely unstudied condition with potentially serious health implications. Figure 1 Figure 1. Disclosures Shanafelt: Hospira: Research Funding; AbbVie: Research Funding; Celgene: Research Funding; Pharmacyclics: Research Funding; Jannsen: Research Funding; GlaxoSmithKline: Research Funding; Genentech: Research Funding. Kay: Gilead: Research Funding; Agios: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Research Funding; Tolero Corporation: Research Funding. Parikh: Pharmacyclics: Research Funding; AstraZeneca: Honoraria; Pharmacyclics: Honoraria.